Responses to Public Comments and Peer Reviews

Fipronil Criteria Derivation Report

using the

Phase II: Methodology for Derivation of Pesticide Water Quality Criteria for the Protection of Aquatic Life in the Sacramento and San Joaquin River Basins

Julie Bower, Ph.D. and

Ronald S. Tjeerdema, Ph.D.

Department of Environmental Toxicology University of California, Davis

February 2017

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Responses to Comments

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Table of Contents Terms, Abbreviations, Acronyms, and Initialisms Used in this

Report ii 1.0 Introduction 1 2.0 Response to Comment to Public Comments 2 2.1. Comment Letter 1 – Linda Dorn, Regional San ......................................... 2 2.2. Comment Letter 2 – Debbie Webster, Central Valley Clean Water

Association .............................................................................................. 17 2.3. Comment Letter 3 – Delyn Ellison-Llyod, City of Roseville Stormwater

Management Program ............................................................................. 20 2.4. Comment letter 4 – Roberta Firoved, California Rice Commission ......... 26 3.0 Response to Comment to Peer Reviews 28 3.1. Peer Review 1 – George Cobb, University of California, Berkeley .......... 28 3.2. Peer Review 3 – Nancy Denslow, University of Florida ........................... 35 3.3. Peer Review 3 – Rita Schoeny, Ph.D., Independent consultant .............. 43 3.4. Peer Review 4 – David C. Volz, University of California, Riverside ......... 53 References Error! Bookmark not defined.

Responses to Comments

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Terms, Abbreviations, Acronyms, and Initialisms Used in this Report Term Definition ACR Acute to Chronic Ratio- used to estimate concentration that

will protect against chronic toxicity CDFG California Department of Fish and Game CVRWQCB Central Valley Regional Water Quality Control Board DPR California Department of Pesticide Regulation ECx The chemical concentration that has an effect on x% of the

test population. Koc Organic Carbon Partition Coefficient LC50 The chemical concentration that is lethal to 50 % of the test

population. LOEC Lowest Observed Effect Level- lowest concentration tested

that has some effect on the test population MATC Maximum Allowable Toxicant Concentration -geometric

mean of LOEC and NOEC NOEC No Observed Effect Level- highest concentration tested that

has no effect on the test population SSD Species Sensitivity Distribution- Statistical probability

distribution of toxicity data UC Davis University of California, Davis US EPA U.S. Environmental Protection Agency Water Quality Objective (WQO)

The limits of water quality constituents or characteristics that are established for the reasonable protection of beneficial uses of water or the prevention of nuisance within a specific area.

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1.0 Introduction This document presents the responses to public comments and peer reviews received on a technical report prepared by the University of California at Davis, Environmental Toxicology Department, under contract (#05-100-150-0) to the Regional Water Quality Control Board, Central Valley Region (Regional Board). This report represents one of five of the end product reports of the third phase of a three-phase project to evaluate, develop and apply a method to derive pesticide water quality criteria for the protection of aquatic life. The first phase of the project was to review and evaluate existing water quality criteria derivation methodologies to determine if there was an existing available method that met the Regional Board’s stated project goals. The review indicated that there is no single method that meets all of the Regional Boards requirements. Therefore, the second phase of the project was to develop a new method that could meet the project requirements. The Phase II report details this new methodology and its application to chlorpyrifos. The third phase of the project was to apply the criteria derivation method to additional pesticides, of which fipronil is one. The fipronil criteria report was submitted to peer review, conducted by external scientific peer reviewers per the requirements of Health and Safety Code Section 57004. These technical reports may be considered by the Regional Board in relation to a Board action, however, the reports do not represent Board Policy and are not regulations. The reports are intended to generate numeric water quality criteria for the protection of aquatic life. However, these should not be construed as water quality objectives. Criteria and guidelines do not have the force and effect of regulation, nor are they themselves water quality objectives. The responses to technical comments on the draft fipronil water quality criteria report are written by UC Davis, which make up the majority of comments. Comments on policy issues were written by Regional Board staff, which is indicated at the beginning of the response.

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2.0 Response to Comment to Public Comments

2.1. Comment Letter 1 – Linda Dorn, Regional San COMMENT 1-1: The draft report incorrectly identifies data as survival when it is for sublethal toxicity endpoints. Section 10.1.2 for Fipronil-sulfide erroneously states that the lowest LC50 value was 9.3 ng/L for Chironomus dilutus (Weston and Lydy 2014). Rather, the reported value is an EC50 and the correct LC50 value is >62.4 ng/L (the LC50 could not be calculated as it was greater than the highest tested concentration). Likewise, Section 10.1.3 for Fipronil-sulfone erroneously states that the lowest LC50 value was 7.9 ng/L for Chironomus dilutus (Weston and Lydy 2014). Rather, the reported value is an EC50 and the corresponding LC50 value is >106 ng/L (the LC50 could not be calculated as it would be greater than the highest tested concentration). Test 1 results for the midge in this study actually report the lowest EC50 of 7.5 ng/L Fipronil-sulfone and lowest LC50 as >102 ng/L.

Response To Comment (RTC) 1-1: The identification of the lowest fipronil-sulfide value has been corrected to be an EC50. Similarly the identification of the lowest fipronil-sulfone value has been corrected to be an EC50. The value has also been corrected to be 7.5 ng/L.

COMMENT 1-2: It is not clear why Fojut et al (2014), a method for deriving SQC, is referenced for the AF approach to calculate the WQC for Fipronil-sulfide (Section 7.1.2). There are also conflicting AFs in Table 3.13 of TenBrook et al. (2009) and Table 17 in Fojut et al. (2014) that should be reconciled so that the WQC calculation approach is clear and an explanation is needed if the more recent SQC associated AFs from 2014 are used instead of those in the 2009 WQC method.

RTC 1-2: Fojut et al. 2014 is a sediment method that includes some discussion of aqueous data. Paragraph three of section 3.5.1 “Assessment factor rationale” explains that the assessment factor (AF) approach for sediment and water are the same and are modeled on the USEPA Great Lakes methodology, which each use aqueous exposure data to calculate AFs. The sediment method (Fojut et al. 2014) is a more recent publication than the aqueous method (TenBrook et al. 2009a) and contains updated AF values in tables 17 and 18 to be used when following the aqueous method. Section 7.1.2 of the draft fipronil report has been updated to include the above explanation for clarification.

COMMENT 1-3: Figure 6 shows one interpretation of acute toxicity data for Fipronil-sulfone, but the regression is extrapolated over an order of magnitude below the lowest data point. There is great uncertainty when

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extrapolating beyond the ranges of data. It would be very helpful to add confidence intervals onto Figure 6 to more accurately describe the error around the 1st and 5th percentile estimates as was done in Figure 4. Adding both the upper and lower 95% confidence limits around these entire regressions would be even more helpful in describing the accuracy of these regressions.

RTC 1-3: Error bars have been added to Figure 6 to match the representation of uncertainty as in Figure 4.

COMMENT 1-4: The chronic WQC for Fipronil-sulfide is calculated as 0.13 ng/L (Section 7.2.2) but then is incorrectly described in the final criteria statement (Section 12.3) as 0.10 ng/L. There is no discussion of the significant figures used to calculate this WQC that would change the number of significant figures and concentrations in McNamera (1990b), which is the basis for this WQC, and were reported to two significant figures.

RTC 1-4: The chronic WQC for fipronil-sulfide has been updated following subsequent review of the data and calculations. The final chronic WQC is reported with two significant figures because the toxicity data are reported with two significant figures.

COMMENT 1-5: The text in Section 7.2.4 (Page 20) states that the only chronic aqueous toxicity value for Fipronil-desulfinyl is an MATC of 1.67 μg/L for Daphnia magna; however, Table 12 only lists one MATC for D. magna and the value is 64 μg/L. Please correct this inconsistently.

RTC 1-5: The value in the fipronil-desulfinyl chronic water quality criteria has been corrected to the value in Table 12.

COMMENT 1-6: Section 8.1.1 (page 21) incorrectly references Table 16 when Table 15 is the correct table containing Fipronil final acute sediment toxicity data.

RTC 1-SC6: The incorrect reference has been updated to Table 15.

COMMENT 1-7: Section 8.1.4 (page 23) incorrectly references Table 17 when it should refer to Table 18 for the lowest sediment EC50 for Fipronil-desulfinyl.

RTC 1-7: This incorrect reference has been updated to Table 18. Table 17 of the sediment reference is also mentioned in this section and clarification has been added.

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COMMENT 1-8: Section 8.1.4 (page 23) has an incorrect conversion from 1.166 μg/g OC to 1.2 ng/g OC Fipronil-desulfinyl. The correct result is 1166 or 1200 ng/g OC (if rounded to two significant figures). This error is carried forward to Section 12.3 (page 40) where the interim acute SQC is incorrectly presented.

RTC 1-8: The incorrect units have been updated to μg/g OC in the conversion and the correct values are now reported in Sections 8.1.4 and 12.3.

COMMENT 1-9: Likewise, Section 8.2.4 (page 25) has an incorrect conversion from 0.204 μg/g OC to 0.20 ng/g OC for the Fipronil-desulfinyl interim chronic SQG. The correct value is 204 ng/g OC. This error is carried forward to Section 12.3 (page 40) where the interim chronic SQC is incorrectly presented.

RTC 1-9: The incorrect units have been updated to μg/g OC in the conversion and the correct values are now reported in Sections 8.2.4 and 12.3.

COMMENT 1-10: Throughout the document there is a misuse of the singular when referring to data (plural). Datum is the singular form. For example, see page 40. “Fipronil and degradates have been monitored in urban environments in California and a summary of this these data is are given to provide context for the use of water quality criteria for these compounds.”

RTC 1-10: This has been corrected throughout the document.

COMMENT 1-11: Section 10.3 (page 29) incorrectly references Table 23 when Table 22 is the correct table.

RTC 1-11: This table reference has been corrected.

COMMENT 1-12: Section 12.2 (Page 37) ambiguously states that “The lowest SMAV in the RR data set of 0.04 μg/g OC…concentration of x ng/L…” Please provide the missing value for “x” which we expect is 0.26 ng/L.

RTC 1-12: The value x for fipronil-sulfone has been updated to 0.26.

COMMENT 1-13: There is no ‘summary’ of ambient monitoring data for Fipronil and its degradates as stated in the last paragraph (page 40). Rather, there is a text discussion of detection frequencies, but no concentration data are presented. Measured ambient concentrations are essential for interpreting the relevance of these draft WQC and SQC and should be presented when available. This discussion also seems to be in

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the wrong place since it refers to Fipronil and degradates yet it is in a section for Fipronil-desulfinyl.

RTC 1-13: A section on ambient concentration data has been added to the final report and a separate header has been added to clarify that it is a separate topic.

COMMENT 1-14: Weston and Lydy (2013) (page 40) and TenBrook et al. (2009a) (page 26) are cited in the Draft Report but are missing from the References Section.

RTC 1-14: The Weston and Lydy reference incorrectly identified the year as 2013 and has been corrected. The reference for TenBrook et al. 2009a has been updated.

COMMENT 1-15: The Draft Report does not define if SQC are based on a dry weight or wet weight sediment concentration basis. This would be helpful to clarify.

RTC 1-15: The organic-carbon normalized sediment concentrations are based on dry weight basis and this clarification has been added to each SQC. These normalized sediment concentrations are used in the calculation of interim bioavailable sediment quality criteria calculations (BSQC).

COMMENT 1-16: Tables 3 and 8 incorrectly identify the toxicity endpoints for Fipronil in Weston and Lydy (2014). Table 3 refers to these as survival endpoints but the values presented are for the sublethal immobilization response. Whereas Table 8 refers to the results as immobilization when reporting the result for survival. These data are also recorded incorrectly in Appendix A. The effect concentration for Helicopsyche sp. in table 8 is also incorrectly reported as >842 μg/L when Weston and Lydy (2014) state the LC50 is >0.842 μg/L as presented.

RTC 1-16: These issues have been corrected in both the data tables and the Appendix.

COMMENT 1-17: Please explain what a bold LC/EC50 value indicates in Tables 3-7, 9-12, and 15-20.

RTC 1-17: Bold indicates the species mean acute value. Each table has been edited to include that description.

COMMENT 1-18: An incorrect value of 0.0634 μg/L EC50 was used in the Fipronil species sensitivity distribution modelling (Appendix E) instead of the reported value of 0.634 μg/L.

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RTC 1-18: This has been corrected and all calculations using the value were redone.

COMMENT 1-19: Some of the RL, LR, and LL data described in Appendix A2 are not shown in Table 14 (see detailed comments for Appendix).

RTC 1-19: Table 14 has been updated to include all data in Appendix A2.

COMMENT 1-20: Toxicity test result rankings should be performed separately for multiple endpoints in a single study. The Draft Report separately evaluated rankings for different species and chemical combinations from individual sources, but various endpoints, which have different methods and control requirements, should be considered independently.

RTC 1-20: When different endpoints result in different ratings they are each listed separately on the Toxicity Data Sheet (TDS). Many TDSs contain multiple endpoints and are listed and rated accordingly as different ‘effects.’

COMMENT 1-21: The overall uncertainty with each draft WQC and SQC is very high and this should be clearly indicated to environmental managers who might adopt them for regulatory use. Some of these uncertainties are discussed in Section 12; however, they are underemphasized and there is not a comprehensive uncertainty discussion or estimate of the magnitude of uncertainty to inform responsible management use of these WQC and SQC. The following points deserve additional recognition and discussion in Section 12.

• Data were insufficient for calculations using EPAs (1985a) WQC protocols. Therefore, SSDs were developed with fewer data than EPA would accept, or Assessment Factors (AFs) were applied to the lowest toxicity value to compensate for the lack of data. Fojut et al (2014) illustrates in Table 17 that the use of AFs will almost always result in acute values lower than the SSD 5th percentile, often by more than one order of magnitude.

RTC 1-21: Information has been added to section 12.1 to point out that the use of AFs is conservative and that the lack of sufficient data to fit a SSD is a significant limitation, but conservative AFs are appropriate when data are so limited.

COMMENT 1-22: Water quality properties (e.g. dissolved organic carbon and total suspended solids) that could bind hydrophobic contaminants and protect aquatic organisms from chemical exposure are not considered in the draft WQC. These are variables in ambient surface waters (more so in stormwater) that are lacking in laboratory toxicity testing waters and

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increases the conservative nature of toxicity test data. Effect levels in lab toxicity tests will therefore be lower than those in ambient waters due to these naturally occurring constituents in surface water.

RTC 1-22: Section 9 of the report addresses water quality effects. There were no studies found on the effects of dissolved or suspended carbon or other particles in the water column for fipronil or its degradates, and this is a significant area of uncertainty particularly for the parent compound fipronil because it has a high Kow, which indicates that binding to solids and DOM may affect the bioavailability of this compound. This limitation in the data set is now highlighted in section 12.1.

