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TABLE OF CONTENTS 

I. Preliminary Work Plan........................................................................................................ 3 

II. Fact Sheet........................................................................................................................... 8 

III. Ecological Risk Assessment............................................................................................ 12 

IV. Human Health Effects Scoping Document ................................................................... 46 

V. Glossary of Terms and Abbreviations .............................................................................. 56 
3

I. Preliminary Work Plan 

Introduction:

The Food Quality Protection Act of 1996 mandated a new program: registration review. All 

pesticides distributed and sold in the United States must be registered by the EPA, based on 

scientific data showing that they will not cause unreasonable risks to human health, workers or 

the environment when used as directed on the product label. The new registration review 

program is intended to ensure 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. Changes in science, public policy, and pesticide use practices will 

occur over time. Through the new registration review program, the Agency periodically 

reevaluates pesticides make sure that as the change occurs, products in the marketplace can be 

used safely. Information on this program is provided at the following website: 

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

The Agency has begun to implement the new Registration Review program and will review each 

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

for registration. 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 is knows about the pesticide 

and what additional risk analyses and data or other 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 and commit to a final 

work plan and schedule for the registration review of quizalofop. 

Quizalofop is a selective post-emergence herbicide used on a number of food and feed crops. It 

was registered for use in the late 1980’s. Quizalofop-ethyl is a 50/50 racemic mixture of R- and 

S-enantiomers. Quizalofop-p-ethyl is the purified R-enantiomer and the pesticidally active 

isomer. 

Anticipated Risk Assessment and Data Needs:

The Agency anticipates conducting comprehensive human health and ecological risk 

assessments, including an endangered species assessment, for all uses of quizalofop. 

Ecological Risk: 

• New ecological risk assessments for all registered uses were conducted in October 

2005. However, the Agency has not conducted a risk assessment that supports a 

complete endangered species determination for quizalofop-ethyl or quizalofop-pethyl and a complete assessment will be conducted for registration review. Please 

refer to Section III, Ecological Risk Assessment Problem Formulation, for a detailed 

discussion of the anticipated risk assessment needs. 
4

• There are two chronic avian studies, which have been submitted. If upon further 

review, these studies do not provide useful information on the reproductive effect of 

quizalofop in birds, new studies will be required. 

• The Agency anticipates needing the following data in order to conduct a complete 

ecological risk assessment, including an endangered species assessment, for all uses:

o (GLN 850.4225) Seedling emergence (Tier 2) for quizalofop-p-ethyl. 

o (GLN 850.4250 ) Vegetative vigor (Tier 2) for quizalofop-p-ethyl. 

o (GLN 850.1350) Chronic early life-cycle toxicity studies for estuarine marine 

invertebrates for quizalofop-p-ethyl. 

• The planned ecological risk assessment will allow the Agency to determine whether 

quizalofop use has "no effect" or "may affect" federally listed threatened or 

endangered species (listed species) or their designated critical habitat. If the 

assessment indicates that quizalofop “may affect" a listed species or its designated 

critical habitat, the assessment will be refined to determine whether use of quizalofop 

is “likely to adversely affect” the species or critical habitat or "not likely to adversely 

affect" the species or critical habitat. 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 (Services), as appropriate. 

Human Health Risk: 

• The current dietary risk assessment for quizalofop-ethyl was conducted according to 

Agency policy and results in no risks of concern. Because the toxicological profile of 

quizalofop-ethyl and quizalofop-p-ethyl are sufficiently similar, the Agency has 

determined the currently available toxicity data on quizalofop-ethyl are adequate to 

support risk assessments reflecting uses of both quizalofop-ethyl and quizalofop-pethyl. Although occupational risk assessments have not been completed for all uses, 

no dermal or inhalation endpoints have been selected because quizalofop-p-ethyl and 

quizalofop-ethyl do not appear to be toxic via dermal and inhalation routes of 

exposure. Based on existing risk assessments, occupational exposure risk appear to 

well below the Agency’s level of concern (LOC). Therefore, additional assessments 

are not needed. 

• The Agency anticipates no revisions to the human health risk assessments. No new 

human health data are required. 

Timeline:

EPA has created the following estimated timeline for the completion of the quizalofop 

registration review. 
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Activities Estimated Month/Year 

Phase 1: Opening the Docket 

Open Public Comment Period for Quizalofop Docket 2007– Dec. 

Close Public Comment Period 2008– Mar. 

Phase 2: Case Development 

Final Work Plan (FWP) 2008– May-July 

Issue DCI 2009– Mar.-May 

Data Submission 2011– Mar.-May 

Preliminary Risk Assessment & Public Comment 2012– Sep.-Nov. 

Close Public Comment Period 2012– Nov.-Jan. 

Phase 3: Registration Review Decision 

Open Public Comment Period for Proposed Reg. Review Decision 2013– Feb.-Apr. 

Close Public Comment Period 2013– Apr.-Jun. 

Final Decision and Begin Post-Decision Follow-up 2013 

Total 6 years 

Guidance for Commenters

The public is invited to comment on EPA’s preliminary registration review work plan and 

rationale. The Agency will carefully consider all comments as well as any additional 

information or data provided prior to issuing a final work plan for quizalofop. 

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. Growers and 

other stakeholders are asked to comment on any trade irritant issues resulting from lack of 

Maximum Residue Limits (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. 

There are 44 U.S. tolerances for quizalofop-p-ethyl and quizalofop-ethyl, but not all of these 

tolerances have been harmonized with MRLs at this time. Tolerances on animal commodities 

have been harmonized with Canada. Other tolerances have not been harmonized, but allowable 

residue levels are similar. Please refer to Section IV of this document, Human Health Effects 

Scoping Document, for a detailed comparison of MRLs. 

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

under section 303(d) of the Clean Water Act, based on information provided at 

http://oaspub.epa.gov/tmdl/waters_list.impairments?p_impid=3. 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 Process” (see: http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-

sop.pdf), in order to ensure they can be used quantitatively or qualitatively in pesticide risk 

assessments. 
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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 or unusually high exposure to quizalofop, compared to the general population. Please 

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

exposure compared to the general population. 

Stakeholders are also specifically asked to provide information and data that will assist the 

Agency in refining the ecological risk assessment, including any species-specific effects 

determinations. 

The Agency is interested in receiving the following information: 

1. confirmation on the following label information 

a. sites of application 

b. formulations 

c. application methods and equipment 

d. maximum application rates in units related to mass per unit area of treatment zone 

e. frequency of application, application intervals, and maximum number of 

applications per season 

f. geographic limitations on use 

2. use or potential use distribution (e.g., acreage and geographical distribution of relevant 

crops) 

3. use history 

4. median and 90th percentile reported use rates (lbs ai/acre) from usage data – national, 

state, and county 

5. application timing (date of first application and application intervals) by crop – national, 

state, and county 

6. sub-county crop location data 

7. usage/use information for non-agricultural uses (e.g., forestry, residential, rights-of-way) 

8. directly acquired county-level usage data (not derived from state level data) 

a. maximum reported use rate (lbs ai/acre) from usage data – county 

b. percent crop treated – county 

c. median and 90th percentile number of applications – county 

d. total pounds per year – county 

e. the year the pesticide was last used in the county/sub-county area 

f. the years in which the pesticide was applied in the county/sub-county area 

9. typical interval (days) 

10. state or local use restrictions 

11. ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian and 

mammalian mortalities) not already reported to the Agency 

12. monitoring data 
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Next Steps:

After the comment period closes, the Agency will review any comments received, and then issue 

a Final Work Plan for this pesticide. 
8

II. Fact Sheet 

The Quizalofop Registration Review Case (#7215) includes two active ingredients:

1. Quizalofop-p-ethyl

2. Quizalofop-ethyl

 

Background Information:

• Quizalofop-p-ethyl is part of Registration Review case number: 7215 

• Quizalofop-p-ethyl PC Code: 128709 CAS#: 100646-51-3 

• Technical registrants: 

o E.I. Du Pont De Nemours Co., Inc. (Company No. 352) 

o Nissan Chemical Industries Ltd. (Company No. 33906) 

• First approved for use in a registered product in 1990. 

• Not subject to reregistration (no Reregistration Eligibility Decision [RED]). 

• There are six FIFRA section 3 registrations and four FIFRA section 24(c) special local 

need registrations 

• Quizalofop-ethyl is part of Registration Review case number: 7215 

• Quizalofop-ethyl PC Code: 128711 CAS#: 76578-14-8 

• Technical registrant: 

o E.I. Du Pont De Nemours and Co., Inc. (Company No. 352) 

• First approved for use in a registered product in 1988, however all end use product 

registrations have been cancelled prior to 1996. 

• No current active end-use products. One active technical registration. 

• Quizalofop-ethyl is a 50/50 racemic mixture of R- and S-enantiomers. Quizalofop-pethyl is the purified R-enantiomer and the pesticidally active isomer. Because the 

toxicological profile of the 50/50 racemic mixture (quizalofop-ethyl) and the Renantiomer (quizalofop-p-ethyl) are sufficiently similar, the Agency has determined that 

the currently available toxicity data on quizalofop-ethyl are adequate to support risk 

assessments reflecting uses of both quizalofop-ethyl and quizalofop-p-ethyl (the Renantiomer). 

• Special Review and Reregistration Division Chemical Review Manager (CRM): Rusty 

Wasem: wasem.russell@epa.gov. 

• Registration Division Product Manager (PM): 

James Tompkins: tompkins.james@epa.gov. 
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Use & Usage Information: 

(For additional details, please refer to the BEAD Appendix A document in the quizalofop 

docket.) 

• Quizalofop is a selective postemergence herbicide that is used to control annual and 

perennial grasses, excluding sedges and broadleaf weeds. 

• Quizalofop is used on food, feed, seed, and for other non-food/non-feed uses. Food, feed, 

and seed uses include the following: grains, legumes, cotton, garlic, mint, soybean, sugar 

beets, sunflower, pineapple, and Chinese cabbage. Non-food/non-feed uses include: 

cottonwood and poplar plantations, and uncultivated areas such as fencerows and 

roadsides. 

• There are no residential uses. 

• Application methods: 

o ground (broadcast, band, or soot spray), or aerial 

o post-emergence of weeds 

• Greatest poundage of quizalofop is used on soybeans. 

• Approximately 30% of mint and 10% of canola/rapeseed, dry beans/peas, and garlic 

crops are treated with quizalofop(according to SLUA). 

Recent Actions:

• In October 2005, Drinking water exposure for quizalofop-p-ethyl (TARGATM) on 

proposed and registered uses were completed. 

• In October 2005, Environmental Fate and Effects Division (EFED) risk assessments were 

completed. 

• In August 2006, Health Effects Division (HED) human health risk assessments were 

completed. 

• In November 2006, Section 3 new use registration request for quizalofop-p-ethyl 

(TARGATM) on sunflowers, flax, wheat and barley were approved. 

Ecological Risk Assessment Status: 

The following ecological outcomes are anticipated based on the limited data and risk 

assessments currently available. Please refer to Section III, Ecological Risk Assessment Problem 

Formulation, for a detailed discussion of the anticipated ecological risk assessment needs. A 

summary follows: 

• Risks are unlikely to exceed the Agency’s LOC for listed and non-listed species for: 

acute risks to aquatic invertebrates, aquatic plants, birds, fish, mammals, terrestrial 

invertebrates. 
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• Risks are unlikely to exceed the Agency’s LOC for listed and non-listed species for: 

chronic risks to aquatic plants, birds, fish, and terrestrial invertebrates. 

• Risks are likely to exceed the Agency’s LOC for listed and non-listed species for chronic 

risks to mammals. 

• Acute and chronic risks to non-target terrestrial plants have not been assessed, but are 

expected to exceed the Agency’s LOC. 

• Uncertainty exists for chronic risks to aquatic invertebrates, since the Agency has no 

chronic toxicity data for risk assessment. These data are required for estuarine 

invertebrates since estuarine animals seem to be more sensitive than freshwater animals 

in acute toxicity tests. 

Human Health Risk Assessment Status:

Please refer to Section IV, Human Health Effects Scoping Document, for a detailed discussion of 

the anticipated risk assessment needs for human health. A summary follows: 

Dietary (Food and Water): 

• Acute dietary risk assessments for quizalofop-p-ethyl and quizalofop-ethyl were deemed 

unnecessary because no toxic endpoint attributable to a single oral dose has been 

identified. Therefore, no acute dietary assessment has been conducted. 

• Chronic dietary risk assessments for quizalofop-p-ethyl and quizalofop-ethyl are 

conservative and unrefined with risks below the Agency’s LOC because the dietary 

analysis was based on tolerance level residues. 

• There are no dietary risks for quizalofop-p-ethyl and quizalofop-ethyl that exceed the 

Agency’s LOC. 

Residential: 

• There are no residential uses of quizalofop-p-ethyl and quizalofop-ethyl. 

Occupational: 

• An occupational assessment was conducted for quizalofop-p-ethyl for the proposed uses 

on barley, flax, sunflower and wheat in 2006. 

• Risk estimates based on inhalation exposures of pesticides handlers and applicators for 

quizalofop-ethyl for barley, flax, sunflower, wheat, cotton, pineapple, and non-crop areas 

are below the Agency’s LOC. 

• Occupational assessments are not necessary for quizalofop-ethyl because there is only a 

technical registration. 

