UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D

. C. , 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

MEMORANDUM PC Code : 122990 D422848 October 3, 2014

SUBJECT: Reclassification of 6 Mesotrione Aquatic Ecotoxicology Studies

From:

Reviewed:

Through :

To: Michael Wagman, Biologis t E nvironmental Risk Branch 6 Environmental Fate and Effects Division (7507P)

Amy Blankinship

, Chemist

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Environmental Fate and Effects Division (7507P)

Mark Corbin, Branch Chief

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Jolene Trujillo

, Chemical Review Manager Linda Arrington, Branch Chief Risk Management and Implementation Branch V Pesticide Re

- evaluation Division (7508P)

As part of the problem formulation for the ecological risk and drinking water exposure assessments for mesotrione (PC Code 122990; D417229), a review of the available ecotoxicological data was performed. While the classification for many of the submitted studies did not change after review (st ill deemed Acceptable), the classification for a number of aquatic toxicity studies did change. The reason(s) for the change in the study classifications varied but included: the occurrence of strongly acidic test conditions in treatments and/or strongly basic conditions in controls, presence of precipitate in samp l es without removal (filtration/centrifugation) prior to analytical analysis, and/or lack of ability to discern a doseresponse. These study limitations introduce uncertainty in the ability to adequately discern a treatment-related effect. With the exception of the study on mesotrione's degradate, MNBA
, effects on green algae 

### (MR ID 4490171 0; this study was already considered supplemen ta l) EFED has reclassified the studies from "Acceptable" to "Supplemental". Further, most of these studies (with the exception ofMRID 44505121, aquatic plant test using the freshwater diatom, Navicula pelliculosa) should only be used qualitatively as they are not of suffiCient quality for quantitative

use in risk assessments. A list of the studies and rationale for reclassification of each study is provided below. In general, while these studies were reclassified, additional data is not requested at this time. The reclassification of the chronic daphnid li fe cycle test (MRID 4450501 0) results in a lack of chronic data for any aquatic invertebrate; however, since the acutemysid toxicity endpoint was much more sensitive than the acute daphnid toxicity endpoint

,

EFED recommends that a new chronic aquatic invertebrate study (850.1350) be requested using mysids. EFED intends to then use the acute and chronic estuarine/marine invertebrate data in an
acute

- to

- chronic ( ACR ) approach to estimate a ch ronic freshwater invertebrate endpoint.

Table 1 : Ecotoxicological data requirements for Mesotrione

MRID Study Classification 1 Remarks

44505121 Supplemental Study was previously identified as acceptable. Study may be used quantitatively in risk assessment. See below for rationale for downgrade.

44901710, 44505007, 44505010, 44505124, 44505122 Supplemental Studies were previously identified as acceptable (or in the case of MRID 44901710, could have been used quantitatively in risk assessment)

. These s tudies may not be used quantitatively in risk assessment. See below for rationale for downgrades.

1 OPPIN Classifications: Acceptable; Acceptable/Guideline; Acceptable/Non

- Guideline; Cited; Confirmatory; Decision Deferred; Extraneous submission; Guideline; In Review; minimum; No Decision; Partially Acceptable; Satisfactory; Screened

- acceptable for review; Screened

- not acceptable; Supplemental; Supplemental/Non

- Guideline; Unacceptable ; Unacceptable/Guideline; Unacceptable/Non

- Guideline; Upgradeable

. 3 EPA Accession Number; No MRID number was assigned for this study.

EFED has reviewed and reclassified the following studies submitted for Mesotrione (PC Code 122990):

Kent, S.J., N. Shillabeer, J.E. Caunter, S.J. Wallace. ZA1296: Acute Toxicity to the Sheepshead Minnow ( Cyprinodon variegatus ). Unpublished study performed by Brixham Environmental Laboratory, Brixham Devon, UK. Laboratory Report No. BL5592/B. Study sponsored by ZENECA Ag Products. Study Completed on Febru ary 16, 1996. MRID 44505007.

This study on s heepshead minnow ( Cyprinodon variegatus ) was initially considered to meet the 850.1075 guideline requirement. However, mesotrione concentrations were above solubility at the two highest treatment levels, no co

- solvent was used and precipitate was formed, although samples were centrifuged prior to chemical analysis. Even at the lowest concentration (100 mg/L (ppm) ), the solution was pale yellow and was progressively darker in each higher test concentration

. S ma ll amounts of precipitate were observed in the 180 and 320 mg/L nominal treatment levels which dis solved after 24 hours

, while precipitate in the higher treatments remained throughout the duration of the test. Initial concentrations were not included in t he mean measurements as the study authors suggested that during the majority of the study the measured concentrations were closer to those values obtained at 48 and 96 hours than the 0

- hour concentrations. Additionally, the pH in the two highest treatment levels was very low (pH<4.5

