UNITED STATESENVIRONMENTAL PROTECTIONAGENCY WASHINGTON D.C., 20460

Office ofChemical Safety And PollutionPrevention

MEMORANDUM Date: 11/06/2012 Subject:

To:

From:

Through: Revised: EPAResponse to Comments Relatedto the PreliminaryProblem Formulation for Ecological Risk and Environmental Fate, Endangered Species, and Drinking Water Assessments forNicosulfuron (PC 129008,DP Barcode 405477)

AndreaMojica, RiskManager Reviewer Kevin Costello, Team Leader RiskManagement and ImplementationBranch (RMIB 4) Pesticide Re-evaluation Division (PRD)**~** 

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Gabriel Rothman,Environmental Scientist

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Mah Shamim, PhD, Chief

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In response to the posting inthe public docket ofthe "RegistrationReview: Preliminary Problem Formulation for Environmental Fate, Ecological Risk, Endangered Species, and Human Health Drinking Water Exposure Assessments for Nicosulfuron" (Document ID EPA-HQ-OPP-2012- 0372-0006 in www.regulations.gov), the registrant E.I. DuPont De Nemours and Company (Dupont) provided comments during the public comments period related to the data requests for both the environmental fate and ecotoxicity studies for nicosulfuron. The purpose of this memorandum is to addressthese comments.

This revised memorandum (modifiedto include the PC code) is separated into the Environmental Fate and Effects Division's (EFED) responses based on whether the comments relate to the fate
or the toxicity ofnicosulfuron. The first section addresses the comments provided by DuPont regarding the environmental fate data gaps section of the EFED problem formulation. The second section addresses the comments concerning the ecotoxicity data gaps section of the EFED problem formulation.

Page 1EnvironmentalFate

DuPont confirmed that the following studies requested in the problem formulation have recently been submitted to the Agency and contends that these studies should address the related data requests:

• AnaerobicAquaticMetabolism (835.4400) for Nicosulfuron: MRID No. 48790905

• IndependentLaboratory Validations (ILVs) for Water and Soil Environmental Chemistry Methods (ECMs) for Nicosulfuron: MRIDNos. 48790913 and 48790914

In addition, DuPont has expressed their intention to submit an Aerobic Soil Metabolism study (835.4100) to address the related data request for nicosulfuron. DuPont claims that this study addresses EFED's concerns related to extraction methods for unextracted residues and the quantity ofsoils that are currently available for considerationinthe risk assessment.
Furthermore, DuPont is requesting a waiver for conducting environmental fate studies including the measurement of Vapor Pressure for the IN-10290 degradate (830.7950) and the Anaerobic Soil Metabolism study for nicosulfuron (835.4200). The summary of the registrant's justificationsbroken downby each study and EFED'sresponses are providedbelow:

830.7950 Vapor Pressure (IN-J0290)

EFED requested the measured vapor pressure for this degradate to clarify its physical chemical properties since it was identified as a residue ofconcern for ecological organisms inthe problem formulation. Volatility of this degradate is uncertain since EpiSuite indicated it was semivolatile with an estimated vapor pressure of 1.74 x 10-3 torr at 25°C yet no volatile materials
were detected in any of the soil metabolism studies. DuPont is requesting a waiver for the following reasons:
1. A study, not submitted to the Agency, indicated that IN-10290 is tightly bound to soils given its average measured Kct value of45 mL!g and 

### Koc value of 1,707 mL/g. Therefore, it is not likelyto be lostto the atmosphere.

2. Another study, not submitted to the Agency, indicated that IN-10290 degrades quickly in soils, with DT50 values ranging between 3

- 11 days. Therefore, any loss of this degradate to the atmosphere would be further restricted due to its rapid degradation in soil.

EFED Response: EFED has reconsidered this data request based on the justification by the registrant described above. EFED agrees to support a waiver request for the measured vapor pressure. However, EFED requests the submittal ofthe above cited studies on soil degradation and soil mobility ofthe IN-J0290 degradate to the Agency to address its fate characterization. In theirjustification, DuPont expressed a willingness to submit these cited studies.

Page 2835.4200AnaerobicSoilMetabolism (Nicosulfuron)

EFED requested additional soils to be evaluated since only one soil 1s currently available. DuPontis requesting a waiverfor the following reasons:

1. The same two major degradates formed in the available soil then in the identical soil evaluated in the aerobic soil metabolism study. Therefore, evaluations ofadditional soils willnotlikelyprovide additional information.

2. An anaerobic aquatic metabolism study has historically been accepted by USEPA in lieu ofananaerobic soil metabolism study.

EFED Response: EFED has reconsidered this data request based on the justification by the registrant described above. EFED agrees to support a waiver request for the anaerobic soil metabolism study.

A revised summary of the status of environmental fate studies based on the correspondence above is provided in Table 1.

Table 1. Status ofenvironmentalfate studies referenced byDuPont related to environmental data gaps.

