Docket Number EPA-HQ-OPP-20 14-0200 

www.regulations.gov 

Imazapyr Preliminary Work Plan 

Registration Review: Initial Docket 

Case Number 3078· 

Approved by: 

Date: 

May2014 

~~P~,:O 

Richard P. Keigwin, Jr. 

Director 

Pesticide Re-evaluation Division 
2

Imazapyr Preliminary Work Plan – Table of Contents

OVERVIEW ................................................................................................................................... 4

ANTICIPATED DATA NEEDS .................................................................................................... 4

STATUTORY AND REGULATORY AUTHORITY................................................................... 4

CHEMICAL FACTS ...................................................................................................................... 5

USE AND USAGE INFORMATION............................................................................................ 6

RECENT ACTIONS....................................................................................................................... 8

ANTICIPATED RISK ASSESSMENTS FOR REGISTRATION REVIEW................................ 8

TIMELINE.................................................................................................................................... 10

NEXT STEPS ............................................................................................................................... 10

Appendix – Additional Areas Considered in the Imazapyr Registration Review .................... 11

References:

This Preliminary Work Plan summarizes the Environmental Protection Agency's current position 

based on the following documents:

1. 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). James Hetrick and Tanja Crk. March 10, 2014.

2. Imazapyr, Isopropylamine Salt: Registration Review Scoping Document for Human Health 

Assessment. Mohsen Sahafeyan, Nancy McCarroll, and Bridgett Bobowiec. March 4, 2014.

3. Imazapyr: Tier I Review of Human Incidents. Shanna Recore. January 23, 2014.

4. BEAD Chemical Profile for Registration Review: Imazapyr (128821) and Imazapyr, 

Isopropylamine salt (128829). Sunil Ratnayake, Cynthia Doucoure, and Derek Berwald. 

March 14, 2014.
3

5. Imazapyr (128821): Screening Level Usage Analysis. April 29, 2013.

6. EFED Table 1 Report: Imazapyr (128821). March 12, 2014.

7. HED Master Label Report: Imazapyr (128821). March 12, 2014.

These and other supporting documents for the imazapyr registration review case may be found in

the docket EPA-HQ-OPP-2014-0200 at http://www.regulations.gov.
4

OVERVIEW

The docket for imazapyr (imazapyr and the isopropylamine salt of imazapyr) is now open, 

initiating the first public comment period for this registration review (docket number EPA-HQOPP-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 post-emergent treatments for control of a broad spectrum of terrestrial and aquatic 

weeds. This Preliminary Work Plan (PWP) document explains what EPA's Office of Pesticide 

Programs knows about imazapyr, highlighting anticipated data and assessment needs, identifying 

the types of information that would be especially useful to the Agency in conducting the review, 

and providing an anticipated timeline for completing the registration review for imazapyr.

The registration review process was designed to include a public participation component to 

solicit input from interested stakeholders. The Agency intends, by sharing this information in the 

docket, to inform the public of what it knows about imazapyr and what types of new data or 

other information would be helpful for the Agency to receive as it moves toward a decision on 

imazapyr. The Agency encourages all interested stakeholders to review the PWP and Appendix 

and to provide comments and additional information that will help the Agency’s decisionmaking process for this chemical. In addition to general areas on which persons may wish to 

comment, there are some areas identified in the PWP and Appendix about which the Agency 

specifically seeks comments and information. Interested stakeholders could include: 

environmental non-profit or interest groups; pesticide manufacturers; agricultural labor or 

commodity groups; commercial, institutional, residential, and other users of pesticides; or the 

public at large.

The Preliminary Work Plan begins by listing the anticipated data needs for imazapyr. Next, it 

discusses the statutory and regulatory authority for Registration Review. Then the document 

provides chemical facts, use and usage information, recent actions, the anticipated risk 

assessments, and a projected registration review timeline for imazapyr. Finally, the Appendix to 

this document includes identification and discussion of some areas that are considered generally 

in Registration Review along with some additional chemical case-specific information.

ANTICIPATED DATA NEEDS

There are no anticipated data needs for the imazapyr registration review. For additional 

discussion of why there are no anticipated data needs, see 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.

STATUTORY AND REGULATORY AUTHORITY

The Food Quality Protection Act (FQPA) of 1996 mandated a registration review program. All 

pesticides distributed or sold in the United States (U.S.) generally must be registered by the 

Environmental Protection Agency (EPA or the Agency), based on scientific data showing that 
5

they will not cause unreasonable risks to human health or the environment when used as directed 

on product labeling. 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 of no unreasonable adverse effects to human health or the 

environment. 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 change occurs, products in the marketplace can be used safely. Information on this 

program is provided on EPA’s website.

