Page 1 of 3

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

PC Codes: 128840, 128848 

DP Barcode: D418728

Date: September 10, 2014

MEMORANDUM

SUBJECT: Registration Review: Preliminary Problem Formulation for Environmental Fate, 

Ecological Risk, Endangered Species, and Human Health Drinking Water 

Exposure Assessments for Imazaquin and the Ammonium Salt of Imazaquin

TO: Wilhelmena Livingston, Chemical Review Manager

Tom Myers, Team Leader

Kevin Costello, Branch Chief

Pesticide Re-evaluation Division (PRD 7508P)

 

FROM: Andrew Sayer, PhD, Biologist

James N. Carleton, PhD, Senior Fate Scientist

ERB IV / EFED (7507P)

THROUGH: Chuck Peck, Environmental Engineer

Thomas Steeger, PhD, Senior Science Advisor 

ERB IV / EFED (7507P)

APPROVED Sarah Winfield, Acting Branch Chief

BY: ERB IV / EFED (7507P)

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation for the environmental fate, ecological risk, endangered species, and drinking water 

exposure assessments to be conducted as part of the Registration Review of imazaquin and the 

ammonium salt of imazaquin (CAS numbers 81335-37-7 and 81335-47-9, respectively; PC 

Codes 128848 and 128840, respectively). The problem formulation describes the preliminary 

ecological risk hypothesis and analysis plan for evaluating and characterizing risk to non-target 

species in support of the Registration Review of imazaquin and its ammonium salt. This 
Page 2 of 3

document also recommends studies that should be included in a generic data call-in (DCI) to 

address uncertainties surrounding the environmental fate and potential ecological effects of 

imazaquin and its ammonium salt. 

Because the ammonium salt of imazaquin dissociates in water to form the carboxylate anion,

“imazaquin” will be used to refer to both imazaquin and its ammonium salt. Both the 

ammonium salt and its carboxylate anion will be considered in this assessment. Four major 

photolytic degradates have been determined by HED to have the potential for toxicity equivalent 

to that of the parent. Because of the paucity of acceptable studies a large compliment of 

environmental fate data are recommended, and pending the submission and review of these (and 

additional ecotoxicity) data, one or more of these degradates may also be considered to be of 

concern to non-human biological receptors. We will re-evaluate degradates of concern for the 

ecological risk assessment once these additional data have been submitted and reviewed. 

The fate database is incomplete based on the environmental fate data requirements outlined in 

the Code of Federal Regulations Title 40 Part 158 (40CFR158) Subpart N1. Environmental fate 

data gaps include:

 §835.1230 Batch equilibrium adsorption/desorption

 §835.2410 Photodegradation on soil 

 §835.2240 Photodegradation in water

 §835.4100 Aerobic soil metabolism (three additional soils)

 §835.4300 Aerobic aquatic metabolism

 §835.4400 Anaerobic aquatic metabolism

 §850.6100 Environmental Chemistry Methods (ECM) and Associated Independent 

Laboratory Validations (ILV) for residues in water 

The ecological database is also incomplete based on the ecological effects data requirements 

outlined in the 40CFR158 Subpart G2. Ecotoxicology data gaps3include:

 Aquatic:

o §850.1025, §850.1035, §850.1045, or §850.1055 Saltwater invertebrate acute 

toxicity 

o §850.1075 Saltwater fish acute toxicity

o §850.1300 Freshwater invertebrate life-cycle

o §850.1350 Saltwater invertebrates life-cycle

o §850.1400 Freshwater fish early-life stage

o §850.1400 Saltwater fish early-life stage

o §850.4400 Aquatic plant growth: Tier II vascular plants

o §850.4500 Aquatic plant growth: Tier II algae (3 species)

o §850.4550 Aquatic plant growth: Cyanobacteria

 

1 CFR. 2013. Title 40 (Protection of the Environment), Chapter 1 (Environmental Protection Agency), Subchapter E (Pesticide 

Programs), Part 158 (Data Requirements for Pesticides), Subpart N (Environmental Fate) http://www.ecfr.gov/cgi-bin/textidx?c=ecfr&SID=ff5c7fef3645e7cd5abceca0b597bccb&tpl=/ecfrbrowse/Title40/40cfr158_main_02.tpl

2 CFR. 2013. Title 40 (Protection of the Environment), Chapter 1 (Environmental Protection Agency), Subchapter E (Pesticide 

Programs), Part 158 (Data Requirements for Pesticides), Subpart G (Ecological Effects) http://www.ecfr.gov/cgi-bin/textidx?c=ecfr&SID=ff5c7fef3645e7cd5abceca0b597bccb&rgn=div6&view=text&node=40:25.0.1.1.9.7&idno=40

3 A complete listing of all the environmental fate and ecotoxicology data gaps, along with justification according to 40 CFR, Part 

158-Subpart G, are listed in Section 9 of this document.
Page 3 of 3

 Terrestrial

o §850.2300 Avian reproduction (upland game species and waterfowl)

o OECD Guideline 237 and Non-Guideline: Honey bee larval acute and chronic 

oral toxicity

o Non-guideline: Honey bee adult acute and chronic oral toxicity

In the absence of the above toxicity data, major uncertainties in the assessment of imazaquin 

include the potential for risk to the following taxa: non-target aquatic fish and aquatic 

invertebrates (chronic exposure), aquatic vascular and nonvascular plants, and birds (chronic 

exposure). 
Page 1 of 35

 

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Human 

Health Drinking Water Exposure Assessments in 

Support of the Registration Review of Imazaquin and 

the Ammonium Salt of Imazaquin

Imazaquin

CAS: 81335-37-7

PC Code: 128848

Ammonium Salt of Imazaquin

CAS: 81335-47-9

PC Code: 128840

Prepared by:

Andrew Sayer, Ph.D., Biologist

Jim Carleton, Ph.D., Senior Fate Scientist

U.S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch IV

1200 Pennsylvania Ave., NW

Mail Code 7507

Washington, DC 20460

Reviewed by: 

Charles Peck, Environmental Engineer

Thomas Steeger, Ph.D., Senior Advisor

September 10, 2014
Page 2 of 35

TABLE OF CONTENTS

1. EXECUTIVE SUMMARY .................................................................................................... 3

2. INTRODUCTION .................................................................................................................. 3

3. USE/USAGE CHARACTERIZATION ................................................................................. 4

4. CONCLUSIONS FROM PREVIOUS ASSESSMENTS....................................................... 5

4.1. Drinking Water Assessment............................................................................................. 5

4.2. Clean Water Act Programs............................................................................................... 6

5. ENVIRONMENTAL FATE AND TRANSPORT................................................................. 7

6. RECEPTORS.......................................................................................................................... 8

6.1. Effects to Aquatic Organisms .......................................................................................... 9

6.2. Effects to Terrestrial Organisms ...................................................................................... 9

6.3. Ecological Incidents....................................................................................................... 10

6.3.1. Ecological Incident Information System..................................................................... 10

6.3.2. Avian Monitoring System............................................................................................ 11

6.3.3. Aggregate Incident Database ..................................................................................... 11

7. EXPOSURE PATHWAYS OF CONCERN ........................................................................ 11

8. ANALYSIS PLAN ............................................................................................................... 12

8.1. Stressors of Concern....................................................................................................... 12

8.1.1. Ecological Risk Assessment........................................................................................ 12

8.1.2. Drinking Water Assessment........................................................................................ 13

8.2. Measures of Exposure .................................................................................................... 13

8.3. Measures of Effect ......................................................................................................... 14

8.4. Endangered Species Assessments.................................................................................. 14

8.5. Endocrine Disruptor Screening Program (EDSP).......................................................... 15

9. PRELIMINARY IDENTIFICATION OF DATA GAPS..................................................... 15

9.1. Environmental Fate ........................................................................................................ 15

9.2. Effects............................................................................................................................. 16

10. REFERENCES .................................................................................................................. 23

Appendix A. BEAD Chemical Profile1........................................................................................ 25

Appendix B. Submitted Environmental Fate and Ecological Effects Studies.............................. 26

Appendix C. EIIS Incidents.......................................................................................................... 29

Appendix D. Aggregate Incident Reports for Imazaquin and the Ammonium Salt of Imazaquin30

Appendix E. SIP Results for Evaluate Potential Risk to Birds and Mammals from Drinking 

Water Exposure............................................................................................................................. 32

Appendix F. STIR Results to Evaluate the Potential for Inhalation Risk to Birds and Mammals

....................................................................................................................................................... 33

Appendix G. Chemical structures of imazaquin and identified major photodegradates .............. 34
Page 3 of 35

1. EXECUTIVE SUMMARY

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation for the ecological risk, environmental fate, endangered species, and drinking water 

assessments to be conducted as part of the Registration Review of imazaquin (PC code 128848; 

CAS No. 81335-37-7) and the ammonium salt of imazaquin (PC code 128840; CAS No. 81335-

47-9). Unless otherwise specified, references to imazaquin throughout this document include 

imazaquin and its ammonium salt. The problem formulation describes the methods planned for 

the completion of drinking water and ecological risk assessments and provides an overview of 

the environmental fate, ecological effects, and potential risks associated with the use of 

imazaquin. The problem formulation also addresses uncertainties unique to the risk assessment 

of imazaquin. This document identifies additional studies for both ecological effects and 

environmental fate that would be beneficial to the conduct of an ecological risk assessment; see 

Section 9 for additional details and explanation. Unless otherwise noted, studies are requested 

for imazaquin (PC code 128848). 