COMMENT 1-23: The use of sublethal toxicity data for deriving acute WQC is highly conservative (see comments below).

RTC 1-23: Immobilization is defined as an appropriate acute endpoint in the UC Davis method. The authors disagree that the use of this endpoint for deriving acute criteria is highly conservative.

COMMENT 1-24: The most sensitive response is selected for use in the criteria calculation when multiple test results are available for a chemical-organism combination in a study. It is not clear why the most sensitive result is used from identical test repetitions rather than the geometric mean of the results, which would be a more accurate reflection of the average organism response and reduce uncertainty introduced from test variability.

RTC 1-24: This has been corrected to use the calculated geometric mean of results from repeated tests.

COMMENT 1-25: Uncertainty in the 5th percentile estimate of the SSD increases as the number of data points decreases. When only three points are used in the SSD (too few data for SSD calculations with the UCD method) the 95th percentile confidence interval on the median 5th percentile of the SSD can vary by a factor of 10 to 1x10^6, depending on the calculation method (Pennington 2003). Including the 95% confidence intervals around each SSD regression would help to illustrate the precision around each regression, or lack thereof.

RTC 1-25: Comment acknowledged.

COMMENT 1-26: As a result, as discussed in Section 10 (page 27), The acute Fipronil SQC (4.2 ng/g OC) is two orders of magnitude lower than the most sensitive effect in any sediment test with this chemical (10-day EC50 of 100 ng/g OC for C. dilutus). The chronic Fipronil-sulfide WQC (0.1 ng/L) is three orders of magnitude lower than the lowest MATC (470

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ng/L). The chronic Fipronil-sulfide SQC (0.4 ng/g OC) is also three orders of magnitude lower than the lowest MATC (160 ng/g OC for immobilization of C. dilutus). These vast differences between the toxicity data and draft derived criteria should raise concern that the criteria are overly conservative. All of these criteria are derived from a sub-lethal endpoint (immobilization) that has not been clearly linked with survival or growth, albeit for a sensitive species. Caution is therefore urged for resource managers considering their use in regulation.

RTC 1-26: Section 8 of the report provides a cautionary statement about the applicability of the sediment criteria due to a lack of diverse data sets. The UC Davis sediment and aqueous methodologies were developed to derive criteria for pesticides in freshwater systems of North America with the express purpose of informing regulators and environmental managers of scientifically sound tolerable levels of these chemicals in water bodies to ensure protection of aquatic life. It is up to regulators to make determinations based on derived criteria. The only solution to a dearth of data that prevents criteria derivation is to conduct further studies that meet the requirements of the method.

COMMENT 1-27: Toxicity results from Weston and Lydy (2014) comprise a large proportion of the toxicity data determined to be Relevant and Reliable. However, it is not clear how they received this RR ranking for sublethal toxicity results and non-standard test organisms given many quality deficiencies. Many of the invertebrates used in these tests were collected from urban streams with no evaluation of the stressors organisms were exposed to prior to collection. Because organisms secured from a wild population lack any guarantee that they will be of the age, size, quality, or condition needed for performing bioassays, procedures exist for proper evaluation and acclimation (USEPA 1985b). ASTM E1706-05 (2010) recommends avoiding tests with organisms from wild populations unless cultured through several generations to help address these concerns. Test organisms should also be identified using an appropriate taxonomic key, and verification should be documented. Furthermore, the degree of manipulation and stress that would have been required to identify these invertebrates to the species level would presumably stress them enough to render them unreliable for a bioassay without a substantial acclimation period. These wild organisms were collected, identified, and used for bioassays after only 24-hours. Laboratory toxicity data for field collected organisms (i.e., as reported in Weston and Lydy 2014) should therefore be considered with caution and not used as a primarily line-of-evidence in WQC derivation unless it meets all the described quality criteria. Further, control survival was less than 90%, an accepted test acceptability criterion for short-term tests, for many of the species and endpoints. Weston and Lydy (2014) state that “90% is often used as a threshold for

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acceptability when testing with standard species,” but that the standards should be relaxed when testing a non-standard species in sub-optimal testing conditions. However, Chironomus dilutus is a commonly used, “standard” bioassay species (formerly known as Chironomus tentans) and standard methods have been developed. EPA (2002) states that control organism survival in short-term acute toxicity tests must be greater than 90% and ASTM E1706-05 (2010) guidance agrees that 90% control organism survival is a minimum test acceptability criteria. Furthermore, precedence suggests that 90% control survival is important even when using non-standard species/procedures. Specifically, in a review of Fipronil studies, EPA (USEPA 2006) classified a study of Hexagenia sp. (one of the species used in Weston and Lydy, 2014) as invalid due to failure to meet a 90% control survival standard.

RTC 1-27: The Weston and Lydy 2014 tests were re-rated using 90% control survival as specified in the method. Additional data was also requested and this data is in the updated Toxicity Data Summaries and the study ratings were updated accordingly.

COMMENT 1-28: We are also concerned over the efficacy of using subjective sublethal toxicity endpoints (i.e., ‘ability to swim’, ‘ability to thrash when prodded’, ‘ability to cling’, and ‘ability to crawl’) for deriving acute WQC. It has not been clearly demonstrated that these results are reproducible among labs, among different cohorts or populations of wild animals, or that the range of ‘normal’ behaviors have been adequately described. Interlaboratory comparisons have shown high variability when evaluating this immobilization response1. The range of control results for these behaviors are also not described in Weston and Lydy (2014). Therefore, it is not known if or how the sublethal toxicity endpoints were compared to a control response and the lack of sublethal performance controls should disqualify these results from an RR rating (note that he survival in a control treatment is not a valid basis for assessing the control performance of sublethal responses). The basis for sublethal toxicity endpoint interpretations should be made clear before these data are used in WQC derivation.

RTC 1-28: Sublethal control response data was requested and received from the author of Weston and Lydy 2014. All test ratings were updated accordingly.

COMMENT 1-29: Finally, the reliability scores for this study do not seem to have followed the UC Davis WQC derivation Method (Tables 3.7 and 3.8 in TenBrook et al. 2009). Results for sublethal behavioral endpoints in Weston and Lydy (2014) should have been assessed Acceptability Rating points based on the lack of appropriate controls (6) and control response within test guidance (8). Acceptability Rating points for tests with field collected organisms should have been further assessed points based the

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lack of information on appropriate size/age/growth phase of organisms (3), no prior contaminant exposure (4), organisms fed 2 h before solution renewal or not fed in acute test (3), and organisms properly acclimated and disease free prior to testing (1). Likewise, the Documentation Ratings for sublethal behavioral responses should have been assessed points based the lack of information on control type (8). Tests with field collected organism should have also been assessed Documentation Ratings points based on the source (5) and age/life stage/size/growth phase (5). These deductions would lower the Documentation scores by 18 points from 85 to 67 and Acceptability scores would be lowered by 25 points from 86 to 71 for some test results. Given these concerns, the Draft Report authors should reconsider the RR ranking of data from Weston and Lydy (2014) and other similar studies.

RTC 1-29: Additional data was requested and received from the author of Weston and Lydy 2014 and all test ratings were updated and corrected accordingly.

COMMENT 1-30: The Draft Report does not provide a description of the cutoff scores for the R, L, and N rankings. Please provide a reference to TenBrook et al. (2009; Table 3.11), which used results for chlorpyrifos to set cutoffs for all pesticides, if this approached was used. It would also be helpful to discuss the applicability of rating Fipronil toxicity data as “R” for reliability (i.e., 74-100 was used in TenBrook et al, 2009) based on a review of chlorpyrifos.

RTC 1-30: The cutoff scores for the R, L, and N rankings are now shown on the title pages of the Appendices, where the data summaries are given and ratings are detailed.

COMMENT 1-31: It is not appropriate to include sublethal toxicity data in the determination of acute WQC when the linkage has not been clearly made with survival, growth or reproduction. The Draft Report should include a discussion and rationale linking these sublethal responses with survival if they are to be used in acute WQC derivation. This would be consistent with previous responses to comments (TenBrook and Tjeerdema, 2009).

“...6 very important and therefore heavily weighted requirements (endpoints linked to survival growth or reproduction, conducted in freshwater, chemical of at least 80% purity, family in North America, report a numerical toxicity values or one is calculable, report a control treatment/response). If a study does not meet one of these requirements the score would be reduced by 15 points. By this system only studies that have all 6 of these requirements will be used in the SSD and calculation of criteria. The lack of one or two of these important parameters would make

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the study available only for supplemental information (not used in the SSD calculation), and a lack of 3 more of these parameters excludes the study from the whole criteria derivation process.” Response to comment 6-5. Page 31. In. TenBrook and Tjeerdema (2009). UC Davis Reponses to Comments 7-5 and 7-6 agree that studies that do not report survival, growth, or reproduction endpoints should not be used as primary lines of evidence to generate WQC. “COMMENT 7-6: Studies that do not report toxicological endpoints of survival, growth, or reproduction (e.g., standard EPA endpoints) should not be used to generate water quality criteria. RESPONSE TO COMMENT 7-6: UCD See response to comment 7-5. RESPONSE TO COMMENT 7-5: ... A study using an impure chemical standard would loose[sic] 15 points (out of 100) and studies with a relevance score of 70-90 are only to be used as supplemental information. So this instance (and those described in comments 7-6, 7-7, 7-8) would receive relevance scores of 85 and would therefore be unacceptable for criteria derivation by this method.” EPA has been clear in describing acute toxicity as being based on lethality within a relatively short time period (USEPA 2002). Regarding acute toxicity endpoints, an expert panel stated, “The results of these tests usually measure lethality, an obvious and easily measured effect, often expressed as the concentration lethal to 50% of the test organisms.” (Chapman 1996). It is also overly conservative to use a sublethal response measured over a 2-4 day exposure as the basis for an acute WQC that applies to a one-hour average concentration.

RTC 1-31: Section 3-2.1.1.3 of the aqueous method (TenBrook et al. 2009) states that immobility as an endpoint is appropriate. All studies were rated according to the method. The sediment method (Fojut et al 2014) states that mortality or growth endpoints are preferred over immobility. The interim acute BSQC for fipronil and fipronil-sulfide have been updated accordingly.

COMMENT 1-32: It is questionable to use toxicity data for sediment dwelling organisms (i.e., Chironomidae) as a primary line of evidence for deriving WQC. These organisms are highly appropriate for determining SQC and would be helpful secondary lines-of-evidence to validate a proposed WQC. If the next most sensitive water-column species was selected for the acute WQC derivation of Fipronil-sulfide (Isoperla sp. with and LC50 of 0.0945 μg/L), then the final acute criterion would be 5.9 ng/L compared to 0.58 ng/L calculated using the sediment-dwelling midge. This alternative acute WQC would be applicable to a one hour average concentration and would be sufficiently protective of aquatic life.

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RTC 1-32: Section 3-2.1 of the aqueous method (TenBrook et al. 2009) identifies study types based on the format of the test rather than on the species itself: “studies of aquatic organisms exposed to a pesticide via water.” Therefore the use of Chironomidae data is considered appropriate according to the method.

COMMENT 1-33: The UC Davis Sediment Method assessment factor approach requires a benthic crustacean as one of the acute data in order to use the Assessment Factor (AF) procedure (section 3.5.2, Fojut et al. 2014), as 'typically available and likely to be relatively sensitive.’ However, the available data indicate that diptera of the family Chironomidae are much more sensitive to Fipronil and its degradates than crustaceans. If the sediment-dwelling larvae are to be used in developing WQC then it would seem that acute data from an insect larvae from the family Chironomidae would be an appropriate requirement for deriving criteria for Fipronil and its degradates.

RTC 1-33: The UC Davis Sediment Method is designed to derive criteria for all types of pesticides, and therefore does not require a particular sensitive species for each class of pesticides or individual pesticide. All relevant and reliable data are used in deriving criteria, and when an assessment factor is used the most sensitive species in the data set is used to calculate criteria with the AF. Thus, there is no need to set out a priori a requirement for particularly sensitive species for an individual pesticide or group of pesticides. A benthic crustacean is required as a baseline toxicity value to use the assessment factor procedure because the AFs were developed using one baseline taxa requirement for the reasons given above (i.e., they are typically available and likely to be relatively sensitive). However, the lowest toxicity value available (which may be any species) is used for criteria derivation.

COMMENT 1-34: Alternative curve fitting should be explored for these data. Figure 6 shows one interpretation of acute toxicity data for Fipronil-sulfone, where the 5th and 1st percentiles are calculated far beyond the range of available data where uncertainty is very high. The fitted curve does not appear to be a best fit and drives overly conservative WQC. It would be more appropriate and increase the scientific validity to assess multiple models to fit the SSD and then select the regression with the best fit (e.g., using the Anderson-Darling statistic). The UCD method of sequential testing for a regression that meets some minimum requirements does not result in a best-fit. It would also be extremely helpful to add confidence intervals for the curve on all SSD figures to more accurately depict the uncertainty in these calculations.

RTC 1-34: The aqueous method was developed after a thorough review of all existing methodologies worldwide. Analysis of different species sensitivity distribution models is explored in section 2-3.1 (TenBrook et al. 2006). The use

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of Burr III and log-logistic distributions (for data sets of >8 and >5 values, respectively) were selected based on analysis of robust data sets for 12 different pesticides.

COMMENT 1-35: The method, including the use of conservative AFs to drive down the derived WQC in the absence of data, has produced draft WQC that are generally below MDLs for most of these parameters for 2 of 3 California Labs (Exhibit 1). Those with NPDES permits in the Central Valley could have WQOs adopted into their permits based on these WQCs that will effectively be at the limit of detection. Although not recognized in the draft Fipronil criteria derivation, quantitation limits may have an impact on the ability of agencies and dischargers to achieve TMDL goals. The ability to detect concentrations below one ppt (less than one ng/L) in a complex matrix such as effluent is even more challenging than detecting these low concentrations in a clean matrix and has not yet been demonstrated. Responses to previous comments have indicated that the recommended criteria are developed independent of considering how they would be implemented and that it is up to the CVRWQCB to determine how they would be adopted and implemented. However, now that other WQC that also fall below achievable quantitation limits have been (e.g., the final 2015 esfenvalerate WQC), were developed for use by CVRWQCB staff this comment should be addressed.

RTC 1-35: Regional Board The development of a Total Maximum Daily Load (TMDL) or pesticide control program is done through a public process with stakeholders, and that is the way that the issue of insufficient detection limits would be addressed if such a program is ever developed for fipronil. At this time, there are no listed water quality impairments for fipronil that require the

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development of a TMDL and the Regional Board has no specific plans for the development of a fipronil control program. If such a control program or TMDL is ever developed by the Regional Board, the issue of detection limits will be addressed through a public stakeholder process, as it has been done for the pyrethroids control program.

