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Halosulfuron-methyl Focus Meeting Summary

September 19, 2012 

3:00 – 4:30 pm

Attendees

Gowan Company (Agent for Canyon Group): Nina Wilson

Exponent: Mark J. Schocken, Ph.D.

Environmental Protection Agency (EPA or Agency): Avivah Jakob (PRD), Tracy Perry (PRD), 

Kaitlin Keller (PRD), Allen Vaughan (EFED), Michael Barrett (EFED)

Objective

The purpose of the meeting was for members of the EPA’s Pesticide Re-evaluation Division 

(PRD) and Environmental Fate and Effects Division (EFED) to meet with Canyon Group, a

technical registrant for halosulfuron-methyl, for the following reasons: 1) discuss usage 

information needed for the registration review ecological risk assessments, and 2) discuss 

anticipated ecotoxicity and environmental fate data requirements and information that could be 

submitted to fulfill these data gaps. 

Presentation

Canyon’s presentation covered:

• overview of halosulfuron-methyl’s registered use patterns;

• the history of the chemical and Canyon Group; and

• ecotoxicity and environmental fate information

o aerobic soil metabolism 

o hydrolysis

o freshwater fish and invertebrate toxicity studies

Discussion

Use/Usage Information

Canyon provided usage information in terms of amounts used in pounds per year by crop, noting 

that halosulfuron-methyl is a small usage product primarily used as a spot treatment. EPA 

requested that Canyon send the information to EPA, as it was not included in the presentation. 

EPA also requested usage information in terms of percent treated of total crop production. 

Environmental Fate Information

Canyon presented a detailed overview of the available aerobic soil metabolism information for 

halosulfuron-methyl. A study conducted for European Union (EU) registrations was discussed 

and was provided to EPA informally in June 2012. Canyon will formally submit this study for 

EPA review prior to the anticipated Data Call-In (DCI) issuance in June 2013. EFED indicated 
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that cursory review of the aerobic soil metabolism studies supports Canyon’s contention that this 

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

different soils. 

EPA is also requiring a Non-Guideline (GLN) enhanced aerobic soil metabolism study because 

of discrepancies between available field and laboratory study results regarding halosulfuronmethyl’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 required 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, are found to be 

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

metabolism study will not likely be required. Canyon presented their analysis of all available 

halosulfuron-methyl field dissipation studies and agreed that differences in the degradation rate 

do not appear to correlate to a single factor, such as pH or organic matter. Canyon has

committed to conducting the enhanced aerobic soil metabolism 10-soil degradation study and 

will submit a protocol for Agency review prior to DCI issuance. The requirements 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 also 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. However, the enhanced hydrolysis study and freshwater 

fish and invertebrate studies remain as data gaps for Canyon until data have been formally 

submitted and reviewed for acceptability.

Follow-up

• Canyon will submit additional usage information measured in terms of percent of total 

crop treated to help refine future risk assessments. 

• EPA and Canyon will continue working together to review available data prior to the DCI 

issuance. 

• Canyon will work with the Agency, prior to DCI issuance, to develop and submit a study 

protocol for the non-GLN, enhanced aerobic soil metabolism study.