Imazaquin is an herbicide for use primarily on soybeans. According market research surveys, 

imazaquin usage on soybeans in the U.S. decreased by several fold between 1998 and about 

2003, then remained roughly steady through 2012 (USEPA, 2014b). Based on available data it is 

generally non-toxic to most taxa (i.e., freshwater fish, freshwater invertebrates, birds and 

mammals). Data are pending review for plants where toxic effects would be expected. The 

Agency has recently posted new guidance for assessing risks of pesticides to bees

4

. Because of 

this, a suite of tests is recommended for evaluating the potential toxicity of imazaquin to bees. 

Based on model information, imazaquin is highly mobile (Koc = 17.5 L/kgoc), persistent under 

most conditions (stable to hydrolysis and anaerobic aquatic degradation; aerobic soil t1⁄2 = 630 

days; aerobic aquatic t1⁄2 = 1260 days), but labile to aqueous photolysis (t1⁄2 <1day). 

2. INTRODUCTION

Imazaquin is a broad spectrum herbicide registered as a preplant, preemergence, and early 

postemergence herbicide for use primarily on soybeans. It is also registered for pre- and 

postemergence weed control on ornamentals and warm season turf grass in both residential and 

non-residential settings. It is also used on turf in both commercial and residential settings and on 

ornamental trees, shrubs, and groundcover. Similar to other imidazolinone herbicides, 

imazaquin is likely systemic, i.e., it is absorbed by both roots and foliage and translocated via 

both xylem and phloem tissues of the plant. It may be transported to regions of the plant where 

growth can take place.

Imazaquin is used mainly across the central Midwest from Kentucky to Illinois and across the 

mid-South in Arkansas, Louisiana and Mississippi. It is an imidazolinone herbicide which 

controls weeds by inhibiting the synthesis of specific amino acids necessary for plant growth. 

 

4 USEPA. 2014. Guidance for Assessing Pesticide Risks to Bees. Office of Pesticide Programs. United States 

Environmental Protection Agency. Available at 

http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/terrestrial_biology_tech_team/Guidance

AssessingPesticideRisk2Bees.pdf
Page 4 of 35

3. USE/USAGE CHARACTERIZATION

Based on information provided in the Biological and Economic Analysis Division (BEAD) 

Chemical Profile (BCP: USEPA, 2014b) for Registration Review, imazaquin is commonly 

formulated as water dispersible granules, wettable powders, soluble concentrates, and 

emulsifiable concentrates (Table 1). Both imazaquin and its monoammonium salt can be

applied using aerial or ground application. The BCP indicates that an average (presumably 

annual) of 56,000 lbs a.e. (acid equivalents) of imazaquin was applied to soybeans in the U.S.

between 2008 and 2012. Registered agricultural uses of imazaquin and imazaquin 

monoammonium salt are limited to soybeans and sod farms. Registered non-agricultural uses 

include landscape ornamentals, residential and commercial lawns and turf, and golf courses.

According to proprietary market research surveys, imazaquin usage on soybeans in the U.S. (in 

terms of both lbs a.e. applied and total area treated), decreased by several fold between 1998 and 

about 2003, then remained roughly steady through 2012 (USEPA, 2014b). From 1998 to 2012

on average 132,000 lbs a.e. were applied to 1.53 million acres each year, for an average annual

application rate of 0.09 lbs a.e. per acre. Product-specific usage data indicate the same trends 

prevailed for both active ingredients (i.e., imazaquin and its monoammonium salt). The states 

with the highest usage in terms of percentage of total pounds a.e. applied nationally during the 

2008-2012 time period were Indiana (37%), Ohio (33%), and Michigan (11 %). The average 

rates of application and numbers of applications annually were similar among these three major 

usage states. Based upon available private market research survey data, BEAD also reported 

15,000 lbs of imazaquin was used (presumably annually) in the turf and ornamental market, 

including 9,000 lbs a.e. applied by lawn care operators and 6,000 lbs a.e. applied to landscapes in 

“the most recent year available” (presumably 2012). No other reports of imazaquin use were 

found for the nonagricultural market. The BCP, which can be found in Appendix A, lists the use 

patterns associated with the active registrations of imazaquin and the monoammonium salt of 

imazaquin. EFED will rely on information in the BCP when estimating environmental exposures 

that result from these registered uses. In order to fulfill its mandate of being protective, EFED 

will employ results of modeling scenarios that generate maximum exposure estimates (i.e., 

concentrations) among registered uses, for both the drinking water and ecological risk 

assessments. Any absence of information on the labels that specifies the maximum single 

application rate, the application interval, the annual maximum rate allowed (lbs a.e./year), or 

application method may result in conservative assumptions.

Table 1. Imazaquin Use Table

Use(s)

Active 

Ingredient

EPA 

Registration 

Number(s)

Application 

Type/ 

Equipment

Max. 

Single 

Applicatio

n Rate (lb 

a.e. /A)

Max # 

Apps./yr

Max # 

Apps./CC

Max. 

Annual 

App. 

Rate (lb 

a.e. /A)

Min 

Retreatme

nt Interval

Lawns 

(commercial/i

ndustrial)

Imazaquin 241-319 ground 0.4954 NS NS NS NS

Cottonwoods 

(forest/shelter

belt)

Imazaquin 241-306 aerial, 

ground 0.245 NS NS 0.245 NS
Page 5 of 35

Golf course 

turf, sod 

farms, 

ornamental 

lawns, 

ornamental 

woody shrubs 

and vines, 

recreation 

area lawns

Imazaquin 241-319 ground 0.4954 NS NS NS NS

Soybeans Imazaquin

241-376, 241-

407, 241-415, 

241-369, 241-

306, 241-405, 

LA070001 

aerial 0.1838 1 NS NS NS

Ornamental 

and/or shade 

trees

Imazaquin 

ammonium 

salt

241-303 ground 1.1 NS NS NS NS

Ornamental 

lawns and 

turf, 

ornamentals 

unspecified

Imazaquin 

ammonium 

salt

73342-4 ground 0.3813 NS NS NS NS

Lawns and 

turf 

(ornamental)

Imazaquin 

ammonium 

salt

241-326 ground 0.4086 NS 2 NS NS

Ornamental 

woody shrubs 

and vines

Imazaquin 

ammonium 

salt

241-303 ground 1.1 NS NS NS NS

Soybeans

Imazaquin 

ammonium 

salt

5905-583 aerial, 

ground NS NS NS NS NS

Soybeans

Imazaquin 

ammonium 

salt

241-289, 241-

307, 241-327

aerial, 

ground 0.133 NS NS 0.26461 NS

1 241-289 only

4. CONCLUSIONS FROM PREVIOUS ASSESSMENTS

4.1. Drinking Water Assessment

An ecological risk assessment has not previously been conducted for imazaquin, although a 

Tolerance Reassessment and Risk Management Decision (TRED) was issued in 2005 (USEPA, 

2005c). As discussed in the TRED, concentrations of imazaquin to which humans may be

potentially exposed through ingestion of drinking water were assessed through evaluations of 

surface water and groundwater monitoring data, and via modeling (D313182: USEPA 2005a and

USEPA 2005b). Surface and groundwater monitoring data were available from the United States 

Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program, and from 

an additional USGS study on pesticide concentrations in high-use areas in the Midwest. 

Maximum concentrations of imazaquin in the monitoring data were 4.89 μg a.e./L in surface 

water and 0.098 μg a.e./L in groundwater (USEPA 2005). For a variety of reasons, monitoring 

data are unlikely to capture maximum historical concentrations, or to represent maximum 

potential future concentrations of most pesticides. Therefore, modeling is used by EFED to 

estimate concentrations expected to be representative of highly (though not necessarily 
Page 6 of 35

maximally) vulnerable waters, and monitoring data are used to further characterize actual 

measured concentrations in water. 

A June 2005 drinking water assessment (DWA) (D313182: USEPA, 2005a) was amended in 

September 2005 (D313182: USEPA, 2005b) to include four major photolytic degradates of 

imazaquin identified in unbuffered, distilled water (3-quinolinecarboxylic acid; 2,3 

quinolinedicarboxylic acid imide; 2,3- dihydro-3-imino-1H-pyrrolo-[3,4b]quinolin-1-one; and 

2,3 quinolinedicarboxylic acid) that HED determined to have the potential to be toxicologically 

equivalent to the parent compound (structures of these degradates and the parent compound are 

given in Appendix G). Exposure modeling was conducted employing an updated aquatic 

photolysis half-life input that took into account the sum of parent imazaquin and these four 

degradates. Results for the use (i.e., turf, at 2 applications/year) that generated the highest 

estimated drinking water concentrations (EDWCs) are presented in Table 2. 

The EDWCs in surface water were generated using the Pesticide Root Zone Model (PRZM;

version 3.12) coupled with the Exposure Analysis Model System (EXAMS; version 2.98.04). 

EDWCs in groundwater were generated using the Screening Concentrations in Ground Water 

(SCI-GROW; version 2.3) model. Concentrations are given in acid equivalents, and represent 

total toxic residues, i.e., parent plus the four degradates of concern. 

Table 2. Imazaquin maximum EDWCs, for use in human health drinking water 

assessment 

Use

Surface water 

(PRZM / EXAMS)

Groundwater

(SCI-GROW)

Acute 

(Peak)

Chronic 

(Annual average)

Acute & Chronic

Turf - 2 apps at 

0.63 lb a.e./A

each

 (total 

residue)

21.8 μg a.e./L 11.6 μg a.e./L 31.1 μg a.e./L

4.2. Clean Water Act Programs

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

under section 303(d) of the Clean Water Act.5 No Total Maximum Daily Loads (TMDLs) or 

section 304(a) water quality criteria have been developed for imazaquin.