COMMENT 1-36: The text in Section 12.2 (page 35) indicates that California Department of Fish and Wildlife have used the EPA method for calculating WQC in cases where only seven of the eight requirements are met when the missing taxon are known to be insensitive. It would be helpful if the data are discussed supporting a conclusion that the missing taxa (i.e., Phylum other than Arthropoda or Chordata such as Rotifera, Annelida, or Mollusca) are insensitive. If data do not support a conclusion that these missing taxa are insensitive then the consequences of this data gap on the WQC should also be discussed.

RTC 1-36: Section 12.2 states that “the missing taxa for fipronil are not known to be insensitive.” Because the missing taxa might be sensitive (data are not available to know whether they are or not), we took the conservative approach and did not calculate an acute WQC using the USEPA 1985 guidelines.

COMMENT 1-37: Fojut et al. (2014) is currently only available as a draft from the referenced State Water Resources Control Board website. The reference to Fojut et al. (2014) in the Fipronil Water and Sediment Quality Criteria Draft Report should be updated to reflect this document is a draft and it would be helpful to indicate which Phase (I, II, or III) report is specifically referenced. It seems that the Phase II report is the one referenced. The appropriateness for SQC to be derived based on draft guidance that has not considered public review should also be made clear to risk managers. Alternatively, if the documents have been finalized then it would be very helpful to reviewers if the final versions could be posted.

RTC 1-37: The UC Davis Sediment Method is still a draft method and has not been finalized. The reference has been updated to indicate it is a draft and refers to Phase II of the method.

COMMENT 1-38: There are many cases where tables are not referenced in the text when numbers from the tables are discussed. This makes it difficult for the reader to find information quickly and it would be helpful to include. For example, Section 8.2.2 would benefit from a reference to Table 20 for the MATC value (0.16 μg/g OC) provided. Section 10.1 would benefit from references to Tables 14 and 21 (which have supplemental data), as well as other tables (with RR data) when used.

Page vii, List of Tables – Tables 21 and 22 are missing from the list of tables. Please add the following:

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Table 21 Supplemental sediment toxicity values excluded from Fipronil/degradates BSQC derivation (found on page 31) Table 22 Threatened, endangered, or rare species predicted values by Web-ICE (found on page 32)

Figure 2 is not referenced in the text. It could be referenced in the third paragraph of the introduction on page 1.

Tables 1 and 2 are not referenced in the text descriptions preceding the tables.

Page 10, Section 5 – The RR sediment studies are summarized in Tables 15-20, not 15-21.

Page 10, Section 5 – Tables 13, 14, and 21 are not referenced in the text.

Page 10, Section 6 – Define SMAV and SMCV on first use (2nd paragraph under aqueous data).

Page 10, Section 6 – There is an error message showing up in the second paragraph that says “(Error! Reference source not found.-7)”. Page 14, Section 7.1.2 – Add a reference to Table 4 when discussing the EC50 value (0.0093 μg/L). Page 15, Section 7.1.3 – Reference to Figure 3 in the first paragraph is incorrect. This should reference Figure 5. Page 17, Section 7.1.4 – Reference Table 6 when discussing the available fish data.

Page 18, Section 7.2.1 – Reference Table 9 for the MATC value (14 μg/L) provided. Page 19, Section 7.2.2 – Reference Table 10 for the MATC value (17 μg/L) provided.

Page 20, Section 7.2.3 – Reference Table 11 for the MATC value (0.97 μg/L) provided. Appendices The page numbering in all the appendices is “C1, C2, C3, etc...” but it would be more helpful if changed to a unique page numbering for each appendix. For example, Appendix A could be A1, A2, A3, etc...and Appendix B could be B1, B2, B3, etc...

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Appendix A Pages C129-130, Fipronil – data for Aedes aegypti reported from Ali 1998 are not listed in Table 14, though study is rated as RL – 95% CI LC50=0.00154 (0.00143-0.00165) μg/L - survival Pages C157-158, Fipronil Sulfide – data for Cheumatopsyche brevilineata reported from Iwafune 2011 are not listed in Table 14; study rated as LL – 95% CI EC50=0.052 (0.042-0.059) μg/L – immobilization

Pages C159-160, Fipronil – data for Cheumatopsyche brevilineata reported from Iwafune 2011 are not listed in Table 14; study rated as LL – 95% CI EC50=0.133 (0.112-0.148) μg/L – immobilization Pages C161-162, Fipronil sulfone – data for Cheumatopsyche brevilineata reported from Iwafune 2011 are not listed in Table 14; study rated as LL – 95% CI EC50=0.066 (0.054-0.078) μg/L – immobilization Pages C163-164, Fipronil desulfinyl – data for Cheumatopsyche brevilineata reported from Iwafune 2011 are not listed in Table 14; study rated as LL – 95% CI EC50=0.177 μg/L – immobilization; Additionally, there is a mistake in the range of confidence interval data. The table has 0.054-0.078 μg/L, but that is for Fipronil sulfone (above) and cannot be the range for a 95% CI of 0.177 μg/L. Pages C165-166, Fipronil carboxamide – data for Cheumatopsyche brevilineata reported from Iwafune 2011 are not listed in Table 14; study rated as LL – 95% CI EC50=4.95 (3.23-26.0) μg/L – immobilization

Pages C167-168, Fipronil – data for Cheumatopsyche brevilineata reported from Yokoyama 2009 are not listed in a Table 14; study rated as LL – 95% CI LC50=0.153 (0.142-0.164) μg/L – survival Page C167 – Typographical error for Test vessels randomized? Result - “Not repoted” should be “Not reported”.

Page C169-170, Fipronil – data for Chironomus crassicaudatus reported from Ali 1998 are not listed in a Table 14; study rated as RL – 95% CI LC50 0.00042 (0.00032-0.00052) μg/L – survival. Pages C195-196, Fipronil sulfide – data for Daphnia magna reported from Iwafune 2011 are not listed in Table 14; study rated LL – 95% CI EC50=28 (22.6-33.8) μg/L – immobilization. Page C228 – Typographical error - “P. clarkia” should be “P. clarkii”. Appendix B

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Page C36-39, Fipronil – data shown for Hyalella azteca from Picard (2015) do not match the H. azteca data presented in Table 15. This appears to be caused by the number of significant figures listed in Table 15 compared to the write up in Appendix B. Table 15 has the LC/EC50 as 13.33 (11.48-15.19) μg/g OC, whereas the LC50 on Page C38 of Appendix B has 13 (11-15) μg/g OC. Please correct this inconsistency.

RTC 1-38: Comments acknowledged. Edits were made as appropriate.

2.2. Comment Letter 2 – Debbie Webster, Central Valley Clean Water Association

COMMENT 2-1: As noted in the draft report, there are insufficient data to utilize the well-established methodology developed by the United States Environmental Protection Agency (USEPA) in developing the proposed water quality criteria for fipronil and its degradates. As an alternative to the USEPA methodology, a methodology was developed by UCD that requires three fewer taxa to develop the proposed water quality criteria for fipronil and its’ degradates. The Central Valley Regional Water Board does not provide adequate information to support the use of the UCD methodology over the USEPA methodology, which has been traditionally used to derive water quality criteria throughout the country.

RTC 2-1: The UCD methodology (UCDM) exists as chapter 3 of a report titled “Methodology for Derivation of Pesticide Water Quality Criteria for the Protection of Aquatic Life – Phase II, Methodology Development and Derivation of Chlorpyrifos” (TenBrook et al. 2009). Chapter 2 of the report provides a thorough review of all existing methodologies worldwide with discussion as it relates to the development of UCDM. Chapter 4 of the report is a case study validating UCDM for the pesticide chlorpyrifos. Readers are referred to this report in section 1 of the draft fipronil report.

COMMENT 2-2: Resulting from the lack of sufficient data, multiple layers of conservative assumptions and adjustments are used to derive the proposed water and sediment quality criteria for fipronil and its’ degradates in the draft report. The cumulative effect of the conservative assumptions and adjustments result in proposed water and sediment quality criteria that appear to be overly stringent with unknown implementation implications. CVCWA and CASA believe that additional research is necessary to develop technically- and scientifically-sound water quality criteria for these constituents.

RTC 2-2: We agree that additional research is needed in order to derive water and sediment criteria for some of these compounds. When toxicity values from highly rated studies are available they should be incorporated into the report.

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COMMENT 2-3: Toxicity test results from Weston and Lydy (2014) represent a significant portion of the toxicity data that were used to develop the proposed water quality criteria. These toxicity tests relied on test organisms that were collected from urban streams approximately 24-hours prior to initiation of the toxicity tests. Because these test organisms were collected from and tested in distinctively different matrices (i.e., urban streams, laboratory water), an evaluation should have been conducted on the test organisms to determine if there were stressors that could affect the outcome of the toxicity tests due to the significant change in environment. Additionally, it is unknown if the test organisms used were of the appropriate age, size, quality, and/or condition that is necessary for toxicity testing. Stressed test organisms that are not allowed to appropriately acclimate may be unreliable for toxicity testing.

RTC 2-3: Additional data was requested and received from the author of Weston and Lydy 2014, including sublethal control response data. All test ratings were updated accordingly and to reflect that some species were field-collected.

COMMENT 2-4: In some situations, it appears that results of the toxicity test controls were not included in the draft report or literature.

RTC 2-4: Sublethal control response data was requested and received from the author of Weston and Lydy 2014. All test ratings were updated accordingly.

COMMENT 2-5: The toxicity tests from Weston and Lydy (2014) utilize subjective observations of sub-lethal endpoints (e.g., impaired movement, immobilization). These sub-lethal endpoints are used to develop the proposed acute water quality criteria. Interlaboratory studies have indicated high variability when evaluating an immobilization endpoint.

RTC 2-5: Section 3-2.1.1.3 of the aqueous method (TenBrook et al. 2009) states that immobility as an endpoint is appropriate. In addition, sublethal control response data was requested and received from the author of Weston and Lydy (2014) and the test ratings were updated accordingly.

COMMENT 2-6: The test organisms used in the toxicity tests were collected 24-hours prior to toxicity test initiation. The lack of a sufficient acclimation period to the typical test conditions may have impacted the sub-lethal endpoints that were assessed in Weston and Lydy (2014).

RTC 2-6: While the acclimation period was shorter than the recommended duration, these tests were otherwise relevant and reliable, and they were included in criteria derivation because there were no other data available for these species and all of these species reside in the watersheds of interest.

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COMMENT 2-7: It is inappropriate to consider sub-lethal toxicity test results in developing acute water quality criteria unless there is a clear linkage between the sub-lethal endpoint(s) and survival, growth, or reproduction. The USEPA clearly identifies acute toxicity as that which is based on mortality over a short time period (USEPA 2002).

RTC 2-7: The UCD method draws from the USEPA method but is a standalone methodology. Section 3-2.1.1.3 of the aqueous UCD method (TenBrook et al. 2009) states that immobility is an appropriate acute endpoint. All studies were rated according to the UCD method.

COMMENT 2-8: The UCDSM relies on toxicity test results from a benthic crustacean (i.e., Hyalella azteca in the draft report) in order to use an AF when insufficient test data are available to meet the five taxa requirements for developing the species sensitivity distribution (SSD). Available data for Chironomus dilutus indicate that it is more sensitive than H. azteca. It appears that the method should be revised to accommodate this more sensitive species.

RTC 2-8: The method itself does not need to be revised to accommodate additional species because the most sensitive species for a given chemical is already used for deriving criteria with an AF according to the method. A benthic crustacean is required as a baseline toxicity value to use the assessment factor procedure, but the lowest toxicity value available (which may be any species) is used for criteria derivation.

COMMENT 2-9: The proposed chronic water quality criteria for fipronil, fipronil-sulfide, and fipronil-sulfone are generally below analytical laboratory detection limits. The inability to accurately determine effluent concentrations from wastewater treatment plants can have significant implementation issues if the proposed water quality criteria are used by the Central Valley Water Board or others to interpret narrative water quality objectives. To date, analytical laboratories have been unable to demonstrate adequate ability to detect low concentrations of fipronil and its degradates in laboratory (i.e., clean) water matrices. Wastewater treatment plant effluent is a more complex matrix that will create further challenges that may result in interferences and/or false positive results.

RTC 2-9: Criteria development is based on empirical toxicity data and not on chemical analysis instrumentation limits of detection. The UC Davis sediment and aqueous methodologies were developed to derive criteria for pesticides in freshwater systems of North America with the express purpose of informing regulators and environmental managers of scientifically sound tolerable levels of these chemicals in water bodies to ensure protection of aquatic life. It is up to regulators to make policy determinations based on derived criteria, which may include consideration of available analytical methods. In the future analytical

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chemistry methods may be developed that can detect very low concentrations of fipronil and its degradates in a range of matrices.

COMMENT 2-10: There appears to be numerous calculation, data transcription, and other editorial errors in the draft report. The data used for developing the proposed water and sediment quality criteria must be comprehensively verified for accuracy. CVCWA and CASA reference the Sacramento Regional County Sanitation District comment letter for these issues.

RTC 2-10: Erroneous values and calculations were corrected during the peer/public review period. Additional data for the Weston and Lydy 2014 studies were received and incorporated during this time as well.

2.3. Comment Letter 3 – Delyn Ellison-Llyod, City of Roseville Stormwater Management Program

COMMENT 3-1: Laboratory control survival for 34% of the tests reported by Weston and Lydy were less than 90%. Control survival of less than 90% is an indication of poor organism quality, poor test conditions, and/or poor test execution. Hence, standard EPA test acceptability criteria for acute tests require control survival of 90% of greater. For tests of fipronil, control survival was less than 90% for Chironomus dilutes (83% and 87% for both tests performed), Baetis tricaudatus (80%), Fallceon quilleri (77%) and Isoperla quinquepunctata (69%). By standard convention and rules of acute toxicity testing, these tests are invalid, and thus should be summarily excluded from the derivation of acute criteria for fipronil. Likewise, test data of similar poor quality (i.e., <90% control survival) should be excluded for fipronil sulfide (tests with C. dilutes and B. tricaudatus) and fipronil sulfone (tests with C. dilutes, B. tricaudatus, Diphetor hageni, I. quinquepunctata, and Hydrophyche sp.).

RTC 3-1: Control survival of <90% is an indicator of an issue with the test. Because these tests were otherwise relevant and reliable, they were included in criteria derivation because there were no other data available for these species and all of these species reside in the watersheds of interest. In addition, sublethal control response data was requested and received from the author of Weston and Lydy (2014) and the test ratings were updated accordingly.

COMMENT 3-2: Acute toxicity tests were performed on wild collected organisms of unknown age and unknown quality. Wild collected organisms were permitted only 24 hours to acclimate prior to use in testing and were not fed which likely resulted in organisms of impaired or compromised quality subject to significant physical and/or environmental stress.

