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INTRODUCTION

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

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

received concerning the Preliminary Work Plan (PWP), which was posted in halosulfuronmethyl's registration review docket (EPA-HQ-OPP-2011-0745). Halosulfuron-methyl is a 

sulfonylurea herbicide that is primarily absorbed through the leaves of plants. Sulfonylurea 

herbicides disrupt the synthesis of amino acids in plants by inhibiting the enzyme acetolactate 

synthase (ALS). 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. Halosulfuron-methyl is registered for use on various 

crops including corn, cotton, nuts, rice, sorghum, soybeans, squash, sugarcane, and fruiting 

vegetables to control broadleaf weeds and annual and perennial sedges. In addition to the 

agricultural food uses, halosulfuron-methyl is also registered for use on turfgrass, ornamentals, 

and a variety of non-crop areas including, but not limited to, airports, cemeteries, fallow noncrop areas, golf courses, landscaped areas, public recreation areas, residential and commercial 

lawns, sod and turf farms, sports fields, tennis courts, race tracks, fairgrounds, and rights-of-way. 

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 

halosulfuron-methyl's registration review planned data needs, risk assessments expected to be 

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

steps.

UPDATES SINCE THE PWP WAS ISSUED

Testing Requirements for Sulfonylurea 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 

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

sufficiently protective of potential impacts to plant reproduction.

Focus Meeting with Technical Registrant. Canyon Group LLC (Canyon), a technical registrant 

of halosulfuron-methyl, plans to submit European Union (EU) ecotoxicity and environmental 

fate data that they believe may satisfy identified data gaps and/or justify why certain data are not 

 1 http://www.epa.gov/oppsrrd1/registration_review/
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needed for the registration review of halosulfuron-methyl. Upon receipt and review of this 

information, EPA will determine any impacts on the planned risk assessments and data needs. 

The Agency held a focus meeting with Gowan Company, an agent for Canyon, on September 19, 

2012 and the following was discussed:

• Enhanced Hydrolysis Study; and Fresh Water Fish and Invertebrate Data- Canyon 

presented information from a recent open literature publication on the hydrolysis of 

halosulfuron-methyl, as well as EU freshwater fish and invertebrate data, and will 

formally submit these studies for Agency review. EPA agrees that these data may fulfill 

several data requirements. However, the enhanced hydrolysis study and freshwater fish 

and invertebrate studies remain as data requirements until data have been formally 

submitted and reviewed for acceptability.

• Aerobic Soil Metabolism Study (GLN 835.4100) & Enhanced Aerobic Soil Metabolism 

Study (Non-GLN)- An enhanced aerobic soil metabolism study (in at least 10 soils) is 

identified as a data gap because of discrepancies between available field and laboratory 

study results regarding halosulfuron-methyl’s persistence in different soils. The study 

should include information (or limited data) on the decline of halosulfuron-methyl in at 

least 10 soils. Full aerobic soil metabolism studies (i.e., with characterization of the 

formation and decline of major degradates) are to be conducted for the two soils where 

halosulfuron-methyl is most persistent. However, if the aerobic soil metabolism data, 

which Canyon will be formally submitting for review by the Agency, is found to be 

acceptable and fulfills GLN 835.4100, this portion of the (non-GLN) enhanced aerobic 

soil metabolism study will not likely be required. The data gaps for GLN 835.4100, 

aerobic soil metabolism and a non-guideline enhanced aerobic soil metabolism study will 

remain until the data have been formally submitted and EPA has completed a full 

evaluation of the data. Canyon agreed to work with the Agency to develop an 

appropriate study protocol. 

For further details, a summary of this meeting is posted in the halosulfuron-methyl registration 

review docket EPA-HQ-OPP-2011-0745. If changes are made to the work plan, data 

requirements, or timeline, the Agency will amend the FWP and announce this amendment in the 

Federal Register.

SUMMARY OF COMMENTS AND AGENCY RESPONSES

During the 60-day public comment period on the halosulfuron-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 Gowan Company LLC, authorized agent for Canyon Group LLC, 

and the FIFRA Endangered Species Task Force. The comments submitted by Canyon address 

the planned ecological risk assessment and 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.