1

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. The regulations governing registration review begin at 40 CFR 155.40. The Agency 

will consider benefits information and data as required by FIFRA. The public phase of 

registration review begins when the initial docket is opened for each case. The docket is the 

Agency’s opportunity to state what it knows about the pesticide and what additional risk analyses 

and data or information it believes are needed to make a registration review decision. After 

reviewing and responding to comments and data received in the docket during this initial 

comment period, the Agency will develop a Final Work Plan (FWP) and anticipated schedule for 

the registration review of imazapyr.

CHEMICAL FACTS

Table 1 provides a summary of the chemical facts for imazapyr.

Table 1: Chemical Facts for Imazapyr

PC code 128821 (imazapyr), 128829 (isopropylamine salt)

Case Number 3078

CAS Number 81334-34-1 (imazapyr), 81510-83-0 (isopropylamine salt)

Year first registered 1985 (technical); however, non-crop end use registered July 1984

Pesticide Type Herbicide

Chemical class Imidazolinone

Reregistration Eligibility 

Decision (RED)

September 2006

Tolerance Reassessment 

Eligibility Decision 

(TRED)

Not applicable; the tolerances were reassessed when new food 

uses were established, 68 FR 55475-55485

Cumulative group Not applicable, imazapyr has not been identified as a member of a 

cumulative group that shares a common mechanism of toxicity

40 CFR Citation Tolerances for imazapyr are established in 40 CFR § 180.500

Dual-use Imazapyr is registered for conventional pesticidal uses only and 

has no registered antimicrobial or biopesticidal uses.

Non-pesticidal uses There are no identified non-pesticidal uses of imazapyr

 

1 http://www.epa.gov/oppsrrd1/registration_review/
6

Table 1: Chemical Facts for Imazapyr

Pesticide Re-evaluation 

Division, Chemical 

Review Manager

Joel Wolf, wolf.joel@epa.gov, 703-347-0228

Registration Division, 

Product Manager

Kable (Bo) Davis, davis.kable@epa.gov, 703-306-0415

USE AND USAGE INFORMATION

Table 2 summarizes the use and usage information for imazapyr. Please see the BEAD Chemical 

Profile for Registration Review: Imazapyr (128821) and Imazapyr, Isopropylamine salt (128829)

in the registration review docket for more details.

Table 2: Imazapyr Use and Usage Information

Summary of Use Imazapyr is a non-selective systemic herbicide registered for use 

as pre- and post-emergent treatments to control broad spectrum of 

terrestrial and aquatic weeds including terrestrial annual and 

perennial grasses; broadleaf weeds; herbs; woody species; and 

riparian and emergent aquatic weed species. In addition, imazapyr 

is registered for use in controlling grasses and broadleaf weeds in 

Clearfield® production systems where the crop is tolerant to 

imidazolinone herbicides.

Use Sites Agricultural Use Sites:

Imazapyr is registered for use on field corn. Imazapyr and the 

isopropylamine salt of imazapyr are registered for use on conifer 

plantations, forestry sites, and grass pastures and rangelands, as 

well as agricultural non-crop areas.

Non-Agricultural Use Sites:

Imazapyr is registered for use on wildlife openings, nonagricultural non-crop areas, animal housing premises (outdoor), 

outdoor residential areas (paved areas, driveways, patios, etc.), 

recreational areas, commercial/institutional/industrial areas, and in 

aquatic sites (ponds, lakes, streams, etc.). Imazapyr is also

registered for use on established turf grass on industrial grounds, 

athletic fields, cemeteries, parks, golf course roughs, and 

institutional grounds. In addition, imazapyr is registered for direct 

application to potable surface water, public waters, private waters, 

livestock watering ponds, and recreational water areas.

Summary of Usage Agricultural usage of imazapyr:

The average annual pounds of a.i. applied has decreased by 86% 

from 19,600 lbs a.i during the period 2003-2007 to 2,700 lbs a.i. 

during the more recent period of 2008-2012.

Non-agricultural usage of imazapyr:

In 2011 ~4200 lbs a.i. was reportedly used on institutional turf 

and lawn care, 50% more than the amount of a.i. used for 
7

Table 2: Imazapyr Use and Usage Information

agriculture; widely reported use as an aquatic herbicide in Florida, 

quantity used unknown; Bureau of Land Management usage 

ranged from ~1200-8000 lbs a.i. from 2003-2011.