Tolerances: 

• The following is a summary of tolerances for quizalofop-p-ethyl according to CFR 

§180.441. 

o quizalofop-ethyl 

 36 tolerances 

o quizalofop-p-ethyl 

 7 tolerances 

 1 tolerance (regional) 
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Data Call-In Status:

• A DCI has not been issued for quizalofop-p-ethyl or quizalofop-ethyl.

• DCI(s) will be issued for quizalofop during the registration review process.

Labels: 

A list of registration numbers may be found in the docket and the labels for quizalofop-p-ethyl 

and quizalofop-ethyl can then be obtained from the Pesticide Product Label System (PPLS) 

website: http://oaspub.epa.gov/pestlabl/ppls.home. 

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EXECUTIVE SUMMARY 

Quizalofop-ethyl (including its R-enantiomer, quizalofop-p-ethyl) is a systemic herbicide that is 

rapidly absorbed by treated foliage and translocated to the roots and other growing points of the 

plant. Affected plant tissues become necrotic/chlorotic and die leaving treated plants stunted and 

non-competitive. It controls annual and perennial grasses. It can be applied using ground boom 

equipment, fixed wing aircraft as broadcast and banded applications, airblast and soil injection 

treatment applications. It is normally applied at low rates. 

Currently, only products containing quizalofop-p-ethyl are registered. There are no active 

registered products containing quizalofop-ethyl. Quizalofop-ethyl is a 50/50 racemic mixture of 

R- and S-enantiomers. Quizalofop-p-ethyl is the purified R-enantiomer. The pesticidally active 

isomer is the R-enantiomer (quizalofop-p-ethyl). 

Quizalofop-ethyl and quizalofop-p-ethyl (the R-enantiomer) were first registered in 1988. As a 

result, they were not subject to review under the re-registration process recently completed under 

FIFRA and FQPA as of August 3, 2006 for chemicals registered prior to 1984. Consequently, 

neither a Re-registration Eligibility Decision (RED) nor a Tolerance Re-registration Eligibility 

Decision (TRED) is available for the Registration Review process of these chemicals. 

The most recent EFED risk assessments were completed in October 28, 2005, which reflect 

current registrations and uses of quizalofop-ethyl and quizalofop-p-ethyl. Based on the results of 

those assessments, the following risk concerns were noted: 

- Chronic risks to listed and non-listed mammals 

- Anticipated risks to listed and non-listed terrestrial plants 

- Potential chronic risks to listed and non-listed estuarine/marine invertebrates. Since the 

toxicological profile of the 50/50 racemic mixture (quizalofop-ethyl) and the Renantiomer (quizalofop-p-ethyl) are not complete, uncertainty exists for this assessment. 

EFED anticipates revisions to the risk assessments based on new application scenarios and 

additional toxicity data requested. A new drinking water assessment may also be needed to 

address any new uses and/or application scenarios and to comply with new EFED guidelines. 
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Table 1 summarizes quizalofop-p-ethyl and quizalofop-ethyl submitted studies and studies that 

are requested to complete the toxicological profile. 

Table 1 List of studies submitted and studies requested

Studies submitted 

quizalofop-p-ethyl 

Studies submitted ** 

quizalofop-ethyl 

Studies requested 

quizalofop-p-ethyl 

Seedling emergence (unacceptable) Avian acute (mallard duck and 

bobwhite quail) 

Seedling emergence based on TEP tier II 

Vegetative vigor (unacceptable) Avian dietary (mallard duck and 

bobwhite quail) 

Vegetative vigor based on TEP tier II 

Chronic bird (mallard duck and 

bobwhite quail) 

Acute rat Chronic estuarine marine invertebrate 

most sensitive species (mysid). 

 No chronic freshwater or estuarine 

marine invertebrate studies were 

submitted therefore a chronic estuarine 

marine invertebrate study is requested to 

quantify risks. This data will also be used 

to estimate chronic values for freshwater 

invertebrates.

non- vascular aquatic plant study 

tier l 

green algae (Selanastrum 

capricornutum)*

Acute freshwater fish (Rainbow 

trout and Bluegill) 

non- vascular aquatic plant study 

tier l 

blue green algae (Anabaena flosaquae) 

Acute freshwater aquatic 

invertebrate (daphnid) 

non- vascular aquatic plant study 

tier l 

estuarine marine diatom 

(Skeletonema costatum) 

Acute estuarine marine fish 

(sheepshead minnow) 

non- vascular aquatic plant study 

tier l 

freshwater diatom (Navicula 

pelliculosa) 

Acute estuarine marine aquatic 

invertebrate (mysid) 

vascular aquatic plant study tier 1 

Duckweed (lemna gibba)*

Chronic freshwater fish (fathead 

minnow) 

Nontarget insects (honeybee) 

* Non vascular plant NOAEC values were not determined for quizalofop-p-ethyl. In the absence of those 

data, EFED based its risk estimation for non vascular plants on data from the NOAEC from the analog 

fenoxaprop-p-ethyl (27 ppb). It is understood that fenoxaprop-p-ethyl is more toxic to non vascular 

plants than quizalofop-p-ethyl (EC50 of 1770 ppb for quizalofop-p-ethyl vs 430 ppb for fenoxaprop -pethyl for Selanastrum capriconutum, the most sensitive species tested for both chemicals), and using data 

from fenoxaprop-p-ethyl may overestimate risk for quizalofop-p-ethyl. However, a chronic RQ of only 

0.23 was observed when comparing the fenoxaprop-p-ethyl NOAEC of 27 ppb to the exposure data of 

quizalofop-p-ethyl at the highest application rate of 0.4125 lb ai/A 
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Therefore, although the above estimated values may not be complete substitutes for missing effects data, 

EFED is confident that listed species LOCs would not be triggered even if assessed with definitive 

NOAEC values. Thus, additional tier II toxicity data will not be requested at this time for non-vascular 

plants. 

Estimated EECs for highest application rate of 0.4125 lb ai/A per season= 0.4125 lb ai/A/ 0.165lb 

ai/A=2.5 2.5x EEC 2.57 ppb (table#6) =6.425 ppb EECs for highest application rate. RQ=6.425 ppb/27 

ppb NOAEC from fenoxaprop-p-ethyl =RQ 0.23 

The NOAEC for lemna gibba however will be equal to the highest nominal concentration of 82.8 ppb. 

** Additional studies for terrestrial and aquatic plants, chronic reproductive bird and chronic aquatic fish 

and invertebrates may be requested if quizalofop-ethyl is registered as an active labeled use. 

PROBLEM FORMULATION 

 

Problem formulation is used to establish the direction and scope of an ecological risk assessment. 

According to the Guidelines for Ecological Risk Assessment (USEPA, 1998), problem 

formulation consists of defining the problem and purpose for the assessment, and developing a 

plan for analyzing and characterizing risk. The critical components of the problem formulation 

are selection of the assessment endpoints, formulation of risk hypotheses and the conceptual 

model, and development of an analysis plan. The analysis plan and supporting rationale are 

aimed at determining whether the uses of quizalofop-p-ethyl and quizalofop-ethyl on NonFood/Non-feed uses (alfalfa, beets, carrot ( including tops), swiss chard, grasses grown for seed, 

cottonwood/poplar plantations, non-agricultural uncultivated areas/soils, onion, ornamental and 

or shade trees, radish spinach and for Food and Feed uses ( agricultural fallow/idleland, barley, 

succulent and dried beans, snap beans, chinese cabbage, eucalyptus, canola, rape, cotton, crambe, 

flax, garlic, lentils, mint, peppermint and spearmint, dried and succulent peas, pineapple, 

soybeans, sugarbeets including tops, sunflower and wheat) could result in exposures that cause 

unreasonable adverse effects (risk) to non-target organisms including those federally listed as 

threatened or endangered (hereafter referred to as “listed”). 

1. INTEGRATION OF AVAILABLE INFORMATION 

The risk assessments available in the docket, and which serve as the basis for this problem 

formulation, include the following: 

• October 28, 2005, Section 3 New use registration request for quizalofop-p-ethyl 

(TARGATM) on sunflowers, flax, wheat and barley (DP 310868) 

• October 28, 2005, Drinking water exposure for quizalofop-p-ethyl (TARGA TM) on 

proposed and registered uses (DP 310868) 

Risks, as identified in these assessments, are: 
16

For mammals: Chronic risk to mammals, based on aerial and ground spray applications, occurred 

for the following crops:(1) sunflowers with a maximum seasonal rate of 0.12 lb ai /acre; (2) flax 

with a maximum seasonal rate of 0.165 lb ai /acre; and (3) wheat and barley with a maximum 

seasonal rate of 0.08 lb ai acre. Chronic RQs ranged from 1.14 to 3.54. 

In addition, exceedences are anticipated for chronic risk to estuarine marine invertebrates with 

higher application rates. Terrestrial plants can not be assessed due to lack of acceptable data, 

however exceedences are anticipated for all modeled scenarios due to the chemical properties 

and mode of action of quizalofop-p-ethyl. 

 

There are no reported incidents for 128711. There is only one incident for 128709 ref.# 1016677-

001 which involved damage to some garden plants after they were exposed to spray drift of 

quizalofop-p-ethyl (Assure II) plus fomesafen sodium (Flexstar). Because the plants were 

exposed to two herbicides, it is uncertain which one or both caused the observed plant damage. 

1. DATA GAPS AND ANTICIPATED DATA NEED 

As mentioned above, the toxicological profile of the 50/50 racemic mixture (quizalofop-ethyl) 

and the R-enantiomer (quizalofop-p-ethyl) are not complete and the currently available toxicity 

data on quizalofop-ethyl are not adequate to support risk assessments reflecting uses of both 

quizalofop-ethyl and quizalofop-p-ethyl (the R-enantiomer). EFED will request additional data 

to complete the toxicological profile for quizalofop-ethyl and quizalofop-p-ethyl (the Renantiomer). 

Below is the preliminary identification of data gaps for the fate and ecological assessment: 

Seedling emergence and vegetative vigor tests The terrestrial seedling emergence and 

vegetative vigor tests for plants exposed to quizalofop-p-ethyl that were submitted to the Agency 

in 1994 were classified as unacceptable. The Agency guidelines require that terrestrial plant 

toxicity testing for herbicides be performed using the typical end-use product (TEP). In addition, 

the above studies lack negative controls and insufficient information demonstrating that the 

concentration of acetone used in the study does not inhibit plant growth. 

 Decision: Seedling emergence and vegetative vigor studies based on TEP are requested for 

terrestrial seedling emergence and vegetative vigor tests for quizalofop-p-ethyl. Seedling 

Emergence (GLN 123-1a/850.4225) Vegetative Vigor (GLN 123-1b/850.4250) 

Chronic estuarine/marine fish toxicity tests - The No Observable Adverse Effect 

Concentration (NOAEC) value of 33 ppb for estuarine/marine fish was estimated by applying the 

acute-to-chronic ratio (ACR) ) from freshwater toxicity tests to the estuarine/marine acute 

toxicity values. In addition, no LOC exceedences occurred for chronic estuarine marine fish 

with RQs <0.01 for the 0.165 lb ai /A scenario. LOC exceedences are not anticipated for chronic 

estuarine marine fish with the higher application rate of 0.4125 lb ai/A per season. 

Decision: Chronic estuarine/marine fish toxicity tests studies are not requested 
17

Estuarine/marine invertebrate Early Life-Cycle toxicity data – No early life stage 

estuarine/marine invertebrate studies were submitted to the Agency. Estuarine marine 

invertebrates are the most sensitive aquatic organisms (mysid) exposed to quizalofop-ethyl. 

Since exceedences are expected from quizalofop-p ethyl and quizalofop-ethyl from many 

application scenarios, the early life-cycle estuarine marine invertebrate study for quizalofop-pethyl with mysid shrimp (most sensitive species tested) will be requested since no active labels 

exist for quizalofop-ethyl. However, if active labels occur for quizalofop-ethyl then additional 

studies for estuarine marine invertebrates would be requested. 

Decision: Chronic early life-cycle estuarine/marine invertebrate toxicity tests studies with 

mysid (most sensitive species) conducted on quizalofop-p-ethyl are requested (GLN 72-

4b/850.1350). 

Freshwater invertebrates Early Life-Stage toxicity test - No early life-stage or full life-cycle 

chronic invertebrate studies were submitted for freshwater or estuarine marine invertebrates. 

However, based on ACRs derived from acute and chronic freshwater fish data, no exceedences 

would occur for chronic freshwater invertebrates exposed to quizalofop-ethyl. 

Decision: An Early life-stage chronic freshwater invertebrate toxicity test for quizalofop-pethyl is not requested. Estimated values derived from ACRs will be sufficient. 

Tier II study for non-vascular plant based on (Selanastrum capricornutum)

NOAECs were not determined for non-vascular plants exposed to quizalofop-p-ethyl to address 

listed species concerns and no studies were submitted for quizalofop-ethyl. A Tier II study which 

defines a NOAEC value would be beneficial in the definitive determination of risks to nonvascular plants. Risks to listed species are currently assessed using data from fenoxaprop-p-ethyl, 

a structural analog of quizalofop-p-ethyl. No LOCs exceedances were noted at the highest 

application rate of 0.4125 lb ai/A per season based on estimated EECs. 

Decision: A Tier II study for non-vascular plants based on Selanastrum capricornutum for 

quizalofop-p-ethyl is not requested at this time. Data may be required for any future use with 

application rates higher than 0.4125 lb ai/A per season. 

