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Table of Contents

Contents

I. Introduction............................................................................................................................. 3

II. Scientific Assessments............................................................................................................ 4

A. Human Health Assessment .................................................................................................... 4

B. Environmental Assessment ................................................................................................... 4

Pollinator Studies and Assessment ......................................................................................... 5

Endangered Species Assessment ............................................................................................ 5

C. Endocrine Disruptor Screening Program ............................................................................... 6

III. Interim Registration Review Decision................................................................................. 7

IV. Next Steps and Timeline...................................................................................................... 7
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I. Introduction

This document is the Environmental Protection Agency’s (EPA or the Agency) Interim 

Registration Review Decision for imazapyr (imazapyr (PC 128821) and the isopropylamine salt

(PC 128829) of imazapyr) and is being issued pursuant to 40 CFR sections 155.56 and 155.58. A 

registration review decision is the Agency's determination whether a pesticide meets, or does not 

meet, the standard for registration in the Federal Insecticide, Fungicide, and Rodenticide Act 

(FIFRA). The Agency may issue, when it determines it to be appropriate, an interim registration 

review decision before completing a registration review. Among other things, the interim 

registration review decision may require new risk mitigation measures, impose interim risk 

mitigation measures, identify data or information required to complete the review, and include 

schedules for submitting the required data, conducting the new risk assessment and completing 

the registration review. For further information on imazapyr, additional documents can be found 

in EPA’s public docket (EPA-HQ-OPP-2014-0200) at www.regulations.gov.

FIFRA, as amended by the Food Quality Protection Act (FQPA) of 1996, mandated the 

continuous review of existing pesticides. All pesticides distributed or sold in the United States 

generally must be registered by the EPA based on scientific data showing that they will not cause 

unreasonable risks to human health or to the environment when used as directed on product 

labeling. The registration review program is intended to make sure that, as the ability to assess 

and reduce risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects. Changes in science, public 

policy, and pesticide use practices will occur over time. Through the registration review 

program, the Agency periodically reevaluates pesticides to make sure that as these changes 

occur, products in the marketplace can continue to be used safely. Information on this program is 

provided as http://www.epa.gov/pesticide-reevaluation/registration-review-process.

In 2006, the Agency implemented the registration review program pursuant to FIFRA 

section 3(g) and will review each registered pesticide every 15 years to determine whether it 

continues to meet the FIFRA standard for registration.

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

annual and perennial grasses, broadleaf weeds, herbs, woody species, and riparian and emergent 

aquatic weed species. The first product containing imazapyr was registered in 1984. The 

Reregistration Eligibility Decision document (RED) for imazapyr was completed in June 2006.

Pursuant to 40 CFR section 155.50, EPA formally initiated registration review for 

imazapyr (case 3078). The following highlights significant events that have occurred during the 

registration review of imazapyr:

 June 25, 2014 – Publication of the Imazapyr Preliminary Work Plan for a 60-day public 

comment period. The Preliminary Work Plan (PWP) was accompanied by the scoping 

document and problem formulation.

 December 3, 2014 - Final Work Plan (FWP) for imazapyr was issued – Three public 

comments were received during the 60-day comment period for the Imazapyr PWP. None 
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of the public comments resulted in changes to the anticipated registration review data 

needs, risk assessments, or timeline.

o The FWP noted that no additional data were needed and that no ecological or 

human health risk assessments would be conducted for the imazapyr registration 

review because sufficient information was available to support a proposed 

registration review decision, pursuant to 40 CFR section 155.53(c)(2).

 August 10, 2015 – The Agency published the Imazapyr Proposed Interim Registration 

Review Decision in docket number EPA-HQ-OPP-2014-0200 for a 60-day public 

comment period. No comments were received during that period. 

 November 2015 – The Agency is now publishing the Imazapyr Interim Registration 

Review Decision, dated November 23, 2015 in docket number EPA-HQ-OPP-2014-0200.

Additional information on imazapyr can be found in EPA’s public docket, EPA-HQ-OPP2014-0200, accessed at www.regulations.gov.

II. Scientific Assessments

A. Human Health Assessment

As indicated in the FWP, EPA did not require a risk assessment for registration review 

because after reviewing the toxicology database for imazapyr, EPA has not identified any human 

health endpoints of toxicological concern and, as a result, has determined that there are no risks 

of concern for dietary, residential, and occupational exposure. Further discussion regarding these 

conclusions can be found in the Imazapyr, Isopropylamine Salt: Registration Review Scoping 

Document for Human Health Assessment, which is available in the imazapyr docket, EPA-HQOPP-2014-0200, accessed at www.regulations.gov.

B. Environmental Assessment

As indicated in the FWP, because there were no significant changes since the last 

imazapyr ecological risk assessment, an updated or revised risk assessment for registration 

review was not needed.

While the last comprehensive risk assessment identified risk to non-target terrestrial 

plants; there was no risk to terrestrial plants from drift exposure alone for the corn use (the 

largest use at over 80% of lbs/a.i. applied). Although there was some potential risk to some 

plants in adjacent fields and some exceedances for non-crop uses, label mitigation required in the 

RED (see the label table1) to reduce spray drift and now on product labels has greatly reduced 

potential risk, as it included, among other things, requirements for the use of coarse or very 

coarse droplets. Risk to aquatic vascular plants was indicated, but such plants are the target pest 

for aquatic uses of imazapyr.