6

 Aquatic benchmarks 

have been established for imazaquin and are available at 

http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm. Any data submitted or 

 

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

6 http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id=885&p_pollutant 

_group_name=PESTICIDES
Page 7 of 35

otherwise located as part of the Registration Review process may be used to revise aquatic life 

benchmarks if applicable. 

5. ENVIRONMENTAL FATE AND TRANSPORT

Very little acceptable environmental fate data exist for imazaquin (Table 3). Available fate 

studies were submitted in the early 1980s and well before the current Office of Chemical Safety 

and Pollution Prevention fate study guidelines were adopted into practice. Even so, most 

submitted studies were, at the time of evaluation, found to be “invalid”, “unacceptable”, or 

otherwise did not fulfill then-existing EPA data requirements outlined under Title 40 Part 158 of 

the Code of Federal Regulations7. The only exceptions to this are the adsorption/desorption 

(Guideline §835.1240; Acc. #146213), hydrolysis (Guideline §835.2120; Acc. #131546), and 

aerobic soil metabolism (Guideline §835.4100; Acc. # 146211) studies. The 

adsorption/desorption study (Fung, 1983; Acc. # 146213) was found to “partially fulfill” data 

requirements, with Freundlich Kads values stated in the DER as “ranging from 0.03 in loamy sand 

to 0.41 in clay loam soil” (individual sorption coefficients were not listed, and units were not 

stated, but were presumably L/kg). The aerobic soil metabolism study provides information on a 

single soil (sandy loam), with a half-life stated simply as “6 - 9 months” in the DER, without 

further explanation. Degradates identified in this study included 2-[(1-carbamoyl-1,2-

dimethylpropyl)-carbamoyl]-3-quinolinecarboxylic acid (at 7.6% of applied radioactivity (AR)), 

CO2 (14.6% of AR), and six unidentified compounds totaling 11% of AR. Studies on soil 

photolysis (Guideline §835.2410; Acc. #146210) and aqueous photolysis (Guideline 

§835.835.2240; Acc. #146209) were determined to be “invalid” and to “not fulfill data 

requirements”, respectively. In both cases there was inadequate characterization of the light 

sources used, and in the case of the aqueous photolysis study, degradates in buffered solution 

were not identified (although, as noted above, the following four major degradates were 

identified in unbuffered, distilled water: 3-quinolinecarboxylic acid; 2,3 quinolinedicarboxylic 

acid imide; 2,3- dihydro-3-imino-1H-pyrrolo-[3,4b]quinolin-1-one; and 2,3 

quinolinedicarboxylic acid). Despite these deficiencies, it may be noteworthy that very rapid 

degradation (i.e., half-lives of less than 1 day) was reported in the aqueous photolysis study. A 

cursory review of fate properties of other imadazolinone herbicides (e.g., imazamox, imazapic, 

imazapyr) reveals that rapid degradation via photolysis in water (though not in soil) is apparently

a consistent feature of chemicals in this class, as is relatively high mobility. Other imidazolinone 

herbicides also tend to be stable to hydrolysis, and to be relatively resistant to aerobic and 

anaerobic metabolism (i.e., only slowly degrading) in both soil and water.

A DWA was conducted in 2005 (USEPA 2005a and 2005b). Despite the fate data weaknesses 

identified in the previous paragraph, modeling was conducted assuming that imazaquin is highly 

mobile (Koc = 17.5 L/kgoc), persistent under most conditions (stable to hydrolysis and anaerobic 

aquatic degradation; aerobic soil t1⁄2 = 630 days; aerobic aquatic t1⁄2 = 1260 days), but labile to 

 

7 CFR. 2014. Code of Federal Regulations Title 40 (Protection of Environment) Chapter 1 (Environmental 

Protection Agency), Subchapter E (Pesticide Programs), Part 158 (Data Requirements for Pesticides), Subpart N 

(Environmental Fate) 158.1300 Environmental Fate Data Requirements Table. http://www.ecfr.gov/cgi-bin/textidx?SID=fffb5e77bf66491652b21b33aed2a12d&node=40:25.0.1.1.9&rgn=div5#40:25.0.1.1.9.12.1.1 (last accessed 

04/17/14).
Page 8 of 35

aqueous photolysis (t1⁄2 <1day). Maximum EDWCs from this modeling, for use by HED in 

human exposure assessment, are listed in Table 2.

Table 3. Chemical Properties and Environmental Fate Characteristics of Imazaquin

Parameter Value Description Source (Bean or 

Acc. #)

Selected Physical/Chemical Parameters

Molecular Mass 311.3 g/mol -- D197157

Molecular Formula C17H17N3O3 -- D197157

Vapor pressure 

(60°C) <10-7

torr -- D197157

Aqueous solubility (mg/L)

(25C) 60 -- D197157

Log octanol-to-water partition 

coefficient (log KOW) (22°C) 2.2 -- D197157

Persistence

Hydrolysis half-life 

(25±1C)

Stable at pH 5

Stable at pH 7

169.8 days at pH 9

acceptable 131546

Aerobic Soil Metabolism half-life

(25±1°C) 6-9 months acceptable 146211

Mobility

Freundlich adsorption coefficients

(KF)

0.03 in loamy sand to 0.41 

in clay loam soil

partially fulfills data 

requirements 146213

6. RECEPTORS

Acute (short-term) toxicity information for imazaquin is based on registrant-submitted studies. 

Reported ecological incidents associated with imazaquin are summarized below.

Tables 4 and 5 provide summaries of the aquatic and terrestrial taxonomic groups, respectively, 

and surrogate species tested to characterize the potential acute ecological effects of imazaquin. 

Based on the available ecotoxicity information, imazaquin is practically non-toxic to aquatic and 

terrestrial animals on an acute exposure basis. However, no chronic toxicity data are available 

for aquatic and terrestrial organisms. While no toxic effects were seen in honey bees (Apis 

mellifera) via the acute contact route of exposure, data are not available on the acute oral toxicity 

of imazaquin to honey bees. There is no information on the toxicity of imazaquin to aquatic 

vascular or nonvascular plants. 

Although no data are available on the toxicity of imazaquin to perching (passerine) birds, the low 

sensitivity of bobwhite quail (Colinus virginianus) and mallard duck (Anas platyrhynchus) to 

imazaquin indicates that further testing on passerines is not needed at this time (USEPA 2014a). 

Two Tier II terrestrial plant studies, i.e., seedling emergence/seedling growth (Guideline 

§850.4100) and vegetative vigor (Guideline §850.4150) conducted with Scepter®, have been 
Page 9 of 35

submitted to the Agency and are currently under review (MRIDs 45011801 and 44996103, 

respectively). Incident reports suggest that terrestrial plants may be sensitive to imazaquin. 

6.1. Effects to Aquatic Organisms

Table 4. Summary of Aquatic Toxicity Studies for Imazaquin

Taxonomic 

Group

Study 

Type Surrogate Species

Toxicity Value

(mg/L active 

ingredient)

Acute 

Toxicity 

Classification Source

Freshwater 

fish1 Acute

Rainbow trout

(Oncorhynchus 

mykiss)

LC50 = 280 Practically 

nontoxic

MRID: 

00131556

Acc. No. 

00072012

Freshwater 

invertebrates Acute Water flea(Daphnia magna)

LC50 = 280 Practically 

nontoxic

MRID: 

00131557

Acc. No. 

00072012

1 Freshwater fish may be used as surrogates for aquatic-phase amphibians.

6.2. Effects to Terrestrial Organisms

Table 5. Summary of Terrestrial Toxicity Studies for Imazaquin

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(units in active 

ingredient)

Acute 

Toxicity 

Classification

Source

Birds1

Acute

Mallard duck 

(Anas 

platyrhynchus)

LD50 > 2150 mg/kg bw Practically 

nontoxic

MRID: 

00131559

Acc. No. 

00072012

Acute

Bobwhite 

quail (Colinus 

virginianus)

LD50 > 2150 mg/kg bw Practically 

nontoxic

MRID: 

00131558

Acc. No. 

00072012

Sub-acute 

dietary

Bobwhite 

quail (Colinus 

virginianus)

LC50 >5000 ppm Practically 

nontoxic

MRID: 

00131560

Acc. No. 

00072012

Mallard duck 

(Anas 

platyrhynchus)

LC50 >5000 ppm Practically 

nontoxic

MRID: 

00131561

Acc. No. 

00072012

Mammals

Acute Oral

Laboratory rat 

(Rattus 

norvegicus)

LD50 >5000 mg/kg bw 

(Male & Female)

Practically 

nontoxic

Acc. No. 

00073706

Acute 

Inhalation

Laboratory rat 

(Rattus 

norvegicus)

LC50 > 5.0 mg/L NA Acc. No. 

00073706
Page 10 of 35

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(units in active 

ingredient)

Acute 

Toxicity 

Classification

Source

Insects Acute 

contact

Honey bee 

(Apis mellifera 

L.)

LD50 >100 μg/bee Practically 

nontoxic

MRID: 

00131562

Acc. No. 