Formulation Type(s) Imazapyr is commonly formulated as soluble and emulsifiable 

concentrates, wettable powder, and water dispersible granules. 

The isopropylamine salt of imazapyr is commonly formulated as 

aqueous and ready-to-use solutions.

Application Method(s) Imazapyr is applied as a ground application using handheld 

equipment (backpack sprayers, sprinkling cans, handgun sprayers, 

high-pressure handwand sprayers) or granular broadcast 

applications using push-type or backpack spreaders. It can also be 

applied as an aerial spray.

Technical Registrant(s) BASF Corporation, E.I. DuPont de Nemours and Co, Agan Chem 

MFG. Ltd, Nufarm Limited, Tide International, USA, Inc., 

Forerock, LLC

No. of Registrations Imazapyr - 32 Section 3 products2

Imazapyr, Isopropylamine Salt – 46 Section 3 products, 10 

Section 24(c) products

Restricted Use No

Guidance for Commenters: Additional areas of use and usage related information

requested for this registration review, and of particular interest to EPA, are described below.

 Information about use in uncultivated non-agricultural areas, outdoor residential areas 

(paved areas, driveways, patios, etc.), and aquatic sites (ponds, lakes, streams, etc.), 

including pounds a.i. applied, application timing, application rate, application method, 

and application frequency.

 Confirmation of the following label information: sites of application; formulations;

application methods and equipment; maximum application rates; frequency of 

application, application intervals, and maximum number of applications per season; and 

geographic limitations on use.

 Use distribution (e.g., acreage and geographical distribution of relevant use sites).

 Median and 90th percentile reported use rates (lbs ai/A) from usage data – national, state, 

and county.

 Typical application timing (date of first application and application intervals) – national, 

state, and county.

 Usage/use information for non-agricultural uses.

 Typical application interval (days).

 State or local use restrictions.

 Foreign technical registrants not listed above who supply technical imazapyr to the US 

market.

 

2 Section 3 product labels can be obtained from the Pesticide Product Label System (PPLS) website 

(http://oaspub.epa.gov/pestlabl/ppls.home).
8

RECENT ACTIONS

An ecological assessment for a special local need FIFRA Section 24(c) was conducted in May 

2010. The FIFRA Section 24(c) action was to allow broadcast application of imazapyr (Arsenal 

PowerLine EPA Reg. No. 241-431) on grass pasture for control of cogongrass (Imperata 

cylindrica) in areas that may be grazed or cut for hay.

ANTICIPATED RISK ASSESSMENTS FOR REGISTRATION REVIEW

The most recent comprehensive human health risk assessment for imazapyr was completed in 

2013 to support import tolerances without U. S. registration for residues of imazapyr on 

imidazolinone-tolerant soybean of Cultivance® weed control system, rapeseed subgroup 20A, 

sunflower subgroup 20B and lentil. The most recent ecological and environmental fate risk 

assessment was completed in August 2010 to add aquatic use sites to the Arsenal PowerlineTM 

herbicide (EPA Reg. No. 241-431) label to allow direct application of imazapyr to potable 

surface water, public waters, private waters, livestock watering ponds, and recreational water 

areas at a maximum rate of 1.5 lb acid equivalents/A per year. Findings and conclusions from 

these risk assessments are summarized in 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.

During registration review, the Agency anticipates the need to conduct a comprehensive

ecological risk assessment, including an 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 has concluded, with reasonable certainty 

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).

Table 3 below summarizes the anticipated registration review risk assessments based on the 

EFED Problem Formulation and HED Scoping Document.
9

Table 3: Anticipated 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), including 

endangered species 

Y A quantitative risk assessment will be conducted

Incidents Will check for 

updates

For a discussion of currently 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 assessment is 

Post-application N 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 currently reported human 

incidents for imazapyr, see page 5 of the Scoping 

Document and the Imazapyr: Tier I Review of Human 

Incidents.
10

TIMELINE

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

review in Table 4 below.

Table 4: Projected Imazapyr Registration Review Timeline

Activities Estimated Date

Opening the Docket

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

Close Public Comment 2014 - August

Case Development

Final Work Plan 2014 - December

Issue DCI N/A

Data Submission N/A

60-day Public Comment Period for Draft Risk 

Assessments3

2016 April - June

Registration Review Decision

60-day Public Comment Period for Proposed 

Registration Review Decision

2017 Jan. - March

Registration Review Decision and Begin Post-Decision 

Follow-up

2017

Total (years) 3

NEXT STEPS

After the 60-day public comment period closes, the Agency will review and respond to any 

comments received in a timely manner and then issue a Final Work Plan for the registration 

review of imazapyr.