Guideline StudyTitle Submitted MRID Status Number 835.4100 Aerobic Soil Metabolism Study 46240901 Additional studiesto (Nicosulfuron) 41082622 be submitted according to DuPont 835.4200 Anaerobic Soil Metabolism 41082623 Additional study Study waived (Nicosulfuron) 850.4400 Anaerobic Aquatic Metabolism 48790905 In Review (Nicosulfuron) 850.6100 IndependentLaboratory 48790913 In Review Validations (ILVs) for 48790914 Environmental Chemistry Methods (ECMs) (Nicosulfuron) 830.7950 Vapor Pressure N/A Waived. However, (IN-J0290) submittal ofregistrant cited mobility and soil degradation studies to the Agency requested to address fate characterization.

Page 3EcologicalEffects

DuPontprovided commentsrelated to the ecotoxicitydatagaps section andhighlighted a number ofstudies that they submittedto the Agency in support ofthe registrationreview ofnicosulfuron. According to DuPont, they submitted studies that are currently in review by EFED to fulfill the guidelines outlined in Table2.

Table2. Status ofnicosulfuron ecotoxicitystudies referenced byDuPontrelated toecotoxicity data gaps. a Guideline StudyTitle SubmittedMRID Status Number 850.2100 Avian Oral Acute 48790909 InReview 850.2300 Avian Reproduction 48354306 In Review 48354307 850.1025 Estuarine/Marine MolluskAcute 48790906 In Review 850.1035 Estuarine/Marine Shrimp Acute 48790907 In Review 850.1075 Estuarine/Marine Fish Acute 48790908 In Review 850.1400 FreshwaterFish Early Life-Stage 48448001 InReview 850.4225/ Seedling EmergenceNegetative N/A Identified as data gap 850.4250 Vigor (Tier II) in EFED's registration review problem

formulation 850.4400/ Aquatic Plant Growth (Tier II) 48354308 In Review 850.5400 48790909 4637030l 43014201 4837640 Non-guideline Terrestrial Plant Reproduction N/A Study not needed for Study risk assessment aN/A=Notavailable. Additional studies to satisfy the guideline have notbeen submitted by the registrant.

Given these submissions, EFED will review this data for acceptability for use in the risk assessment. EFED notes thattwo ofthe studies, one an avian acute oral study and one an aquatic vascular plant study withLemna, have the same MRID (48790909) in the comments by DuPont. EFED has confirmed that this MRID belongs to the avian oral acute study with a passerine species. Itis unclear why DuPontreferred to this MRID also as a plant study. Itis possible that DuPont meant to cite MRID 48790910, which is a non-vascular plant study with Skeletonema costatum that addresses 850.5400, not 850.4400 as stated in the comments from DuPont. EFED also notes thattwo ofthe studies inthe comments on aquatic non-vascularplants do nothave full MRID citations (4637030 and 4837640). Itis also possible that DuPont meantto refer to MRID 46370301 (study with Selenastrum capricornutum) and MRID 48376501 (study withAnabaena jlosaquae). This latter study was conducted with a formulated product. DuPont also refers to
an aquatic vascular plant study (MRID 48354308) to fulfill guideline 850.4400. This study is currently in review, but it also appears to be conducted with a formulated product. For aquatic planttoxicitytesting, the 40 CFRpart 158 guidelines for toxicitytesting typicallyrequire the test to be conducted with the technical grade active ingredient. However, EFED will review the
Page4submitted studies highlighted above and determine the value ofadditional data related to aquatic vascular plants. Finally, EFED confirms the need for acceptable tier II terrestrial plant toxicity studies as outlinedinthe registrationreviewpreliminaryproblemformulation.

In contrast to the majority of toxicity studies, DuPont believes that the terrestrial plant reproduction study is not necessary for the risk assessment. DuPont suggests that the standard tests are sufficiently protective of all effects on terrestrial non-target plants, including reproductive effects. EFED agrees with DuPontregarding the plantreproduction study. EFED's Plant Technical Team (PTT) conducted an analysis ofavailable SU plantreproduction data from the open literature and the registrant-submitted data for chlorsulfuron and concluded that data from the 850.4150 vegetative vigor guideline study are sufficiently protective of potential impacts to plant reproduction. Acetolactate synthase (ALS) inhibitors primarily affect metabolically-active meristem tissues. When plants are exposed at a young, vigorously growing life-stage, effects are expressed primarily as inhibition ofvegetative growth (i.e. biomass, shoot length). As plants mature these effects are less pronounced. However, as plants enter their reproductive life-stage, the metabolically-active tissue will include flower and seed production. Plants exposed to SU herbicides during the reproductive life stage are likely to exhibit adverse effects on reproduction, generally expressed as reduced seed number or reduced seed weight. Based on the latest data analysis, these effects are expected to occur at similar concentrations to those effects determined in the guideline vegetative vigor studies (850.4150) so additional data
on effects to plant reproduction are not necessary for the registration review risk assessment for nicosulfuron.

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