00072012

Terrestrial 

plants

Seedling 

Emergence NA In Review NA MRID: 45011801

Terrestrial 

plants

Vegetative 

Vigor NA In Review NA MRID: 44996103

NA: Not Applicable

1 Birds may be used as surrogates for terrestrial-phase amphibians and reptiles.

6.3. Ecological Incidents

Three databases were searched for ecological incidents possibly associated with imazaquin: the 

Ecological Incident Information System (EIIS), the aggregate incident database, and the Avian 

Incident Monitoring System (AIMS). The EIIS is an OPP database that houses ecological 

incidents that have been reported to the Agency (USEPA 2007a). When available, EIIS includes 

date and location of an incident, type and magnitude of effects observed in various species, 

use(s) of pesticides known or suspected of contributing to the incident, and results of any 

chemical residue analysis or other analyses conducted during incident investigation. EIIS 

incidents are categorized according to the certainty that the incident resulted from pesticide 

exposure. The AIMS database is administered by the American Bird Conservancy and contains 

publicly available data on reported avian incidents involving pesticides. Many of the incidents 

listed in this database are also in the EIIS. The aggregate incident reports provide counts of 

ecological incidents considered “minor.” These are reported to the Agency quarterly by 

registrants.

6.3.1. Ecological Incident Information System

EIIS contains 5 incidents for imazaquin, all of which involved damage to terrestrial plants (see

Tables C-1 and C-2 in Appendix C). Many of the incidents were attributable either to direct 

application of the imazaquin product or to spray drift. Four incidents were attributed to 

imazaquin proper and one was attributed to the ammonium salt of imazaquin. Of the incidents

associated with imazaquin proper, one was determined to be a registered use, one was a misuse; 

for the remaining two incidents, it was not reported whether the incident was a result of a 

registered use or a misuse. The certainty index for attributing the incidents specifically to 

imazaquin use ranged from “probable” to “possible” for all 4 incidents. The application method 

was spray in each incident, except for the one instance of soil incorporation from seed treatment

(there is no longer a seed treatment registered use). For the ammonium salt of imazaquin, the 

application method was spray, but the use method was undetermined, and the certainty index was 

categorized as a “possible”. 
Page 11 of 35

Incident reports for non-target organisms typically provide information only on acute mortality 

events and plant damage. Sub-lethal effects in organisms such as abnormal behavior, reduced 

growth and/or impaired reproduction may not be readily apparent and may go unreported; 

therefore, an absence of incident reports does not necessarily equate to an absence of incidents.

6.3.2. Avian Monitoring System

AIMS was searched on April 8, 2014 and revealed no avian incidents associated with imazaquin 

or the ammonium salt of imazaquin.

6.3.3. Aggregate Incident Database

In addition to the incidents recorded in EIIS, registrants have reported minor imazaquin and/or 

ammonium salt of imazaquin incidents to the Agency in aggregate reports. Registrants reported 

57 minor plant incidents with products registered containing imazaquin (Table D-1, Appendix 

D). Registrants reported 19 minor plant incidents and 1 minor fish and wildlife incident with 

products registered containing the ammonium salt of imazaquin (Table D-2, Appendix D). 

Unless additional information to the contrary on these aggregated incidents becomes available, 

they will be assumed to be representative of registered uses of imazaquin in the risk assessment. 

As noted in the preceding section, the number of incident reports cannot be considered as a 

comprehensive representation of all possible incidents that may have occurred as a result of the 

use of a pesticide. During the risk assessment associated with Registration Review of imazaquin, 

these databases will be checked again, and any new incidents will be evaluated to determine if 

they represent current use patterns of imazaquin. 

7. EXPOSURE PATHWAYS OF CONCERN

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must include a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure.

The environmental fate properties of imazaquin indicate the following transport mechanisms for 

potential exposure to aquatic and terrestrial organisms:

 Direct contact

 Spray drift

 Runoff

 Consumption of contaminated food (sprayed food)

 Consumption of contaminated water

 Root uptake (plants)

For terrestrial organisms, the major routes of exposure to imazaquin are considered to be direct 

contact as a result of direct application and spray drift and dietary ingestion of plants, animals, 

and/or soil that have imazaquin residues as a result of direct application, spray drift, and runoff. 
Page 12 of 35

For aquatic animal species, the major route of exposure to imazaquin is considered to be uptake 

via the respiratory surface (gills) or the integument from surface water/sediment that has 

imazaquin residues as a result of spray drift and runoff.

For terrestrial (upland and semi-aquatic) non-target plants, the major routes of exposure to 

imazaquin are considered to be direct contact as a result of direct application and spray drift and 

root uptake via treated soil or soil contaminated via spray drift and runoff.

For aquatic plants, the major routes of exposure to imazaquin are considered to be uptake from 

surface water/sediment containing imazaquin residues as a result of spray drift, runoff, and 

leaching to groundwater from soil where such groundwater is used for irrigation purposes.

Drinking water and inhalation exposure pathways were screened using the SIP (Screening 

Imbibition Program) and STIR (Screening Tool for Inhalational Risk) programs; SIP and STIR are 

described in detail at: http://www.epa.gov/oppefed1/models/terrestrial/index.htm. 

SIP results showed acute exposure to imazaquin through drinking water does not represent a 

potential concern for mammals or birds (LOC exceedances not expected). Data are insufficient 

to determine the likelihood of adverse effects to mammals and birds from chronic exposure to

imazaquin through ingestion of drinking water. (Appendix E). Modeling results using STIR 

indicate that exposure to imazaquin through inhalation is not likely to be significant for birds or

mammals (no LOC exceedances are expected via this potential route of exposure; Appendix F). 

8. ANALYSIS PLAN

8.1. Stressors of Concern

In order to address stressors of concern, the potential for adverse effects on the environment from 

exposure is estimated. The use, environmental fate, and ecological effects of imazaquin are 

characterized and integrated to assess the risks. This integration is accomplished using a risk 

quotient (ratio of exposure concentration to effects concentration) approach. Although risk is 

often defined as the likelihood and magnitude of adverse ecological effects, the risk quotientbased approach does not provide a quantitative estimate of likelihood and/or magnitude of an 

adverse effect. However, as outlined in the Overview Document (USEPA 2004), the likelihood 

of effects to individual organisms from particular uses of imazaquin is estimated using the probit 

dose-response slope and either the level of concern (discussed below) or actual calculated risk 

quotient value. This will be revisited and may be revised depending upon the information 

submitted by the public in response to the opening of the Registration Review docket for 

imazaquin.

8.1.1. Ecological Risk Assessment

The stressors of concern are as follows:

 Terrestrial environment: parent imazaquin and its ammonium salt 

 Aquatic environment: parent imazaquin and its ammonium salt
Page 13 of 35

 Drinking water: Four major photolytic degradates were determined by HED to have the 

potential for toxicity equivalent to that of the parent:

o 3-quinolinecarboxylic acid

o 2,3 quinolinedicarboxylic acid imide

o 2,3-dihydro-3-imino-1H-pyrrolo-[3,4b]quinolin-1-one

o 2,3 quinolinedicarboxylic acid) 

Pending receipt of additional fate and ecotoxicity data, EFED may consider one or more of these 

degradates to also be stressors of ecological concern. Given the unacceptable status of many of 

the existing environmental fate studies, it is not possible to discount the possibility that 

additional, as-yet unidentified degradates of concern may also be formed in the environment. 

8.1.2. Drinking Water Assessment

Despite the gaps in the fate database, previous DWAs (DP Barcode D313182) employed SCIGROW and PRZM/EXAMS to estimate concentrations of imazaquin (parent and total toxic 

residues) in groundwater and surface water, respectively. The Health Effects Division (HED)

has determined that an updated DWA is needed to support future human health dietary risk 

assessments for imazaquin. The DWA will be revisited using the currently approved EFED tools 

PRZM-Ground Water (PRZM-GW) and Surface Water Concentration Calculator (SWCC), and 

employing conservative default inputs where appropriate in the case of missing fate data (e.g., 

aqueous photolysis). Any available monitoring data will be considered as well. Historically, the 

stressor of concern for drinking water has been parent imazaquin plus four specific degradates 

(3-quinolinecarboxylic acid; 2,3 quinolinedicarboxylic acid imide; 2,3- dihydro-3-imino-1Hpyrrolo-[3,4b]quinolin-1-one; and 2,3 quinolinedicarboxylic acid). Additional environmental 

fate studies will be considered to determine whether additional degradates should be included in

residues of concern. 

8.2. Measures of Exposure 

EFED will use standard available models (Table 5) to evaluate potential exposures to aquatic 

and terrestrial organisms as described at http://www.epa.gov/pesticides/science/models_db.htm. 

Available monitoring data will also be considered.

Estimated concentrations of mobile and persistent herbicides, such as imazaquin, in irrigation 

water may be calculated to determine potential risk to irrigated crops. As detailed above, the 

persistence and mobility of imazaquin indicate the potential for the chemical to reach ground and 

surface water. 

Because imazaquin is likely systemic, applications can result in absorption and translocation of 

imazaquin throughout plant tissues. Birds, mammals, and terrestrial invertebrates may be 

exposed through ingestion of leaves, seeds, pollen, or other edible portions of plants. Leaves or 

other plant parts containing imazaquin residues may also fall to the ground or directly into water,

potentially resulting in post-application releases of imazaquin to soil and/or water. Screeninglevel estimates of exposure via such routes may be conducted as part of the preliminary 

assessment for Registration Review. 
Page 14 of 35

Aquatic exposure will be based on estimated environmental concentrations (EECs) in a 

waterbody that is considered vulnerable and presumed representative of ponds and low-order 

streams and will be generated using the EFED Surface Water Concentration Calculator (SWCC), 

which essentially implements current versions of PRZM and EXAMS. Terrestrial exposure will 

be estimated using a model (TREX; version 1.5) that assumes direct application to a variety of 

avian and mammalian food items. Exposure to terrestrial plants will be estimated using a model 

(TerrPlant; version 1.2) that assumes imazaquin drifts or moves with runoff to adjacent habitats. 