This section does not capture every comment made on the PWP nor all of the Agency’s 

responses. Summarized below are public comments that addressed the anticipated registration 

review data needs, risk assessments, and are of a broader regulatory nature. Public comments 

and EPA responses in their entirety are located in the docket, EPA-HQ-OPP-2011-0745. 

Summarized public comments and Agency responses related to the anticipated ecological risk 

assessment or data needs are in the EFED Response to Public Comments Submitted on the 
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Halosulfuron-methyl Preliminary Workplan, dated September 20, 2012. No comments were 

received on the anticipated human health risk assessment or data needs.

Comments submitted by Gowen Company LLC, Authorized Agent for Canyon Group 

LLC in EPA-HQ-OPP-2011-0745-0010.

1. Comment: EPA outlined a requirement for further testing for aerobic soil metabolism of 

halosulfuron-methyl, Guideline 835.4100 and a non-guideline enhanced aerobic soil metabolism 

study. A previously submitted aerobic soil metabolism study, MRID 42139410, was carried out 

using an acidic and an alkaline soil that had variance in other soil properties as well. To address 

EPA’s concerns, an additional laboratory study of the transformation of halosulfuron-methyl in 

soil will be submitted under separate cover.

Response: Cursory review of the aerobic soil metabolism data supports Canyon’s contention 

that this study might add to the understanding of the variability in halosulfuron-methyl 

degradation in different soils. However, these data have not been formally submitted or 

reviewed. Therefore, the requirements for Guideline 835.4100, aerobic soil metabolism and a 

non-guideline enhanced aerobic soil metabolism study will remain until the data have been 

formally submitted and EPA has completed a full evaluation of the data.

2. Comment: Canyon disagrees with EPA’s requirement for a non-guideline hydrolysis study 

for halosulfuron-methyl. A previously submitted study, MRID 42139409 was acceptable and 

fulfilled Guideline 835.2120, hydrolysis. It is well known that hydrolysis rates of halosulfuronmethyl, and other sulfonylureas (SUs), change with regard to pH and temperature. There are 

several recent papers in the published literature that address this issue for SUs in general and 

for halosulfuron-methyl in particular. Canyon believes that an additional study will not provide 

new or additional data that can be used to refine the halosulfuron-methyl risk assessment.

Response: The Agency does not believe Canyon Group has provided sufficient justification that 

the change in halosulfuron-methyl hydrolysis rates, with factors such as pH and temperature, has 

been adequately addressed solely from the existing guideline study. Often in standard hydrolysis 

studies, pesticides degrade with a predictable, defined trend of increasing or decreasing rate, with 

increasing or decreasing pH reflecting a single dominating site for hydrolysis on the pesticide 

molecule; or at least consistent effects at multiple active sites. Although there was a trend for an 

increase in the halosulfuron-methyl hydrolysis rate with higher pH in the standard guideline 

study, this does not appear to be a consistent trend in the environment as some field dissipation 

rates were slower than expected. Also a published study seems to confirm that there are more 

complex trends affecting the hydrolysis rate. Per the September 19, 2012 meeting between EPA 

and Canyon, this study will be formally submitted by Canyon and reviewed by the Agency.

However, the enhanced hydrolysis study remains as a data requirement until the data have been 

formally submitted and reviewed for acceptability.

3. Comment: Canyon disagrees with EPA’s requirement for a non-guideline non-target plant 

reproductive toxicity test. It is reasonable to conclude that effects on reproduction and growth in 

terrestrial plants would be comparable to those in higher aquatic plants such as Lemna gibba. 

Consequently, it should not be necessary to conduct further studies with terrestrial plants as it 

can be concluded that the toxicity end points in the seedling emergence and vegetative vigor 

studies are conservative and represent a worst case for growth and reproduction.

Response: The Agency is aware of new information suggesting that effects observed in plant 
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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 warranted for this class of compounds, or 

if data from the vegetative vigor guideline study are sufficiently protective of potential impacts 

to plant reproduction.