Environmental Fate Data and Sediment Toxicity Data for the degradate quizalofop acid: 

Quizalofop-p-ethyl is anticipated to degrade quickly in soil to the major degradate, quizalofop 

acid. Previous assessments assume that quizalofop acid is the main species present in water, and 

that it is of equivalent toxicity as the parent. Furthermore, for exposure, this degradate was 

presumed to be stable via hydrolysis and photolysis, and in anaerobic environment (soil and 

water). With those assumptions, only chronic risks to listed and non-listed freshwater and 

estuarine marine invertebrates were anticipated, however not fully characterized due to lack of 

toxicity data. 

Decision: Based on the current database for quizalofop-p-ethyl, environmental fate data for 

quizalofop acid are not required. However, if further assessment indicates toxicity and risks to 

aquatic organisms, those data may be requested for a refined risk characterization. 
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2. PESTICIDE TYPE, CLASS, AND MODE OF ACTION 

Quizalofop-p-ethyl is a selective, post-emergence organic phenoxy herbicide that belongs to a 

subclass of phenoxy compounds known as Aryloxyphenoxys (fops). Quizalofop-p-ethyl is 

absorbed by the treated foliage and translocated to the roots and other growing points of the 

plant. Herbicides categorized as arloxyphenoxys have several modes of action which are as 

follows: (1) In terrestrial and aquatic vascular and nonvascular plants--- inhibition of acetyl CoA 

carboxylase (ACCase), a key enzyme in lipid biosynthesis; (2) In terrestrial and aquatic vascular 

and non-vascular plants-inhibition of cell mitosis or immediate termination of mitosis once 

exposure has been known to occur; (3) In terrestrial and aquatic vascular and non-vascular 

plants- inhibition of Acetyl-CoA carboxylase and the fatty acid synthesis pathway causes an 

inhibition of thylakoid membrane formation, chloroplast formation and multiplication, and 

finally a halt of cell membrane formation and cell division. 

4. STRESSOR SOURCE AND DISTRIBUTION 

The sources of the stressor considered are quizalofop -p-ethyl (PC Code 128709), quizalofopethyl (PC Code 128711), and quizalofop acid, the major degradate of concern. 

Quizalofop-p-ethyl is stable to hydrolysis at pH’s 5 and 7. Hydrolysis occurs at pH 9 with a half 

life of 2 days. Quizalofop-p-ethyl is stable to photolysis in water and soil. Acceptable aerobic 

soil metabolism study show that quizalofop-p-ethyl degrades with a half-life of 1 day to 

quizalofop acid and phenolic compounds. Quizalofop acid is considered to be the major exposure 

concern. Based on available fate studies, the acid is less persistent than the parent under aerobic 

conditions but more mobile than the parent compound. Its soil metabolism half lives in aerobic 

environment range from 4 to 8 weeks, depending on soil types. As for mobility, the mean 

adsorption Koc of quizalofop acid is 476 (which is classified as moderately mobile), whereas the 

mean adsorption Koc value of quizalofop-p-ethyl is 1816 (which is classified as slightly mobile). 

No additional environmental fate data are available for quizalofop acid. 

As mentioned above, quizalofop-p-ethyl degrades quickly to form quizalofop acid, the major 

concern of aquatic exposure would be from this degradate. This degradate was also detected in 

livestock tissues and is included in the tolerance expression and the HED risk assessment. Its 

toxicity level was determined by HED to be equivalent or less than that of the parent. As for 

exposure, in the absence of fate data, the solubility was assumed to be equivalent to those of the 

parent and all abiotic degradation (hydrolysis and photolysis) and anaerobic metabolism 

processes, non existing.

Currently, quizalofop-p-ethyl is applied as a ground spray, aerial, air blast and soil injection 

applications. Trade and other names of products containing quizalofop-p-ethyl include: (1) 

Assure II; (2) Matador; (3) Dupont Assure II ;(4) MON 78746. 
19

Quizalofop-p-ethyl is registered for several food crops and it is used to control the growth of 

perennial and annual grasses, weeds and vines. During the period of 2000-2006, approximate 

annual usage for quizalofop-p-ethyl and quizalofop-ethyl was 89,500 pounds. The usage data for 

quizalofop-p-ethyl and quizalofop-ethyl does not distinguish between the two chemicals. 

Quizalofop-ethyl did not have an active product registration during the period of data collection. 

The greatest poundage of quizalofop is used on soybeans (SLUA from BEAD). 

Quizalofop accounts for 30% of mint treated, 10% of canola/rape seed with a maximum of 20% 

treated, followed by dry beans/peas and garlic averaging 10% of the crop treated (SLUA from 

BEAD). While these data provide some insight into the historic use of quizalofop-p-ethyl, 

herbicide use changes with the varying resistance of pest plants; predicting total use 

prospectively is difficult since it may be based on the susceptibility of a particular pest plants to a 

specific herbicide. 

Terrestrial exposure is based on direct spray application on food items including short grass, 

seeds, and broadleaf plants and insects resulting from applications of quizalofop-p-ethyl at the 

maximum label rates. Exposure to aquatic organisms is the result of runoff and spray drift from 

labeled applications, and is functionally the amount of compound in the water that would directly 

contact organisms. The magnitude of exposure estimates is largely dependent on the biology of 

the receptor (e.g., food consumption rate), the use patterns, and environmental fate and transport 

characteristics of the pesticide. 

5. OVERVIEW OF PESTICIDE USAGE 

Quizalofop-p-ethyl is a herbicide that is used to control weeds in Non-Food/Non-feed uses 

(alfalfa, beets, carrot ( including tops), swiss chard, grasses grown for seed, cottonwood/poplar 

plantations, non-agricultural uncultivated areas/soils, onion, ornamental and or shade trees, 

radish spinach and for Food and Feed uses ( agricultural fallow/idle land, barley, succulent and 

dried beans, chinese cabbage, canola, eucalyptus, rape, cotton, crambe, flax, garlic, lentils, mint, 

peppermint and spearmint, dried and succulent peas, pineapple, soybeans, sugarbeets including 

tops, sunflower, and wheat). Quizalofop-p-ethyl is formulated as a wettable powder, soluble 

concentrate and liquid, and can be applied as various spray treatments such as; ground, soil 

injection, aerial and air blast. 

The currently approved quizalofop-p-ethyl application rates for agricultural uses range from 

0.0650 lb ai/acre (cotton) to 0.2063 lb ai/acre (pineapple) for a single application (BEAD 2007) 

with a seasonal maximum label rate of 0.4125 lb ai/acre (pineapple). For non-agricultural uses 

the maximum rate per application is 0.2063 lb ai/acre (ornamental and/or shade trees) with a 

seasonal maximum label rate of 0.4125 lb ai/acre (ornamental and/or shade trees) (BEAD 2007). 

6. ENVIRONMENTAL FATE SUMMARY 

Quizalofop-p-ethyl has a relative low water solubility of 0.4 mg/L. In organic solvents 
20

such as acetone, hexane, and ethanol, quizalofop-p-ethyl is very soluble. It has a vapor pressure 

of 3 x mm Hg (@ 20'~) and a calculated Henry's law constant of 3.7 x atm-m3/mole. 

The hydrolysis rate is pH variable; with the half-life of 600 days at pH 5, 30 days at pH 7, and 

2 days at pH 9. Supplemental studies also show that quizalofop-p-ethyl is moderately mobile 

with Kads of 1.5-1.9 in sandy loam soil, and immobile in silt loam soil with Kads of 16-20. 

Existing data from the Environmental Fate and Effects Division (EFED) files show conflicting 

results between laboratory studies and field studies. The acceptable laboratory aerobic soil 

metabolism study shows that quizalofop-p-ethyl degrades microbially with a half-life of 1 day in 

sandy loam and silt loam soils. However, quizalofop-p-ethyl was persistent in the field with halflives of 145 and 364 days for studies conducted in IL and CA, respectively. The inconsistency in 

results between the laboratory and the field studies may be due to differences of pHs and 

microbial populations in the soil media used, and differences between the purposes of each 

study. 

The acceptable fish accumulation study indicated that quizalofop-p-ethyl did not bioaccumulate 

with 28-day values of 1X and 4X for exposure concentrations of 0.004 and 0.04 mg/L, 

respectively. 

As for the acid degradate, in the absence of data, previous assessment assumes that it is stable to 

both biotic and abiotic degradation and it has equivalent solubility to the parent. 

7. ECOLOGICAL EFFECTS SUMMARY 

Table 2 provides taxonomic groups and test species used to indicate the potential for ecological 

effects in this screening-level risk assessment. Within each of these very broad taxonomic 

groups, an acute and/or chronic endpoint is selected from the available test data. 

Table 2. Taxonomic Groups and Most Sensitive Test Species Evaluated 

for Ecological Effects of quizalofop-ethyl and quizalofop-p-ethyl*

Taxonomic group Example(s) of representative species Endpoint Used

Birdsa Bobwhite quail (Colinus virginianus) 

Mallard duck (Anas platyrhynchos) 

Acute LD50

Acute LC50 

Chronic, NOAEC* 

Mammals Laboratory rat (Rattus norvegicus) Acute LD50 

NOAEC 

Terrestrial insects Honeybees (Apis mellifera) Acute Oral LD50 N/A 

Acute Contact LD50

Freshwater fishb Rainbow trout (Oncorhynchus mykiss) 

Bluegill sunfish (Lepomis macrochirus) 

Fathead minnow (Pimephales promelas)

Acute LC50

Acute LC50

Chronic NOAEC 
21

Table 2. Taxonomic Groups and Most Sensitive Test Species Evaluated 

for Ecological Effects of quizalofop-ethyl and quizalofop-p-ethyl*

Taxonomic group Example(s) of representative species Endpoint Used

Freshwater invertebrates Water flea (Daphnia magna) 

 

Acute EC50 

NOAEC N/A no study 

submitted. Estimated values 

will be used in future 

assessments. 

Estuarine/marine fish Sheepshead minnow (Cyprinodon 

variegatus) 

Acute LC50

Estuarine/marine invertebrates Mysid shrimp (Mysidopsis bahia) 

Eastern oyster (Crassostrea virginica) 

Acute EC50

NOAEC N/A no studies 

submitted 

 

Terrestrial plants* Monocots – N/A 

Dicots – N/A 

Seedling Emergence 

Vegetative Vigor EC25 N/A 

unacceptable studies 

submitted. 

 

Vascular aquatic plants* Duckweed (Lemna gibba) Tier1 Acute EC50 

NOAEC N/A in previous 

risk assessments. Future 

risk assessment will use 

highest concentration value 

as NOAEC. 

 Non-vascular aquatic plants* Green algae (Selanastrum capricornutum ) 

Tier I 

Acute EC50 

NOAEC or EC05 N/A Since 

a maximum growth 

inhibition observed was 

19% from the tier I study a 

NOAEC value from a Tier 

II test would quantify risks. 

However, EFED will 

quantify risks to listed 

species through estimated 

values and analog data. 

a

Birds are used as surrogates for terrestrial phase amphibians and reptiles (US EPA, 2004). b

Freshwater fish are used as surrogates for aquatic phase amphibians (US EPA, 2004). 

*Studies were conducted on quizalofop-p-ethyl only. Studies not identified by an asterisk were conducted on quizalofop-ethyl. 
22

8. ECOSYSTEMS AT RISK 

The ecosystems that could be potentially at risk due to agricultural use of quizalofop-p-ethyl 

include terrestrial and aquatic (lakes, ponds, streams) habitats in proximity to quizalofop-p-ethyl 

use areas. These habitats may be at risk from drift and/or runoff of quizalofop-p-ethyl from use 

areas. The estuarine/marine ecosystems are likely at less risk since they are typically further 

from agricultural areas and are characterized by large volumes of water. However, in some areas 

adjacent to estuarine/marine environments where agriculture dominates the landscape, risks to 

estuarine/marine ecosystems cannot be excluded. 

Organisms of concern include birds, mammals, reptiles, fish, and terrestrial and aquatic 

invertebrates, plants, and amphibians. The assessment endpoints are intended to reflect 

population sustainability and community structure within ecosystems and hence relate back to 

ecosystems at risk. If risks are expected for given species/taxa based on the screening-level 

assessment, then risks might be expected to translate to higher levels of biological organization. 

Identifying specific ecosystems at risk in a screening-level assessment is beyond the scope of the 

effort. 

8.1 Receptors 

The aquatic receptors likely to be exposed to quizalofop-p-ethyl include fish, invertebrates, 

aquatic stages of amphibians and plants living in waterways adjacent to or downstream from 

treated areas. 

Terrestrial receptors likely to be exposed to quizalofop-p-ethyl include birds, mammals, reptiles, 

and terrestrial stages of amphibians that may occur in treated fields and terrestrial plants adjacent 

to, or down slope from treated areas. 

8.2. Assessment Endpoints 

Assessment endpoints are defined as “explicit expressions of the actual environmental value that 

is to be protected.” Operationally, the environmental value is represented by an ecological entity 

and associated attributes or characteristics. The assessment endpoints for this ecological risk 

assessment will be survival, growth, and reproduction of terrestrial and aquatic animals and 

plants. Specifically, this assessment will address birds, mammals, reptiles, amphibians, 

terrestrial and aquatic invertebrates, terrestrial and aquatic plants, and fish. These endpoints, in 

turn, are meant to reflect population sustainability and community diversity within ecosystems. 