For more information on the various models that will be used in the risk assessment see the links 

as outlined in Table 6.

Table 6. List of the various models and the related taxa for which the models will be used.

Environment Taxa of 

Concern Model(s) Link

Aquatic

Fish/ 

Invertebrates

/Plants

SWCC (PRZM & 

EXAMS)

http://www.epa.gov/oppefed1/models/

water/

Terrestrial

Vertebrate TREX (dietary 

item)

http://www.epa.gov/oppefed1/models/t

errestrial/trex/trex_v1_5_2_webversion

.xlsm

Plant

TerrPlant (Run-off) http://www.epa.gov/oppefed1/models/t

errestrial/index.htm#terrplant

AgDRIFT (Spray 

drift)

http://www.agdrift.com/AgDRIFt2/Do

wnloadAgDrift2_0.htm

AGDISP (Spray 

drift)

http://www.continuumdynamics.com/pr-agdisp.html

8.3. Measures of Effect 

Toxicity data presented in Section 6 of this problem formulation will be used to calculate risk 

quotients. Any additional acceptable information submitted by the registrant or found in the 

open literature prior to conduct of the risk assessment will also be considered. The open 

literature studies are identified using EPA’s ECOTOXicology database (ECOTOX) (USEPA

2007b), which employs a literature search engine for locating chemical toxicity data for aquatic 

life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide 

insight into the direct and indirect effects of pesticides on biotic communities from adverse 

effects to species that are sensitive to the chemicals and from changes in structure and functional 

characteristics of the affected communities.

8.4. Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to federally threatened and/or endangered (listed) species from 

registered uses of pesticides in Registration Review. The process for evaluating potential risks to listed 

species is further described at: http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm.
Page 15 of 35

8.5. Endocrine Disruptor Screening Program (EDSP)

Imazaquin was not included in either the first group of 67 chemicals issued an order to conduct 

Tier 1 EDSP testing nor the second list of 109 chemicals. For additional information the EDSP 

program, visit http://www.epa.gov/endo/. 

9. PRELIMINARY IDENTIFICATION OF DATA GAPS

9.1. Environmental Fate

Table 7 identifies environmental fate studies by Accession number that offer data for each 

guideline requirement, as well as study classifications and whether or not further data are needed 

in order to support risk assessment. 
Page 16 of 35

Table 7. Submitted Environmental Fate Data for Imazaquin

OCSPP 

Guideline Data Requirement

Submitted 

Studies 

(Accession #)*

Study 

Classification

Are 

additional 

data 

needed?

Justification and 

Assumptions EPA Will Make 

in the Absence of Data

835.2120 Hydrolysis 072014/131546 Acceptable No Submitted data were found 

acceptable.

835.2240 Aqueous Photolysis 073704/146209 Unacceptable Yes

Required data for terrestrial 

food and non-food use 

chemicals.

835.2410 Soil Photolysis 073704/146210 Invalid Yes

Required data for terrestrial 

food and non-food use 

chemicals.

835.4100 Aerobic Soil 

Metabolism 073704/146211 Acceptable Yes

Available study provides data 

for one soil (a sandy loam). 

Data are needed for three 

additional soils.

835.4300

Aerobic 

Aquatic 

Metabolism

NA Yes

Required data for terrestrial 

food and non-food use 

chemicals.

835.4400 Anaerobic Aquatic 

Metabolism NA Yes

Required data for terrestrial 

food and non-food use 

chemicals.

835.4200 Anaerobic Soil 

Metabolism 073704/146212 Invalid No

Not needed if acceptable 

anaerobic aquatic data are 

submitted.

835.1230/

835.1240

Adsorption/ 

Desorption and 

Leaching

073704/146214 Partially fulfills 

data requirement Yes

Required data for terrestrial 

food and non-food use 

chemicals.

835.6100 Terrestrial 

Field Dissipation 073704/131564 Does not fulfill data requirement No

The combination of acceptable 

aerobic soil and soil photolysis 

studies, if submitted, should 

address any concerns regarding 

degradate formation and 

decline.

850.6100 ECM/ILV NA Yes

*Where two numbers are given, the first number is the Accession number written on the DER itself. The second number is the 

number under which the DER is filed in Documentum.

9.2. Effects

Table 8 and 9 identify ecological effects studies for aquatic and terrestrial organisms, 

respectively, by MRID that offer data for each guideline requirement, as well as study 

classifications and whether or not further data are needed in order to support risk assessment. 

Table 8. Submitted Aquatic Ecological Effects Data for Imazaquin

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are additional 

data needed?

Justification and Assumptions 

EPA Will Make in the Absence 

of Data

850.1010 Freshwater 

invertebrate 

acute toxicity

00131557 Acceptable No NA
Page 17 of 35

850.1025

850.1035

850.1045

850.1055

Saltwater 

invertebrate 

acute toxicity 

None NA Yes No data are available with which 

to assess acute risk to saltwater 

invertebrates. Acute toxicity 

data for estuarine/marine 

invertebrates are required under 

40 CFR, Part 158-Subpart G to 

determine if there is a risk 

concern. Data are required for 

one estuarine/marine invertebrate 

using TGAI 1.

850.1075 Freshwater fish 

acute toxicity 

00131554 Acceptable No NA

00131555 Acceptable No NA

00131556 Acceptable No NA

850.1075 Saltwater fish 

acute toxicity 

None NA Yes No data are available with which 

to assess acute risk to saltwater 

fish. Acute toxicity data for

estuarine/marine fish are 

required under 40 CFR, Part 

158-Subpart G to determine if 

there is a risk concern using 

TGAI 1.

850.1300 Freshwater 

invertebrate 

life-cycle 

None NA Yes No data are available with which 

to assess chronic risk to 

freshwater invertebrates. 

Chronic toxicity data for

freshwater invertebrates are 

required under 40 CFR, Part 

158-Subpart G to determine if 

there is a risk concern using 

TGAI1. 

850.1350 Saltwater 

invertebrates 

life-cycle 

None NA Yes No data are available with which 

to assess chronic risk to saltwater 

invertebrates. Chronic toxicity 

data for saltwater invertebrates 

are conditionally required under 

40 CFR, Part 158-Subpart G

using TGAI1to determine if 

there is a risk concern. Data are 

required on estuarine/marine 

species if the product meets any 

of the following conditions:

i) Intended for direct application 

to the estuarine or marine 

environment; ii) Expected to 

enter this environment in 

significant concentrations 

because of its expected use or 

mobility patterns; iii) If the acute 

LC50 or EC50 <1 mg/l; iv) If the 

estimated environmental 

concentration (EEC) in water is 

≥0.01 of the acute EC50 or LC50
Page 18 of 35

or if any of the following 

conditions exist: A) Studies of 

other organisms indicate the 

reproductive physiology of fish 

and/or invertebrates may be 

affected. B) Physiochemical 

properties indicate 

bioaccumulation of the pesticide. 

C) The pesticide is persistent in 

water (e.g., half-life in water > 4 

days). 

850.1400 Freshwater fish 

early-life stage

None NA Yes No data are available with which 

to assess chronic risk to 

freshwater fish. Chronic toxicity 

data for freshwater fish are 

required under 40 CFR, Part 

158-Subpart G to determine if 

there is a risk concern using 

TGAI

1

. EFED recommends that 

the most sensitive species used 

to assess acute risk is utilized in 

the chronic toxicity test. 

850.1400 Saltwater fish 

early-life stage 

None NA Yes No data are available with which 

to assess chronic risk to saltwater 

fish. Estuarine/marine fish early 

life stage data are conditionally 

required under 40 CFR, Part 

158-Subpart G to determine if 

there is a risk concern using 

TGAI

1

. Data are required on 

estuarine/marine species if the 

product meets any of the 

following conditions:

i) Intended for direct application 

to the estuarine or marine 

environment; ii) Expected to 

enter this environment in 

significant concentrations 

because of its expected use or 

mobility patterns; iii) If the acute 

LC50 or EC50 <1 mg/l; iv) If the

estimated environmental 

concentration (EEC) in water is 

≥0.01 of the acute EC50 or LC50

or if any of the following 

conditions exist: A) Studies of 

other organisms indicate the 

reproductive physiology of fish 

and/or invertebrates may be 

affected. B) Physiochemical 

properties indicate 

bioaccumulation of the pesticide. 

C) The pesticide is persistent in 

water (e.g., half-life in water > 4 

days). 
Page 19 of 35

1TGAI=Technical Grade Active Ingredient; TEP=Technical End-Use Product

NA: Not Applicable

Table 9. Submitted Terrestrial Ecological Effects Data for Imazaquin

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Justification and Assumptions 

EPA will Make in Absence of 

Data

850.2100 Avian oral 

toxicity

00131559 Acceptable No NA1

00131558 Acceptable NA1

850.2200 Avian dietary 

toxicity 

00131560 Acceptable No NA

00131561 Acceptable

850.2300 Avian 

reproduction

None NA Yes No data have been submitted to 

assess effects on avian 

reproduction. Avian reproduction 

studies are needed as part of the 

data set under 40 CFR, Part 158-

Subpart G to determine if there is 

a risk concern using TGAI2.