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Moreover, wild collected organisms not kept in culture cannot be verified to be disease free, nor is a site of collection being from areas with “minimal development” (as described by the authors in their publication) sufficient evidence of no prior contaminant exposure. Organisms that have undergone stress can be more susceptible and sensitive to other stressors, such as chemical exposure (e.g., fipronil), thus resulting in measurement bias. Evidence for poor organisms condition included “unacceptable mortality” (as described by the authors in their publication) in test organisms used in tests taken to the standard acute toxicity test duration of 96 hours, hence the performance and reporting of test data for tests of only 48 hours for six of the 14 test species tested. Poor control survival in such a large percentage of reported tests, as summarized in the bullet above, is further evidence of likely poor organism condition.

RTC 3-2: The rating tables for the field-collected organisms were updated to reflect their origin and acclimation period. Section 3-2.1.1.1 defines acute toxicity exposures for insects as lasting from 24-96 hours so the varying lengths of some tests did not cause them to lose points in the rating scheme. While the acclimation period was shorter than the recommended duration, these tests were otherwise relevant and reliable, and they were included in criteria derivation because there were no other data available for these species and all of these species reside in the watersheds of interest.

COMMENT 3-3: Acute toxicity test data were generated on sublethal endpoints, such as inability to swim, inability to cling, inability to crawl, and inability to thrash. Sublethal endpoints are notoriously subjective, and prone to bias and poor inter-laboratory replication. The authors provide no evidence that the scoring of sublethal endpoints was standardized (i.e., lack of any inter-laboratory calibration), such as the standardized use of a stimulus (i.e., squirting with a pipette), or a fixed duration of observation (i.e., observation of organism behavior for 5 minutes). Moreover, given the demonstrated and provable concerns regarding organism quality (i.e., poor laboratory control survival, shortened test duration), it is very likely possible the observation of impaired organism behavior was due to environment, test condition/design, and/or organism condition. Unfortunately, the authors did not report the sublethal behavioral responses of their control organisms, which not only would have provided a means of evaluating this concern, but is a critical step in qualifying organism responses across treatments. Rather, only control survival was reported. The subsequent use of sublethal endpoint data in the derivation of water quality criteria is no insignificant matter, as many of the reported EC50 values (sublethal endpoint) were 2 to nearly 10 times lower than the reported LC50 values (survival endpoint). In fact, in over half of the tests reported, the LC50 could not be calculated, as the true LC50 was greater than the maximum spike concentration tested (i.e., reported as a > value).

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RTC 3-3: Sublethal control response data was requested and received from the author of Weston and Lydy (2014) and the toxicity data summaries have been updated with this information and scoring. The sublethal endpoints were all determined be fall under the category of immobilization. Section 3-2.1.1.3 of the aqueous method (TenBrook et al. 2009) states that immobility is an appropriate acute endpoint. All studies were rated according to the method.

COMMENT 3-4: In an attempt to mitigate for acclimation stress (an admission of the authors own concern for the impaired condition and quality), Weston & Lydy performed the acute tests at in situ test temperatures measured at the time of organism collection. These test temperatures ranged from 8 to 23°C. This introduces a level of measurement uncertainty given the possible temperature dependence of organism sensitivity to fipronil. The authors correctly note this concern themselves, stating “…species comparisons could be confounded by a temperature dependence of fipronil toxicity, much as there is for pyrethroids.” This is especially problematic when the data are used in a species sensitivity distribution.

RTC 3-4: The range of range of species required by the method to calculate the criterion using a species sensitivity distribution includes species from a range of temperatures. Examples include the requirement of a cold water fish from the family Salmonidae. It is reasonable to expand the typical temperature range if suitable species are available, as in Weston and Lydy 2014. The methodology does not allow for rating adjustments based solely on temperature ranges of species unless the temperature is out of range of its natural habitat. The lowest temperature species from Weston was Taenionema sp. at 8°C. Cursory research on the internet indicates that this species typically occupies cold lotic habitats, making this seemingly low temperature reasonable. The highest temperature from Weston was 23°C, which is in the range of tests on other species in the data set (see L. macrochirus by Bettencourt 1992a and I. punctatus by Dionne 1997). When considering the effect of the Weston and Lydy 2014 values in the data sets that utilized an SSD to calculate criteria, it is apparent that they are all greater than the criteria. The fipronil criterion is at least 1.5 times smaller than the lowest Weston and Lydy value (0.02 µg/L versus 0.0324 µg/L). The derived acute aqueous criteria for fipronil-sulfone is 0.0013 µg/L compared to the lowest Weston and Lydy value of 0.0075 µg/L, a difference of more than five times. The acute aqueous criterion for fipronil-sulfide was derived using the AF method and Weston and Lydy 2014 values were not utilized. Even then, the criterion of 0.00062 µg/L is a factor of 15 lower than the lowest Weston and Lydy value in the data set at 0.0093 µg/L.

COMMENT 3-5: All fipronil and degradate treatment concentrations were not measured. Rather, a single treatment in each test was measured for “verification” (each test was reported to contain 4-7 treatments),

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presumably under the assumption that if the single measured treatment was within some unspecified range of acceptability, all other treatment concentrations must similarly be acceptable. In actuality, in the relatively few treatments measured, concentrations ranged from 66-131% of nominal. Most important, the authors noted that the point estimates (EC50 and LC50) were in fact calculated off the uncorrected nominal concentrations, as calculation on the basis of measured concentrations was not possible.

RTC 3-5: The toxicity data sheet tables and ratings have been updated to reflect the lack of measured concentrations, reducing each by 3 points for documentation.

COMMENT 3-6: Given the concerns listed above, it is difficult to understand UCD’s basis for such high relevancy and reliability ratings for the Weston and Lydy toxicity values. At a minimum, the scoring of these data should be re-evaluated, and take into account appropriate point deductions for: 1. Poor control performance (<90% survival), 2. Use of nominal concentrations in calculation of point estimates,

3. Lack of verifiable organism quality metrics (i.e., age/size, prior contaminant exposure, adequate acclimation, disease free, etc.), and 4. Lack of verified test conditions that are within tolerance range of organisms.

While it is the City’s contention that all data corresponding to control survival of <90% be summarily excluded from criteria development, following the relevance and reliability scoring procedures detailed in the UCD criteria development methodology, and appropriately deducting points for the laboratory control responses outside of commonly accepted test acceptability requirements, would result in a corresponding relevance rating of L (less relevant/reliable); per the UCD criteria development methodology such rated data is not to be used for criteria derivation. Appropriately deducting points for the other unreported or unverified test conditions listed above would only further reduce the overall relevancy and reliability ratings.

RTC 3-6: See RTC 3-1, 3-2, 3-3 and 3-5.

COMMENT 3-7: Outside the context of the formulaic rating system of the UCD criteria development methodology, the City is gravely concerned with the derivation of criteria using sublethal endpoints that have not been vetted through inter-laboratory calibration studies. Measuring behavior responses in organisms in a standardized and reproducible manner is extremely difficult. Without standardization, what would appear to be clearly impaired behavior to one analyst could appear as unimpaired to

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another. Moreover, use of wild collected organisms of unknown and unverified condition compounds the likelihood of error in measuring behavioral responses. Without reporting the behavioral response in controls (as was done for the survival endpoint), the prospect that impaired behavior was also present in the controls cannot be evaluated. Given the particular concerns regarding poor organism condition, and the supporting evidence thereof (i.e., poor lab control survivability and need for truncated test duration), the sublethal EC50 point estimates should not be used in criteria derivation as such criteria would likely be used for future regulatory planning and enforcement purposes.

RTC 3-6: The sublethal control response data were received from the authors for the Weston and Lydy (2014) study and these data are now included in the final report so that it is now known to what degree control organisms exhibited immobility. This study was re-rated based on the additional information received from the authors and many tests were rated as relevant and reliable and were included in criteria derivation.

COMMENT 3-8: The City has detailed its objections to the use of assessment factors and default acute-to-chronic ratios (ACR) in prior submitted comments for pyrethroid criteria. Those prior detailed concerns are no different for criteria derived for fipronil and its degradates. The desire for a quantifiable numeric value should not override a reasonable level of scientific uncertainty.

RTC 3-7: Comment acknowledged.

COMMENT 3-9: It is the City’s understanding that the UCD sediment quality criteria methodology was never finalized. There is questionable value in deriving “interim” sediment quality criteria values from an incomplete methodology. The City requests that, until a time the UCD methodology is finalized and an unqualified and scientifically defensible sediment criteria can be derived including sufficient data from source literature), that the interim bioavailable sediment quality criteria be removed from the draft UCD fipronil criteria report in its entirety.

RTC 3-9: The UC Davis sediment method is still a draft method, which is why the sediment criteria are called “interim” criteria. The sediment method will not be finalized until additional data becomes available to properly vet it. The continued effort of developing interim sediment criteria is done to continue gathering data that could be used to finalize the method. The introduction to section 8 of the fipronil report states clearly that the values are not recommended for regulatory use: "The UC Davis Sediment Methodology (UCDSM) is considered only a framework and not a final method because large diverse data sets were not available to use in the development of the method. For this reason, the resulting bioavailable sediment quality criteria (BSQC) are termed interim values, and are

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not recommended for use as firm regulatory values. The term interim is used because there is a high degree of uncertainty in the values because they are based on so few data and species. In order to aid the method development process, sediment toxicity data were gathered for fipronil and interim BSQC were calculated. The interim BSQC calculations are described to provide information to environmental managers, but are not intended to be used as regulatory values." Section 1.2 of the sediment method discusses these issues as well.

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2.4. Comment letter 4 – Roberta Firoved, California Rice Commission

COMMENT 4-1: We provide comments on fipronil in the event the usage pattern impacts the outcome of the overall assessment. Fipronil is an insecticide not registered for use on California rice with no future pending or proposed uses. Therefore, rice has no relevance to fipronil and should be removed from the assessment and report. Data is available on rice because approximately ten years ago, fipronil was evaluated as a potential tool for Rice Water Weevil control at the Rice Experiment Station in Biggs, California. In conjunction with the field trials, the Rice Research Board funded studies at the University of California, Davis on the environmental fate of fipronil. Unfortunately, fipronil does not have a fit in the California rice culture. The U.S. Environmental Protection Agency (U.S. EPA) registered fipronil on rice over ten years ago with the insecticide applied to the crop in the Southern rice states. However, fipronil was never registered for use on rice in California. The California Department of Pesticide Regulation registers and enforces the use of all pesticides sold and used in the state. All pesticides sold and used in the United States must first receive registration from the U.S. EPA and then licensing in the perspective states where sales and use will occur. California is the only state with a program that registers the pesticide after it receives the U.S. EPA registration. Not all pesticides registered by the U.S. EPA automatically receive registration in California. In the final stages of the registration process, the U.S. EPA establishes tolerance from the mandatory data including pesticide residue. The tolerance is the allowable residue of the specific pesticide on a food or feed commodity. “We set tolerances, which are the maximum amount of a pesticide allowed to remain in or on a food, as part of the process of regulating pesticides. In some countries tolerances are called maximum residue limits (MRLs).” ~ U.S. EPA, Office of Pesticide Programs The tolerance for fipronil on rice is listed in the Federal Code of Regulation. Title 40: Protection of Environment. §180.517 Fipronil; tolerances for residues. Rice, grain. 0.04 parts per million. The tolerance for fipronil on rice at the federal level does not, and will not, translate to sales and use on California rice. In checking with the companies registering fipronil, and reviewing product labels, the rice uses no longer exist in the United States.

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We have provided the clarification of the registration status for fipronil on California rice in the event the lack of usage impacts the outcome of the total assessment and report.

Response to comment 4-1: Comment acknowledged.

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3.0 Response to Comment to Peer Reviews

3.1. Peer Review 1 – George Cobb, University of California, Berkeley

The findings of the draft fipronil criteria report are given in italics and the responses of the reviewer are given below the italicized text.

REVIEW 1-1: 1. The physical-chemical data for fipronil and its degradates is accurate and complete. Yes, data included are accurate to the extent that current experimental methodology allows. Section 3 of the Water and Sediment Quality Criteria Report: Phase III contains requisite detail of likely transformation products (Figure 2, page 3), their properties (p.2-5), and transformation processes. This assemblage of data provides a robust understanding of properties and reaction processes that involve for fipronil and its transformation products. Several different determinations are provided for most physical chemical properties of fipronil and its transformation products in Section 3 of the Criteria Report which increases the confidence in the accuracy of estimates that may be derived from averaging.

RTC 1-1: Comment acknowledged.

REVIEW 1-2: 2. Ecotoxicity data screening resulted in a high quality (relevant and reliable) data set for criteria derivation and did not result in removal of pertinent high quality data from the data set used for criteria derivation. The data screening process determines which specific toxicity results will be used for criteria calculation, thus only relevant and reliable data should remain in the final data set. The relevant and reliable data are further prioritized in order to result in robust and appropriately protective criteria. It is also important that high quality data are not screened out of the final data set used for criteria calculation. a. Ecotoxicity data used for criteria derivation with control survival <90%

did not bias the calculated criteria.

Including such data in the absence of a sufficient number of studies with >90% survival is acceptable. Some more pertinent species to a particular assessment may be less frequently cultured or more variable in survival. These data quality are sufficient to allow a better estimate than any other

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approach for assessing toxicity. The fact that studies with >90% survival were unavailable suggests that toxicity assessments for these species should be prioritized in the near future.

RTC 1-2: Comment acknowledged.

REVIEW 1-3: b. Use of toxicity values for field collected organisms with acclimation period less than 48 hours did not bias the calculated criteria.

While acclimation intervals are important for a number of reasons. The absence of other data forces the use of available, high-quality data for this assessment. This situation points to a need for future evaluation of toxicities in these species. After several tests are completed, new data could be used to refine this assessment. It should also be noted that optimization of culturing conditions is not necessarily a simple task. Finally, for some environmentally relevant species survival, fecundity, and growth are difficult to manage in laboratory situations.

RTC 1-3: Comment acknowledged.

REVIEW 1-4: 3. The acute water quality criteria, if attained, are likely to protect aquatic organisms from harmful physiological effects that result from short-term exposures to fipronil and/or its degradates and the criteria calculated are technically valid. The acute water quality criteria are unlikely to be either under- or overprotective. a. The acute criteria derived via assessment factors, described below,

result in criteria that are valid and protective and are not overly conservative.

The rationale for assessment factors was well conceived, and they were properly employed in development of acute criteria. It has long been accepted that using responses of multiple sensitive taxa along with uncertainty factors will provide reasonable assessment factors to protect sensitive species. This approach has received wide national acceptance and has undergone national and international peer review. The primary reason for this process to produce assessment factors that are not protective is to omit toxicity assessments of sensitive species. This is the reason that including some tests with moderate control mortality is essential for a protective assessment.

