2

INTRODUCTION

This is the Environmental Protection Agency’s (EPA or the Agency) Final Work Plan (FWP) for 

the registration review of primisulfuron-methyl. This work plan addresses public comments 

received concerning the Preliminary Work Plan (PWP), which was posted in primisulfuronmethyl’s registration review docket (EPA-HQ-OPP-2011-0844). Primisulfuron-methyl is a 

selective post-emergent sulfonylurea herbicide absorbed and transported throughout the plant 

roots and foliage. The mechanism of action is the inhibition of amino acid synthesis in plants 

through inhibition of acetolactate synthase (ALS). ALS is the first common enzyme in the 

biosynthesis of branched-chain amino acids (valine, leucine, and isoleucine). ALS inhibition in 

plants adversely affects plant growth and reproduction. Although the sulfonylurea herbicides all 

act upon the same enzyme system in plants, that system is not present in humans or other 

mammals. 

The Agency is implementing the registration review program pursuant to Section 3(g) of the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each registered 

pesticide every 15 years to determine whether it continues to meet the FIFRA standard for 

registration. Changes in science, public policy, and pesticide use practices occur over time. The 

registration review program is intended to make sure that, as the ability to assess risk evolves and 

as policies and practices change, all registered pesticides continue to meet the statutory standard. 

The public phase of registration review begins when the initial docket is opened for each case. 

Information on this program is provided on the Agency’s website1.

The FWP begins with any updates since the PWP was issued. Next is a summary of substantive 

comments received during the public comment period for the PWP concerning anticipated data 

needs, expected risk assessments, or the estimated timeline identified in the PWP, and a 

summary of the Agency’s responses to those comments. This section is followed by 

primisulfuron-methyl’s registration review planned data needs, risk assessments expected to be 

conducted, and the projected registration review timeline. Last, there is a discussion of next 

steps.

UPDATES SINCE THE PWP WAS ISSUED

Proposed Tolerance Revocation. On May 9, 2012, EPA published a proposed rule revoking the 

tolerances for primisulfuron-methyl on sweet corn (40 CFR 180.452: corn, sweet, forage and 

corn, sweet, stover). See 90 FR 27164. The Agency expects to publish the final rule revoking 

the primisulfuron-methyl tolerances on sweet corn in September 2012. There are no active U.S 

registrations for use of primisulfuron-methyl on sweet corn. 

Testing Requirements for Sulfonyl Urea Herbicides. The Agency is aware of new information 

suggesting that effects observed in plant reproductive toxicity studies conducted with 

sulfonylurea herbicides occur at concentrations similar to those at which effects were observed in 

the guideline vegetative vigor studies (850.4150). The Agency is currently evaluating this 

information to determine if additional testing beyond the standard vegetative vigor studies is 

 

1

http://www.epa.gov/oppsrrd1/registration_review/
3

warranted for this class of compounds, or if data from the vegetative vigor guideline study are 

sufficiently protective of potential impacts to plant reproduction.

SUMMARY OF COMMENTS AND AGENCY RESPONSES

During the 60-day public comment period on the primisulfuron-methyl PWP, which opened on 

March 28, 2012 and closed on May 29, 2012, the Agency received two sets of public comments. 

Comments were submitted by the technical registrant, Syngenta Crop Protection, and by the 

FIFRA Endangered Species Task Force (FESTF). The comments do not address the timeline 

described in the PWP, but they do address the planned ecological data requirements. In the 

PWP, EPA also solicited comments on the specific topics of environmental justice, water quality 

concerns, and trade irritants, but no comments or information were received on those issues.

Public comments on the primisulfuron-methyl PWP and EPA responses are summarized below. 

A detailed summary of public comments and EPA’s responses related to the anticipated 

ecological risk assessment and data needs are in the July 30, 2012 memo, The Environmental 

Fate and Effects Division responses to Syngenta and FESTF Comments on the Primisulfuronmethyl Preliminary Work Plan (PWP) for Registration Review, located in the public docket. 

Comments submitted by Syngenta Crop Protection in EPA-HQ-OPP-2011-0844-0009. 

1. Comment: The Primisulfuron-methyl Summary Document states that this pesticide was

first registered in 1991. This should be corrected to 1990.

Response: Syngenta is correct. Primisulfuron-methyl was first registered in March 1990.

2. Comment: Syngenta has noticed a value of 0.0268 lb ai/A listed as the maximum 

application rate for corn. However, a higher value is provided on the EPA-approved 

Beacon herbicide label (EPA Registration Number 100-705). This product has a 

maximum application rate of 0.0356 lb ai/A.

Response: The Agency has verified that the use rate provided by Syngenta is correct for 

the cited product label (EPA Registration Number 100-705). The label spreadsheet has 

been revised and updated to reflect this information. The revised spreadsheet, PRD Label 

Data Report: Food/Feed & Non-Food/Non-Feed Uses Considered in the Registration 

Review Work Planning for Primisulfuron-methyl, dated June 20, 2012, is located in 

docket EPA-HQ-OPP-2011-0844.