850.3020 Honey bee 

acute contact 

toxicity

00131562 Acceptable No NA

OECD 

Guideline 

237 and 

NonGuideline: 

Honey bee 

larval acute 

and chronic 

oral toxicity

None NA Yes Although data for 850.3020 

honey bee acute contact toxicity 

indicates imazaquin is practically 

non-toxic to honey bees, EFED 

has no data on the acute and 

chronic oral route of exposure. 

Therefore, data are needed to 

determine if there is an acute oral 

risk to the honey bee using 

TGAI2,3.

850.4400 Aquatic plant 

growth: Tier II 

vascular plants

None NA Yes No data are available with which 

to assess risk to aquatic vascular 

plants. Toxicity data are needed 

under 40 CFR, Part 158-Subpart 

G to determine if there is a risk 

concern using TGAI or TEP1. 

850.4500 

(previously 

850.5400)

Aquatic Plant 

Growth: Tier II 

algae

None NA Yes Toxicity data on three species 

are needed under 40 CFR, Part 

158-Subpart G to determine if 

there is a risk concern using 

TGAI or TEP1. Tests with a 

freshwater diatom, marine 

diatom, freshwater green alga, 

and cyanobacterium are 

recommended.

850.4550 Aquatic Plant 

Growth: 

Cyanobacteria

None NA Yes
Page 20 of 35

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed for 

risk 

assessment?

Justification and Assumptions 

EPA will Make in Absence of 

Data

NonguidelineHoney bee 

adult acute 

and chronic 

toxicity 

None NA Yes Similar to other imidazolinone 

herbicides, imazaquin is a likely

systemic herbicide. It is absorbed 

by both roots and foliage and 

translocated via both xylem and 

phloem. It may be transported to

regions of the plant where growth 

can take place. There may be a 

variety of opportunities for the 

herbicide to be applied when 

plants may be in bloom and 

attractive to pollinators. 

Therefore, this test is needed to 

evaluate the potential for direct 

and systemic exposures to larval 

bees using TGAI2,3.

850.4100 Terrestrial 

plant toxicity:

Seedling 

emergence

45011801 NA Not at this 

time –

pending 

review

These data are currently in 

review. Studies establishing nontarget plant toxicity for herbicides 

are essential for establishing the 

extent of off-site drift impacts.

850.4150 Terrestrial 

plant toxicity:

Vegetative 

vigor

44996103 NA Not at this 

time –

pending 

review

These data are currently in 

review. Studies establishing nontarget plant toxicity for herbicides 

are essential for establishing the 

extent of off-site drift/run-off

impacts.

1Although an acute oral study for a passerine species has not been submitted to the Agency, a data gap has not been identified at this time. Low 

avian toxicity (no mortality and no sublethal effects) was demonstrated in the submitted studies.

2TGAI=Technical Grade Active Ingredient; TEP=Technical End-Use Product

3Data on TEP is required if the formulation may enhances the toxicity of the chemical.

NA: Not Applicable

EPA recently posted its guidance8for assessing risks of pesticides to bees and consistent with this

guidance a suite of tests is recommended for evaluating the potential toxicity of pesticides to 

bees. Although data from the acute contact toxicity test (OCSPP 850.3020) with young adult 

honey bees (Apis mellifera) indicates imazaquin is practically non-toxic to bees on an acute 

exposure basis, there is uncertainty regarding the potential acute and chronic effects of the 

compound on honey bee larval development and survival as well as potential for chronic effects

of adult bees. Similar to other imidazolinone herbicides, imazaquin is a likely systemic 

herbicide. Residues may be present in pollen and/or nectar and represent a route of exposure for 

bees through both contact and ingestion. Therefore, additional data on pollinators is needed to 

fully characterize the risk associated with imazaquin use to all developmental stages of honey 

bees, as sensitivity may vary according to life-stage and length of exposure (adult vs. larval and 

 

8 USEPA. 2014. Guidance for Assessing Pesticide Risks to Bees. Office of Pesticide Programs. United States 

Environmental Protection Agency. Available at 

http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/terrestrial_biology_tech_team/Guidance

AssessingPesticideRisk2Bees.pdf
Page 21 of 35

acute vs. chronic, respectively). As described in the guidance for assessing risks to bees, 

depending on the outcome of the screening-level risk assessment, additional studies of bees at 

the colony level under semi- and full-field conditions may also be recommended.

Guideline Number: Non-Guideline

Study Title: Larval Honey Bee Acute and Chronic Oral Toxicity

Rationale for Requiring the Data

These studies are needed to evaluate potential effects of technical grade active ingredient (TGAI) on

honey bees. Imazaquin is registered as a pre-plant, pre-emergence, and early post-emergence broad 

spectrum herbicide for use soybeans, ornamentals, turfgrass, ornamental trees, shrubs, and groundcover 

where spray drift may land on blooming non-target plants and result in residues in pollen and nectar 

(which could then be transported to the hive by forage bees). Similar to other imidazolinone herbicides, 

imazaquin is likely to be systemic. It is absorbed by both roots and foliage and can translocated via both 

xylem and phloem to pollen and/or nectar where it would represent a route of exposure to bees. Residues 

can in turn be brought back to bee colonies where in-hive bees, including young adult and developing 

brood (i.e., eggs, larvae and pupae), may be exposed. 

The Agency finalized its framework to assess risk to pollinators9and recommends these studies for all use 

sites where potential exposure to pollinators may occur. Although EPA has not developed a guideline for 

this study, the 21-day larval toxicity study currently under development by OECD10 provides a draft 

guidance protocol for potentially assessing both the acute and chronic toxicity to developing brood (larvae 

and pupae) from repeat exposure pesticides. Registrants are at liberty though to submit a separate acute 

(single dose) larval toxicity study following OECD TG 23711 as well as the 21-day repeat dose chronic 

toxicity study. For the chronic toxicity study though, since no guideline is available, a protocol is required 

to be submitted for EPA review and approval prior to study initiation.

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

The larval toxicity studies provide data on the effects of technical grade active ingredient (TGAI) on 

developing bees from acute (short-term) and chronic (longer term) exposure and will be used for 

estimating risk to individual (solitary) bees as well as bee colonies (social bees). Risk estimates based on 

these data will be considered along with other lines of evidence to determine whether higher-tier studies 

are needed at the whole colony level.

These data are needed for risk assessments conducted in support of Registration Review as well as future 

endangered species assessments. The data would allow the Agency better characterize the potential for 

risk to insects (including beneficial pollinators) from the use of imidazolinone-class chemicals. These data 

may help the Agency determine whether any mitigations are needed. If the Registration Review and any 

future endangered species risk assessments are performed without these data, the Agency would have to 

assume that imidazolinone-class chemicals "may affect" insects, including bees and beneficial pollinators, 

directly (and endangered species from other taxa indirectly), and uses of imazaquin might need to be 

restricted in areas where pollinators could be exposed. 

 

9 USEPA et al.. 2014. Guidance for Assessing Pesticide Risks to Bees. http://www2.epa.gov/sites/production/files/2014-

06/documents/pollinator_risk_assessment_guidance_06_19_14.pdf

10 OECD. 2013. OECD Draft Guidance Document Honey Bee (Apis mellifera) Larval Toxicity Test, Repeated Exposure. Revision of June 2013 

draft GD, 25 November 2013. http://www.oecd.org/env/ehs/testing/Draft_GD_honeybees_rep_exp_for_2nd_CR_25_November_2013.pdf

11 OECD. 2013. OECD Guidelines for the Testing of Chemicals Honey bee (Apis mellifera) larval toxicity test, single exposure. OECD/OCDE 

237 Adopted: 26 July 2013. http://www.oecdilibrary.org/docserver/download/9713171e.pdf?expires=1408719503&id=id&accname=guest&checksum=9CA53CFD8192A7A5F5715D9D335

1A841
Page 22 of 35

Guideline Number: Non-Guideline

Study Title: Adult Honey Bee Acute Oral Toxicity

Rationale for Requiring the Data

This study is needed to evaluate potential effects to honey bees from a single dose of technical grade 

active ingredient (TGAI). Imazaquin is registered as a pre-plant, pre-emergence, and early postemergence broad spectrum herbicide for use soybeans, ornamentals, turfgrass, ornamental trees, shrubs, 

and groundcover where spray drift may land on blooming non-target plants and result in residues in pollen 

and nectar (which could then be transported to the hive) or in direct contact with bees. 

Similar to other imidazolinone herbicides, imazaquin is a likely systemic herbicide. It is absorbed by both 

roots and foliage and translocated to pollen and/or nectar via both xylem and phloem where it would 

represent a route of exposure to bees. Residues can in turn be brought back to bee colonies where in-hive 

bees, including young adult and developing brood (i.e., eggs, larvae and pupae), may be exposed. . 

The Agency finalized its framework to assess risk to pollinators12. EPA now requires these studies for all 

use sites where potential exposure to pollinators may occur. Although EPA has not developed a guideline 

for this study, the Organization for Economic Cooperation and Development (OECD) has developed a 

formal test guideline for an acute oral toxicity study with adult honey bees (OECD TG21313) that may be 

used to assess the acute oral toxicity for adult bees.