Given the breadth of species included in the assessment (up to 18), the assessment is unlikely to be overly conservative, even after that number of taxa are evaluated. Any perceived over protection can be easily assessed by testing of additional taxa by producers or users of fipronil. The use of immobilization or mortality as an effect endpoint also limit the

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likelihood that the assessment is overly protective. It would be helpful to include the text in section 7.1.1 stating that immobilization or survival were the endpoints for acute tests in this assessment. This may be self-explanatory to experts, but would help reader who are not steeped in the practice of risk assessment.

RTR 1-4: The following sentence has been added to section 7.1 to make it clear which endpoints are used for acute criteria derivation: Acute criteria are calculated based on short-term toxicity tests (up to 96-hour exposure duration) testing survival or immobilization endpoints.

REVIEW 1-5: It would also be helpful to know in the main document what the most sensitive species was, even if the requisite 5 taxa are available for SSD analysis.

RTR 1-5: In the final report, each criteria derivation section has been revised to state the most sensitive species in the RR data sets. Further information on sensitive species can be found in section 10.1 (Sensitive Species).

REVIEW 1-6: 4. The chronic water quality criteria, if attained, are likely to protect aquatic organisms from harmful physiological effects that result from long-term (i.e., any long period or a duration that covers a substantial portion of an organism’s life span) exposures to fipronil and/or its degradates and the criteria calculated are technically valid. a. The chronic water quality criteria derived via acute-to-chronic ratios are

valid and protective and are not overly conservative. With the dearth of data available, it is difficult to make an argument for an assessment being overly conservative. The data that is available was used and reliable Acute-to-chronic ratios were employed. More taxa would be better to reduce uncertainty and to eliminate the need for ACRs, but failing that, this assessment is certainly not overly conservative. The real question here is whether ACRs are sufficiently protective. ACR provides chronic thresholds of 3.2 ng/L for fipronil, 0.14 ng/nl for fipronil sulfide, and 0.17 ng/L for fipronil sulfone. Measured data show F=17ug/L FS=17 ug/L FSO2=0.79 ug/L. The large difference in measured chronic toxicity data and ACR calculations is that Daphnia dominate the chronic toxicity database and these are over 1000X less sensitive than are benthic invertebrates.

RTR 1-6: We agree that chronic toxicity data for benthic invertebrates, which are known to be more sensitive to fipronil and degradates than daphnids, would be very useful in determining if the chronic criteria are adequately protective.

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REVIEW 1-7: Please note that on p. 18 there should be no units for the calculated SMACR.

RTR 1-7: The units from all species mean acute-to-chronic ratios have been removed.

REVIEW 1-8: 5. The interim acute bioavailable sediment quality criteria were conservatively derived and denote a concentration protective of the most sensitive aquatic life while highlighting data gaps and future studies needed for more robust analysis. Due to the limitations on available data and remaining uncertainty in the UC Davis Sediment Criteria Derivation Methodology, the interim acute bioavailable sediment quality criteria should not be utilized as regulatory values. a. The interim acute bioavailable sediment quality criteria for fipronil and

its degradates are not recommended to be utilized as regulatory values because they may be overly conservative because the data available only account for two species, one of which is known to be particularly sensitive to fipronil and degradates based on the aqueous data sets, and when few data are available the derivation method is conservative to account for cases in which it is unknown whether the available species are relatively sensitive.

The decision that one sensitive species may make an assessment overly conservative has merit in cases where many species are tested. In the case of fipronil and its transformation products, the highest number of species tested is 18. Thus even in the most expansive aspect of the fipronil assessment, the most sensitive species will represent the 5.56th centile of an SSD if toxicities are well correlated to dose. Therefore, the logic does not hold that the high sensitivity of Chironomus dilutus will produce an overly conservative BSQC in this case. The most sensitive species tested in essence provides a close approximation of the criterion value derived from an SSD. The only reasons that the currently available data would not produce a 5 centile toxicity value is that 1) there are other more sensitive species, or 2) Chironomus dilutus is much more sensitive than would be predicted from a probability distribution. It would appear to take 5-6 additional species to develop an SSD that will allow determination of an anomaly in the sensitivity of Chironomus dilutus. With these factors in mind, the BSQC should be used until 5-6 additional species are tested with proper protocols.

This rationale pertains to the other fipronil transformation products. The lack of data for some of the transformation products does, in fact, disallow computation of a BSQC. It seems reasonable to omit BSQCs in the cases where no data are available, although it could be argued that if all BSQC data are to be interim, the transformation products could be assigned

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values equal to the highest BSQC determined for fipronil or a transformation product.

RTR 1-8: Comment acknowledged.

REVIEW 1-9: 6. The interim chronic bioavailable sediment quality criteria were conservatively derived and denote a concentration protective of the most sensitive aquatic life while highlighting data gaps and future studies needed for more robust analysis. Due to the limitations on available data and remaining uncertainty in the UC Davis Sediment Criteria Derivation Methodology, the interim chronic bioavailable sediment quality criteria should not be utilized as regulatory values. a. The interim chronic bioavailable sediment quality criteria for fipronil and its degradates are not recommended to be utilized as regulatory values because they may be overly conservative because the data available only account for two species, one of which is known to be particularly sensitive to fipronil and degradates based on the aqueous data sets, and when few data are available the derivation method is conservative to account for cases in which it is unknown whether the available species are relatively sensitive. Please see response to Section 5 above. To reiterate the most sensitive species from a 20 species sensitivity distribution would be the 5th centile. Until several more species are tested, the Chironomus BSQC data can not reasonably be determined to be overly conservative.

RTR 1-9: Comment acknowledged.

REVIEW 1-10: 7. The water quality criteria were not adjusted based on water quality effects, specific ecotoxicity data, or effects in other environmental compartments; the derived criteria are scientifically sound and technically valid based on the available information on these topics.

This approach is relatively well justified. There are some more conservative (no reduction in toxicity from sorption to organic matter, constant exposures, rather than pulses) and less conservative (no mixture effects, no salinity or oxygen stresses) aspects of the assessment that may be refined by further data. On balance, these factors probably balance one another.

Also, a ternary mixture of pesticides only showed 2.4x more toxic than the individual components. Thus, the 2x safety margins seem to account for this type of effect, but can not account for both species sensitivity and more-than-additive behavior in mixtures.

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The decision not to make adjustments to water quality guidelines is sound even though several sensitive species are far more sensitive than is the criterion. The technical reasons are sound, because the sensitive species are mosquitoes, which would be considered pests and are within the label uses of fipronil. Thus considering these mosquito species is not warranted.

The consideration of ecosystem studies showed limited data regarding fipronil toxicity. This study showed a single species with an LC50, and that value was not below the calculated WQC for fipronil.

Effects on other compartments should be minimal. This conclusion is made partially considering that water and sediment quality criteria are both evaluated in this assessment. If both criteria were not reported, then added modeling or consideration would be needed.

The determination is correct that limited chronic dietary toxicity would be expected for terrestrial species. The single improvement to this evaluation would be to determine the ratio of mallard susceptibility to insecticides as compared to the most sensitive standard avian test species. That safety factor could be incorporated. However, this is unlikely to provide useful information in this situation since the current estimate is above the aqueous solubility of fipronil. The comment is made more for future assessments. This also points to the need for adequate assessments of aquatic and terrestrial species regardless of the compartment most likely to receive the pesticide.

RTR 1-10: Comment acknowledged.

REVIEW 1-11: 8. The assumptions, limitations, and uncertainties regarding derivation of the water quality criteria are accurate and include all factors that significantly affect the resulting criteria. These sections of the report and the methodology demonstrate that the water quality criteria are accurate and include needed factors, to the extent possible. It is unfortunate that there were too few high quality studies to determine a) chronic WQC for fipronil; b) acute and chronic WQC for some fipronil transformation products; and c) acute and chronic sediment quality criteria for fipronil and transformation products. The omission of plant species is reasonable given the mode of action anticipated for fipronil and its primary transformation products. The need for further bioavailability, mixture, and ecosystem studies are obviously needed to improve the overall risk assessment. There is no way to include unavailable data in this assessment.

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RTR 1-11: Comment acknowledged. Plant studies were not omitted but rather were not available for fipronil or any of its transformation products.

REVIEW 1-12: 9. The acute and chronic water quality criteria are appropriate to protect aquatic organisms in the entire Central Valley of California, including the Sacramento River and San Joaquin River Basins as well as the Tulare Lake Basin.

The water quality criteria should be protective of species in the Central Valley of California. The water quality data are sufficiently robust to apply to this geographic region. Caution should be used in applying these criteria more broadly in North America as aqueous constituents, river flow, slope and biogeochemistry of rivers and watersheds are important in determining actual toxicities of pesticides.

RTR 1-12: Comment acknowledged.

REVIEW 1-13: The Big Picture Reviewers are not limited to addressing only the specific topics presented above. Additionally, we invite you to contemplate the following “Big Picture” questions. (a) In reading the Draft Water Quality Criteria Report, are there any

additional scientific issues that should be part of the scientific portion of the water quality criteria derivation that are not described above? If so, comment with respect to the derivation of water quality criteria.

The Report is complete with the possible exception of the interim nature of the BSQC. As noted in the earlier comments, a single most sensitive species in a 20 species sensitivity distribution represents the 5th centile of sensitivity. Thus limiting the enforcement of BSQC because the most sensitive species may be overly protective is not well supported. This aspect of SSDs should be considered as a rationale to use the most sensitive species as the species exhibiting 5th centile sensitivity.

RTR 1-13: Please refer to RTC 3-9.

REVIEW 1-14: (b) Taken as a whole, are the scientific portions of the water quality criteria derivations based upon sound scientific knowledge, methods, and practices?

The assessment is thorough and comprehensive.

RTC 1-14: Comment acknowledged.

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3.2. Peer Review 3 – Nancy Denslow, University of Florida

REVIEW 2-1: There was a comprehensive review of the literature for Ecotoxicity data related to fipronil and fipronil degradates. The published studies were separated into three groups, single species, ecosystem, and terrestrial wildlife. Careful evaluation of each study was conducted, which allowed further segregation of the studies relative to their relevance and reliability. Criteria were developed for how to categorize a study and each study was scored according to the criteria.

To receive an R for relevance, scores had to be > 90, and for reliability, scores had to be >74. These scores are viewed to be as inclusive as possible. Less relevant and less reliable scores were between 70-89 and between 60-73, respectively and these received an L for each of these criteria. Studies below these ranges received an N for not relevant or not reliable and are not considered. Only studies with RR scores for relevancy and reliability were used in calculations of water quality criteria. Studies with lower scores (LR, RL, or LL) were used to further evaluate the criteria to see if it would be protective for sensitive, threatened or endangered species. The scoring criteria for the studies were stringent and explicit. The scoring did not result in removal from consideration of any study with high quality data. I agreed with the scoring criteria used to evaluate the studies.

RTR 2-1: Comment acknowledged.

REVIEW 2-2: For acute toxicity water criteria evaluation, twenty studies received scores of RR for fipronil, ten for fipronil sulfide, eighteen for fipronil-sulfone, two for fipronil desulfonyl, and one for fipronil-carboxamide. When more than one study addressed the same species, then a geometric mean was calculated for the LC/EC50s determined in the studies. The endpoints for which LC/EC50s were determined included immobilization and survival, both of which relate to population level effects. Since fipronil is an organofluorine neurotoxic insecticide that targets the nervous and muscular systems, these endpoints are reasonable. Several studies that covered some of the same species were removed as their endpoints or time points were less sensitive than the final group selected. This was deemed reasonable, as these studies added little to the determination.

Several acute aqueous toxicity values were from tests in which control survival was <90%. I agree that these toxicity values were both relevant and reliable and should be included in the group of studies used to calculate acute water quality criteria even though the survival of controls

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was only 69-87%. It is better to include these studies in order to include more species for the criteria derivation and they fit the parameters of the UC Davis method for judging overall relevance and reliability. It is important to note that data for these species only resided within these studies and the species, for example Chironomus dilutus, are important to the target watershed. This species was one of the more sensitive species to fipronil, fipronil sulfide and fipronil sulfone.

For chronic toxicity studies, three studies had scores of RR for fipronil, one for fipronil sulfide, two for fipronil sulfone, and one for fipronil desulfonyl with growth, survival and reproduction represented in the evaluated endpoints. Several studies with daphnia were removed from consideration as more sensitive endpoints were available and these studies did not add information for the determination. One study with alga was also removed as it was impossible to calculate a MATC.

Supplementary aqueous toxicity studies included a large number of studies for fipronil and degradates that were reviewed but not used in deriving water quality criteria as they were classified as less reliable for a number of reasons including (1) controls were not adequately described or their responses were not acceptable, (2) received a very low reliability score, (3) no standard method was cited, (4) toxicity value was not calculable, or (5) experiments were performed in sea water. These studies were consulted after deriving the water quality criteria and in all cases with the exception of one, the species would be protected by the final criteria concentrations. The species for which the criteria might not be protective included several mosquito species and a midge. They were excluded because actual concentrations of fipronil were not provided and therefore it was impossible to determine if the reported LC50s were reliable. The criteria should not be overly protective. But, if new toxicity data on these species should become available, then they should be considered. Otherwise, the newly established water quality criteria are protective for both acute and chronic exposures.

RTR 2-2: Comment acknowledged.

REVIEW 2-3: Acclimation of organisms for less than 48 h is deemed appropriate as in many cases the studies were to examine early life stages and it would have been impossible to capture these life stages with longer acclimation periods. For the studies in question, individuals in both the control and treatment groups were acclimated for the same length of time, thus any issues due to acclimation would have been perceived for both groups. A period of 24 h is sufficient for cell processes to adapt to the aqueous environment. All studies included in the development of the water criteria measured water parameters that could influence the endpoints and these were in the expected range. Thus, it is unlikely that the aqueous

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environment in the absence of the chemical could have caused changes in the endpoints measured.

There were a few studies where control survival was less than 90%, for example for Chironomus dilutus. It is possible that this less than optimum survival could be due to the 24 h acclimation period. In this study, the age of the organisms at the start of the experiment is not stated. However, all other parameters measured in the study were acceptable. These organisms were obtained from the University of California Berkeley lab culture and are therefore deemed to be of high quality. There were also several toxicity values in the aqueous exposure data sets that were from tests in which the organisms were collected from the field rather than cultured in a laboratory. These studies included the following organisms: Diphetor hageni, Fallceon quilleri, Helicopsyche sp., Hydropsyche sp., Isoperla quinquepunctata, Nectopsyche sp., Serratella micheneri, Taenionema sp. These organisms were studied in California in the watershed of interest and they are difficult to culture in the laboratory. These organisms were not the most sensitive and therefore did not contribute overwhelmingly to the water quality criteria. However, their inclusion allowed the use of a species sensitivity distribution, which is a more robust method for calculating water quality criteria. In addition, there were no other studies that included these species. I agree with the authors that it was best to include these studies, even though they were not perfect. This made for a more robust data set.

