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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 imazapyr (imazapyr and the isopropylamine salt of imazapyr). This 

work plan addresses public comments received concerning the Preliminary Work Plan (PWP), 

which was posted in the imazapyr registration review docket (EPA-HQ-OPP-2014-0200). This 

case includes the following active ingredients: imazapyr (PC code 128821) and the 

isopropylamine salt (PC code 128829) of imazapyr, the two collectively hereafter referred to as 

imazapyr. Imazapyr is a non-selective systemic herbicide registered for use as pre- and postemergent treatments for control of a broad spectrum of terrestrial and aquatic weeds. 

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 website.1

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 registration 

review planned data needs, risk assessments expected to be conducted, and the projected 

registration review timeline for imazapyr. Lastly, there is a discussion of next steps. 

UPDATES SINCE THE PWP WAS ISSUED 

EPA believes at this time that an updated ecological risk assessment is not required for 

registration review. There have been no changes to the use pattern and no new ecological effects 

or environmental fate data that changes the overall risk conclusions drawn in the 2010 ecological 

risk assessment. The screening level risk assessment indicated risk to non-target terrestrial plants 

(monocots and dicots) and aquatic vascular plants from imazapyr use, based on the highest 

application rate from a variety of use patterns. 

This change in planned registration review risk assessments has resulted in a change in the 

projected registration review timeline. Prior to completing the imazapyr registration review case, 

pursuant to the Endangered Species Act (ESA), EPA will conduct a comprehensive endangered 

species assessment for all uses of imazapyr. 

 

 

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 http://www.epa.gov/oppsrrd1/registration_review/ 
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SUMMARY OF COMMENTS AND AGENCY RESPONSES 

During the 60-day public comment period on the imazapyr Preliminary Work Plan, which 

opened on June 25, 2014 and closed on August 25, 2014, the Agency received 3 public 

comments. Comments were submitted by the Center for Biological Diversity (CBD), the FIFRA 

Endangered Species Task Force (FESTF), and an anonymous public citizen. The comments do 

not address the timeline described in the PWP, but 2 comments address the planned ecological 

risk assessment. 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. 

None of the public comments resulted in changes to the anticipated registration review data 

needs, risk assessments, or timeline. Summarized public comments and Agency responses are in 

Responses to Public Comments on the Imazapyr Preliminary Work Plan. Public comments and 

EPA responses in their entirety are located in the docket, EPA-HQ-OPP-2014-0200. 

PLANNED DATA NEEDS 

There are no planned data needs for imazapyr based on the Registration Review – Preliminary 

Problem Formulation for the Ecological Risk Assessment and Drinking Water Exposure 

Assessment to be Conducted for Imazapyr and Imazapyr Isopropylamine (PC Code 128829 

(isopropylamine salt) and 128821 (imazapyr acid) and Imazapyr, Isopropylamine Salt: 

Registration Review Scoping Document for Human Health Assessment. The planned data needs 

have not changed from what was included in the PWP. 

RISK ASSESSMENTS FOR REGISTRATION REVIEW

Because an updated screening level risk assessment is not needed, during registration review the 

Agency will conduct a comprehensive endangered species assessment for all uses of imazapyr. 

For human health, EPA will not require a risk assessment for registration review because after 

reviewing the toxicology database for imazapyr, EPA believes at this time that dietary, 

occupational, and residential exposures to imazapyr do not pose a significant human health risk 

and, therefore, risk assessments are not needed. This is because, although there is potential for 

exposure to imazapyr and although the existing toxicology studies do not use doses up to the 

limit dose, the available data are high quality and no hazard was identified from the toxicity 

studies. Prior to completing the imazapyr registration review case, pursuant to FFDCA section 

408(p), EPA will make a determination regarding imazapyr under the Endocrine Disruptor 

Screening Program (EDSP). The Agency will also make a determination under the Endangered 

Species Act (ESA) prior to completing the imazapyr registration review case. 

Table 1 below summarizes the planned registration review risk assessments based on the EFED 

Problem Formulation and HED Scoping Document and has been updated since the PWP to 

reflect changes to the planned risk assessments. 

 
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Table 1: Planned Risk Assessments for the Imazapyr Registration Review 

Type of Risk Assessment Conduct? Notes 

Ecological and Environmental Fate 

Comprehensive ecological 

(species to be assessed 

include terrestrial and aquatic 

organisms) 

N Because there have been no significant changes since 

the last ecological risk assessment, an updated or 

revised risk assessment will not be conducted. 

Comprehensive endangered 

species (species to be 

assessed include terrestrial 

and aquatic organisms) 

Y A quantitative risk assessment will be conducted. 

Incidents Will check for 

updates 

For a discussion of reported ecological incidents for 

imazapyr, see page 14 of the Problem Formulation. 

Human Health 

Dietary 

Food N Because imazapyr does not pose a dietary (food and 

drinking water) risk, a quantitative dietary risk 

assessment is not required. 

Drinking water N 

Occupational 

Handlers (mixers, loaders, 

applicators) 

N Because imazapyr does not pose an occupational 

risk, an updated or revised occupational risk 

Post-application N assessment is not required. 

Residential 

Handlers N Because imazapyr does not pose a residential risk, an 

updated or revised residential risk assessment is not 

required. 

Post-application N 

Other 

Aggregate N Evaluates the combined risk from dietary and 

residential exposures. 

Cumulative N Imazapyr has not been identified as a member of a 

cumulative group that shares a common mechanism 

of toxicity. 

Tolerances N 

Incidents Will check for 

updates 

For a discussion of reported human incidents for 

imazapyr, see page 5 of the Scoping Document and 

the Imazapyr: Tier I Review of Human Incidents. 

 
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TIMELINE

EPA has created the following estimated timeline for the completion of the imazapyr registration 

review in Table 2 below. The projected timeline has been updated to reflect changes to the 

planned risk assessments. 

Table 2: Registration Review for Imazapyr – Projected Registration Review Timeline

Activities Estimated Date 

Opening the Docket 

Open Docket and 60-day Public Comment Period June 2014 – 

Completed 

Close Public Comment August 2014 – 

Completed 

Case Development 

Final Work Plan December 2014 – 

Completed 

Issue DCI N/A 

Data Submission N/A 

60-day Public Comment Period for Draft Risk Assessments N/A 

Registration Review Decision 

60-day Public Comment Period for Proposed Interim Registration Review 

Decision 

2015 April - June 

Registration Review Interim Decision and Begin Post-Decision Follow-up2 2015 

Total (years) 1 

NEXT STEPS 

After issuing the Final Work Plan, the Agency will prepare a Proposed Interim Registration 

Review Decision for imazapyr. The Agency expects to issue a Proposed Interim Registration 

Review Decision for a 60-day public comment period in 2015. 

 

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 A final decision on the imazapyr registration review case, in accordance with 40 CFR Section 155.158, will occur 

after an EDSP FFDCA section 408(p) determination has been made as well as an ESA determination.