UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D

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OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

PC Code: 122009 DP Barcode: 422361 Date: October 24, 2014
MEMORANDUM Subjects: Review ofBCS-C060720 (Degradate ofMesosulfuron-methyl) Vascular Aquatic Plant Toxicity Study (MRID 4944 7202) in Support of Registration Review

To:

From: and EFED Response to Registrant's Data Waiver Request for Vascular Aquatic Plant Toxicity Testing with BCS-CV14885, a Degradation Product ofMesosulfuronmethyl Jolene Trujillo, Chemical Review Manager Jill Bloom, Team Leader Linda Arrington, Branch Chief Risk Management and Implementation Branch V Pesticide Re

- Evaluation Division (7508P) Michael Lowit, Ph.D., Ecologist

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.. Sujatha Sankula, Ph.D

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### -0"\) Environmental Fate and Effects Division (7507P)
Review of BCS-C060720 (De gradate of Mesosulfuron-methyl) Vascular Aquatic Plant Toxicity Study
The Environmental Fate and Effects Division (EFED) evaluated a study ofBCS-C060720 (degradate ofmesosulfuron-methyl) toxicity to Lemna gibba, an aquatic vascular plant, in support of Registration Review (Table 1). Please refer to the attached DER for additional details.
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### v urn mary S tu dy Tes t Sp ec ies M RID Study S umm ary Classificatio n 850.4400 Frond number yield, Frond number growth rate, (Aquatic Frond area yield, Frond area growth rate vascular plant ICso > 13 mg ai/L toxicity) Lemna gibba 49447202 Acceptable LOAEC > 13 mg ai/L NOAEC 2': 13 mg ai/L Degradate (98.3% purity) Endpoints affected: none

### 2 Data Waiver Request for Vascular Aquatic Plant Toxicity Testing with BCS-CV14885 EFED reviewed a waiver request from the registrant, Bayer Crop Science AG, in response to the data call-in (DCI) issued as part of the registration reviewof mesosulfuron-methyl. The registrant is requesting a waiv er for vascular aquatic plant toxicity testing (OCSPP 850.4400; Lemna spp.) with BCS-CV14885, a degradation produc t of mesosulfuron-methyl based on the available Lemna gibba toxicity data for BCS-CO60720, a structurally similar compound. In the waiver request the registrant asserts that toxicity to Lemna within the sulfonylurea herbicide class is dependent on the intactness of the methyl ester function of the phenyl ring moiety and that toxicity typically decreases whenthe methyl ester is hydr olyzed to a carboxylic acid. BCS-CV14885 (a carboxylic aci d) is structurally relate d to BCS-CO60720 (the methyl ester variant of BCS-CV14885); both compounds ar e categorized into a carbamoyl-guanidine type structural class. The registrant recently submitted an aquatic vascular plant toxicity study for BCS-CO60720 (MRID 49447202, review presented above). This acceptable study showed no toxicity at the maximum application rate (NOAEC ≥13 mg ai/L), suggesting that BCSCO60720 is at least four orders of magnitude less toxic than mesosulfuron-methyl to Lemna gibba (NOAEC = 0.00019 mg ai/L; MRID 45386310). Therefore, BCS-CV14885 is likely much less toxic than mesosulfuron-methyl given its structural similar ity to BCS-CO60720 and that carboxylic acids are generally less toxic than methyl ester vari ants within a structure class. In the absence of BCS-CV14885 toxicity data , EFED will assume that BCS-CV14885 and BCSCO60720 are equally toxic to aquatic vascular plants. EFED recommends waiving vascular aquatic plant toxicity testing (OCSPP 850.4400; Lemna spp.) with BCS-CV14885 given the lack of toxi city of BCS-CO60720 (the methyl ester variant of BCS-CV14885) compared to mesosulfuron-methyl.