 

1 Available at http://archive.epa.gov/pesticides/reregistration/web/pdf/imazapyr_red.pdf
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Pollinator Studies and Assessment

When initially scoping the registration review for imazapyr, EPA did not identify the 

need for any additional studies to evaluate potential effects on pollinators. However, since the 

issuance of the June 2014 Guidance for Assessing Pesticide Risks to Bees2, EPA has begun to 

require these data where applicable. EPA is currently determining whether additional pollinator 

data are needed for active ingredients in registration review whose dockets opened prior to June 

2014. For those active ingredients where EPA determines that additional pollinator exposure and 

effects data are necessary to help make a final registration review decision, EPA intends to issue 

a DCI to obtain these data. In the near future, EPA will provide further information and 

guidance on this effort. The pollinator studies that could be required are included in Table 1 

below. The Agency will require data it believes are needed to help inform the pollinator risk 

assessment.

Table 1. Potential Pollinator Data Requirements

Guideline # Study

850.3030* Honey bee toxicity of residues on foliage

850.3040** Field testing for pollinators

Non-Guideline*

(OECD 213)

Honey bee adult acute oral toxicity

Non-Guideline*

(OECD 237)

Honey bee larvae acute oral toxicity

Non-Guideline* Honey bee adult chronic oral toxicity

Non-Guideline* Honey bee larvae chronic oral toxicity

Non-Guideline** Residues in pollen and nectar/field residue analysis

Non-Guideline**

(OECD 75) Semi-field testing for pollinators (tunnel or colony feeding studies)

*Tier 1 (Laboratory-based studies)

**Tier 2 and 3 (Semi-field and full field colony-level studies) The need for a higher tier test for pollinators will be determined 

based upon lower-tiered tests and/or other lines of data and the need for a refined pollinator risk assessment.

Endangered Species Assessment

In November 2013, the EPA, along with the Services and the USDA, released a summary 

of their joint Interim Approaches for assessing risks to endangered and threatened (listed) species 

from pesticides. The Interim Approaches were developed jointly by the agencies in response to 

the National Academy of Sciences’ (NAS) recommendations and reflect a common approach to 

risk assessment shared by the agencies as a way of addressing scientific differences between the 

EPA and the Services. The NAS report3outlines recommendations on specific scientific and 

technical issues related to the development of pesticide risk assessments that EPA and the 

Services must conduct in connection with their obligations under the ESA and FIFRA. 

 

2 http://www2.epa.gov/sites/production/files/2014-

06/documents/pollinator_risk_assessment_guidance_06_19_14.pdf

3 http://www.nap.edu/catalog.php?record_id=18344
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The joint Interim Approaches were released prior to a stakeholder workshop held on 

November 15, 2013. In addition, the EPA presented the joint Interim Approaches at the 

December 2013 Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues 

Research and Evaluation Group (SFIREG) meetings. The agencies also held stakeholder 

workshops in April and October 2014, allowing additional opportunities for stakeholders to 

comment on the Interim Approaches. Additional workshops are planned to enhance stakeholder 

involvement. As part of a phased, iterative process for developing the Interim Approaches, the 

agencies will also consider public comments on the Interim Approaches in connection with the 

development of upcoming Registration Review decisions. The details of the joint Interim 

Approaches are contained in the white paper “Interim Approaches for National-Level Pesticide 

Endangered Species Act Assessments Based on the Recommendations of the National Academy 

of Sciences April 2013 Report”4, dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, this Interim Decision for Imazapyr does not contain an ESA analysis

that includes effects determinations for specific listed species or designated critical habitat. Once 

the agencies have fully developed and implemented the scientific methods necessary to complete 

risk assessments for endangered and threatened (listed) species and their designated critical 

habitats, these methods will be applied to subsequent analyses for imazapyr as part of completing 

this registration review.

C. Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential 

adverse outcomes from exposure to chemicals. Collectively, these studies include acute, 

subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, 

developmental, reproductive, and general or systemic toxicity. These studies include endpoints 

which may be susceptible to endocrine influence, including effects on endocrine target organ 

histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, 

reproductive loss, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates 

acute tests and chronic studies that assess growth, developmental and reproductive effects in 

different taxonomic groups. As part of its most recent registration decision for imazapyr, EPA 

reviewed these data and selected the most sensitive endpoints for relevant risk assessment 

scenarios from the existing hazard database. However, as required by FFDCA section 408(p), 

imazapyr is subject to the endocrine screening part of the Endocrine Disruptor Screening 

Program (EDSP). 

EPA has developed the 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 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 

 

4 http://www.epa.gov/espp/2013/nas.html
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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 dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of 

chemicals identified for EDSP screening was published on June 14, 20135and includes some 

pesticides scheduled for Registration Review and chemicals found in water. For further 

information on the status of the EDSP, the policies and procedures, the lists of chemicals, future 

lists, the test guidelines and the Tier 1 screening battery, please visit our website.6 

In this interim decision, EPA is making no human health or environmental safety findings 

associated with the EDSP screening of imazapyr. Before completing this Registration Review, 

the Agency will make an EDSP FFDCA section 408(p) determination.

III. Interim Registration Review Decision

In accordance with 40 CFR Sections 155.56 and 155.58, the Agency is issuing this 

Interim Registration Review Decision. Except for the EDSP, ESA, and pollinator components of 

this case, EPA’s Interim Registration Review Decision for imazapyr is that (1) no additional data 

are required at this time; and (2) no changes to the affected registrations or their labeling are 

needed at this time.

In this interim registration review decision, EPA is making no human health or 

environmental safety findings associated with the EDSP screening of imazapyr, nor is it making 

an endangered species finding. EPA’s registration review decision for imazapyr will depend 

upon the result of an EDSP FFDCA section 408(p) determination, complete pollinator 

determination, and ESA determination.

IV. Next Steps and Timeline

A. Interim Registration Review Decision

A Federal Register Notice will announce the availability of this Interim Registration 

Review Decision for imazapyr. A final decision on the imazapyr registration review case will 

occur after an EDSP FFDCA section 408(p) determination, complete pollinator determination, 

and ESA determination.

 

5 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.

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