4. Comment: EPA outlined a requirement for Guideline 850.1010, acute toxicity freshwater 

invertebrate test, and Guideline 850.1075, acute freshwater fish toxicity test, because 

halosulfuron-methyl will be directly applied to water when used on rice. In response to this 

requirement, Canyon has provided study reports testing a formulated product on freshwater fish 

and aquatic invertebrates.

Response: Cursory review of these studies supports Canyon’s contention that the toxicity 

exhibited by the products derives from the active ingredient, as the toxicity endpoints are 

comparable. However, the studies have not been formally submitted to EPA. Therefore, 

Guidelines 850.1010, acute toxicity freshwater invertebrate and 850.1075, acute freshwater fish 

toxicity remain as data gaps for Canyon until the data have been formally submitted and 

reviewed for acceptability. 

5. Comment: EPA outlined a requirement for submission of environmental chemistry methods 

for halosulfuron-methyl and its metabolites in soil and water along with an independent 

laboratory validation, Guidelines 835.6100 and 835.6200 (Footnote 7 of 40 CFR 158.1300). 

Canyon Group provided a detailed listing of the analytical methods that have been historically 

submitted to the Agency. Canyon stated that all of these methods will be resubmitted but notes 

that a method for halosulfuron-methyl and its major metabolites has been shown to be robust 

and reproducible over a two-year period.

Response: The summary of the available analytical methods is useful, but an independent 

laboratory validation of a method or methods for halosulfuron-methyl and its major metabolites 

in soil and water will still be required.

Comment submitted by FIFRA Endangered Species Task Force in EPA-HQ-OPP-2011-

0745-0009.

1. Comment: The FIFRA Endangered Species Task Force (FESTF) submitted a comment that

neither of the halosulfuron-methyl technical registrants are members of the FESTF; and

therefore, must provide a formal offer-to-pay to FESTF in conjunction with their support of the 

active ingredient, or develop similar data on their own to provide for EPA risk assessments for 

registration review.

Response: The Agency thanks FESTF for its comment. However, Canyon Group is a joint 

venture between Gowan Company and Nissan Chemical Industries. As Gowan is a member of 

FESTF, EPA expects that Gowan could rely on any FESTF data used for risk assessment 

purposes. 

PLANNED DATA NEEDS

The table below summarizes the planned data needs for halosulfuron-methyl based on 

Registration Review: Preliminary Problem Formulation for the Environmental Fate and
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Ecological Risk, Endangered Species and Drinking Water Assessments for Halosulfuron-methyl,

March 8, 2012, the Halosulfuron-methyl: Human Health Assessment Scoping Document in 

Support of Registration Review, March 6, 2012, and EFED Response to Public Comments 

Submitted on the Halosulfuron-methyl Preliminary Workplan, dated September 20, 2012.

Planned Data Needs for Halosulfuron-methyl’s Registration Review

Guideline 

Number Study Title Test Material

Estimated 

Timeframe

(Months from 

receipt of DCI)

835.4100 Aerobic Soil Metabolism (two soils) TGAI 24

835.4300 Aerobic Aquatic Metabolism TGAI 24

835.6100 Terrestrial Field Dissipation2 TGAI 12

835.6200 Aquatic Field Dissipation TEP 24

850.1010 Acute Toxicity Freshwater Invertebrates TEP 12

850.1075 Acute Freshwater Fish Toxicity TEP 12

860.1650 Submittal of Analytical Reference Standards3 PAI; residue of 

concern

24

870.7800 Immunotoxicity TGAI 12

NONGDLN Enhanced Aerobic Soil Metabolism Study4 TGAI 48

NONGDLN Enhanced Hydrolysis Study5 TGAI 12

NONGDLN

Special Study for Non-target Plant Reproductive 

Toxicity6 TEP 24

TGAI = technical grade active ingredient; TEP = typical end-use product; PAI= pure active ingredient.

