Docket Number: EPA-HQ-OPP-2009-0755 

www.regulations.gov

Hexazinone Final Work Plan 

Registration Review 

August 2010 

Introduction: 

This is EPA’s Final Work Plan (FWP) for the registration review of hexazinone. 

The FWP includes the expected registration review timeline. The FWP also addresses 

public comments received concerning the Preliminary Work Plan (PWP) in the 

Summary Document posted in the hexazinone registration review docket (EPA-HQOPP-2009-0755), and any other comments concerning the initial docket postings. The 

Summary Document provided information on what EPA knows about the pesticide and 

what additional risk analyses and data or information the Agency believes are needed to 

make a registration review decision. 

The Agency is implementing the registration review program and will review 

each registered pesticide every 15 years to determine whether it continues to meet the 

Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) standard for registration. 

Changes in science, public policy, and pesticide use practices will 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 at: 

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

Hexazinone is a herbicide that was first registered in the United States in 1975 for 

general weed control in non-cropland areas, and is currently registered for use on alfalfa, 

blueberries, forest trees, pasture and range grasses, ornamental plants, pineapples, and 

sugarcane to control broadleaf weeds, grasses, and some woody plants. Hexazinone is a 

triazine herbicide, but it is structurally and toxicologically dissimilar to the other triazine 

herbicides such as atrazine. Therefore, hexazinone has not been included in any 

cumulative assessment. 

Comments Received on Preliminary Work Plan: 

 The hexazinone registration review docket received five comments during the 60-

day comment period on the PWP, which began on May 6, 2010 and ended on July 7, 

2010. Although the hexazinone registration review docket was scheduled to open on 

March 31, 2010, with a public comment period ending on June 1, 2010, the supporting 

documents were not posted to the docket until May 6, 2010, so the public comment 

period was extended to the proceeding 60 days. The comments received resulted in the 

removal of three anticipated data requirements and the need for the Agency to revise its 

registration review ecological risk problem formulation document. However, the 

comments received do not change the timeline detailed in the hexazinone PWP. 

Risk Assessment and Data Needs: 

The Agency anticipates conducting an ecological risk assessment for hexazinone, 

including an endangered species assessment. The Agency also anticipates conducting 

human health risk assessments for hexazinone. 

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Ecological Risk: 

• The Agency has conducted a risk assessment that supports a complete endangered 

species determination for the California Red-Legged Frog (CRLF) as well as 

Pacific salmon and steelhead. The CRLF assessment resulted in a “Likely to 

Adversely Affect” determination for both direct and indirect effects to the CRLF. 

The Agency concluded that hexazinone will not present a direct effect on Pacific 

salmon and steelhead or their critical habitat. These assessments were submitted 

to the Services for initiation of formal consultation. 

• Terrestrial plant toxicity data (Guidelines 850.4100 and 850.4150), which were 

identified in the PWP as data needs, will not be required. Information submitted 

by the registrant during the PWP public comment period was sufficient to satisfy 

these data requirements. For more details, see the “Summary of Comments 

Received During the Comment Period” section of this document. 

• EPA anticipates needing the following guideline studies for hexazinone in order 

to conduct a complete environmental fate and ecological risk assessment during 

the registration review of hexazinone:

o 835.4100 Aerobic Soil Metabolism 

o 835.4200 Anaerobic Soil Metabolism 

o 835.4300 Aerobic Aquatic Metabolism 

o 835.4400 Anaerobic Aquatic Metabolism 

o 835.6100(7) Independent Laboratory Validation of Environmental 

Chemistry Analytical Method for Soil 

o 835.6200(7) Environmental Chemistry Analytical Method for Water and 

an Associated Independent Laboratory Validation 

o 850.2100 Avian Oral Toxicity (Passerine species) 

• Please refer to EFED Registration Review Problem Formulation for Hexazinone 

dated January 12, 2010, located in the hexazinone docket, for a detailed 

discussion of the anticipated ecological risk assessment needs. 

Human Health Risk: 

• While there are no registered residential uses of hexazinone, it is registered for 

use on industrial turf grass, and current labels do not restrict this use in residential 

settings. Since this could potentially result in post-application residential 

exposure, the Agency intends to conduct a residential risk assessment during 

registration review. A new aggregate risk assessment may also be needed. 

• The Agency intends to conduct a drinking water exposure assessment for 

registration review. 

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• The hexazinone tolerance expression (40 CFR 180.396) will be reviewed during 

registration review to ensure that it appropriately covers the metabolites and 

degradates of hexazinone and that it specifies the residues to be measured for each 

commodity. 

• The Agency anticipates an updated occupational and occupational postapplication risk assessments will be needed for hexazinone. The new 

occupational post-application risk assessment will use data from the Agricultural 

Reentry Task Force to update the exposure estimates based on current transfer 

coefficients. In addition, the existing 48 hour Restricted Entry Interval (REI) may 

be revisited. 

• The Agency anticipates that a revised dietary assessment will be needed. 