Assessment endpoints and toxicity data used to evaluate the assessment endpoints are identified 

in Table 2 and Table 3. 
23

9. CONCEPTUAL MODEL 

The conceptual model used to depict the potential ecological risk associated with quizalofop-pethyl is generic and assumes that as an herbicide, quizalofop-p-ethyl can affect terrestrial and 

aquatic organisms if environmental concentrations are sufficiently elevated as a result of the 

proposed label uses. A diagram of the conceptual model is presented in Figure 1. All of the use 

scenarios for quizalofop-p-ethyl involve spray applications such as: ground, aerial, air blast of 

the pesticide to foliage as well as soil injection. Although not evident from the diagram, 

quizalofop-p-ethyl degradation prior to runoff is explicitly considered. Runoff includes transport 

of quizalofop-p-ethyl and its degradate in a dissolved state as well as quizalofop-p-ethyl and its 

degradate adsorbed to eroded sediment. 

As there are multiple spray applications of the pesticide to foliage of the proposed labeled use 

patterns, degradation on the foliage between applications is considered in the terrestrial 

assessments. A default foliar dissipation rate of 35 days will be used in the terrestrial risk 

assessments since no foliar dissipation studies are available. The default value represents an 

upper bound on expected foliar dissipation rates across all pesticides, based on data in Willis and 

McDowell (1987). For aquatic assessments, the microbial degradation on foliage is assumed 

stable, but wash-off of the foliage will be considered using the default wash-off coefficient 

assumption of 0.5 cm-1. Spray drift will be considered in the aquatic assessments as a route of 

loading to the pond, with higher levels of spray drift for aerial applications than ground spray 

applications. 

For terrestrial assessments, spray drift is not directly considered. However, since the evaluation 

of risk is done for on-field foliage, non-target foliage receiving spray drift should reduce 

pesticide loading and the assessment based on the on-field residues which would represent an 

upper bound estimate. A variety of food types (e.g., short grass, long grass, broadleaf plants) 

will be assessed regardless of the type represented by the target crop, as a variety of food types 

exist on and off the treated field. 

In aquatic environment, once quizalofop-p-ethyl reaches a water body, the pesticide is 

partitioned between the water column, suspended sediment, and bed sediment at a ratio based on 

the pesticides’ physical/chemical properties. Degradation by abiotic hydrolysis, photolysis, and 

microbial mediated metabolism are taken into account. The route of exposure to fish is uptake of 

quizalofop-p-ethyl and its degradate dissolved in the water column through the gills and 

integument. 

Quizalofop-p-ethyl does not bio-accumulate in fish. BCFs have 28-day values of 1X and 4X for 

exposure concentrations of 0.004 and 0.04 ml/L, respectively. 

For birds and mammals, only the dietary route of exposure is considered. Uncertainties may 

include the lack of information on exposure from soil ingestion as well as exposure from other 

pathways such as inhalation and dermal routes. 
24

Figure 1. Conceptual model of the fate/transport and effects of quizalofop-p-ethyl in the 

environment. 

This updated conceptual model will be used in the next assessment which will 

incorporate additional applications 

Food Web 

Dynamics 

Perturbing Forage or 

Prey Availability 

Habitat Alteration: impacting nesting 

ability, ability to seek cover, etc. 

Individual Terrestrial 

Animals

Reduced Survival 

Reduced Growth 

Reduced Reproduction 

Individual Terrestrial 

Plants

Seedling Emergence 

Vegetative Vigor 

Individual Aquatic 

Vertebrates and 

Invertebrates

Reduced Survival 

Reduced Growth 

Reduced Reproduction 

Bioaccumulation 

Aquatic Plant 

Population

Reduced 

Growth Rates 

and Biomass 

Terrestrial Animals

Birds, Mammals, Reptiles, 

Terrestrial-phase 

Amphibians, Bees 

Terrestrial 

Upland Plants 

Wetland/ 

Riparian 

Plants 

Aquatic Invertebrates 

Aquatic Vertebrates 

Aquatic Plants 

Quizalofop-p-ethyl applied by ground spray, aerial, airblast and soil injection 

applications 

Volatilization/ 

Wind 

Suspension* 

Ground 

Deposition 

Spray Drift Runoff/ 

Erosion 

Leaching 

(Infiltration/ 

Percolation) 

Terrestrial 

Food Residues 

(foliage, fruit, 

insects) 

Upland 

Foliage/ 

Soil 

Riparian/ 

Wetland 

Foliage/Soil 

Surface 

Water, 

Sediment 

Dietary 

uptake 

Direct Contact/ 

Root Uptake 

Gill/ Integument 

Uptake 

Direct Contact/ 

Root Uptake 

Groundw

ater 

Direct 

Ingestion 

* Volatilzation is not expected to be an exposure of concern due to a low vapor pressure of 3.0 x 10-7 mmHg@20o

C 
10. RISK HYPOTHESES 

Hypothesis: Nontarget terrestrial and aquatic animals and plants are at risk of direct and indirect 

effects resulting from labeled uses of quizalofop-p-ethyl. 

11. ANALYSIS PLAN 

The analysis plan is the final step in problem formulation. During this step measures of 

exposure and measures of effect are used to evaluate the risk hypotheses and are listed in Tables

2 and 3 for a specific assessment endpoint. The RQ is obtained by dividing the measures of 

exposure for a particular assessment endpoint by the measures of effect for that endpoint. 

11.1. Measures of Exposure

 

Measures of exposure for quizalofop-p-ethyl that will be used in this assessment are obtained 

from modeling efforts only, since national-scale monitoring data were not identified. Exposure 

models used for this assessment include the suite of standard exposure models commonly used in 

pesticide risk assessments (EPA, 2004). Generally, aquatic exposure estimates are generated 

from EFED models and incorporate maximum proposed use rates and empirically-derived fate 

properties. Aquatic exposure will be estimated using the PRZM/EXAMS model and will consist 

of aquatic EECs derived using a water body that is vulnerable and representative of static ponds 

and first order waterways. 

Measures of exposure for terrestrial mammals, birds, reptiles, and amphibians similarly 

incorporate maximum proposed use rates but rely less on fate properties. Instead, terrestrial 

exposure estimates are derived directly from empirically determined observations of pesticide 

residues on various terrestrial food items. For numerous applications for a given use, the 

exposure model incorporates a first-order decay rate dependent on the soil half-life of the 

chemical. In place of unavailable foliar dissipation data, the default foliar dissipation half-life of 

35 days will be used. The currently used terrestrial exposure model is TREX v.1.3.1. 

Exposure to terrestrial plants will be estimated using the TerrPlant model that assumes 

quizalofop-p-ethyl drifts or moves with runoff to adjacent areas. However, acceptable terrestrial 

plant toxicity data has not been submitted. Therefore, risks to terrestrial plants can not be 

determined. 

Based on preliminary EECs and the assumptions discussed above, chronic risks at the highest 

labeled application rate are expected for all non-listed and listed mammals and estuarine marine 

aquatic invertebrates (0.4125 lbs a.i./A per season). Risks are expected as well for non-listed and 

listed species of terrestrial plants inhabiting semi-aquatic and dry areas based on exposures of 

quizalofop originating from the maximum application rate. Because of the potential risk from 

direct effects to the listed and non-listed taxa described above, should exposure occur, listed 

species in all taxa may potentially be affected indirectly due to alterations in their habitat (e.g., 

food sources, shelter, and areas to reproduce). 

25
If the planned ecological risk assessment continues to indicate that quizalofop may potentially 

impact, either directly or indirectly, listed species or critical habitat, and therefore does not 

support a “not likely to adversely affect” determination, further refinements will be made. This 

will involve determining whether use of quizalofop “may affect” a particular listed species, and 

if so, whether it is “likely to adversely affect” the species, or in the case of designated critical 

habitat, whether use of the pesticide may destroy or adversely modify any principle constituent 

elements for the critical habitat, and if so, whether the expected impacts are “likely to adversely 

affect” the critical habitat. The first step in the process is to improve the exposure estimates 

based on refining the geographic proximity of quizalofop use and the listed species and/or 

critical habitat. If there is no geographic proximity, this information would support a 

determination that quizalofop use will have no effect on the species or critical habitat. If after 

conducting the first step of this analysis the Agency determines that geographic proximity exists, 

both potential direct effects and any potential indirect effects of the pesticide use will be 

examined. This process is consistent with the Agency's Overview Document. The Agency will 

consult as necessary with the U.S. Fish and Wildlife Service and National Marine Fisheries 

Service (collectively ‘the Services’), consistent with the Services' regulations. 

If the screening level risk assessment identifies potential concerns for indirect effects on listed 

species, the next step for EPA and the Services would be to identify which listed species and 

critical habitat are potentially implicated. Analytically, the identification of such species and 

critical habitat can occur in either of two ways. First, the agencies could determine whether the 

action area overlaps critical habitat or the occupied range of any listed species. If so, EPA would 

examine whether quizalofop potential impacts on non-endangered species would affect the listed 

species indirectly or directly affect a constituent element of the critical habitat. Alternatively, the 

agencies could determine which listed species depend on biological resources, or have 

constituent elements that fall into, the taxa that may be directly or indirectly impacted by 

quizalofop. Then EPA would determine whether the use of quizalofop overlaps the critical 

habitat or the occupied range of those listed species. 

11.2. Measures of Effect 

Aquatic plants and animals 

(1) Freshwater Fish 

Four acute toxicity studies using both the bluegill sunfish (Lepomis macrochirus) and rainbow 

trout (Oncorhynchus mykiss) indicated that quizalofop-ethyl is slightly to very highly toxic to 

freshwater fish on an acute toxicity basis based on values of LC50 460 ppb ( MRID 00146951), 

LC50 870 ppb ( MRID 00146680), LC50 10720 ppb ( MRID 00128210), LC50 2820 ppb ( MRID 

00128210), . The bluegill sunfish was the most sensitive species tested with an LC50 value of 

460 ppb (MRID 00128210). EFED used the LC50 value of 460 ppb for evaluating acute risks to 

freshwater fish. The guideline requirement for 72-1c and 72-1a acute aquatic fish was fulfilled 

(MRID 00146951).

A freshwater fish early life-stage chronic toxicity test on fathead minnow (Pimephales promales) 

26
was used to evaluate the chronic toxicity of quizalofop-ethyl. Results from the study indicated a 

No Observed Adverse Effect Level (NOAEL) of 11 ppb based on decrease in larval survival, 

weight. EFED used this value for evaluating chronic risk to freshwater fish. This guideline 

requirement for 72-4a for the early life-stage fish was classified as supplemental (MRID150109). 

(2) Freshwater Invertebrates 

Three acute freshwater toxicity tests using the Daphnia magna indicated that quizalofop-ethyl is 

moderately toxic to freshwater invertebrates on an acute toxicity basis based on the EC50 values 

of 2120 ppb (MRID 00128210), 6400 ppb (MRID 00146951) and 3900 ppb (MRID 411616-01). 

EFED used the EC50 of 3900 ppb to evaluate risks to freshwater invertebrates which was not the 

most sensitive value. Therefore, the EC50 of 2120 ppb value will be assessed to use in future risk 

assessments. Although, the guideline requirement for 72-2a was fulfilled for the acute 

freshwater invertebrate study based on the EC50 of 3900 ppb, the EC50 of 2120 ppb value will be 

assessed to use in future use in risk assessments(MRID 411616-01) (MRID 00128210). 

A freshwater invertebrate early life-stage toxicity test for freshwater invertebrates exposed to 

quizalofop-ethyl was not submitted to the Agency. No early life-stage invertebrate studies were 

submitted for freshwater invertebrates. Estimated values from ACRs will be accepted pending 

submission of requested a chronic estuarine marine invertebrate (mysid) study conducted on 

quizalofop-p-ethyl. 

(3) Estuarine/Marine Fish 

One estuarine/marine fish acute toxicity test, using the sheepshead minnow (Cyprinodon 

variegates), test indicated that quizalofop-ethyl is moderately toxic to estuarine/marine fish on an 

acute toxicity basis based on the LC50 value of 1400 ppb. Therefore, EFED used the LC50 value 

of 1400 ppb for evaluating acute risks to estuarine marine fish. The guideline requirement 72-3a 

for the acute toxicity to estuarine marine fish was fulfilled. (MRID 402422-09). 

No early life-stage estuarine marine fish studies were submitted to the Agency. Estimated values 

from ACRs will be used in future risk assessments from acute and chronic freshwater fish and 

acute estuarine marine fish toxicity studies. 

(4) Estuarine/Marine Invertebrates 

Two estuarine/marine acute toxicity tests exposing the mysid shrimp, Americamysis bahia, to 

quizalofop-ethyl indicated that quizalofop-ethyl is highly toxic to estuarine/marine invertebrates 

on an acute toxicity basis based on the EC50 values of 250 ppb (MRID 402422-05) and 150 ppb 

(MRID 402422-04). EFED used the EC50 of 250 ppb to evaluate risks to estuarine marine 

invertebrates which was not the most sensitive value. Therefore, the EC50 150 ppb value will be 

assessed to use in future risk assessments. Although, the guideline requirement for 72-2a was 

fulfilled for the acute estuarine marine invertebrate study based on the EC50 of 250 ppb, the EC50

27
of 150 ppb value will be assessed to use in future use in risk assessments (MRID 402422-05) 

(MRID 402422-04). 