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

These data are used in conjunction with acute contact data obtained through OCSPP 850.302014 to 

estimate the acute toxicity of technical grade active ingredient (TGAI) to individual young adult honey 

bees. The studies also provide slopes for the dose-response curves that can in turn be used for estimating 

the likelihood of individual effects and sublethal effects observed in the study will be used to further 

characterize effects observed following a single exposure to the technical grade material. Data obtained 

from this study will be used in estimating acute risk to individual adult bees. Risk estimates based on 

these data will be considered along with other lines of evidence to determine whether higher-tier studies 

are needed at the whole colony level.

These data are needed for risk assessments written in support of Registration Review as well as for future 

endangered species assessments. These data would allow the Agency to better characterize the potential 

for risk to insects (including beneficial pollinators) from the use of imidazolinone-class chemicals. These

data may help the Agency determine whether any mitigations are needed. If the Registration Review and 

any future endangered species risk assessments are performed without these data, the Agency would have 

to assume that imidazolinone-class chemicals "may affect" insects, including bees and beneficial 

pollinators, directly (and endangered species from other taxa indirectly), and uses of imazaquin might 

need to be restricted in areas where pollinators could be exposed. 

 

12Ibid USEPA et al. 2014. 

13 OECD. 1998. OECD Guidelines for the Testing of Chemicals Honeybees, Acute Oral Toxicity Test. OECD/OCDE 213 Adopted 21st

September 1998. http://www.oecdilibrary.org/docserver/download/9721301e.pdf?expires=1408726996&id=id&accname=guest&checksum=29D93505197D8AB40C63E8F0DFB4

47D0

14 USEPA. 2012. Ecological Effects Test Guidelines OCSPP 850.3020: Honey Bee Acute Contact Toxicity Test. Office of Chemical Safety and 

Pollution Prevention (7101). EPA-712-C-019. January 2012. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0154-

0016
Page 23 of 35

Guideline Number: Non-Guideline

Study Title: Adult Honey Bee Chronic Oral Toxicity

Rationale for Requiring the Data

This study is needed to evaluate the effects of repeat exposure to technical grade active ingredient (TGAI) 

on honey bees. Imazaquin is registered as a pre-plant, pre-emergence, and early post-emergence broad 

spectrum herbicide for use soybeans, ornamentals, turfgrass, ornamental trees, shrubs, and groundcover 

where spray drift may settle on blooming non-target plants and result in residues in pollen and nectar and 

represent a route of exposure to bees. 

Similar to other imidazolinone herbicides, imazaquin is a likely systemic herbicide. It is absorbed by both 

roots and foliage and translocated via both xylem and phloem to pollen and/or nectar where it would 

represent a route of exposure to bees. Residues can in turn be brought back to bee colonies where in-hive 

bees, including young adult and developing brood (i.e., eggs, larvae and pupae) may be exposed. 

The Agency finalized its framework to assess risk to pollinators15 and these studies for all use sites where 

potential exposure to pollinators may occur. Although EPA has not developed a guideline for this study 

and OECD has yet to finalize test guidance for chronic studies, efforts are currently underway to develop 

standardized guidelines for assessing effects from chronic (10-day) repeat exposures to adult bees in the 

laboratory. Since no guideline is available, a protocol should be submitted for EPA review and approval 

prior to study initiation.

Practical Utility of the Data

How will the data be used and how could the data impact the Agency’s future decision-making? 

The 10-day chronic toxicity study with young adult bees provides data for assessing effects on bees from 

repeat exposure to technical grade active ingredient (TGAI). Data obtained from this study will be used in 

estimating chronic risk to individual (solitary bees) adult bees and well as potential risks to the honey bee 

colony (social bees). Risk estimates based on these data will be considered along with other lines of 

evidence to determine whether higher-tier studies are needed at the whole colony level.

These data are needed for the risk assessment written in support of Registration Review as well as for 

future endangered species assessments. These data would allow the Agency to better characterize the 

potential for risk to insects (including beneficial pollinators) from the use of imidazolinone-class 

chemicals. These data can be used by the Agency to determine whether any mitigations are needed. If the 

Registration Review and any future endangered species risk assessments are performed without these 

data, the Agency would have to assume that imidazolinone-class chemicals "may affect" insects, including 

bees and beneficial pollinators, directly (and endangered species from other taxa indirectly), and uses of 

imazaquin might need to be restricted in areas where pollinators could be exposed. 

10. REFERENCES

USEPA. 1994. Review of Studies for Unconditional Registration: 000241-00287 SCEPTER 

Herbicide Technical. Akiva Abramovitch. 04/18/94. DP Barcode: D197157.

U. S. Geological Survey (USGS). 2003. 1997 Pesticide Use Maps. NAWQA Pesticide National 

Synthesis Project. September 3, 2003.

 

15 Ibid USEPA et al. 2014
Page 24 of 35

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=1997&map=IMAZAQUIN

&hilo=H 

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs. United States Environmental Protection Agency (USEPA). Environmental Fate and 

Effects Division. Office of Pesticide Programs. Available at 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf (Accessed April 8, 2014)

USEPA. 2005a. Drinking Water Assessment for Imazaquin and its Salts. Keara Moore. 

06/21/05. DP Barcode: D313182

USEPA. 2005b. Amendment to Drinking Water Assessment for Imazaquin and its Salts. Keara 

Moore. 09/27/05. DP Barcode: D313182

USEPA. 2005c. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment 

Progress and Risk Management Decision (TRED) for Imazaquin. December 2005. EPA 738-R00-009.

USEPA. 2007a. Ecological Incident Information System. 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf

USEPA. 2007b. 40 CFR Part 158. Pesticides; Data Requirements for Conventional Chemicals: 

Final Rule. 72 FR 60934. October 26, 2007

USEPA. 2014a. Imidazolinone passerine bird study discussion. Office of Pesticide Programs, 

Potomac Yard South. Meeting held 3/13/14

USEPA. 2014b. Biological and Economic Analysis Division (BEAD) Chemical Profile for 

Registration Review: Imazaquin (128848) and Imazaquin, monoammonium salt (128840).

USEPA, PMRA and CDPR, 2014c. Guidance for Assessing Pesticide Risks to Bees. Office of 

Pesticide Programs, USEPA, Washington D.C. Health Canada Pest Management Regulatory 

Agency, Ottawa, ON, Canada. California Department of Pesticide Regulation, Sacramento, 

CA. June 23, 2014.
Page 25 of 35

Appendices

Appendix A. BEAD Chemical Profile1

1Double-click to open the file
Page 26 of 35

Appendix B. Submitted Environmental Fate and Ecological Effects Studies

Environmental Fate Studies

Accession # Citation Reference

072014/131546 Herbicide AC 252,214: The Hydrolysis of carbon-14 Labeled AC 252,214. B. Reichert. 

American Cyanamid Company. Report No. PD-M. Volume 20-9. April 25, 1983. Acc. No. 

072014.

073704/146209 Barringer, D. June, 1985. Scepter herbicide, imazaquin (AC 252,214): Photolysis in aqueous 

solution. American Cyanamid Company, Princeton, NJ. Report No. PD-M. Acc. No. 073704. 

Vol. 22, Sec. 15.

073704/146210 Barringer, D. and P. Stanley-Millner. June 1985. Scepter herbicide, imazaquin (AC 252,214): 

Photolysis on soil thin-layers. American Cyanamid Company, Princeton, NJ. Acc. No. 

073704. Vol. 22, Sec. 16.

073704/146211 Mallipudi, M. September, 1983. Scepter herbicide (AC 252,214): aerobic soil metabolism of 

carboxyl carbon-14 labeled AC 252,214 [3-quinolinecarboxylic acid, 2-(4-i sopropyl-4-

methyl-5-oxo-2-imidazolin-2-yl)-] in sandy loam soil, American Cyanamid Company, 

Princeton, NJ. Report No. PD-M. Acc. No. 073704. Ref. Vol. 20, Sec. 23.

073704/146212 Mallipudi, M., B. Knoll, and A. DaCunha. May, 1985. Scepter herbicide, imazaquin (AC 

252,214): Anaerobic soil metabolism of carboxyl carbon-14 labeled AC 252,214 [3-

quinolinecarboxylic acid, 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-] in sandy loam 

soil. American Cyanamid Company, Princeton, NJ. Report No. PD-M. Acc. No. 073704. 

Ref. Vol. 22, Sec. 11
Page 27 of 35

073704/146213 Fung, C. September, 1983. Scepter herbicide (AC 252,214): Adsorption and desorption 

coefficients for soils. American Cyanamid Company, Princeton, NJ, Report No. PD-M. Acc. 

No. 073704. Vol. 20, Sec. 24.

073704/146214 Mangles, G., and L. Lucas. June, 1985. Scepter herbicide, imazaquin (AC 252,214): 

Adsorption/desorption on soil. American Cyanamid Company, Princeton, NJ. Report No. 

PD-M. Acc. No. 073704. Vol. 22, Sec. 19.

073704/131564 Mallipudi, M., B. Knoll, and P. Stanley-Millner. September, 1983. Scepter herbicide ( AC 

252,214) : Field dissipation of carboxyl carbon-14 labeled AC 252,214 [3-

quinolinecarboxylic acid, 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl-)-]. American 

Cyanamid Company, Princeton, NJ. Report No. PO-M. Acc. No. 073704. Vol. 20, Sec. 22.