 

3 The regulations governing Registration Review generally require the Agency to provide a public comment period 

of at least 30 calendar days for draft risk assessments; see 40 CFR Part 155.53(c). For conventional pesticides, the 

Agency plans to provide a 60 calendar day public comment period generally for draft risk assessments.
11

Appendix – Additional Areas Considered in the Imazapyr Registration 

Review

PUBLIC COMMENTS AND FEEDBACK:

Guidance for Commenters: The areas below highlight topics of special interest to the Agency 

where your comments, data submissions, or reference to sources of additional information could 

be of particular use.

Trade Irritants:

Through the registration review process, the Agency intends to solicit information on trade 

irritants and, to the extent feasible, take steps toward facilitating irritant resolution. The Agency 

will work to harmonize tolerances and international maximum residue limits (MRLs) and may 

modify tolerance levels to do so, when possible. Growers and other stakeholders are asked to 

comment on any trade irritant issues resulting from lack of MRLs or disparities between U.S. 

tolerances and MRLs in key export markets, providing as much specificity as possible regarding 

the nature of the concern.

Water Quality:

Imazapyr is not identified as a cause of impairment for any water bodies listed as impaired under 

section 303(d) of the Clean Water Act.

4

 In addition, no Total Maximum Daily Loads (TMDL) 

have been developed for imazapyr.

5

 More information on impaired water bodies and TMDLs 

can be found at the Agency’s website.

6 The Agency invites submission of water quality data 

for this pesticide. To the extent possible, data should conform to the quality standards in 

Appendix A of the OPP Standard Operating Procedure: Inclusion of Impaired Water Body and 

Other Water Quality Data in OPP’s Registration Review Risk Assessment and Management

Process7in order to ensure they can be used quantitatively or qualitatively in pesticide risk 

assessments.

Environmental Justice:

EPA seeks to achieve environmental justice, the fair treatment and meaningful involvement of all 

people, regardless of race, color, national origin, or income, in the development, implementation, 

and enforcement of environmental laws, regulations, and policies. To help address potential 

environmental justice issues, the Agency seeks information on any groups or segments of the 

population who, as a result of their location, cultural practices, or other factors, may have 

atypical, unusually high exposure to imazapyr compared to the general population. Please 

comment if you are aware of any sub-populations that may have atypical, unusually high 

exposure compared to the general population.

 

4 http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885

5http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollutant_

group_name=PESTICIDES

6 http://www.epa.gov/owow/tmdl/

7 http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm
12

ENDANGERED SPECIES:

A risk assessment that supports a complete endangered species determination has not been 

conducted for imazapyr. The ecological risk assessment planned during registration review will 

allow the Agency to determine whether use of imazapyr has “no effect” or “may affect” federally 

listed threatened or endangered species (listed species) or their designated critical habitats. When 

an assessment concludes that a pesticide’s use “may affect” a listed species or its designated 

critical habitat, the Agency will consult with the U.S. Fish and Wildlife Service and/or National 

Marine Fisheries Service (the Services), as appropriate.

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 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, 20138and includes some pesticides 

scheduled for registration review and chemicals found in water. Neither of these lists should be 

construed as a list of known or likely endocrine disruptors. 

 

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

chemicals.
13

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.9

HUMAN STUDIES:

Occupational and Residential

Past imazapyr risk assessments rely in part on data from studies in which adult human subjects 

were intentionally exposed to a pesticide to determine their dermal and inhalation exposure. 

Many such studies, involving exposure to many different pesticides, comprise generic pesticide 

exposure databases such as the Pesticide Handlers Exposure Database (PHED), the Agricultural 

Reentry Task Force (ARTF) Database, and the Outdoor Residential Exposure Task Force 

(ORETF) Database. EPA has reviewed all the studies supporting these multi-pesticide generic 

exposure databases, and has found no clear and convincing evidence that the conduct of any of 

them was either fundamentally unethical or significantly deficient relative to the ethical 

standards prevailing at the time the research was conducted. All applicable requirements of 

EPA’s Rule for the Protection of Human Subjects of Research (40 CFR Part 26) have been 

satisfied, and there is no regulatory barrier to continued reliance on these studies.

 

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