, likely due to the addition of the test substance )
, and may have caused the toxicity in those treatment levels, rather than the inherent toxicity of the test compound. Sublethal effects including sounding, loss of balance, wea kness, rapid respiration and ceased swimming were observed in all treatment groups except the lowest concentration (100 ppm). Previously, theLC 50 from this study was reported as 520 ppm. Due to the issues discussed , this LC 50 value is

not considered valid. However, since no mortality or sublethal effects were observed at the 100 ppm concentration level, the observed NOAEC is considered to be 100 ppm , and t he 96

- Hr LC 50 is considered to be greater than 100 ppm. Since these values are approximately 3

- 4 orders of magnitude above the expected maximum EECs f rom all recently conducted assessments (US EPA, 2014; D 415369 )
, acute risk is not anticipated to be likely to this taxa and a new acute mortality study for an estuarine/marine fish is not requested a t this time.

Morris, D.S., H. Kelso, N. Shillabeer, N.J. Williams, and S.J. Wallace. ZA1296: Chronic Toxicity to Daphnia magna. Unpublished study performed by Brixham Environmental Laboratory, Brixham Devon, UK. Laboratory Report No. BL5832/B. Stud y sponsored by ZENECA Ag Products. Study Completed on January 31, 1996. MRID 44505010

. This study on the waterflea, Da phnia magna

, was initially classified as acceptable. During the

re

- evaluation of the study, several deficiencies were noted with this study including that the three highest treatment solutions (≥ 320 mg/L) had extremely acidic conditions (pH 3.8

— 4.7) which likely caused the toxicity observed in those treatment levels, rather than any inherent toxicity of the test compound. Additionally, t hose concentrations also had precipitates in their solutions (it appears that the undissolved material was separated from the solutions prior to sample analysis, but the study does not state how the separation was accomplished) . However, a more serious problem with this study is that the most sensitive endpoint, dry weight, did not exhibit a dose

response relationship where as at the lowest treatment concentration (97 mg/L) , mean dry weight

was significantly reduced by 46 % compared to controls, but at the next highest treatment group of 180 mg/L, mean dry weight was reduced 18 % compared to controls and was not considered statistically significant ly different than control daphnids . Since mortality was 100% at all higher treatment levels, the dose

- response relationship for dry weight in the study cannot be determined from only those two treatment levels that had surviving daphnids and which had highly inconsistent results. Therefore, the classification of this study is now supplemental and may only be used qualitatively in a risk assessment.

As a result of this reclassification, there are no data available for mesotrione’s effects to aquatic invertebrates. The lack of this data is a major data gap. However, since mesotrione was much more acutely toxic ( ~250x) to mysids than to daphnids, EFED is requesting that an estuarine/marine life cycle test be conducted with the mysid, Mysidopsis bahia (OPPTS 850.1350)

. A new chronic freshwater invertebrate test is not requested at this time. EFED intends to use t he data generated from the chronic estuarine/marine life cycle test to calculate an Acute

- to

- Chronic Ratio (ACR) and derive a freshwater invertebrate chronic value from this ACR using t he available acute daphnid data.

Smythe, D.V., S.J. Kent, and N. Shi llabeer. ZA1296: Toxicity to the Blue

- Green Alga Anabaena flos

- aquae . Unpublished study performed by Brixham Environmental Laboratory, Brixham Devon, UK. Laboratory Report No. BL5801/B. Study sponsored by ZENECA Ag Products. Study Completed on July 13, 1996. MRID 44505122

. This study on the blue

- green algae, Anabaena flos

- aquae was initially classified as acceptable. However, precipitate formed in the highest test concentration (175 mg/L) and there was no filtration or centrifugation of test samples prior to chemical analysis . Additionally, the pH in thetwo highest treatment concentrations (96 and 175 mg/L) declined to very acidic conditions over

the course of the test (pH 3.6

— 4. 1) which is likely to have caused the cell death at these concentratio ns, rather than any inherent toxicity of the test chemical. For these reasons, the classification of the study is changed to supplemental, for qualitative use only for the I C 50 endpoint . However, since pH levels remained within test guideline conditions at all other concentrations, the calculated NOAEC for this study remains at 56 ppm, and the I C 50 is reported as > 56 ppm. As these endpoint values are much higher (≥ 3 orders of magnitude) than the maximum EECs predicted from any previous assessment for m esotrione uses and the available data (including this study) indicate that nonvascular aquatic plants do not appear to be particularly sensitive to mesotrione, a new study is not requested at this time.