In terms of human and wildlife dietary values, there is nothing much in the existing literature to indicate sensitivity to fipronil or degradates. Food tolerances set by the FDA for humans range from 0.005 to 1.5 mg/Kg, well above the water quality criteria determined for ecological species.

Toxicity values determined for the mallard duck (acute oral LC50 > 2,150 mg/Kg) also are much higher than the values for the most sensitive species. Thus it is deemed that humans and terrestrial wildlife would be protected by the water quality criteria established in this risk assessment.

RTR 2-3: Comment acknowledged.

REVIEW 2-4: When deriving acute water quality criteria it is important to not be under or over protective. The methods used by the UC Davis group achieved this goal. The methods used to determine whether or not a sensitivity distribution could be used to calculate the water quality criteria are less stringent than the EPA methods but they are valid because this analysis gives a more realistic value that is protective but not overly conservative. The analysis of toxicity data following a species sensitivity distribution is more likely to provide protection for the intended species. In

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addition, if insufficient species have been examined for toxicity, it is valid to use the lowest acute toxicity and divide this by an assessment factor of 8 to estimate the 5th percentile of the distribution.

To calculate acute criteria using the UC Davis Method, a species sensitivity distribution is fit to the acute data set if five required taxa are available. If the five required taxa are not fulfilled, then there are too few data to fit a statistical distribution, and instead the lowest acute toxicity value is divided by an assessment factor in order to estimate the 5th percentile of the distribution.

A species sensitivity distribution analysis was only possible for acute aquatic levels of fipronil and fipronil sulfone because for both of these there were at least 5 different taxa represented, which met the requirements for the analysis. In fact there were more than 8 taxa represented for both fipronil and fipronil sulfone. For fipronil, it was possible to use the Burr Type III distribution procedure to determine the median 5th percentile at 50% confidence level. For fipronil sulfone, the log-logistic distribution was used, as the Burr Type III did not fit the data set. Both of these distributions were correctly displayed. Since the data used to calculate the 5th percentile values are based on LC50s, it is appropriate to divide the 5th percentile values by a factor of 2 to obtain the final water quality criteria.

For fipronil sulfide and fipronil desulfonyl, there were insufficient taxa represented in the toxicity tests and thus assessment factors had to be used. This can be done if at least one of the taxa included is from the family Daphniidae, which was the case only for fipronil sulfide. For fipronil sulfide there were three taxa represented and an assessment factor of 8 was used to divide the lowest toxicity value to get an estimate of the 5th percentile. While it is accepted that this assessment factor will be conservative, the fact that sufficient data does not exist for a more balanced analysis has to be recognized. The lowest acute toxicity value for fipronil-sulfide was for the midge Chironomus dilutus, which was divided by the assessment factor of 8 to estimate the 5th percentile of the species sensitivity distribution for fipronil-sulfide. The calculated value was then divided by a factor of 2 to obtain the final water quality criteria. The taxa that were available for fipronil desulfonyl did not include the family Daphniidae, thus a water quality criteria was not calculated.

It is recognized that the assessment factor employed was originally derived for organochlorines, organophosphates and pyrethroids, and not directly for fipronil, which is an organofluorine insecticide. However, like the other pesticides, fipronil and its degradates are neurotoxic. The assessment factor is more realistic than usual assessment factors because it was derived directly from pesticide values. The assessment

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factor was viewed as acceptable and probably conservative. This is very reasonable since very little data exists for fipronil sulfide. It was appropriate to not calculate an acute criterion for fipronil-carboxamide since there were insufficient toxicity values for aquatic organisms.

RTR 2-4: Comment acknowledged.

REVIEW 2-5: It was more difficult to calculate a chronic water quality criteria for fipronil or its degradates because insufficient taxa were represented in the toxicity data for species sensitivity distributions. For this type of analysis, toxicity values for at least 5 taxa are required. Because this was not the case for fipronil or its degradates, acute to chronic ratios (ACR) were used to calculate the final criteria, when sufficient data was available. The ACR for each species was calculated as the acute toxicity value (for example the LC50) divided by the chronic toxicity value, which is the geometric mean between the NOEC and LOEC for that species, when paired data existed for both acute and chronic toxicity. From these values, a multispecies ACR can be calculated if there are at least three species represented, including an invertebrate, a fish and one additional species. In this case, the 5th percentile of the acute SSD or the criteria obtained with an assessment factor is used and this is divided by the multispecies ACR. However if less than three species are represented (invertebrate, fish plus one other), then default ACRs are included in the calculation. The default ACR of 11.4 was previously derived for organochlorine, organophosphate and pyrethroid pesticides and was used when a multispecies ACR could not be calculated directly. This methodology was deemed to be appropriate for fipronil and its degradates.

Fipronil: There were three taxa represented in the data set with paired acute to chronic toxicity values for fipronil. However, only one of the datasets for rainbow trout was robust. Thus to calculate the multispecies ACR, the species specific ACR for rainbow trout was used and two default ACRs were used (one each for the two daphnia species). This gave a species mean ACR of 12.1. Using the acute value obtained for fipronil of 39 ng/L and dividing this by 12.1 the chronic water quality criterion was calculated to be 3.2 ng/L. This methodology was deemed acceptable and reasonable because of the available data for fipronil.

Fipronil-sulfide: There was sufficient information to calculate an ACR for Daphnia magna based on paired data sets. But lacking were paired data for a fish and a third important species. Thus, to calculate a species specific ACR, it was necessary to use two default ACRs. Using this information it was possible to calculate a chronic water quality criterion of 0.14 ng/L. This is a conservative criterion but it is deemed reasonable because of the available data for fipronil sulfide.

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Fipronil-sulfone: The calculation of the chronic criterion for fipronil-sulfone was deemed reasonable. For this fipronil degradate, the ACR was based on the acute value calculated for paired data for Daphnia magna and two default ACRs (for fish and a third species). Two default ACRs were included because of the lack of paired acute and chronic data for a fish and a third important species. Note, the default ACR is based on a different class of pesticides, but was deemed reasonable for this study. Using this information it was possible to calculate a chronic water quality criterion of 0.17 ng/L. This is a conservative criterion but it is deemed reasonable due to the lack of extensive data for this degradate.

Fipronil-desulfinyl: A chronic criterion could not be calculated for fipronil-desulfinyl because an acute 5th percentile value or estimate was not available for this degradate, thus an acute-to-chronic ratio could not be applied for calculation of a chronic criterion. This is considered reasonable.

Fipronil-carboxamide: A chronic criterion could not be calculated for fipronil-carboxamide because an acute 5th percentile value or estimate was not available for this degradate, thus an acute-to-chronic ratio could not be applied for calculation of a chronic criterion. This is considered reasonable. The chronic water quality criteria calculated based on available data were considered reasonable and valid. The report specifies exactly how each value was developed and the assumptions used were all correct and considered scientifically sound.

RTR 2-5: Comment acknowledged.

REVIEW 2-6: The UC Davis Method provides guidance on several topics that may result in adjustments to the criteria that are initially calculated. This guidance includes incorporating documented water quality effects quantitatively into the final criteria, comparison to toxicity data for sensitive species, threatened and endangered species, and ecosystem effects (e.g., from mesocosm studies), and checking that the water quality criteria concentrations would not lead to environmental harm in sediment or air, or due to bioaccumulation up the food chain. In many cases, insufficient information is available to fully assess these categories or where information was available, it did not indicate that the criteria required adjustment. No adjustments were made to the criteria, which, the authors conclude is scientifically sound and technically valid.

Among the water quality effects that were considered by the team, there were no studies that suggested bioavailability of fipronil or its degradates

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would change the water quality criteria. Review of the data indicates this to be correct.

There is probably insufficient data in the literature to address mixture effects fully. Binary mixtures suggest the fipronil and degradates would be additive. There is one study that suggests greater than additive toxicity in a ternary mixture of fipronil with atrazine and imidacloprid for saltwater shrimp larvae up to 2.4-fold. Even if this value were taken into account in determining acute or chronic criteria for shrimp, it would not decrease the level of the criteria. The criteria were not adjusted for mixture effects. I agree with this decision.

Other water quality parameters were also considered. Dissolved organic matter can change photolysis of fipronil and how it may be further degraded. But, this did not result in changes to the water quality criteria as fipronil degradates have their own criteria and therefore the environment would be protected regardless of changes in photolysis.

Sensitive species: It was concluded by the authors that most sensitive species would be protected by the criteria. I agree with this conclusion. There were two mosquito species that were reported to be more sensitive to fipronil than the criteria in studies that were less than reliable. However, because the actual concentrations of fipronil were not measured in these studies, these values cannot be considered. Thus there was no adjustment to the criteria. Other sensitive species that were not considered in the derivation of the criteria showed toxicity levels for fipronil and degradates that were higher than the criteria, thus these organisms would be protected by the criteria. No change in the criteria was necessary. This was viewed as scientifically sound.

RTR 2-6: Comment acknowledged.

REVIEW 2-7: The UC Davis Method was originally intended to provide protection for aquatic life in the Sacramento River and San Joaquin River Basins because that was the geographic scope of interest when the project was initiated. However, the authors conclude that these criteria would be appropriate for any freshwater ecosystem in North America, unless species more sensitive than those represented by the species examined in the development of the present criteria are likely to occur in the ecosystems of interest. The species used to develop the criteria are not limited to those that occur in the Sacramento River and San Joaquin River Basins and include any species that is from a Family that is represented in North America. I agree with this conclusion, as the data that was used to develop the criteria looked at all available literature and studies, regardless of location. Thus, the criteria would be protective of all organisms from the families so far examined. The criteria can be applied

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to other locations in California and to other locations in North America. The criteria can also be applied to saltwater locations, as this study showed that toxicity values in salt water were lower than fresh water.

RTR 2-7: Comment acknowledged.

REVIEW 2-8: In my opinion, this study to derive acute and chronic water quality criteria was well done. The methodology used was previously well described and validated in a document entitled “Methodology for Derivation of Pesticide Water Quality Criteria for the Protection of Aquatic Life.” This methodology was used correctly and precisely. In establishing the chronic to acute relationships, a default species specific ACR needed to be used when insufficient paired data sets for taxa were available. The default ACR was previously calculated for organochlorine, organophosphate and pyrethroid pesticides. This value is an estimate and probably conservative but it could be tweaked for fipronil and its degradates with more paired studies. With the available data sets at the present time, the best scientific knowledge was applied in deriving these water quality criteria. It is my opinion that periodic review of the literature (for example every 5-10 yrs) could be performed to see whether the criteria should be adjusted in either direction.

RTR 2-8: Comment acknowledged.

REVIEW 2-9: Taken as a whole, the water quality criteria derivations in this report were performed with sound scientific knowledge. The methods were previously stipulated in a very comprehensive report for organochlorine, organophosphate and pyrethroid pesticides. While fipronil and its degradates are in a different class of chemicals, the derivations performed for the other pesticides cover the toxicity parameters that needed to be investigated for fipronil. The report is very well done, very clearly written and the best methods and practices were used.

RTR 2-9: Comment acknowledged.

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3.3. Peer Review 3 – Rita Schoeny, Ph.D., Independent consultant

The findings of the draft fipronil criteria report and/or the accompanying explanation are given in italics and the responses of the reviewer are given below the italicized text.

REVIEW 3-1: The draft text was poorly written in many sections, verging on incomprehensible in some. The descriptions of methods were inappropriately terse, leaving out citations, rationales for choices, and other information needed to support the derived criteria. While this is a technical document, it is important that it be understood by others than the cognoscenti. I assume that the Water Board will be called upon to defend the legitimacy of its values in a number of venues. Without a clear and comprehensible criteria document this defense will not be possible. It will be worth the effort of re-writing for clarity, including the definition of vague or jargon terms, as well as plainer, more explicit English. I suggested editorial changes in a marked-up Word copy of the text, and I provided many marginal notes containing questions or requesting clarification.

Note that in section 12.3, the authors recommend that the criteria be generalized to ecosystems outside the central California valley. Thus, is it critical that the criteria document be complete and comprehensible.

RTR 3-1: Additional description of methods and rationale has been added throughout the final report so that the document may be easier understood by a variety of readers.

REVIEW 3-2: Many places in the text there is no reference to tables or other places where input values can be found; one way to correct this is to provide not only reference to the table, but also a hyperlink. Hyperlinking could also be done for the constant references to UCDM and references. Another suggestion is to insert the tables in the text at the point they are referenced (or should be referenced). This would minimize the risk a calling out tables that are not to be found in the draft.

RTR 3-2: Readers are able to reference data tables via the Table of Contents, which includes table numbers, descriptions, and page numbers.

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REVIEW 3-3: There are no table legends! To make matters worse, not all abbreviated terms are in the list. For example, Table 3: Nom? Meas?

RTR 3-3: The table headings have been updated to ensure that all abbreviations are described and more description of the table is given.

REVIEW 3-4: Discussion of fipronil mode of action (MOA) should be presented at the beginning of the document. There is confusion (at least in my mind) about the rationale for using AF derived from data on other organic pesticides (e.g. section 7.1.2). There are a few sentences in 7.1.2 alluding to differences (I think) between fipronil MOA and that of other organic pesticides with a neurotoxic endpoint. This, however, is very unclear, and the (terse) description of this MOA does not appear until section 9.2.

RTR 3-4: Section 2 of the final report has been amended to include MOA and other overview information: “Fipronil is a phenylpyrazole insecticide used to control ants, cockroaches, termites, and fleas (such as in topical pet medications). It is a neurotoxin that acts by over-exciting insect nerve and muscle systems by blocking GABA-gated chloride channels and glutamate-gated chloride (GluCl) channels.”

REVIEW 3-5: Section 9.2 does not make sense as written, other than to convey that there are few studies wherein fipronil was tested in conjunction with other pesticides. Also ought there be some discussion of mixtures of fipronil and degradates? There is a section describing the few studies on degradate formation under varying conditions.

RTR 3-5: No highly rated studies were available that addressed mixtures of fipronil and its degradates, but because they are all expected to have the same mode of action they can reasonably be assumed to have additive toxicity. Section 9.2 has been updated to recommend that additive toxicity of fipronil and its transformation products are considered additively when detected together.

REVIEW 3-16 The draft text does not always adhere to common mathematical notation (e.g. in equations) or scientific writing conventions (e.g. write out an acronym or abbreviation at its first appearance, but then continue to use the acronym throughout the chapter or the rest of the document).

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RTR 3-6: Comment acknowledged. Edits were made as appropriate throughout the report. Acronyms have now been written out the first time they are used, and readers are able to look up acronym definitions on page viii as well.