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 halosulfuron-methyl. The Agency 

does not anticipate conducting updated dietary, residential, aggregate, or occupational risk 

 2 See footnote 7 of 40 CFR 158.1300. The DCI will require only the environmental chemistry analytical method and independent 

laboratory validation portions of GLN 835.6100, Terrestrial Field Dissipation. 3 Analytical reference standards are available for halosulfuron-methyl and the 3-CSA (3-chlorosulfonamide acid) metabolite but 

not for the rearrangement ester (RRE) of halosulfuron-methyl. An analytical reference standard for the RRE of halosulfuronmethyl must be submitted to the EPA National Pesticide Standards Repository. 4 The DCI will require a protocol be submitted within 90 days of receipt of the DCI for review and approval by the Agency prior

to initiation of this study.

5 The DCI will require the protocol for GLN 835.2120, hydrolysis be followed. Suggested parameters include testing at pHs of 5, 

7, and 9 and at temperatures of 10, 15, 20, and 25 C for 60 days (and additionally pH 4, 6, and 8 at 15 C), and analysis for 

halosulfuron-methyl and potential major hydrolysis products. 6 The Agency is currently evaluating new information to determine if additional testing beyond the standard vegetative vigor 

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

potential impacts to plant reproduction.
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assessments during registration review. No risks above the Agency’s level of concern were 

identified in the most recent human health assessment; and changes in Agency models and 

policies that have occurred since that assessment are not expected to alter risk conclusions. 

Therefore, the Agency plans to rely on the most recent comprehensive human health assessment 

in making its registration review decision. If the results of the additional toxicity study that is 

expected to be required changes assessment endpoints or uncertainty/safety factors, the Agency 

will reconsider the need for an updated human health risk assessment.

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

Problem Formulation and HED Scoping Document. The planned assessments have not changed 

from what was included in the PWP.

Planned Risk Assessments for Halosulfuron-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 

Incidents Y For a discussion of halosulfuron-methyl's reported 

ecological incidents, see page 26 of the Problem 

Formulation.

Human Health

Dietary

Food N If the results of the additional toxicity study that is 

expected to be required changes assessment endpoints 

or uncertainty/safety factors, the Agency will 

reconsider the need for updated human health dietary 

risk assessments.

Drinking water N

Occupational

Handlers (mixers, loaders, 

applicators)

N If the results of the additional toxicity study that is 

expected to be required changes assessment endpoints 

or uncertainty/safety factors, the Agency will 

reconsider the need for updated human health 

occupational risk assessments.

Post-application N

Residential

Handlers N If the results of the additional toxicity study that is 

expected to be required changes assessment endpoints 

or uncertainty/safety factors, the Agency will 

reconsider the need for updated human health 

residential risk assessments.

Post-application N

Other

Aggregate N Evaluates the combined risk from dietary and 

residential exposures.

Cumulative N
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Planned Risk Assessments for Halosulfuron-methyl's Registration Review

Type of Risk Assessment Conduct? Notes

Other

Tolerances Y The Agency anticipates updating the current 

halosulfuron-methyl tolerance expression in 40 CFR 

§180.479 to be consistent with the Chemical 

Abstracts Service (CAS) nomenclature or the 

International Union of Pure and Applied Chemistry 

(IUPAC) nomenclature. 

Incidents Y For a discussion of halosulfuron-methyl's reported 

human incidents, see page 10 of the Scoping 

Document.

TIMELINE

EPA has created the following estimated timeline for the completion of halosulfuron-methyl's

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

Registration Review for Halosulfuron-methyl – Projected Registration Review Timeline

Activities Estimated Date

Opening the Docket

Open Docket and Public Comment Period March 2012 – Completed

Close Public Comment May 2012 – Completed

Case Development

Final Work Plan Sept. 2012 –Completed

Issue DCI April – June 2013

Data Submission April – June 2017

Open Public Comment Period for Draft Risk Assessments Oct. – Dec. 2018

Close Public Comment Period Jan. – March 2019

Registration Review Decision

Open Public Comment Period for Proposed Registration Review Decision April – June 2019

Close Public Comment Period July – Sept. 2019

Registration Review Decision and Begin Post-Decision Follow-up 2020

Total (years) 8

NEXT STEPS

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

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

mid-2013.