 

No early life-stage estuarine marine invertebrate studies were submitted to the Agency. Since no 

chronic studies were submitted for either freshwater or estuarine marine aquatic invertebrates 

and exceedences may occur for higher use rates (pineapple and ornamental turf) especially for 

estuarine marine invertebrates, EFED requests an early life-stage estuarine marine invertebrate 

(mysid) study conducted on quizalofop-p-ethyl. to quantify risks for estuarine marine 

invertebrates. In addition, the NOAEC values from this estuarine marine invertebrate study will 

also be used to estimate NOAEC values for freshwater invertebrates derived from ACRs. 

 (5) Estuarine/Marine Mollusks 

An estuarine/marine acute shell deposition toxicity test exposing the eastern oyster to quizalofopethyl indicated that quizalofop-ethyl is highly toxic to estuarine/marine mollusks on an acute 

toxicity basis based on the EC50 value of 187 ppb (MRID 402422-07). An Eastern oyster-larvae 

(bivalve) study was sited in earlier assessments as EC50 79 ppb on canola (March 1997) and mint 

(February 1993) however no references were made. 

 (6) Aquatic Plants 

The tier I test with non-vascular green alga Selenastrum capricornutum exposed to quizalofop-pethyl showed a maximum of 19 % inhibition at the mean measured test concentration of 1770 

ppb (MRID 432356-01). Since an EC50 was not determined from any of the tier I aquatic plant 

tests, the value of EC50 > 1770 ppb will be used in future risk assessments to determine risks to 

aquatic non-vascular plants exposed to quizalofop-p-ethyl. 

Two additional Tier I aquatic non-vascular plant studies using the freshwater diatom Navicula 

pelliculosa and the estuarine/marine diatom Skeletonema costatum, showed a maximum of 3% 

inhibition at a test concentration of 98 ppb and 1.8% stimulation at a test concentration of 82 

ppb exposed to quizalofop-p-ethyl, respectively ( MRID 432709-01 and MRID 432709-02). 

The aquatic vascular plant Lemna gibba from a Tier I study, showed no adverse response to 

quizalofop-p-ethyl exposure with EC50 >82.8 ppb (MRID 432585-01). 

 The results of the Anabaena flos-aque aquatic plant study (MRID 432356-02) conducted on 

quizalofop-p-ethyl was not incorporated in the 2005 risk assessment but will be in future risk 

assessments. 

Non vascular plant NOAEC values were not determined for quizalofop-p-ethyl. In the absence of 

those data, EFED based its risk estimation for non vascular plants on data from the NOAEC for 

analog fenoxaprop-p-ethyl (27 ppb). It is understood that fenoxaprop-p-ethyl is more toxic ethyl 

to non vascular plants than quizalofop-p-ethyl (EC50 of 1770 ppb for quizalofop-p-ethyl vs 430 

ppb for fenoxaprop -p-ethyl for Selanastrum capriconutum, the most sensitive species tested for 

28
both chemicals), therefore using data from fenoxaprop-p-ethyl may overestimate risk for 

quizalofop-p-ethyl. 

No effects occurred at the highest concentration of 82.8 ppb for lemna gibba, therefore EFED 

will use the NOAEC value of 82.8 ppb for vascular plants in future risk assessments. 

 Terrestrial organisms 

 

 (1) Birds 

Five studies on the acute toxicity of quizalofop-ethyl (oral and dietary toxicity) to birds 

indicated that quizalofop-ethyl is practically non-toxic to the mallard duck (water-fowl) and the 

bobwhite quail (upland game bird) on acute oral and dietary toxicity basis. The LD50 values for 

the avian acute oral toxicity tests were: Mallard duck LD50 >2,000 mg kg-bw and Bobwhite 

Quail LD50>2,000 mg /kg-bw. The LC50 values for the avian acute dietary toxicity tests were as 

follows: Mallard Duck LC50>5,000 mg kg-diet; Bobwhite quail LC50 >5,000 mg /kg-diet; and 

Bobwhite quail LC50 >5620 mg/kg-diet. Therefore, EFED used the LD50 >2,000 mg kg-bw and 

LC50 >5,000 mg kg-diet values for evaluating acute oral and dietary risks to birds. NOAEC 

values were not determined. The guideline requirements 71-1 and 71-2 for the acute oral and 

dietary toxicity to birds were fulfilled. (MRID 00128210, MRID 00147574). 

Based on provisional review of two avian chronic reproductive toxicity studies using quizalofopp-ethyl, it appears that quizalofop-p-ethyl does not pose potential reproductive inhibition to birds 

based on a chronic toxicity basis. No reproductive effects were observed in a bobwhite quail 

study, resulting in a NOAEC value of 1000 ppm (MRID 466071-01). 

 However, there did appear to be a reduction in hatchability at the highest dose tested (1000 ppm 

a.i.) in the mallard duck study. There was an apparent reduction in hatchlings as a percentage of 

live 3-week embryos in the 1000 ppm a.i. treatment group, resulting in a NOAEC of 500 ppm 

(MRID 466071-02). However, it is not clear before a full review of the data whether this 

observed effect was statistically significant (p>0.05). 

 (2) Mammals 

Wild mammal testing is required on a case-by-case basis only, and is dependent on the results of 

lower tier laboratory mammalian studies, intended use patterns, and pertinent environmental fate 

characteristics. In most cases, rat or mouse toxicity values obtained from the Agency’s Health 

Effects Division (HED) are used as surrogates for wild mammal toxicity testing. 

The acute toxicity of quizalofop-ethyl was evaluated using the laboratory rat. The acute toxicity 

of quizalofop-ethyl differed between male and female rats with females showing greater 

sensitivity than males. The LD50 values were 870 mg/kg bw (fema1es) and 1088 mg/kg 

bw(males) and a combined LD50 value of 979 m a g for both males and females. For the 

purposes of this risk assessment, the lower male-specific value of 870 mg/kg was used. 

29
As with the mammalian acute toxicity data, the mammalian chronic toxicity data are obtained 

from the Agency's Health Effects Division (HED) and are considered representative of wild 

mammals. These studies provide adequate toxicity data on the potential effects of chronic 

quizalofop-p-ethyl exposure in mammals. In rats, the No Observable Adverse Effect Level 

(NOAEL) was 5mgkg/day for a decreased in male and female pup body weight, which 

corresponds to approximately to a dietary level of 100 ppm (mg a.i.kg feed). It should also be 

noted that the male adults and some male pups experienced testicular atrophy. In females signs 

of uterus atrophy were noticeable in the adults and the offspring. . 

 (3) Terrestrial Invertebrates 

 

Acute toxicity of quizalofop-ethyl to terrestrial non-targeted beneficial insects was assessed 

where honey bees, Apis millifera, were exposed to quizalofop-ethyl via acute contact route. The 

acute contact LD50 value was 50ug/bee which classifies quizalofop-ethyl as practically non-toxic 

to non-targeted beneficial terrestrial insects on an acute contact toxicity basis. The study was 

classified as acceptable (MRID 150942). 

 (4) Terrestrial Plants 

 At this time EFED is requesting that the registrant re-submit terrestrial plant toxicity tests 

(e.g., Seedling Emergence and Vegetative Vigor Tests) with the typical-end-use product of 

quizalofop-p-ethyl. Previously submitted terrestrial plant studies were deemed unacceptable by 

EFED biological reviewers. 

 The measures of effects will either be the results of actual tests or will be derived or assumed 

based on other data. Where data is lacking and extrapolated effects endpoints cannot be reliably 

estimated, risk will be presumed unless data is submitted. In cases where risk is presumed, but 

cannot be quantified based on lack of data, conservative assumptions will be made, and some 

analyses will not be able to be conducted. 

Assessment endpoints and toxicity data used to evaluate the assessment endpoints are identified 

in Table 3 and Table 4. 

30
 

Table 3. Summary of terrestrial assessment endpoints and proposed measures 

of effects for the screening level risk assessment of quizalofop-ethyl and 

quizalofop-p-ethyl. All studies are conducted on quizalofop-ethyl unless 

otherwise indicated 

Assessment Endpoint Measurement Endpoint 

Avian Survival Northern bobwhite quail Colinus virginianus LD50 > 

2000mg/kg bw 

Mallard duck Anas platyrhynchos LD50 > 2000 mg/kg BW 

Avian Reproduction and/or 

Survival*** 

Northern bobwhite quail (Colinus virginianus) 

NOAEC 1000 mg/kg diet 

Mallard duck (Anas platyrhynchos) 

NOAEC 500 mg/kg diet 

Mammalian Survival Laboratory rat 

Rattus rattus 870 mg/kg-bw 

Mammalian Reproduction and/or 

Survival 

Laboratory rat 

Rattus rattus NOAEC 100 mg/kg/diet 

 NOAEL 5 mg/kg/day 

Terrestrial Plants Survival and 

Growth*** 

Seedling emergence and vegetative vigor 

submitted studies were classified as unacceptable based on 

errors in toxicity determination and plant testing based on 

technical grade active ingredient (TGAI) instead of typical 

end use (TEP). These studies were conducted on 

quizalofop-p-ethyl. No quizalofop-ethyl seedling 

emergence and vegetative vigor studies were submitted. 

Non-target Beneficial Insect Survival Honey bee (acute contact) 

Apis meliferus 50 μg a.i./L 

 

31
Table 4. Summary of aquatic assessment endpoints and proposed measures of 

effects for the screening level risk assessment of quizalofop-ethyl and quizalofop-pethyl. All studies are conducted on quizalofop-ethyl unless otherwise indicated 

Assessment Endpoint Measurement Endpoint 

Freshwater Fish Survival Rainbow trout (Oncorhynchus mykiss) 

 LC50 870 ppb 

Bluegill sunfish (Lepomis macrochirus) 

LC50 460 ppb 

Freshwater Fish Reproduction 

an/or Survival Rainbow trout (Oncorhynchus mykiss) 

NOAEC 11 ppb 

Freshwater Invertebrate Survival Water flea (Daphnia magna) 

 EC50 3900* 

Freshwater Invertebrate 

Reproduction and/or Survival 

NOAECs will be estimated in future assessments based on ACRs, 

pending submission of a chronic estuarine marine invertebrate 

(mysid) toxicity study conducted on quizalofop-p-ethyl. 

Marine/Estuarine Fish Survival Sheepshead minnow (Cyprinodon variegatus) EC50 1400 ppb 

Marine/Estuarine Fish 

Reproduction and/or Survival 

 Chronic NOAEC 33ppb** 

Marine/Estuarine Invertebrate 

Survival 

Eastern oyster 

Crassostrea virginica EC50 187 ppb 

Mysid shrimp 

Americamysis bahia EC50 250 ppb* 

Marine/Estuarine Invertebrate 

Reproduction and/or Survival 

 Request submission of a chronic estuarine marine invertebrate 

(mysid) toxicity study conducted on quizalofop-p-ethyl. 

Aquatic Vascular and Non-vascular 

Plant Survival and Growth*** 

Tier I aquatic vascular plant (Lemna gibba) EC50>82.8 ppb 

Tier I aquatic vascular plant (Lemna gibba) NOAEC 82.8 ppb will be 

used in future risk assessments 

Tier I non-vascular plant (Selanastrum capricornutum) EC50>1770 

ppb 

* The most sensitive EC50 values for endpoints were not used to calculate RQs and will be reviewed for future risk 

assessments. Mysid shrimp, EC50 150 ppb and acute freshwater invertebrate EC50 2120 ppb 

** ( 2005 risk assessment calculated incorrectly as 513.3 ) 

*** Studies conducted on quizalofop-p-ethyl

32
11.3. Preliminary Identification of Data Gaps for Fate and Ecological Assessment 

Table 5 below, identifies fate and ecological studies, which are missing or are not acceptable, 

and may be requested to assess risk to the environment: 

Table 5. Preliminary Identification of Data Gaps for Fate and Ecological Assessment* 

Fate and Ecological 

Taxa studies 

Description of study Projected status of data 

gap 

Basis for decision 

Estuarine/marine fish Chronic study for 

estuarine/marine fish was not 

submitted 

Study not requested Acute to chronic ratios will be 

sufficient to not request study 

 

Chronic freshwater and estuarine 

marine invertebrate studies 

Chronic toxicity data to 

freshwater and estuarine marine 

invertebrate studies were not 

submitted 

Study requested for chronic 

estuarine marine invertebrate 

(mysid) conducted on quizalofopp-ethyl. No study is requested for 

chronic freshwater invertebrate 

Since no chronic invertebrate 

studies were submitted and 

chronic invertebrate 

exceedences may occur with 

estuarine marine invertebrates at 

higher application rates 

(pineapple and ornamental turf), 

a chronic estuarine marine 

invertebrate study is requested. 

ACRs will be sufficient to 

evaluate chronic freshwater 

invertebrates from receipt of 

the chronic estuarine marine 

invertebrate study. 

Seedling Emergence and 

Vegetative Vigor Terrestrial Plant 

studies 

Studies submitted for terrestrial 

plants based on quizalofop-pethyl were determined 

unacceptable due errors in 

toxicity determination and the 

use of TGAI instead of TEP 

formulation. 