REVIEW 3-7: I have noted many places below where the explanatory text in the request for review was easier to understand, more comprehensive, or just better written than the draft criteria text.

RTR 3-7: Additional description of methods and rationale has been added throughout the final report so that the document may be easier understood by a variety of readers.

REVIEW 3-8: The term “data” is a plural noun.

RTR 3-8: This has been corrected throughout the report.

REVIEW 3-9: I highly recommend that the discussion of the data screening process be expanded. What is provided in section 5 does not suffice and is difficult to understand.

RTR 3-9: Additional discussion has been added to section 5 to further describe the data screening process.

REVIEW 3-10: Ecotoxicity data used for criteria derivation with control survival <90% did not bias the calculated criteria.

There are several acute toxicity values in the aqueous exposure data sets that are from tests in which control survival was <90%.

These toxicity values still rated as relevant and reliable according to the UC Davis method because the tests followed standard procedures and other test parameters were acceptable, although they were rated down for acceptable control response. In these tests, control survival ranged from 69-87%. These tests represent 4 of 18 species for fipronil, 2 of 8 species for fipronil sulfide and 5 of 15 species for fipronil sulfone. The authors concluded that it was appropriate to include all of these toxicity values in criteria derivation because overall the tests were of high quality and rated as both relevant and reliable in accordance with the UC Davis method. There were no other data available for these species and all of these species reside in the watersheds of interest, thus the authors concluded that it was important to include them in criteria derivation as long as the test rated relevant and reliable. In particular, the most sensitive species in the data sets,

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Chironomus dilutus, had control survival ranging from 70-87% in six tests (two tests for each compound) and the authors concluded that removing this data would likely lead to under-protective criteria because chironomids do reside in the watersheds of interest. The above point was not discussed in the text, and it should be, considering that the issue of control survival was specifically raised for scientific peer review. It’s not reasonable to assume that readers will wade through appendices and identify the difficulties with the chosen data. The conclusion of the authors (and their rationale) to include these data in criterion derivation should be presented both in the section wherein the criterion is derived as well as in the discussions of uncertainties and limitations.

RTR 3-10: The issue of some of the data used to calculate criteria having <90% control survival has been added to section 12.1 (Assumptions, limitations, uncertainties) in the final report, so that this issue is highlighted and transparent. The study that this finding refers to was included in the peer review package and we apologize that it was not referenced clearly in the peer review request so that you could easily find it.

REVIEW 3-11: Note that the cut-off values for R, L, and N are not provided in the appendices either. Is it arbitrary, or are they defined in the 2009 UCDM?

RTR 3-11: Section 5 of the fipronil report outlines the use of numeric rating schemes for single-species effects studies that assigns R, L, or N ratings for aqueous and sediment studies. The cut-off values for rating R, L, and N are defined in the UCDM and UCDSM. The numeric scoring range for each rating has been added to the title page of each Appendix that contains toxicity data summaries or rating tables to clarify the cut-off values to the reader.

REVIEW 3-12: Use of toxicity values for field collected organisms with acclimation period less than 48 hours did not bias the calculated criteria. There are also several toxicity values in the aqueous exposure data sets that are from tests in which the organisms were collected from the field rather than cultured in a laboratory.

The standard acclimation period for field-collected organisms is a minimum of 48 hours, but in these tests the organisms were acclimated for 24 hours prior to testing. These toxicity values still rated as relevant and reliable according to the UC Davis method because the tests followed standard procedures and other test parameters were acceptable, although

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they were rated down for appropriate acclimation and potentially having prior exposure to contaminants. The authors concluded that it was appropriate to include all of the above-mentioned toxicity values in criteria derivation because overall the tests were of high quality and rated as both relevant and reliable in accordance with the UC Davis method.

There were no other data available for these species and all of these species reside in the watersheds of interest, thus the authors concluded that it was important to include them in criteria derivation as long as the test rated relevant and reliable. The point above re[garding] acclimation time is not described anywhere in the text. As for the issue of control survival, this ought to be discussed (with choice rationale) in section on criterion derivation and in assumptions and limitations. I can’t judge whether the rationale provided above is sufficient; I’m not convinced that the data rating is appropriate, without some indication that there really was minimal effect of the short acclimation period. At the least the discussion provided by laboratory study authors ought [to] be provided. Furthermore, even in the request for review, the specific studies under questions in points 2a and 2b should be referenced by study author and year. Unreasonable to expect the reviewers to track down the studies from the appendices. Not that I didn’t try; found 16 instances wherein “acclimation” was used in a data evaluation, and none for “control survival”.

RTR 3-12: The issue of using toxicity data from tests with field-collected organisms that were not acclimated for the standard acceptable duration has been added to section 12.1 (Assumptions, limitations, uncertainties) in the final report, so that this issue is highlighted and transparent. The study that this finding refers to was included in the peer review package and we apologize that it was not referenced clearly in the peer review request so that you could easily find it.

1. REVIEW 3-13: The acute water quality criteria, if attained, are likely to protect aquatic organisms from harmful physiological effects that result from short-term exposures to fipronil and/or its degradates and the criteria calculated are technically valid. The acute water quality criteria are unlikely to be either under- or overprotective.

a. The acute criteria derived via assessment factors, described below, result in criteria that are valid and protective and are not overly conservative.

To calculate acute criteria using the UC Davis Method a species sensitivity distribution is fit to the acute data set if five required taxa are available. If the five required taxa are not fulfilled, then there are too few data to fit a

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statistical distribution, and instead the lowest acute toxicity value is divided by an assessment factor in order to estimate the 5th percentile of the distribution. The assessment factors were determined for the UC Davis method based on acute data sets for 16 pesticides, including organochlorines, organophosphates, and pyrethroids. The magnitude of the assessment factors decrease as the number of available taxa increases because the uncertainty of lacking a sensitive species decreases. Assessment factors are commonly used in criteria methodologies to calculate criteria when few toxicity data are available and the UC Davis method is the only source of assessment factors based solely on pesticide data. The 5th percentile value (either determined from the species sensitivity distribution or estimated with an assessment factor), is divided by 2 to calculate an acute criterion because this provides an estimate of a no-effect level from lethal effect toxicity values. There is very little description of rationales for choices in the draft text. I have marked several places where citations, definitions, descriptions, or at least hyperlinks to methodology should be supplied. It is very difficult to judge from the text if the 2009 methodology has been appropriately applied. For example, the description above from the request for review is more complete and coherent than that provided in the text. The paragraph above at least tells the reader why the 5th percentile is divided by 2 to determine the acute criterion. However, in the absence of a citation I am at a loss to ascertain if the rationale for dividing by 2 is grounded in empirical observations, theory or what.

RTR 3-13: Additional description of methods and rationale has been added to section 7 (Water quality criteria calculations) of the final report so that the process and rationale for deriving criteria may be easier understood by a variety of readers.

REVIEW 3-14: The description above for AF is also more comprehensive than that in the text. But neither makes a reasonable argument for the implied difference in effects or mode of action between fipronil and the organochlorines, organophosphates, and pyrethroids. Please see other comments on mode of action.

RTR 3-14: This additional description of the use of AFs has been added to the final report.

REVIEW 3-15: The draft report provides a couple of figures illustrating the acute criterion. These are not discussed as to whether they demonstrate the likelihood that the calculated criteria will be protective of aquatic life.

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RTR 3-15: The aqueous method was developed after a thorough review of all existing methodologies worldwide. Analysis of different species sensitivity distribution models (SSD) is explored in section 2-3.1 (TenBrook et al. 2006). Water quality criteria calculations are presented in section 7. Figures 4 in section 7.1.1 for fipronil and figure 6 in section 7.1.3 for fipronil-sulfone are included in the report as visual comparisons of each final data set to the derived criteria using the chosen SSD. The statistical models were chosen for the aquatic method after a thorough analysis of water quality methods worldwide. Sections 9-11 discuss the protection potential for each criterion considering specific environmental circumstances (if studies were available for such a discussion).

REVIEW 3-16: The text does not provide a rationale for the use of the assessment factor of 8. The arguments for use of AF are incomplete and circular. In discussion of AF, is there any way to gauge the likelihood of under- or over-conservatism in their application? The text mentions something about dependence “on the representation of sensitive species in the available data set”.

The text says only this regarding the determination of the AF: “This value was divided by an AF of 8 because there are acceptable data from three taxa (Table 17, Fojut et al. 2014)”. In the absence of the paper, which is not part of the 2009 UCDM, how is one to determine whether the AF is appropriate?

And the dividing by 2 for criterion is not given a rationale in the text.

RTR 3-16: Fojut et al. (2014) is the UC Davis sediment method that includes some discussion of aqueous data. Paragraph three of section 3.5.1 “Assessment factor rationale” explains that the assessment factor (AF) approach for sediment and water are the same and are modeled on the USEPA Great Lakes methodology, which each use aqueous exposure data to calculate AFs. The sediment method (Fojut et al. 2014) is a more recent publication than the aqueous method (TenBrook et al. 2009a) and contains updated AF values in tables 17 and 18 to be used when following the aqueous method. Section 7.1.2 of the draft fipronil report has been updated to include the above explanation for clarification.

REVIEW 3-17: The derived chronic criteria are certainly quite low, in the ng to 0.1 ng range. This appears to be the result of large adjustment or uncertainty factors in the absence of fipronil- and fipronil degradate-specific data. This is in line with UCDM and other more general established methods of assessment. Whether this is overly conservative

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cannot be ascertained from the draft text. A discussion of how these criteria compare with other neurotoxic pesticide criteria would provide some useful context.

RTR 3-17: Adjustments to the derived criteria were not made for fipronil or any of its degradates. The low levels derived for fipronil chronic water quality criteria are similar or higher than those derived for pyrethroids, which are also neurotoxic pesticides.

REVIEW 3-18: To calculate chronic criteria with the UC-Davis method a species sensitivity distribution is fit to the chronic data set if five required taxa are available. In many cases, there are too few data to fit a statistical distribution, and instead an acute-to-chronic ratio (ACR) is used to calculate a chronic criterion. Acute-to-chronic ratios for individual species are calculated with empirical data for the constituent of interest as the acute toxicity value (e.g., LC50) divided by the chronic toxicity value (e.g., the geometric mean of the NOEC and LOEC). If empirical ACRs are available for one invertebrate, one fish, and one additional important species, then these are used to calculate a multispecies ACR. The chronic criterion is then calculated using the 5th percentile (or whichever percentile was used to calculate the acute criterion) of the acute SSD (or if estimated using an assessment factor) and the multispecies ACR. If empirical ACRs are not available for a given pesticide, then a default ACR is used. The default ACR is 11.4 and was derived based on multispecies ACRs for 10 pesticides, including organochlorines, organophosphates, and pyrethroids.

The above paragraph would be a very useful addition to the draft text.

RTR 3-18: This additional description of the use of ACRs has been added to the final report.

REVIEW 3-19: As far as I can ascertain after much puzzling through acronyms, the UCDM was appropriately applied.

RTR 3-19: Comment acknowledged.

REVIEW 3-20: I did not review the sediment criteria, as my expertise in this area is limited. I did make some comments on the text. I concur with the provision of the interim BSQC, but suggest that the caveats be made more explicit. In particular, the statement “interim bioavailable sediment

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quality criteria (BSQC) are not appropriate for use as regulatory values because of remaining uncertainty in the UC Davis Sediment Criteria Derivation Methodology” be emphasized throughout and included at the beginning of the section.

RTR 3-20: The above statement is taken from the introduction to sediment criteria derivation in Section 8 and this point has also been added to section 12.1 (Assumptions, limitations, uncertainties).

7. REVIEW 3-21: The water quality criteria were not adjusted based on water quality effects, specific ecotoxicity data, or effects in other environmental compartments; the derived criteria are scientifically sound and technically valid based on the available information on these topics. I saw no sound basis for adjustments as indicated in the charge question above. The endangered species table is Table 21, and I suggest that it be included in this section to support the conclusions.

RTR 3-21: Comment acknowledged regarding adjustments to the criteria. The reference to the endangered species table has been corrected to Table 21 in section 10.3.

7. REVIEW 3-22: The assumptions, limitations, and uncertainties regarding derivation of the water quality criteria are accurate and include all factors that significantly affect the resulting criteria. I suggest weighing the impact of the data needs described in section 12. I doubt that all the data gaps are equivalent in terms of their effect on what appear to be good enough criteria.

RTR 3-22: Additional discussion has been added to section 12 to highlight which data gaps are more important.

REVIEW 3-23: The acute and chronic water quality criteria are appropriate to protect aquatic organisms in the entire Central Valley of California, including the Sacramento River and San Joaquin River Basins as well as the Tulare Lake Basin. I don’t recall this being explicitly described in the introduction to the document, nor explicitly supported in section 12. Is the Weston and Lydy (2014) provided as support for generalizing the criteria across California? There is no mention of the Tulare Lake Basin in the draft text. This

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should be explicitly described in section 12. Or some other rationale (described completely) be provided.

RTR 3-23: The draft report states that the criteria are applicable to the Sacramento River and San Joaquin River watersheds because that was the geographic scope that the UCDM and UCDSM were intended to cover. However, criteria derived by these methods utilize toxicity tests with species from families that reside in North America, so the finding is that these criteria would also be appropriate to protect aquatic life in the Tulare Lake basin, as well as other freshwater ecosystems in North America.

REVIEW 3-23: Please see my comments at the beginning of this review. In short, the criteria document is not ready for release in its current state. It is difficult to read, descriptions are missing or incomplete, and several conclusions and choices are not specifically supported.

RTR 3-23: Revisions to the text and additional description and rationale has been added to the final report so that is comprehensible and clear to a variety of readers.

REVIEW 3-24: Given that I am still trying to find the references underlying the questions of control survival and acclimation period, I am hard pressed to guarantee that there are no other issues to be gleaned from the appendices. Please note that I have identified places in the test wherein I feel that support for conclusions is incomplete.

RTR 3-24: Comment acknowledged. Refer to RTR 3-10.

REVIEW 3-25: Taken as a whole, are the scientific portions of the water quality criteria derivations based upon sound scientific knowledge, methods, and practices? I think so. But would not bet my career on it, given the deficiencies in writing and presentation that I have identified throughout the draft document.

RTR 3-25: Comment acknowledged.

REVIEW 3-26: [Reviewer provided editorial comments throughout an electronic version of the report.]

RTR 3-25: Edits were made as appropriate.

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3.4. Peer Review 4 – David C. Volz, University of California, Riverside

REVIEW 4-1: The physicochemical data for fipronil and fipronil degradates appears to be accurate and mostly complete based on information provided within Section 2. However, the authors should address the specific comments below to help clarify several uncertainties and enhance the overall dataset.

RTR 4-1: Comment acknowledged.