Shillabeer, S.J. Kent, and D.V. Smyth. ZA1296: Toxi city to the Green Alga Selenastrum capricornutum . Unpublished study performed by Brixham Environmental Laboratory, Brixham Devon, UK. Laboratory Report No. BL6113/B. Study sponsored by ZENECA Ag Products. Study Completed on August 27, 1997. MRID 445051 24

This study conducted with the green algae, Pseudokirchneriella subcapitata (formerly described

as Selenastrum capriocornutum ) was initially classified as acceptable. However, the pH in the control and lowest two treatments (0.39 and 0.82 mg/L) reached very basic conditions (pH 9.9

--- 10.0) by the end of the test, which may indicate that the algal cultures had grown to the extent they were at the upper bound of the test systems carrying capacity. These high pH levels are unlikely to repres ent actual conditions in the environment and may have inhibited performance in each of these groups , most importantly in the control group . This leads to uncertainty around the IC 50 estimate. As such, the classification of t his study is now supplemental and the IC 50 estimate should not be used quantitatively in risk assessment. While controls may be compromised in these suboptimal co n ditions, as the pH was similar in the two lowest treatments and controls and growth rates remained similar between these t wo lowest treatments compared to controls, it is expected that these treatment levels would still be similar to controls under the optimal conditions suggested by the guideline recommendations. Therefore, the NOAEC of 0.39 mg/L is still considered valid a nd the I C 50 is now considered to be > 0.82 mg/L. Since there is still a large difference between these endpoints and either the most sensitive aquatic plant data (duckweed IC 50 of 17.7 ppb) or the maximum EECs predicted fr om past assessments ( USEPA, 2014, D 415369 )
, a new study is not requested at this time.

Smythe, D.V., S.J. Kent, and N. Shillabeer. ZA1296: Toxicity to the Freshwater Diatom Navicula pelliculosa

. Unpublished study performed by Brixham Environmental Laboratory, Brixham Devon, UK. Labo ratory Report No. BL5780/B. Study sponsored by ZENECA Ag Products. Study Completed on June 29, 1996. MRID 44505121

This study conducted with the freshwater diatom, Navicula pelliculosa was initially classified as acceptable. However, the dose

- response relationship observed in the study was not what is typically expected in algal toxicity studies. The test substance appeared to elicit progressively increasing stimulation of algal colonies with concentration (11

— 46% stimulation compared to controls) exc ept for the very highest concentration of 92 mg /L which experienced a 96% decrease in cell density compared to the control plants. Due to this lack of a dose

- response relationship and the resulting lack of confidence around the IC 50 estimate (for which 95 % confidence intervals could not even be defined) , the study is classified as Supplemental, but maybe used for quantitative purposes in risk assessment. The study’s NOAEC and EC 25 are 46 mg/L

and 68 mg/L, respectively. These endpoints are significantly higher than other available endpoints for aquatic plants. A new study with freshwater diatoms is not requested at this time.

Smythe, D.V., S.J. Kent, and N. Shillabeer. MNBA: Toxicity to the Green Alga Selenastrum capricornutum . Unpublished study pe rformed by Brixham Environmental Laboratory, Brixham Devon, UK. Laboratory Report No. BL6066/B. Study sponsored by ZENECA Ag Products. Study Completed on July 31, 1997. MRID 44901710

. This study conducted with the green algae, Pseudokirchneriella sub capitata (formerly described

as Selenastrum capriocornutum ) was initially classified as Supplemental due to it only being conducted for 72 hours (following OECD’s TG 201 guideline) , rather than the EPA 850.4500 guideline recommendation of 96 hours

. Althou gh the study is still considered S upplemental, this

rev iew is meant to indicate that the data contained within should no longer be considered of quantitative value, but may only be used for qualitative purposes in risk assessment. This clarification is du e to the fact that the pH in the control and four lowest treatment groups rose to very high basic levels (pH 9.5

— 10.0) and declined to very acidic levels (<4.5) in the three highest treatment doses. These high and low pH’s are unlikely to represent releva nt conditions in the environment and are likely to have impacted both control performance and each treatment level’ s performance. It is likely that the 100% inhibition exhibited in the three highest treatment doses were due to the acidity caused b y the tes t compound and may not reflect any inherent toxicity of the test chemical. The combined effects of these pH issues result in a high degree of uncertainty around the I C 50 and NOAEC endpoints and make comparison with the green algae study ( MRID 44505124
, see above ) with parent mesotrione difficult. However, in this study since the pH of the control and three lowest concentrations (3.3

— 10 mg/L) was similarly high and only minimal inhibition (<3%) was observed in these concentrations compared to controls

. W hile the green algae study with parent mesotrione had significant inhibition at concentrations as low as 1.5 mg/L, it does not appear that MNBA is likely as toxic as parent mesotrione t o non

vascular aquatic plants. Although there is still some uncertain ty as to the comparison of MNBA’s toxicity to vascular aquatic plants (which are much more sensitive to parent mesotrione than non

- vascular aquatic plants) compared to parent mesotrione, new data for this taxa is not requested at this time. In the absence of additional data, conservative assumptions may be made in the risk assessment, such as considering MNBA as toxic to vascular aquatic plants as parent mesotrione.

References

USEPA, 2014

. Mesotrione: Drinking Water Exposure Assessment for New Use on M esotrione

- Tolerant Soybean. (DP Barcode 415369 ). April, 2014. USEPA/OPPTS/OPP.