Additional studies requested Seedling Emergence and 

Vegetative Vigor Terrestrial 

Plant studies conducted on 

quizalofop-p-ethyl are necessary 

to determine risks to terrestrial 

plants and buffers from spray 

drift. 

Existing fate and eco-toxicity 

data on the degradate (quizalofop 

acid) to determine risks to aquatic 

organisms 

Existing fate studies and 

ecotoxicity data were not 

submitted on the degradate 

(quizalofop acid) 

Existing fate and eco-toxicty data 

from the registrant are not 

requested for the degradate at this 

time. 

The parent quizalofop-p-ethyl 

can be easily converted to 

quizalofop acid. Additional 

ecotoxicity data such as; 

sediment toxicity studies are not 

requested for the degradate at 

this time unless additional fate 

and ecotoxicity data indicate an 

increased toxicity exposure to 

aquatic organisms. 

 

 

33
Non-vascular plant study 

(Selanastrum capricornutum) 

Maximum growth inhibition 

observed was 19% from a tier I 

study and a NOAEC could not be 

determined 

Additional study not requested Since a maximum growth 

inhibition observed was 19% 

from a tier I study and a NOAEC 

a Tier II test would quanitify 

risks. However, EFED will 

quantify risks to listed species 

through estimated values and 

analog data. 

Foliar dissipation residue data Foliar dissipation data studies or 

related data were not available 

 Study not requested Chronic mammal exceedences 

will still occur with current 

NOAEC 100 mg/kg diet 

endpoint even if the halflife is 1 

day. Therefore,A default foliar 

dissipation rate of 35 days will 

be used in the modeling in place 

of the data if study is not 

submitted. 

*The fate and transport database for quizalofop-p-ethyl is complete. 

 

 12. OPEN LITERATURE 

Previous assessments did not include open literature data as identified by ORD, MED ECOTOX 

literature search program. 

13. NEW ASSESSMENT DECISION 

EFED needs additional data (or will apply alternate effects assumptions) and would need to 

conduct new assessments for all registered outdoor uses. The new assessments are needed 

because of the following: 

(a) Not all toxicity data were available for the 2005 assessment. 

These data include: chronic study in estuarine/marine fish (72-4c), chronic life cycle 

toxicity studies in invertebrates (72-4b, 72-4d), seedling emergence and vegetative vigor 

for terrestrial plants (122-1/123-1) and aquatic toxicity data for the quizolofop acid 

degradate. 

(b) Currently used models were not included in all risk assessments. 

(c) Aquatic assessments were performed on “old” scenarios and models. New assessments 

are required to accurately assess toxic effects to aquatic. 

(d) Some uses and application type scenarios were not assessed for ecological risk or 

 did not include current terrestrial or aquatic models. 

These scenarios include Non-Food/Non-feed uses (alfalfa, beets, carrot ( including tops), 

swiss chard, grasses grown for seed, cottonwood/poplar plantations, non-agricultural 

uncultivated areas/soils, onion, ornamental trees, shade trees, radish, spinach and for 

Food and Feed uses (agricultural fallow/idleland, succulent and dried beans, snap beans, 

34
chinese cabbage, canola, eucalyptus, rape, cotton, crambe, garlic, lentils, mint, 

peppermint and spearmint, dried and succulent peas, pineapple, soybeans, sugarbeets 

including tops. 

 

(e) Open literature data, as identified by ORD, MED ECOTOX literature search program, 

were not included in previous assessments. 

 

 (f) A Tier II drinking water assessment of surface water was performed based on Index 

 Reservoir settings (October 28, 2005, Section 3 New use registration request 

 for quizalofop-p-ethyl (TARGA TM) on sunflowers, flax, wheat and barley (DP 310868) 

 with the highest seasonal application rates of 0.1925 and 0.20625 lb ai/A. The 

simulation produced estimated drinking water concentrations (EDWC) of 5.25 ppb for 

acute exposure, 1.99 ppb for chronic exposure, and 1.34 ppb for cancer exposure. For 

ground water sources, the Tier I drinking water predicted EDWC of 0.15 ppb for both 

acute and chronic exposure. For this drinking water exposure purpose, the assessment is 

focused on the specific label uses. 

All crop uses for quizalofop-p-ethyl according to the TARGA label are tabulated below 

based on 2005 drinking water exposure assessment. 

 

Use Modeling Scenario Seasonal Rate Application Scheme 

Mint OR 0.20625 (lb/ac) 2 applications 

Dry Beans MI 0.1925 2 applications 

Sugarbeets MN 0.171875 2 applications 

Flax 0.165 2 applications 

Canola and Crambe ND 0.12375 2 applications 

Cotton CA, MS, NC 0.12375 2 applications 

Soybeans MS 0.12375 2 applications 

Sunflowers 0.12375 2 applications 

Lentils 0.09625 2 applications 

Dry and Succlent Peas 0.09625 2 applications 

Snap Beans OR 0.09625 2 applications 

Barleys 0.0825 1 application 

Wheat ND 0.0825 1 application 

If additional crop uses have higher seasonal application rates, a new drinking water 

assessment needs to be completed. 

14. SUMMARY OF RISK 

Summary of Risks Identified for Use on Sunflowers, Flax, Wheat and Barley (DP 310868)

Estimated LOC exceedences for are summarized in Table 6 below. The risk conclusions are 

based on previously conducted risk assessments and anticipated exceedences for maximum use 

rates. The most recent risk assessment conducted on sunflowers, flax, wheat and barley 

(D310868, 2005) employed the more current models used in the ecological risk assessment. The 

35
label maximum single application rates for sunflowers, flax, wheat and barley are as follows: (1) 

sunflowers with a maximum seasonal rate of 0.12 lb ai /acre; (2) flax with a maximum seasonal 

rate of 0.165 lb ai /acre; and (3) wheat and barley with a maximum seasonal rate of 0.08 lb ai 

acre. 

 The maximum use and application rate for quizalofop-p-ethyl is for pineapples, ornamental and/ 

or shade trees at 0.4125 lb ai/A (2 applications@ 0.2063 lb ai/A and 7 day intervals). The 7 day 

interval was applied because label information did not specify intervals between applications. 

Anticipated LOC exceedences from the above maximum use rate would be chronic mammal 

with RQs ranging from 1.72 to 8.18. Terrestrial plants can not be assessed due to lack of 

acceptable data, however exceedences are anticipated for all modeled scenarios due to the 

chemical properties and mode of action of quizalofop-p-ethyl. 

Aquatic EECs for the maximum application rates for labeled crops and PRZM/EXAMS 

scenarios need to be determined. However, chronic risks to estuarine marine invertebrates for 

quizalofop-p-ethyl are uncertain based on estimated values derived from the acute and chronic 

freshwater fish (rainbow trout). The RQ of 0.64 for chronic estuarine invertebrates derived from 

the estimated values for the 0.165 lb ai/A application scenario is close in value to the chronic 

LOC = 1.0 Table 7). Therefore, exceedences are anticipated for chronic risk to estuarine marine 

invertebrates with higher application rates. Since no chronic studies were submitted for chronic 

risks to either freshwater or estuarine marine invertebrates and uncertainty exists for possible 

LOC exceedences for chronic risks to estuarine marine invertebrates for higher application rate 

scenarios, a chronic study for estuarine marine invertebrate (mysid) study is requested. 

Table 6. LOC exceedences for quizalofop-p-ethyl from use on sunflowers, flax, wheat and barley.* 

Use Endpoint Birds Mamma

ls 

Terr. 

Plants 

Insects FW 

fish 

SW 

Fish 

FW 

Inverts 

SW 

Inverts 

Aquatic 

Plants 

Acute Not 

assesse

d 

sunflowers, 

flax, wheat 

and barley 

Reproductive 9

pineapple, Acute 9

ornamental 

and/ or 

shade trees 

Reproductive 9 9

• All risk conclusions are based on previously conducted risk assessments (D310868) Degradate toxicity was not 

 included 

9 Risk is anticipated to be > any of the Agency’s LOC 

 Blank cells indicate no LOC exceedences 

Aquatic Organisms 

Based on the Tier II (PRZM/EXAMS) modeling, the 2005 risk assessment on flax, sunflowers, 

barley and wheat showed no acute LOC exceedence for aquatic organisms. The highest 

modeled application rate scenario for the above crops was flax, which was based on 1 aerial 

application at a single rate of 0.165 lb ai/acre. Table 7 summarizes the quizalofop-p-ethyl EECs 

(2.57 μg a.i./L (peak), 2.33 μg a.i./L (21-day), 2.03 μg a.i./L (60-day)) and the toxicity data used 

in the assessment on flax. 

36
Endpoint selection for mysid shrimp and daphnia magna will be reviewed since the most 

sensitive endpoints were not selected for RQ calculation from the 2005 assessment. For acute 

toxicity to mysid shrimp the most sensitive endpoint EC50 150 ppb and for Daphnia magna the 

most sensitive endpoint was EC50 2120 ppb. The NOAEC for estuarine marine fish was 

calculated incorrectly as 513.3 ppb and would have to be determined based on the most sensitive 

endpoint selected. NOAECs were not determined for the Tier I vascular and non-vascular plants 

to address listed species concerns. Since no effects occurred at the single dose concentration 

value of 82.8 ppb for Lemna gibba, this value will be used as the NOAEC for vascular plants in 

future risk assessments. Although a 19% inhibition occurred based Selanstrum capricornutum 

(Tier I study), an additional study to determine a NOAEC value will not be requested at this time 

for non-vascular plants because estimated EECs would result in RQs which are below the LOC 

based on analog data. Many DERS are based on 1985-1988 statistical programs and outdated 

criteria, therefore these DERs will be reviewed and updated to current EPA standards. An 

Eastern oyster-larvae (bivalve) study was sited in earlier assessments as EC50 79 ppb (on Canola 

March 1997 and Mint February 1993). 

37
Table 7. Aquatic EECs and RQs for quizalofop-p-ethyl based on a single application of 

0.165 lb ai/acre per season (the max.(EECs) label application rate to flax). 

Taxa Toxicity EEC* RQ 

FW Fish Acute LC50: 460 ppb 2.57 ppb (peak EEC) RQ<LOC=(<0.01)

Chronic NOAEC: 11 ppb 2.03 ppb (60-day EEC) RQ<LOC=(<0.01)

FW Invertebrate Acute EC50: 3900 ppb*** 2.57 ppb RQ<LOC=(<0.01)

Chronic NOAEC ++ 

Estimated NOAEC value of 26.8 based 

on an acute EC50 value of 2120 ppb 

would result in RQ< LOC=0.09  

2.57 ppb N/A 

Acute EC50: >82.8 ppb 2.57 ppb 

RQ<LOC=(<0.02)

FW Vascular 

Aquatic Plants 

NOAEC: was not determined (Lemna 

gibba ) tier 1stud y . However, the 

NOAEC value of 82.8 ppb will be used 

in future risk assessments 

2.57 ppb N/A 

Acute EC50: (>1770ppb Selenastrum 

capricornutum ) 

2.57 ppb 

RQ<LOC=(<0.01) 

 Non-vascular 

Plants and Algae 

 NOAEC:not determined 2.57 ppb N/A 

Acute LC50 1400 ppb (Sheepshead 

minnow)

2.57 ppb 

RQ<LOC=(<0.01)

Estuarine/Marine 

Fish 

Chronic NOAEC 33ppb**  

( 2005 risk assessment calculated 

incorrectly as 513.3 ) 

2.03 ppb 

RQ<LOC=(<0.06) 

Estuarine/Marine Mysid shrimp, EC50: 250 ppb*** 2.57 ppb RQ<LOC=(<0.01) 

Invertebrates 

Chronic NOAEC: ++ 

Estimated NOAEC value of 3.6 based 

on an acute EC50 value of 150 ppb 

would result in RQ< LOC=0.64**** 

2.33 ppb (21-day EEC) N/A 

Estuarine/Marine Acute EC50: 187 ppb 2.57 ppb RQ<LOC=(<0.01)

Mollusc 

*Derived for one application of 0.165lb a.i./acre aerial application (flax) 

** Chronic NOAEC derived using acute to chronic ratio due to lack of submitted data. 

*** The most sensitive EC50 values for endpoints were not used to calculate RQs and will be reviewed for future 

risk assessments. Mysid shrimp, EC50 150 ppb and acute freshwater invertebrate EC50 2120 ppb 

**** Estimated values were derived from quizalofop-ethyl acute and chronic freshwater fish (rainbow trout) 

studies 

++ Data not available

There are insufficient data to establish a definitive toxicity endpoint for estuarine marine and 

freshwater invertebrate chronic effects for quizalofop-ethyl. To estimate potential chronic 

estuarine marine and freshwater invertebrate endpoints for quizalofop-ethyl the relationship 

between established acute and chronic freshwater fish (rainbow trout) endpoints for quizalofopethyl were considered. A ratio was determined between the acute and chronic freshwater fish 

38
endpoints used for RQ calculation from quizalofop (870 ppb acute freshwater fish (rainbow 

trout)/ 11 ppb chronic freshwater fish (rainbow trout) =79). The largest ratio between acute 

endpoint and chronic endpoint was applied to the most sensitive quizalofop acute estuarine 

marine and freshwater invertebrate value to derive estimated chronic endpoints as described in 

Table 8. 