• Based on comments by the registrant, the Agency will reassess hexazinone 

toxicity categories and endpoints for the upcoming registration review human 

health risk assessment. 

• The field rotational crops data (Guideline 860.1900), which was identified as a 

data need in the PWP, will not be required. Information submitted by the 

registrant during the PWP public comment period was sufficient to satisfy this 

data requirement. The Agency anticipates establishing a tolerance of 0.50 ppm 

for inadvertent hexazinone residues in/on corn stover, sorghum stover, and wheat 

straw. For more details, see the “Summary of Comments Received During the 

Comment Period” section of this document. 

• The toxicity and residue chemistry databases are complete with the exception of 

the following guideline studies, which the Agency anticipates requiring in order to 

conduct a complete human health assessment: 

○ 870.3465 28-Day Inhalation Toxicity

○ 870.7800 Immunotoxicity (rats) 

○ 870.6200 Neurotoxicity Battery (acute and subchronic studies)

• Please refer to Hexazinone: Registration Review Scoping Document for Human 

Health Assessments dated January 12, 2010, located in the hexazinone docket, for 

a detailed discussion of the anticipated human health risk assessment needs. 

Endocrine Disruptor Screening Program: 

As required under FFDCA section 408(p), EPA has developed the Endocrine 

Disruptor Screening Program (EDSP) to determine whether certain substances (including 

pesticide active and other ingredients) may have an effect in humans or wildlife similar to 

an effect produced by a “naturally occurring estrogen, or other such endocrine effects as 

the Administrator may designate.” The EDSP employs a two-tiered approach to making 

the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays 

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to identify the potential of a chemical substance to interact with the estrogen, androgen, 

or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening 

and are found to have the potential to interact with E, A, or T hormonal systems will 

proceed to the next stage of the EDSP where EPA will determine which, if any, of the 

Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to 

identify any adverse endocrine related effects caused by the substance, and establish a 

quantitative relationship between the dose and the E, A, or T effect. 

Between October 2009 and February 2010, EPA is issuing test orders/data call-ins 

for the first group of 67 chemicals, which contains 58 pesticide active ingredients and 9 

inert ingredients. This list of chemicals was selected based on the potential for human 

exposure through pathways such as food and water, residential activity, and certain postapplication agricultural scenarios. This list should not be construed as a list of known or 

likely endocrine disruptors. 

Hexazinone is not among the group of 58 pesticide active ingredients on the 

initial list to be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must 

screen all pesticide chemicals. Accordingly, EPA anticipates issuing future EDSP 

orders/data call-ins for all registration review cases, including those for which EPA has 

already opened a registration review docket for a pesticide active ingredient. 

For further information on the status of the EDSP, the policies and procedures, the 

list of 67 chemicals, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/. 

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Timeline: 

EPA has created the following estimated timeline for completion of the 

registration review for hexazinone. 

Registration Review for Hexazinone– Projected Registration Review Timeline

Activities Estimated Date 

Opening the docket 

Open Docket and Public Comment Period 2010 – March 

Close Public Comment 2010 – May 

Case Development 

Final Work Plan 2010 – August 

Issue DCI 2011 – Apr.- June 

Data Submission 2013 – Apr. - June 

Open Public Comment Period for Preliminary Risk Assessments 2014 – Oct. - Dec. 

Close Public Comment Period 2015 – Jan. – Mar. 

Registration Review Decision 

Open Public Comment Period for Proposed Registration Review 

Decision 

 2015 – Apr. – June. 

Close Public Comment Period 2015 – July – Sept. 

Final Registration Review Decision and Begin Post-Decision Follow-up 2016 

Total (years) 6 

Summary of Comments Received During the Comment Period: 

The hexazinone registration review docket was open for a 60-day comment period 

beginning on May 6, 2010. Technical registrant DuPont submitted comments on the 

registration review Problem Formulation and Scoping documents. The comments 

challenge the Agency’s understanding of issues related to environmental fate, ecotoxicity, 

and residue chemistry of hexazinone, as well as the need for several data requirements 

anticipated in the PWP. Additionally, the registrant pointed out an error in the Agency’s 

registration review Scoping Document. Page 20 of the document indicates that an acute 

neurotoxicity study was submitted. However, the Agency has not received such a study. 

The Agency appreciates the registrant’s correction. 

A description of the comments received and the Agency’s response to these 

comments is available in the following documents, which are located in the hexazinone 

registration review docket: 

EFED Registration Review Problem Formulation for Hexazinone, August 19, 

2010. 

Hexazinone. Response to Comments from the Revised Registration Review 

Scoping Document for Human Health Risk Assessments, August 16, 2010. 

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Finally, in the PWP, the Agency solicited comments on three specific topics: 

environmental justice, water body impairment, and trade irritants. No comments or 

information were received during the comment period concerning these issues. 

Next Steps: 

Risk assessments will be conducted as detailed in the Risk Assessment and Data 

Need section of this document. As noted previously, the Agency will require several 

studies through the Data Call-In process to conduct complete human health, ecological, 

and endangered species risk assessments for all uses of hexazinone.

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