Ecological Effects Studies

MRID Citation Reference

71-1 Avian Single Dose Oral Toxicity

131559

Fletcher, C. (1983) Report to ...: Acute Oral Toxicity Study with AC 252,214 Technical in 

Mallard Ducks: BLAL No. 82 DD 16. (Unpublished study received Oct 14, 1983 under 241-

EX-108; prepared by Bio-Life Assoc., Ltd., submitted by American Cyanamid Co., 

Princeton, NJ; CDL:072012-G) 

131558

Fletcher, D. (1983) Report to ...: Acute Oral Toxicity Study with AC 252,214 Technical in 

Bobwhite Quail: BLAL No. 82 QD 17. (Unpublished study received Oct 14, 1983 under 241-

EX-108; prepared by Bio-Life Assoc., Ltd., submitted by American Cyanamid Co., 

Princeton, NJ; CDL:072012-F) 

71-2 Avian Dietary Toxicity

131560

Fletcher, D. (1983) 8-Day Dietary LC50 Study with AC 252,214 Technical in Bobwhite 

Quail: BLAL No. 82 QC 20. (Unpublished study received Oct 14, 1983 under 241-EX-108; 

prepared by Bio-Life Assoc., Ltd., submitted by American Cyanamid Co., Princeton, NJ; 

CDL:072012-H) 

131561

Fletcher, D. (1983) 8-Day Dietary LC50 Study with AC 252,214 Technical in Mallard 

Ducklings: BLAL No. 82 DC 20. (Unpublished study received Oct 14, 1983 under 241-EX108; prepared by Bio-Life Assoc., Ltd., submitted by American Cyanamid Co., Princeton, 

NJ; CDL:072012-I) 

72-1 Acute Toxicity to Freshwater Fish

131554

Cohle, P.; McAllister, W. (1982) Acute Toxicity of AC 252,214 to Channel Catfish (Ictalurus 

punctatus): Static Bioassay Report #29713. (Unpublished study received Oct 14, 1983 under 

241-EX- 108; prepared by Analytical Bio-Chemistry Laboratories, Inc., submitted by 

American Cyanamid Co., Princeton, NJ; CDL:072012-B) 

131555

Cohle, P.; McAllister, W. (1982) Acute Toxicity of AC 252,214 to Bluegill Sunfish (Lepomis 

macrochirus): Static Bioassay Report #29711. (Unpublished study received Oct 14, 1983 

under 241-EX- 108; prepared by Analytical Bio-Chemistry Laboratories, Inc., submitted by 

American Cyanamid Co., Princeton, NJ; CDL:072012-C) 

131556

Cohle, P.; McAllister, W. (1982) Acute Toxicity of AC 252,214 to Rainbow Trout 

(Oncorhynchus mykiss formerly Salmo gairdneri): Static Bioassay Report #29712. 

(Unpublished study received Oct 14, 1983 under 241-EX-108; pre- pared by Analytical BioChemistry Laboratories, Inc., submitted by American Cyanamid Co., Princeton, NJ; 

CDL:072012-D) 

72-2 Acute Toxicity to Freshwater Invertebrates

131557

Forbis, A.; Kintner, D. (1982) Acute Toxicity of AC 252,214 to Daphnia magna: Static 

Acute Bioassay Report #29714. (Unpublished study received Oct 14, 1983 under 241-EX108; prepared by Analytical Bio-Chemistry Laboratories, Inc., submitted by American 

Cyanamid Co., Princeton, NJ; CDL:072012-E) 

141-1 Honey bee Acute Toxicity

131562

Atkins, E. (1983) Letter sent to T. Wang dated Mar 14, 1983 Testing 252,214 against honey 

bees|. (Unpublished study received Oct 14, 1983 under 241-EX-108; prepared by Univ. of 

California-- Riverside, Dept. of Entomology, submitted by American Cyanamid Co., 

Princeton, NJ; CDL:072012-J) 

123-1 Seed germination/seedling emergence and vegetative vigor
Page 28 of 35

44996103

Canez, V.; Chetram, R.; Goodman, V. (1997) Tier 2 Nontarget Terrestrial Plant Vegetative 

Vigor Phytotoxicity Study Using AC252214 (Imazaquin) in a 1.5 AS Formulation: Lab 

Project Number: 96572: ECO 96-110: 954-96-110. Unpublished study prepared by ABC 

Labs., California. 306 p. {OPPTS 850.4250} 

45011801

Canez, V.; Chetram, R.; Goodman, V. (1997) Nontarget Terrestrial Plant Seedling 

Emergence Phytotoxicity Study Using AC 252214 (Imazaquin) in a 1.5 AS Formulation: Lab 

Project Number: 96571: ECO-96-109. Unpublished study prepared by ABC Labs. 238 p. 

{OPPTS 850.4225} 
Page 29 of 35

Appendix C. EIIS Incidents

Table C-1. Incidents in the EIIS for PC 128848: Imazaquin as of 4/8/14

Type

Incident 

ID Use Site

Start 

Date Legality Certainty State County

Total 

Magnitude

Appl. 

Rate

Appl. 

Method Air/Gnd Formulation Product

Plants

I000360-

014 Beans 1/1/1993 Registered Use Possible MO

160 ac 

beans N/R

Soil 

incorporation

Seed 

treatment Scepter

Plants

I005880-

054

Agricultural 

Area 5/2/1997

Misuse 

(accidental) Probable WI 1.3 acres Spray Gnd Scepter

Plants

I005880-

057

Agricultural 

Area 6/1/1997 Undetermined Probable MN Unknown Spray Gnd Scepter

Plants

I005880-

059

Agricultural 

Area 6/1/1997 Undetermined Probable WI Unknown Spray Gnd Scepter

Abbreviations: Appl.=Application; N/R=Not Recorded

1 Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), UN=Unknown

2 Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable. N/R=Not Reported

3 Formulation Code: DF=Dry Flowable; EC=Emulsifiable Concentrate; F=Flowable; G=Granular; WDG=Water Dispersable Granule; WP=Wettable Powder

Table C-2. Incidents in the EIIS for PC 128840: Ammonium Salt of Imazaquin as of 4/8/14

Type

Incident 

ID

Use 

Site

Start 

Date Legality Certainty State County

Total 

Magnitude

Appl. 

Rate

Appl. 

Method Air/Gnd Formulation Product

Plants

I016225-

001 N/R 4/5/2005 Undetermined Possible IL Fayette 1 acre N/R Spray

Roundup + 

Plateau

Abbreviations: Appl.=Application; N/R=Not Recorded

1 Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), UN=Unknown

2 Certainty Code: 0=Unrelated, 1=Unlikely, 2=Possible, 3=Probable, 4=Highly Probable. N/R=Not Reported

3 Formulation Code: DF=Dry Flowable; EC=Emulsifiable Concentrate; F=Flowable; G=Granular; WDG=Water Dispersable Granule; WP=Wettable Powder
Page 30 of 35

Appendix D. Aggregate Incident Reports for Imazaquin and the Ammonium Salt of Imazaquin

Table D-1. Aggregate Incident Reports for Imazaquin
Page 31 of 35

Table D-2. Aggregate Incident Reports for the Ammonium Salt of Imazaquin
Page 32 of 35

Appendix E. SIP Results for Evaluate Potential Risk to Birds and Mammals from 

Drinking Water Exposure

Table 1. Inputs

Parameter Value

Chemical name Imazaquin

Solubility (in water at 25oC; mg/L) 60

Mammalian LD50 (mg/kg-bw) 5000

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 0

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Avian LD50 (mg/kg-bw) 2150

Avian test species mallard duck

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet)

Bobwhite quail NOAEC (mg/kg-diet)

NOAEC (mg/kg-diet) for other bird species 0

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird species 0

Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 10.3200 10.3200

Adjusted toxicity value (mg/kg-bw) 3845.8028 0.0000

Ratio of exposure to toxicity 0.0027 0.0000

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Due to insufficient data, risk 

cannot be precluded

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 48.6000 48.6000

Adjusted toxicity value (mg/kg-bw) 1116.3346 0.0000

Ratio of exposure to acute toxicity 0.0435 0.0000

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Due to insufficient data, risk 

cannot be precluded

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, 

when aggregated with other routes (i.e ., diet, inhalation, dermal), pesticide exposure through drinking water may 

contribute to a total exposure that has potential for effects to non-target animals.
Page 33 of 35

Appendix F. STIR Results to Evaluate the Potential for Inhalation Risk to Birds 

and Mammals

Screening Tool for Inhalation Risk

This tool is designed to provide the risk assessor with a rapid method for determining the potential

significance of the inhalation exposure route to birds and mammals in a risk assessment.

Input

Application and Chemical Information

Enter Chemical Name Imazaquin

Enter Chemical Use herbicide

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 311

Enter Chemical Vapor Pressure (mmHg) 2.00E-08

Enter Application Rate (lb a.i./acre) 0.5

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 2150

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 5000

Enter Lowest Rat Inhalation LC50 (mg/L) 5

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 3.35E-04

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 4.21E-05

Adjusted Inhalation LD50 1.20E+01

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.51E-06 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 5.28E-02

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 4.41E-03 Exposure not Likely Significant

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 3.35E-04

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 5.29E-05

Adjusted Inhalation LD50 2.98E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.78E-07 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 6.64E-02

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 2.23E-04 Exposure not Likely Significant

**NOTE**: When entering values, press the "Enter" key in 

order to update linked cells.
Page 34 of 35

Appendix G. Chemical structures of imazaquin and identified major 

photodegradates

Imazaquin

3-quinolinecarboxylic acid

2,3 quinolinedicarboxylic acid imide

2,3-dihydro-3-imino-1H-pyrrolo-[3,4b]quinolin-1-one
Page 35 of 35

2,3 quinolinedicarboxylic acid