Table 8 Summary of Calculations for Estimated Endpoints 

ENDPOINT 

DESIRED For 

Quizalofop-p-ethyl 

Acute/Chronic 

Quizalofop-ethyl =ratio 

Acute Endpoint 

quizalofop/ratio= 

endpoint Estimated Endpoint 

Chronic freshwater 

invertebrate daphnia( 

endpoint in section 3)*

870 ppb/11 ppb=79 rainbow 

trout 2120 ppb/79=26.8 ppb 

NOAEC 

26.8 ppb 

Chronic estuarine marine 

invertebrate mysid( 

endpoint in section 3**) 

870 ppb/11 ppb=79 rainbow 

trout 150 ppb/79=1.8 ppb 

NOAEC 

1.8 ppb 

*Chronic freshwater invertebrate daphnia: 2.57 ppb/NOAEC 26.8 ppb= RQ 0.09 for 0.165 lb ai/acre 

**Chronic estuarine marine invertebrate mysid: 2.57ppb/NOAEC 1.8 ppb= RQ 1.4 for 0.165 lb ai/ acre 

Terrestrial Organisms 

 

No acute or chronic exceedences occurred for birds from the 2005 assessment for sunflowers, 

flax, barley and wheat. Also, no acute or chronic exceedences will occur for birds based on the 

proposed highest maximum seasonal rate of 0.4125 lb a.i./A (2 applications @ 0.2063 lb ai/A 

and 7 day intervals) and the non-definitive LD50 bw (>2000 ppm) and LC50 (>5000 ppm) diet. 

Acute RQs were not calculated for birds from uses on sunflowers, flax, barley and wheat.. 

However, because the LD50 bw (>2000 ppm) and LC50 (>5000 ppm) diet were greater than the 

highest dosage administered for bobwhite quail, quizalofop was characterized as practically nontoxic to birds. 

Based on provisional review of two avian chronic reproductive toxicity studies using quizalofopp-ethyl, it appears that quizalofop-p-ethyl does not pose potential reproductive inhibition to birds 

based on a chronic toxicity basis. 

Chronic RQs ranged from <0.01- 0.08 from the NOAEC 500 mg/kg-diet value and <0.01-0.04 

NOAEC 1000 mg/kg-diet value from uses on sunflowers, flax, barley and wheat. 

Table 9. Avian dietary based chronic RQ values based on a bobwhite quail NOAEC=1000 and a 

mallard duck NOAEC= 500 mg/kg for 0.12, 0.17 and 0.08lb ai/A application scenarios derived 

from the 2005 risk assessment. 

39
Table 9. Avian dietary-based chronic RQ values for proposed uses of Quizalofop-p-ethyl 

based on upper-bound Kenaga residues. (Bobwhite Quail NOAEC=1000; and Mallard 

duck NOAEC= 500 mg/kg)

Use/App. 

Method

Application Rate lbs. ai/A 

(# app / interval, days) Food Items

Upper Bound EEC 

(mg/kg)a

Chronic RQ 

(EEC/ NOAEC)

Short grass 28.80 0.061

0.032

Tall grass 13.20 0.031

0.012

Broadleaf plants/small insects 16.20 0.031

0.022

Sunflower 0.12/ 1 application 

Fruits, pods, seeds, and large 

insects 

1.80 <<0.011

<<0.012

Short grass 40.80 0.081

0.042

Tall grass 18.70 0.041

0.022

Broadleaf plants/small insects 22.95 0.051

0.022

Flax 0.17/ 1 application 

Fruits, pods, seeds, and large 

insects 

2.55 0.011

<0.012

Short grass 19.20 0.041

0.022

Tall grass 8.80 0.021

0.012

Broadleaf plants/small insects 10.80 0.021

<0.012

Barley/Wheat 0.08/ 1 application 

Fruits, pods, seeds, and large 

insects 

1.20 <0.011

<0.012

1

. The mallard duck NOAEC of 500 mg/kg/diet was used in estimating chronic RQs

2

. The bobwhite quail NOAEC of 1000 mg/kg/diet was used in estimating chronic RQs 

 No acute LOC exceedences occurred for 15g, 35g and 1000g mammals that consume short 

grass, tall grass, broadleaf plants/small insects, fruits pods large insects and seeds for all modeled 

scenarios (2005 assessment) Table 10. No acute LOC exceedences will occur for mammals 

based on the proposed highest maximum seasonal rate of 0.4125 lb ai/A (2 applications@ 0.2063 

40
lb ai/A and 7 day intervals). 

Chronic LOCs were exceeded for 15 g and 35 g mammals that consume short grass, tall grass, 

broadleaf plants/small insects and 1000 g mammals that consume short grass with chronic RQs 

ranging from 0.01 to 3.54 for upper-bound Kenaga residues (2005 assessment Table 11). The 

chronic RQs were also exceeded for the mean Kenaga values as shown in (2005 assessment) 

Table 12. It is therefore expected that higher application rate use scenarios will result in even 

greater chronic RQs exceedences for mammalian organisms. 

Therefore, chronic exceedences (dose based) will occur for mammals based on the proposed 

highest maximum seasonal rate of 0.4125 lb ai/A (2 applications@ 0.2063 lb ai/A and 7 day 

intervals) with RQs ranging from 0.05 to 8.8. 

Table 10. Mammalian dose-based acute RQ values for proposed uses of Quizalofopethyl based on a rat LD50 = 870 mg/kg-bw and upper-bound Kenaga values. 

Use/App. Mammalian Acute Risk Quotients (upper-bound Kenaga residues) 

Method

Application 

Rate lbs. a.i./A 

(# app / 

interval, days)

Body 

Weight, g Short 

Grass Tall Grass

Broadleaf 

Plants/Small 

Insects

Fruits/pods/ 

large insects

Seeds

15 0.01 0.01 0.01 <0.01 <0.01 

35 0.01 0.01 0.01 <0.01 <0.01 

Sunflower 0.12/ 1 

application 

1000 0.01 <0.01 <0.01 <0.01 <0.01 

15 0.02 0.01 0.01 <0.01 <0.01 

35 0.02 0.01 0.01 <0.01 <0.01 

Flax 0.17/ 1 

application 

1000 0.01 <<0.01 0.01 <0.01 <0.01 

15 0.01 <0.01 0.01 <0.01 <0.01 

35 0.01 <0.01 <0.01 <0.01 <0.01 

Barley and 

Wheat 

0.08/ 1 

application 

1000 <<0.01 <0.01 <0.01 <0.01 <0.01 

41
Table 11. Mammalian dose-based chronic RQ values for proposed uses of Quizalofop-pethyl based on a rat reproductive NOAEL of 5 mg/kg /day and upper-bound Kenaga 

residues. 

Use/App. Mammalian Chronic Risk Quotients (upper-bound Kenega values) 

Method

Application 

Rate lbs. a.i./A 

(# app / 

interval, days)

Body 

Weight, g Short 

Grass Tall Grass

Broadleaf 

Plants/Small 

Insects

Fruits/pods/ 

large insects

Seeds

15 2.50* 1.15* 1.41* 0.16 0.03 

35 2.13* 0.98 1.20* 0.13 0.04 

Sunflower 0.12/ 1 

application 

1000 1.14* 0.52 0.64 0.07 0.02 

15 3.54* 1.62* 1.99* 0.22 0.05 

35 3.02* 1.39* 1.70* 0.19 0.02 

Flax 0.17/ 1 

application 

1000 1.62* 0.74 0.91 0.10 0.02 

15 1.67* 0.76 0.94 0.10 0.02 

35 1.42* 0.65 0.80 0.09 0.023 

Barley and 

Wheat 

0.08/ 1 

application 

1000 0.76 0.35 0.43 0.05 0.01 

*exceeds the chronic risk LOC (RQ > 1.0) for non-listed and listed species. 

Table 12. Mammalian dose-based chronic RQ values for proposed uses of Quizalofopp-ethyl based on a rat reproductive NOAEL of 5 mg/kg /day and mean Kenaga residues. 

Use/App. Mammalian Chronic Risk Quotients (Mean Kenega values)

Method

Application 

Rate lbs. a.i./A 

(# app / 

interval, days)

Body 

Weight, g Short 

Grass Tall Grass

Broadleaf 

Plants/Small 

Insects

Fruits/pods/ 

large insects

Seeds

15 0.9 0.40 0.50 0.07 0.02 

35 0.80 0.30 0.40 0.06 0.01 

Sunflower 0.12 

1000 0.40 0.20 0.21 0.03 0.01 

15 1.30* 0.53 0.66 0.09 0.05 

35 1.07* 0.50 0.60 0.19 0.02 

Flax 0.17 

1000 0.60 0.24 0.30 0.05 0.01 

15 0.60 0.30 0.31 0.05 0.01 

35 0.50 0.21 0.30 0.04 0.01 

Barley and 

Wheat 

0.08/ 1 

application 

1000 0.30 0.11 0.14 0.02 <<0.01 

*exceeds the chronic risk LOC (RQ > 1.0) for non-listed and listed species. 

42
Seedling emergence and vegetative vigor studies were classified as unacceptable, therefore RQs 

were not calculated for terrestrial plants. 

15. RESIDUES OF QUIZALOFOP-P-ETHYL AND QUIZALOFOP ACID 

DEGRADATE IN WATER AND THE TERRESTRIAL ENVIRONMENT

The acceptable aerobic soil metabolism study shows that quizalofop-p-ethyl degrades 

microbially with a half-life of 1 day in sandy loam and silt loam soils. Degradation products are 

quizalofop acid, phenolic compounds, and CO2. Supplemental studies also show that 

quizalofop-p-ethyl is moderately mobile with Kads of 1.5-1.9 in sandy loam soil, and immobile in 

silt loam soil with Kads of 16-20. 

Existing data from the Environmental Fate and Effects Division (EFED) files show conflicting 

results between laboratory studies and field studies. The acceptable laboratory aerobic soil 

metabolism study shows that quizalofop-p-ethyl degrades microbially with a half-life of 1 day in 

sandy loam and silt loam soils. However, quizalofop-p-ethyl was persistent in the field with 

half-lives of 145 and 364 days for studies conducted in IL and CA, respectively. The laboratory 

studies indicate that dissipation occurs quickly via aerobic and anaerobic degradation, however, 

the field studies suggest that quizalofop-p-ethyl is persistent in the field. The differences may be 

due to differences of the microbial populations in the different soil media. 

 DRINKING WATER RESIDUE PROFILE

The Agency does not have monitoring data available to perform a quantitative drinking water 

risk assessment for quizalofop-P ethyl at this time. A Tier II drinking water assessment 

prepared by the Environmental Effects and Fate Division (EFED) is summarized below 

(D310868, J. Lin, 10/25/2005). 

Quizalofop ethyl is rapidly converted to quizalofop acid, which appears to be persistent. 

Likely residues of quizalofop ethyl and the quizalofop acid in surface drinking water were 

estimated using the PRZM -EXAMS to simulate pesticide transport as a result of runoff and 

erosion from agricultural fields. For evaluating ground water residues, a Tier I Screening 

Concentration In Ground Water (SCIGROW) model was used. Among the various uses, a 

scenario on dry beans at 0.1925 lb ai/A/season in the state of Michigan was used to predict the 

"worst case" estimate of drinking water concentration (EDWCs). The EDWCs obtained by 

these two models are summarized in Table 13. 

 Table 13. Drinking Water EDWCs for Quizalofop ethyl (ppb)

Model Used Acute Chronic Cancer 

PRZM/EXAMS 5.25 1.99 1.34 

SCIGROW 0.15 0.15 

43
New drinking and ground water assessments will be required due to proposed maximum 

seasonal application rates resulting in 0.4125 lb ai/A for ornamental trees, shade trees and 

pineapple. Chemical structures for quizalofop and fenoxaprop analogs are summarized in 

Table14. 

 Table 14. Chemical name and structure of quizalofop-p-ethyl and quizalofop-ethyl 

 Chemical structure of quizalofop acid, the degradate of concern, is not available. 

 Chemical name and structure of fenoxaprop -p-ethyl and fenoxaprop-ethyl 

 (analogs used to derive estimated toxicity values for non-vascular plants)

Common Name/Number Chemical Structure 

Quizalofop-p-ethyl

Quizalofop-ethyl 

 

 

Fenoxaprop-p-ethyl 

O

O

O

O

N

O

Cl

 

Fenoxaprop-p 

OH

O

O

O

N

O

Cl

44
The following test materials are listed as quizalofop-ethyl: 

INY 6202 

NC 302 

Lot 8002 

INY 6202-15 

NB 9083-86 

The following test materials are listed as quizalofop-p-ethyl: 

IN 79376 

DPX 79376

45

mice, and dogs. The risk assessments reflect current FQPA policies, address susceptibility of 

infants and children, the FQPA Safety Factor, and aggregate exposures. The current risk 

estimates are below Agency levels of concern for all population subgroups as a result of dietary 

exposures (inclusive of food and drinking water). These risk estimates are generally conservative 

and health-protective and should not underestimate exposure and risk. Residential exposures to 

quizalofop-ethyl and quizalofop-p-ethyl are not anticipated; there are no registered residential 

uses. Based on the combination of low hazard (via dermal and inhalation routes) and exposure 

potentials, HED determined that occupational risk assessments were not required. No new data 

are required. HED anticipates no revisions to the risk assessments for existing uses of 

quizalofop-ethyl and quizalofop-p-ethyl. 