3. Comment: The Problem Formulation for environmental fate and ecological risk cites a 

NOAEC of 0.41 mg/ai/L for a daphnia study. The original report for this study (MRID 

41418609) cites the NOAEC as 0.70 mg/L but the reviewer recalculated the NOAEC to 

be 0.41 mg/L based on the low mean measured test substance concentration for days 7 

and 14 of the study. On these days, the pH in the exposure tanks varied from 7.5 to 8.1, 

thus influencing the solubility of the test substance. Syngenta suggests that the NOAEC 

be calculated based on the mean measured test substance concentration for the entire 

exposure period, from day zero to day 21.
4

Response: EPA will re-evaluate this study to determine if the NOAEC needs to be 

corrected. 

4. Comment: Two studies in the rat, MRIDs 00403312 and 40512009, are not included in 

the citation reference section of the problem formulation document.

Response: Although these two MRIDs2 were referenced earlier in the Problem 

Formulation, Syngenta is correct: EPA omitted the complete citation for these studies 

from the Problem Formulation. These citations will be included in future risk assessment 

documents. In addition, the Agency has identified a typographical error in Table 7 on 

page 22 of the Problem Formulation. The MRID number for the acute oral toxicity study 

in rats (MRID 00403312) is incorrect; the correct MRID number is 40331206. The 

correct citations for these two studies are as follows: 

40331206 Maedgen, J. (1986) Acute Oral Toxicity in Rats: CGA-136872 Tech: 

Laboratory Study No. 4011-86. Unpublished study prepared by Stillmeadow, 

Inc. 13 p.

40512009 Schardein, J. (1987) Two-generation Reproduction Study in Albino Rats with 

CGA-136872: Laboratory Study No. 382-115. Unpublished study prepared 

by International Research and Development Corporation. 604 p.

5. Comment: EPA is asking for an avian reproduction study (in both Bobwhite quail and 

Mallard Duck) for the degradate CGA-171683. Avian reproductive toxicity data (in

mallards, MRID 40512004) are available for the parent compound, primisulfuronmethyl. These data for the parent compound show that no reproductive effects occurred 

at the highest dose tested (500 mg/kg/day). Chronic exposure of birds to a soil 

concentration at such concentration is unlikely, and additional chronic avian data with 

the soil degradate would not likely change the risk conclusion for primisulfuron-methyl.

Response: No ecological toxicity data are available for the soil degradate CGA-171683,

and the toxicity and risk from this degradate to terrestrial organisms are a significant area 

of uncertainty. CGA-171683 is a unique sulfonylurea degradate which is mobile and 

likely to be persistent in the environment; 75% of the degradate remains in the 

environment for 12 months after application of primisulfuron-methyl. Therefore, both 

acute and chronic exposures to terrestrial species may occur. The avian reproduction

toxicity study is the only long-term study available to evaluate the toxicity of this 

degradate in the terrestrial environment. The value for understanding the relative toxicity 

of CGA-171683 and the parent in the terrestrial environment is high; until data indicate 

CGA171683 is not toxic, EPA would assume risks of concern to terrestrial animals and a

“may effect” finding for federally listed threatened and/or endangered species.

 

2 Master Record Identification Number
5

Comments submitted by the FIFRA Endangered Species Task Force (FESTF) in EPA-HQOPP-2011-0844-0010. 

1. Comment: The FIFRA Endangered Species Task Force (FESTF) submitted its 

information management system containing Nature Serve Data (MRID 47260101) to 

fulfill the data requirements described in PR Notice 2000-2. This submission provides 

the best available data for the proximity analysis of primisulfuron data use and locations 

of endangered species. Syngenta is a member of FESTF and is entitled to rely on the 

FESTF data to support primisulfuron-methyl. 

Response: The Agency thanks FESTF for its comment and data submission. EPA will 

consider this information as it conducts the registration review for primisulfuron-methyl. 

PLANNED DATA NEEDS

The table below summarizes the data needs for primisulfuron-methyl based on the Registration 

Review-Preliminary Problem Formulation for Ecological Risk and Environmental Fate, 

Endangered Species, and Drinking Water Assessments for Primisulfuron methyl, Primisulfuronmethyl. Health Effects Division (HED) Scoping Document for Registration Review, and The 

Environmental Fate and Effects Division responses to Syngenta and FESTF Comments on the 

Primisulfuron-methyl Preliminary Work Plan (PWP) for Registration Review. The data needs 

have not changed from what was included in the PWP. 

Planned Data Needs for Primisulfuron-methyl’s Registration Review

Guideline 

Number Study Title Test Material

Estimated 

Timeframe

(Months from 

Receipt of 

DCI)

835.4300 Aerobic Aquatic Metabolism TGAI 24

835.4400 Anaerobic Aquatic Metabolism TGAI 24

835.6100 Terrestrial Field Dissipation (Environmental Chemistry 

Methods)3 TGAI 24

835.6200 Aquatic Field Dissipation (Environmental Chemistry 

Methods)4 TGAI 12

850.2100 Avian Acute Oral Toxicity (passerine species) TGAI 12

850.2300 Avian Reproduction (bobwhite quail and mallard 

duck)5 Degradate 24

 

3 Data are currently in review for GLN 835.6100, terrestrial field dissipation. Although data have been submitted to 

EPA, this GLN will be considered a data gap until the data have been reviewed and found to be acceptable. An 

environmental chemistry analytical method (ECM) and independent laboratory validation (ILV) are required for soil 

as part of this guideline. 