REVIEW 4-2: Section 3, pg. 3: Similar to the remaining sections of this report, please insert an opening paragraph that summarizes the available physicochemical data and, more importantly, addresses the potential sources of variability (which, in some cases, span orders of magnitude) observed within certain parameters for fipronil, fipronil-sulfide, fipronil-sulfone, and fipronil-desulfinyl. For example, the Kocs for fipronil range from 396 to 37,154 L/kg. Without providing a discussion, it’s unclear whether these discrepancies are a result of differences in study quality or experimental conditions (e.g., soil type, temperature, pH, etc.).

RTR 4-2: An introductory paragraph has been added to this section to explain that physical-chemical data are relevant to criteria derivation in that they enhance the interpretation of toxicity data. Physical-chemical data are drawn from original studies, when available, and from the resources provided in Tables 3.1 and 3.2 in the method (TenBrook et al. 2009). In many cases the test conditions for the physical-chemical parameters are not included in those resources, and this information is also included in the introductory paragraph.

REVIEW 4-3: Section 3, pgs. 4-5: Within the opening paragraph of Section 3, please clarify the justification for calculating geometric means – especially considering that these means do not reflect the significant amount of variability for certain parameters. In addition, it would be useful to indicate whether these geometric means are ultimately considered or used for deriving water and sediment quality criteria. If not, then please delete the geometric means, as these numbers are a bit misleading.

RTR 4-3: The UCD methodology (UCDM) directs that if several values are available for the same physical-chemical parameter, and all were obtained by acceptable methods, then the geometric mean of the values measured at the same temperature should be used. This guidance is followed in section 3 of the draft fipronil report. In some cases the temperature of the test was unknown and the geometric mean was calculated anyway. The geometric mean is used because there can be considerable variability in the physical-chemical parameters and the geometric mean indicates

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a central tendency that is less influenced by outliers than the arithmetic mean. In many cases, detailed experimental information is not available for physical-chemical parameters and the values cannot be thoroughly evaluated, so the geometric mean is used as the central tendency to account for the potential variability in values. Physical-chemical parameters are used in criteria development in various ways, such as determining if the test concentrations in a toxicity test exceeded the solubility of the chemical, considering whether the chemical degrades significantly in the test duration, or whether the chemical is likely to bioaccumulate.

REVIEW 4-4: Octanol-water partitioning coefficients (Kow) for fipronil degradates were not provided since experimental data were not available. However, two out of four fipronil Kows provided were based on predictions by the BioByte Bio-Loom program. Therefore, using BioByte Bio-Loom or another program (e.g., US EPA’s EPISuite), predicted Kows for fipronil degradates should be provided to ensure that the dataset is complete. Otherwise, if the authors have concluded that experimental Kows are only valid for this report, then fipronil Kows derived from Tomlin 1997 and Donovan and Pescatore 2002 should be deleted.

RTR 4-4: Predicted Kow values for fipronil degradates have been added to section 3 of the report from Bio-Loom and EPISuite. All values available from designated sources and types of sources as specified in Tables 3.1 and 3.2 in the method (TenBrook et al. 2009) were included in the draft fipronil report. In an effort to be as comprehensive as possible, values will not be deleted simply because other values were unavailable.

REVIEW 4-5: Section 3, pgs. 6-8: If geometric means are calculated for other parameters, then geometric means should be calculated and included for hydrolysis, aqueous photolysis, aerobic biodegradation, and anaerobic biodegradation half-lives included within Table 2.

RTR 4-5: Geometric means have been added to tables 1 and 2.

REVIEW 4-6: The study rating system did result in high-quality data, and the use of data with control survival <90% or acclimation periods <48 hours likely did not introduce significant bias when calculating criteria. However, as discussed below, a more important question and concern is whether, as a result of the study rating system used, the calculated criteria are biased as a result of discarding ~70% of usable data points

RTR 4-6: Comment acknowledged.

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REVIEW 4-7: An additional concern is that the majority of toxicity data used to calculate criteria were derived from one study by Weston and Lydy 2014.

RTR 4-7: There was a general lack of data available for degradates of fipronil. Section 12.1 of the final fipronil report has been amended with the following statement to address the concern that the bulk of the data was derived from studies in a single paper: “The majority of the acute aquatic data for fipronil degradates originated from a single journal article by Weston and Lydy 2014. Although the methodology’s numeric rating system was designed to provide objective analysis regardless of the origin of any given study, it would be ideal to have a wider range of data available from multiple laboratories to ensure that the datasets are not influenced by laboratory-specific procedures.”

REVIEW 4-8: Section 4, pg. 9: Both subsections on wildlife LC50 and NOEC values should be moved to Section 5, as the UDCM rating system is not discussed until Section 5. In addition, wildlife toxicity data represent a subset of ecotoxicity data, so it’s unclear why discussion of these data is separate from the other ecotoxicity data.

RTR 4-8: The “Human and wildlife dietary values” section has been moved to be after the “Ecotoxicity data” section in the final report.

REVIEW 4-9: Sections 5-6, pgs. 9-11: Although the UCDM and UCDSM study rating system appears to be a reasonable and scientifically defensible approach for identifying and relying on high-quality toxicity data for water/sediment quality criteria, this rating system is too stringent for prioritizing data within this report, as toxicity data for fipronil and fipronil degradates are relatively sparse compared to other well-studied pesticides (e.g., atrazine). Therefore, by only relying on certain “relevant and reliable (RR)” toxicity data as the basis for calculating criteria, the authors have, in addition to 14 studies rated as not relevant, disregarded the vast majority of usable data – i.e., approximated or less sensitive RR data as well as “supplemental” studies that were rated as “relevant and less reliable (RL)”, “less relevant and reliable (LR)”, or “less relevant and less reliable (LL). If included, these additional data may have resulted in different water/sediment quality criteria based on the methods used within Section 7. For example, it appears as though the majority of discarded data for fipronil was within the range of 1-100 ug/L (this can also be seen as a large gap within Figure 4), raising questions about whether inclusion of these data would have resulted in a different fit of the Burr Type III distribution to the cumulative frequency curve.

RTR 4-9: Studies that do not rate RR have deficiencies that prevent them from being useful for criteria derivation. Some parameters are deemed highly important and will down-rate a study both in terms of relevance and reliability as

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they relate to freshwater pesticide water and sediment quality for the protection of aquatic life in the Central Valley watersheds. Such parameters include the use of freshwater species, valid endpoints, high chemical purity, the ability to calculate toxicity values, and the use of controls. All data in the datasets (both highly rated and supplemental) is considered in section 10 of the report. In this way all data is included in the criteria derivation process to avoid exclusion of particularly sensitive species due to study design and rating.

REVIEW 4-10: In addition, there are also concerns that the majority of RR data used to calculate criteria were derived from one study by Weston and Lydy 2014, raising questions about whether this study is adequately representative of other available toxicity studies.

RTR 4-10: See RTR 4-7.

REVIEW 4-11: Moreover, as a result of only relying on certain RR data, the authors were also forced to use assessment (i.e., safety) factors for some criteria calculations since toxicity data were limited (which was a direct result of discarding data) – an approach that may have introduced more uncertainty vs. relying on all usable data in the absence of assessment factors. Indeed, in some cases, the authors were unable to calculate criteria since requirements for taxa-specific data and assessment factor procedures were not met following data reduction. To address this concern, the authors should consider comparing existing criteria within the report with criteria that are calculated based on the full data set (RR, RL, LR, and LL) without the use of assessment factors (assuming taxa-specific data requirements are met).

Below is a table that summarizes the number and percent of excluded RR, RL, LR, and LL data relative to the full RR + supplemental dataset; data points were summed for each group and compound based on information provided within the data tables provided at the end of the report. As shown below, ~70% (157/224) of usable data points (RR, RL, LR, and LL) were discarded as a result of the rating system used within this report.

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RTR 4-11: See RTR 4-9.

REVIEW 4-12: The acute water quality criteria are likely to be protective of aquatic organisms. However, as discussed above, there are concerns that, as a result of discarding the vast majority of usable data, the criteria may be overprotective – especially considering that the acute criteria for fipronil-sulfide (0.62 ng/L) and fipronil-sulfone (1.3 ng/L) are below current analytical detection limits for both compounds. Likewise, as a direct result of discarding data, the use of assessment factors may have led to overprotective criteria (vs. relying on usable data in the absence of assessment factors).

RTR 4-12: Including the data that is considered supplemental (ratings of RL, LR, or LL) or the RR data points excluded from criteria derivation would not make the criteria less “overprotective.” RR data points are excluded to result in one representative value per species – this reduction process does not reduce the number of species represented, it is a process to choose one representative endpoint for a given species, so this process would not change whether a SSD or AF is used for criteria derivation. The supplemental data may represent other species that were not included in criteria derivation, but they are not used because the toxicity values are not considered relevant or reliable. For fipronil-sulfide and fipronil-desulfinyl, including the supplemental data would still require the use of an AF for criteria derivation because the required taxa for using a SSD are not all available in the supplemental data set. Criteria development is based on empirical toxicity data and not on chemical analysis instrumentation limits of detection (See RTC 2-9). Criteria that are below analytical detection limits do not indicate that the criteria are overprotective, but

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rather indicate that lower detection limits may be useful to environmental managers.

REVIEW 4-13: Section 7.1.1, pg. 11 and Section 7.1.3, pg. 16: Only the 5th percentile at the 50% confidence limit was used for calculating criteria. Therefore, it’s unclear why the other estimates (5th percentile at the 95% confidence limit, and 1st percentile at the 50% and 95% confidence limit) were reported, as this may create unnecessary confusion among readers. Recommend deleting or inserting a statement providing justification for including these numbers within the report.

RTR 4-13: These other estimates are included in the report to give environmental managers additional information about the uncertainty in the median estimates and give them the ability to choose a different estimate to calculate criteria if it is deemed appropriate in their watershed. The final criteria statements in section 12.3 make it clear which set of criteria are the recommended values.

REVIEW 4-14: Section 7.1.1., Figure 4 and Section 7.1.3, Figure 6: Please add minor tick marks to the x- and y-axis so it’s easier to estimate the 5th percentile by hand. In addition, please change the scale of the y-axis to 0.01 to 1 since no data points are below 0.01.

RTR 4-14: Tick marks have been added to the axes. The scale of the y-axis will remain at 0.001-1 to make it clear to readers that data has not been hidden by the truncated axis, otherwise the 1st percentile marker would be difficult to interpret.

REVIEW 4-14: The chronic water quality criteria are likely to be protective of aquatic organisms. However, as discussed above, there are concerns that, as a result of discarding the vast majority of usable data, the criteria may be overprotective – especially considering that the chronic criteria for fipronil (3.2 ng/L), fipronil-sulfide (0.14 ng/L), and fipronil-sulfone (0.17 ng/L) are near or below current analytical detection limits for all three compounds. Likewise, as a direct result of discarding data, the use of ACRs may have led to overprotective criteria (vs. relying on usable data in the absence of ACRs).

RTR 4-14: See RTR 4-12.

REVIEW 4-15: The interim acute bioavailable sediment quality criteria are likely to be protective of aquatic organisms. However, as discussed above, there are concerns that, as a result of discarding the majority of usable data, the interim criteria may be overprotective – especially considering that the criteria for fipronil (4.2 ng/g), fipronil-sulfide (3 ng/g), and fipronil-sulfone (2 ng/g) are near or below the current analytical detection limits for all three compounds.

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RTR 4-15: See RTR 4-9 and RTR 4-12.

REVIEW 4-16: Section 8.1.4, pg. 23: Since all other interim acute BSQCs are reported at ng/g OC, please add one more line that converts the interim acute BSQC for fipronil-desulfinyl from 1.2 ug/g OC to 1200 ng/g OC.

RTR 4-16: This has been added.

REVIEW 4-17: The interim chronic bioavailable sediment quality criteria are likely to be protective of aquatic organisms. However, as discussed above, there are concerns that, as a result of discarding the majority of usable data, the interim criteria may be overprotective – especially considering that the criteria for fipronil (0.7 ng/g), fipronil-sulfide (0.4 ng/g), and fipronil-sulfone (0.3 ng/g) are below the current analytical detection limits for all three compounds.

RTR 4-17: See RTR 4-9 and RTR 4-12.

REVIEW 4-18: Section 8.2.4, pg. 25: Since all other interim chronic BSQCs are reported at ng/g OC, please add one more line that converts the interim chronic BSQC for fipronil-desulfinyl from 0.20 ug/g OC to 200 ng/g OC.

RTR 4-18: This has been added.

REVIEW 4-19: The water quality criteria have adequately considered the available information about bioavailability, mixtures, water quality effects, etc.

RTR 5-19: Comment acknowledged.

REVIEW 4-20: Section 11.1, pg. 31: Within the second paragraph, the authors state that a default BMF of 1 was used yet a BMF of 10 is within the NOEC water equation toward the bottom of the page. Since 1250/321 = 3.89, this is presumably a typo within the equation and needs to be corrected.

RTR 4-20: This calculation has been corrected.

REVIEW 4-21: The authors should insert a section that addresses the potential uncertainty associated within discarding usable data. Ideally, the authors should consider comparing existing criteria within the report with criteria that are calculated based on the full data set (RR, RL, LR, and LL) without the use of assessment factors (assuming taxa-specific data

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requirements are met). Based on the results of this comparison, the authors should then quantify this uncertainty and discuss how inclusion/exclusion of data points alters the calculated criteria.

RTR 4-21: Use of supplemental data (rated RL, LR, and LL) would not provide sufficient data to derive criteria using SSDs for any of the compounds for which AFs were used to derive criteria, so it is not possible to do the comparison suggested by the reviewer.

REVIEW 4-22: Given that the calculated water quality criteria are in the low ng/L range, it is unlikely that fipronil and fipronil degradates will negatively impact aquatic organisms within the entire Central Valley of California if these criteria are met.

RTR 4-22: Comment acknowledged.

REVIEW 4-23: As discussed above, the authors may have introduced significant bias in the calculated criteria by discarding ~70% of usable data points. Therefore, the authors should systematically address the potential uncertainty associated with inclusion/exclusion of data. The authors should also acknowledge and address the shortcomings of using certain criteria that are near or below current analytical detection limits in water and sediment. In other words, how will it be possible to benchmark water and sediment concentrations if certain criteria are below current analytical detection limits? What if fipronil and fipronil degradates are not detected within water and sediment samples? Would this still be a cause for concern for aquatic organisms?

RTR 4-23: The UC Davis method is intended to provide protective levels of pesticides that if not exceeded would not cause adverse physiological effects to aquatic organisms and are based on empirical toxicity data and do not account for current analytical detection limits. Analytical detection limits change over time as methods and instrumentation are developed and current detection limits are relatively close to the derived criteria (less than an order of magnitude above criteria). Environmental managers will determine the levels that require regulatory action, and they may take analytical detection methods into account when determining this.