UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

Office of Chemical Safety 

And Pollution Prevention 

MEMORANDUM Date: 11/06/2012 

Subject: 

To: 

From: 

Through: 

Revised: EPA Response to Comments Related to the Preliminary Problem 

Formulation for Ecological Risk and Environmental Fate, Endangered Species, 

and Drinking Water Assessments for Nicosulfuron (PC 129008, DP Barcode 

405477) 

Andrea Mojica, Risk Manager Reviewer 

Kevin Costello, Team Leader 

Risk Management and Implementation Branch (RMIB 4) 

Pesticide Re-evaluation Division (PRD) ~ LJ2___ 

Gabriel Rothman, Environmental Scientist ~~ / /-::;- fl.. 

Jose.ph DeCant, ~cologist /~~-<;J' l / '! ,;._( '{ r;·_:"j- 1/-(.. ~~ Envuonmental R1sk Branch::S' // 

Environmental Fate and Effects Division (EFED) 

Mah Shamim, PhD, Chief ~/.._f-:.._..._~,'--L LLL 

Environmental Risk Branch 5 I// l 'LEnvironmental Fate and Effects Division (EFED) 

In response to the posting in the public docket of the "Registration Review: 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 address these comments. 

This revised memorandum (modified to 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 of nicosulfuron. 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. 

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Environmental Fate 

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: 

• Anaerobic Aquatic Metabolism (835.4400) for Nicosulfuron: MRID No. 48790905 

• Independent Laboratory Validations (IL V s) for Water and Soil Environmental Chemistry 

Methods (ECMs) for Nicosulfuron: MRID Nos. 48790913 and 48790914 

In addition, DuPont has expressed their intention to submit an Aerobic Soil Metabolism study 

(83 5.41 00) 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 of soils that are currently available for consideration in the 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 

justifications broken down by each study and EFED's responses are provided below: 

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 of concern for ecological organisms in the 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 of 45 mL!g and Koc value of 1,707 mL/g. 

Therefore, it is not likely to be lost to the atmosphere. 

2. Another study, not submitted to the Agency, indicated that IN-10290 degrades 

quickly in soils, with DT 50 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 of the above cited studies on soil 

degradation and soil mobility of the IN-J0290 degradate to the Agency to address its fate 

characterization. In their justification, DuPont expressed a willingness to submit these cited 

studies. 

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835.4200 Anaerobic Soil Metabolism (Nicosulfuron) 

EFED requested additional soils to be evaluated since only one soil 1s currently available. 

DuPont is requesting a waiver for 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 of additional 

soils will not likely provide additional information. 

2. An anaerobic aquatic metabolism study has historically been accepted by USEP A in 

lieu of an anaerobic 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 of environmental fate studies referenced by DuPont related to environmental data 

gaps. 

Guideline Study Title Submitted MRID Status 

Number 

835.4100 Aerobic Soil Metabolism Study 46240901 Additional studies to 

(Nicosulfuron) 41082622 be submitted according 

to DuPont 

835.4200 Anaerobic Soil Metabolism 41082623 Additional study 

Study waived 

(N icosulfuron) 

850.4400 Anaerobic Aquatic Metabolism 48790905 In Review 

(N icosulfuron) 

850.6100 Independent Laboratory 48790913 In Review 

Validations (IL V s) for 48790914 

Environmental Chemistry 

Methods (ECMs) 

(N icosulfuron) 

830.7950 Vapor Pressure N/A Waived. However, 

(IN-J0290) submittal of registrant 

cited mobility and soil 

degradation studies to 

the Agency requested 

to address fate 

characterization. 

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Ecological Effects 

DuPont provided comments related to the ecotoxicity data gaps section and highlighted a number 

of studies that they submitted to the Agency in support of the registration review of nicosulfuron. 

According to DuPont, they submitted studies that are currently in review by EFED to fulfill the 

guidelines outlined in Table 2. 

Table 2. Status of nicosulfuron ecotoxicity studies referenced by DuPont related to ecotoxicity 

data gaps. a 

Guideline Study Title Submitted MRID Status 

Number 

850.2100 Avian Oral Acute 48790909 In Review 

850.2300 Avian Reproduction 48354306 In Review 

48354307 

850.1025 Estuarine/Marine Mollusk Acute 48790906 In Review 

850.1035 Estuarine/Marine Shrimp Acute 48790907 In Review 

850.1075 Estuarine/Marine Fish Acute 48790908 In Review 

850.1400 Freshwater Fish Early Life-Stage 48448001 In Review 

850.4225/ Seedling EmergenceN egetative 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= Not available. Additional studies to satisfy the guideline have not been submitted by the 

registrant. 

Given these submissions, EFED will review this data for acceptability for use in the risk 

assessment. EFED notes that two of the studies, one an avian acute oral study and one an aquatic 

vascular plant study with Lemna, 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. It is unclear why DuPont referred to this MRID also as a plant study. It is 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 that two of the studies in the comments on aquatic non-vascular plants do not have full 

MRID citations (4637030 and 4837640). It is also possible that DuPont meant to refer to MRID 

46370301 (study with Selenastrum capricornutum) and MRID 48376501 (study with Anabaena 

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 

plant toxicity testing, the 40 CFR part 158 guidelines for toxicity testing typically require the test 

to be conducted with the technical grade active ingredient. However, EFED will review the 

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submitted studies highlighted above and determine the value of additional data related to aquatic 

vascular plants. Finally, EFED confirms the need for acceptable tier II terrestrial plant toxicity 

studies as outlined in the registration review preliminary problem formulation. 

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 DuPont regarding the plant reproduction study. EFED's 

Plant Technical Team (PTT) conducted an analysis of available SU plant reproduction 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 of vegetative 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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