4

See footnote 7 of 40 CFR 158.1300. The DCI will require only the environmental chemistry analytical methods 

and independent laboratory (ILV) portions of this guideline, rather than the full field dissipation study.

5 The DCI will require that this study be conducted with the fluorinated degradate CGA-171683.
6

Planned Data Needs for Primisulfuron-methyl’s Registration Review

Guideline 

Number Study Title Test Material

Estimated 

Timeframe

(Months from 

Receipt of 

DCI)

Non-GLN Special Study for Non-target plant reproductive 

toxicity6 TEP 24

870.7800 Immunotoxicity Study TGAI 12

TGAI = Technical Grade Active Ingredient; TEP = Typical End-Use Product; Degradate = CGA-171683.

RISK ASSESSMENTS FOR REGISTRATION REVIEW

During registration review, the Agency will conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, for all uses of primisulfuron-methyl. For human 

health, EPA will evaluate the need to conduct revised dietary, residential, and occupational risk 

assessments during registration review. If toxicological endpoints or points of departure are 

revised based on the data that are required for registration review, they will be considered in the 

new assessments, as well as any changes to the standard operating procedures or default 

exposure assumptions.

The table below summarizes the planned registration review risk assessments based on the EFED 

Problem Formulation and HED Scoping Documents for primisulfuron-methyl. The planned

assessments are unchanged from the PWP.

Planned Risk Assessments for Primisulfuron-methyl’s Registration Review

Type of Risk Assessment Conduct? Notes

Ecological and Environmental Fate

Comprehensive ecological 

(species to be assessed include 

terrestrial and aquatic 

organisms), including 

endangered species 

Y To date, EPA has not conducted a comprehensive 

ecological risk assessment supporting a complete 

endangered species determination for primisulfuronmethyl. 

Incidents Y For a discussion of primisulfuron-methyl’s reported 

ecological incidents, see page 9 and Appendix C of 

the Problem Formulation.

 

6 The Agency is currently evaluating new information to determine if the vegetative vigor guideline study is

sufficiently protective of potential impacts to plant reproduction.
7

Planned Risk Assessments for Primisulfuron-methyl’s Registration Review

Type of Risk Assessment Conduct? Notes

Human Health

Dietary

Food Y EPA may need to update the drinking water 

assessment to include the degradate CGA-171683

and will revise the dietary assessment accordingly.

Drinking water Y

Occupational

Handlers (mixers, loaders, 

applicators)

N In the 2002 risk assessment, occupational handler 

risks were significantly below EPA’s level of concern 

(MOEs > 100,000). 

Post-application Y EPA will evaluate potential post-application exposure 

from harvesting treated sod, which was previously 

not assessed. 

Residential

Handlers N Primisulfuron-methyl is not registered for residential 

use. 

Post-application Y There are currently no registered residential uses. 

However, there are several Special Local Need (SLN)

registrations for use on Kentucky bluegrass for sod 

production. Because there are no restrictions on the 

transfer of treated sod to residential sites, residential 

post-application exposure might occur as a result of 

exposure to treated sod. EPA will evaluate potential 

post-application residential/bystander exposure from 

treated sod.

Other

Aggregate Y EPA will evaluate the combined risk from dietary and 

residential exposures.

Cumulative N Primisulfuron-methyl is not a member of a 

cumulative group for human health effects. 

Tolerances Y EPA will modify the tolerance expression to reflect 

current policies. In addition, EPA is revoking 

primisulfuron methyl tolerances on sweet corn 

because there are no active registrations on sweet 

corn. 

Incidents N No human health incidents have been reported for 

primisulfuron-methyl. See page 7 of the Scoping 

Document for further details. 
8

TIMELINE

EPA has created the following estimated timeline for the completion of primisulfuron-methyl’s

registration review. The projected timeline has not changed since the PWP.

Registration Review for Primisulfuron-methyl – Projected Registration Review Timeline

Activities Estimated Date

Opening the Docket

Open Docket and 60-day Public Comment Period March 2012 –

Completed 

Close Public Comment May 2012 – Completed 

Case Development

Final Work Plan Sept. 2012 –

Completed 

Issue DCI 2013 – April-June

Data Submission 2015 – April-June

Open 30-day Public Comment Period for Draft Risk Assessments 2016 – Oct.-Dec.

Close Public Comment Period 2017 – Jan.-March

Registration Review Decision

Open 60-day Public Comment Period for Proposed Registration Review 

Decision 

2017 – April-June

Close Public Comment Period 2017 – July-Sept.

Registration Review Decision and Begin Post-Decision Follow-up 2018

Total (years) 6

NEXT STEPS

As noted previously, the Agency plans to require several environmental fate, ecological effects, 

and human health studies for primisulfuron-methyl through a data call-in, expected to be issued 

in the spring of 2013.