Introduction. Quizalofop-ethyl (including its R-enantiomer, quizalofop-p-ethyl) is a systemic 

herbicide that is rapidly absorbed by treated foliage and translocated to the roots and other 

growing points of the plant. Affected plant tissues become necrotic/chlorotic and die leaving 

treated plants stunted and non-competitive. It controls annual and perennial grasses. It can be 

applied using ground boom equipment and by fixed wing aircraft as broadcast and banded 

applications. It has low application rates. 

Products containing quizalofop-ethyl and quizalofop-p-ethyl are currently registered. 

Quizalofop-ethyl is a 50/50 racemic mixture of R- and S-enantiomers. Quizalofop-p-ethyl is the 

purified R-enantiomer. The pesticidally active isomer is the R-enantiomer (quizalofop-p-ethyl). 

HED determined that the toxicological profile of the 50/50 racemic mixture (quizalofop-ethyl) 

and the R-enantiomer (quizalofop-p-ethyl) are similar, and that the currently available toxicity 

data on quizalofop-ethyl are adequate to support risk assessments reflecting uses of both 

quizalofop-ethyl and quizalofop-p-ethyl. 

Use Pattern and Exposure Potential. It is registered for use on a variety of food/feed use 

agricultural crops and non-agricultural crops. Food uses include: grains, legumes, cotton, garlic, 

mint, sugar beets, sunflower, pineapple, and Chinese cabbage. Several crops are grown for seed 

only, including: carrot, alfalfa, beets, Swiss chard, radish, onion, and spinach. Non-agricultural 

crops include: cottonwood and poplar plantations and uncultivated areas, such as fencerows and 

roadsides. No lawn, sidewalk, driveway, tennis court, or similar public areas have been 

registered as use sites. Based on its registered use patterns, there is the potential for dietary (via 

food and water) and occupational exposures to quizalofop-ethyl and quizalofop-p-ethyl. 

Homeowner exposures via residential uses are not expected. 

Hazard Characterization. Quizalofop-ethyl and quizalofop-p-ethyl are considered to be 

toxicologically similar. HED based this determination on a comparison of toxicity data submitted 

for the registration of quizalofop-ethyl and a subset of toxicity data for quizalofop-p-ethyl. 

Specifically, toxicity data available for quizalofop-p-ethyl included: an acute oral study in the 

rat, 90-day subchronic feeding studies in the rat and mouse, and three mutagenicity studies. 

Results from these studies were similar to results obtained from the same studies using 

47
quizalofop-ethyl. Conclusions regarding the toxicity of quizalofop-ethyl are applicable to 

quizalofop-p-ethyl. 

The toxicity database for quizalofop-ethyl was reviewed in 1994 and reevaluated in October 

1997 to specifically assess sensitivity in infants and children under FQPA. The toxicity database 

was found to be substantially complete and adequate to assess risk under FQPA. HED has 

determined that the currently available toxicity data on quizalofop-ethyl are adequate to support 

risk assessments reflecting uses of both quizalofop-ethyl and quizalofop-p-ethyl. No additional 

toxicity data for either quizalofop-ethyl or quizalofop-p-ethyl are required. No toxicity studies 

involving human subjects were relied upon in any of the risk assessments conducted for 

quizalofop-ethyl or quizalofop-p-ethyl. 

Toxicity endpoints selected for risk assessment in 1994 were confirmed in the 1997 reevaluation. 

The FQPA Safety Factor was reduced to 1X and the current risk assessments reflect this 

reduction. HED believes the FQPA Safety Factor reflected in the current risk assessment for 

quizalofop-ethyl is supported by the available toxicity and exposure information on quizalofopethyl and that the risk assessments are protective of human health. 

The toxicity database includes acceptable developmental studies in rats and rabbits, 

reproduction/fertility studies in rats, subchronic studies in rats and dogs, chronic studies in rats 

and dogs, carcinogenic studies in rats and mice, mutagenicity screens, and a 28-day dermal 

toxicity study in rats, as well as information on the metabolism and pharmacokinetics of 

quizalofop-ethyl. A search of the open literature was conducted for toxicity studies involving 

quizalofop-ethyl using NIH’s PubMed, SCRIUS, Science Direct, and a full text medical journals 

search. No in vivo toxicity testing studies or other information that would be relevant to HED’s 

human health risk assessments were found from 1995 to the present. NCEA’s IRIS shows no 

activity on quizalofop-ethyl since the late 1980s. No new toxicity data have been submitted. 

The liver is the primary target organ for repeated doses of quizalofop-ethyl. Effects on the liver 

manifested as increased liver weights and histological changes in the liver. Liver effects and 

decreases in body weight gain and food consumption as a result of repeat dosing were seen in 

subchronic and chronic/carcinogenicity studies in rats, mice, and dogs. Metabolism and excretion 

occur quickly in the rat. No toxic effects attributable to a single oral dose of quizalofop-ethyl 

were identified. 

It is classified in Toxicity Category III (low acute toxicity) for dermal, inhalation, eye and skin 

irritation. No localized or systemic effects were associated with a dermal dose of up to 2000 

mg/kg/day. As a result of this finding and a lack of developmental effects, no dermal toxicity 

endpoint was selected. In addition to quizalofop-ethyl’s classification as a Category IV 

inhalation toxicant, its use pattern indicates low single and seasonal maximum application rates, 

its vapor pressure is 1 x 10-4 kPa (meaning it is considered a non-volatile chemical for outdoor 

uses), and risk estimates (MOEs) for inhalation exposures are approximately 1000 or greater. As 

a result of these findings, no inhalation toxicity endpoint was selected. Based on the lack of 

dermal effects and negligible inhalation exposures, occupational risk assessments were neither 

required nor conducted. 

48
Quizalofop-ethyl does not appear to be a neurotoxic chemical; there were no signs of 

neurotoxicity in the available toxicity studies for quizalofop-ethyl. Specifically, treatmentrelated effects on brain weight or histopathology (non-perfused) of the nervous system were not 

observed in any study, there was no evidence of developmental anomalies in the nervous system 

of the fetus at maternal doses up to 300 mg/kg/day in rats and 60 mg/kg/day in rabbits, and there 

was no evidence of neurotoxicity on the functional development of offspring during the postnatal 

portion of the developmental toxicity study in rats. 

No special sensitivity was seen in rats and rabbits in utero as a result of exposure to quizalofopethyl. Exposure to quizalofop-ethyl at doses causing liver and body weight effects in adult 

animals did not lead to effects in fetuses. Exposure to quizalofop-ethyl at doses causing body 

weight effects in adult animals resulted in similar effects in offspring. As a result, the FQPA 

Safety Factor was reduced to 1X. 

Califrornia lists quizalofop-ethyl as a reproductive toxicant. Quizalofop-ethyl was first listed in 

1994 under California’s Proposition 65: the Safe Drinking Water and Toxics Enforcement Act 

and the Toxics Release Inventory (TRI). The listing was based on a 26-week feeding study in 

dogs conducted in 1982 in which 2 of 6 male dogs showed atrophy of some seminiferous tubules 

at the highest dose tested (10 mg/kg/day). The effect was not so severe as to cause disturbance of 

spermatogenesis. These effects could not be repeated in a follow-up study conducted over a 52-

week period in 1985 in which dogs were fed the same doses as in the 1982 study. There were no 

treatment-related effects in the follow-up study. 

Quizalofop-ethyl is currently classified as a “Group D “ carcinogen, i.e., not classifiable as to 

human carcinogenicity. 

Given the toxicological and chemical similarities between quizalofop-ethyl and the R-enantiomer 

(quizalofop-p-ethyl), the two compounds will be referred to as quizalofop in the remainder of 

this document. 

To assess risk associated with chronic dietary (oral) exposures to quizalofop, a chronic reference 

dose (cRfD) of 0.009 mg/kg/day has been established. The cRfD was selected from a combined 

chronic/carcinogenicity toxicity study in rats in which no effects were noted at 0.9 mg/kg/day 

and anemia and liver effects were noted at 4 mg/kg/day. The cRfD is based on the lowest and 

most conservative endpoint in the toxicity database. The cRfD reflects a 100-fold safety factor 

for inter- and intra-species variability. Because the FQPA safety factor was reduced to 1X, the 

chronic population adjusted dose (cPAD) is equivalent to the cRfD. The cRfD selected to assess 

risks from chronic dietary exposures to quizalofop is protective of the reproductive effects seen 

in 26-week study in the dog. Toxic endpoints for acute dietary and occupational risk assessments 

have not been selected for the reasons discussed above. 

Dietary Exposure and Risk Estimates. Dietary risk estimates for exposures to quizalofop in 

food and drinking water are below levels of concern. They reflect current policy and practice. 

The tolerance expression and residues of concern for risk assessment for registered uses need not 

be revised. The dietary risk assessments include all permanent tolerances (Section 3 

registrations). There are adequate residue data reflecting the use of all existing formulations on 

49
representative commodities; the dietary exposure database is complete. No new residue data 

have been submitted. There are no issues concerning residue chemistry and no new data are 

required. 

An acute dietary risk assessment was not conducted because no toxic endpoint attributable to a 

single oral dose was identified in the toxicity database. Chronic dietary risk for the general 

population was estimated to be 11% of the chronic Population Adjusted Dose (cPAD) and 29% 

of the cPAD for children 1 to 2 years old. Chronic dietary risk estimates are conservative and 

unrefined. They reflect tolerance level residues and 100% crop-treated values were assumed for 

all commodities. Drinking water exposures were assessed for a scenario for dry peas in Michigan 

using direct incorporation of estimated environmental concentrations (EECs) into the chronic 

dietary analyses. The drinking water assessment reflects current policy and practice. The current 

dietary risk assessments provide conservative, health protective, high-end estimates of exposure 

to quizalofop residues in food and water. The current dietary risk assessments are not expected to 

underestimate risks. 

Residential Exposure and Risk Estimates. Quizalofop-containing products are not registered 

for use in/on residential or public recreational sites; there are no registered lawn or garden uses. 

No residential risk assessments were conducted. 

Aggregate Risk Estimates. Risk estimates for aggregate exposures to quizalofop are below 

levels of concern. Average exposures in food and drinking water were combined and compared 

to the appropriate endpoint to estimate chronic aggregate risk. 

Occupational Exposure and Risk Estimates. As stated previously, occupational risk 

assessments are not required and have not been conducted for quizalofop. Quizalofop is not toxic 

via the dermal route; therefore, no dermal endpoint was selected. Quizalofop is a Category III 

Inhalation Toxicant indicating low toxicity by the inhalation route, it is not volatile, and it has 

low use rates. All of these factors indicate that use of quizalofop will not lead to inhalation 

exposures of concern. To support this qualitative assessment, HED has estimated risks from 

inhalation exposures for workers applying and handling quizalofop products for a number of 

high acreage crops using a screening-level analysis. This screening-level analysis uses 

maximum use rates, maximum acreage, and the cRfD to estimate inhalation risks. Risk estimates 

based on inhalation exposures of pesticide handlers (mixers, loaders, applicators) for barley, flax, 

sunflower, wheat, cotton, pineapple, and non-crop areas are all below HED’s level concern. The 

Margins of Exposure (MOEs) resulting from this screening assessment range from >500 to 

160,000 are not of concern as they are well above 100. In summary, based on quizalofop’s low 

toxicity via the dermal and inhalation routes, its physical/chemical properties, low exposure 

potential, and a screening-level analysis indicating that there are no inhalation exposures of 

concern, occupational risk assessments were not conducted. A 12-hour Restricted Reentry 

Interval (REI) has been established and is reflected on the labels of all registered products. 

Public Health and Incident Reports. Very few incidents of poisoning associated with 

exposures to quizalofop have been reported. This finding supports HED’s risk assessment, which 

indicates that both exposure to and toxicity of quizalofop are low. Since 1988 when it was first 

registered, a total of 18 reports of poisoning incidents have been reported. The Poison Control 

50
Center (PCC), reporting from 1993 to 2005, cites 10 incidents. All individuals affected were 

adults; the effects reported were headache, eye and throat irritation. OPP’s Incident Data System 

(IDS) reports 8 incidents. The incidents are associated with a variety of symptoms including 

rashes, cramping, swelling, diarrhea, nausea, dizziness, lethargy, and hypothermia. None of 

these effects is consistent with the toxicity database for quizalofop. Quizalofop is not an acutely 

toxic chemical, there is no indication of neurotoxicity, and the majority of toxic effects seen in 

the animal studies were systemic effects that were the result of repeated dosing, such as liver and 

body weight effects. The National Institutes of Occupational Safety and Health’s Sentinel Event 

Notification System (NIOSH SENSOR) reported 5899 cases of poisoning incidents between 

1998 and 2003. None of these reported incidents was associated with quizalofop. 

Cumulative Risk Assessments. The Agency has not determined whether quizalofop shares a 

common mechanism of toxicity with other chemical substances, and whether a cumulative 

assessment is warranted. The following reference contains information regarding determination 

of common mechanisms of toxicity: “Guidance for Identifying Pesticide Chemicals and Other 

Substances that have a Common Mechanism of Toxicity” (January 29, 1999). To date, the 

Agency has assessed the potential for a common mechanism of toxicity for four groups of 

chemicals: organophosphates, N-methyl carbamates, S-triazines, and chloroacetanilides. If 

quizalofop is determined to share a common mechanism of toxicity with other substances, then 

methods for aggregating exposures and risks will be developed. Until quizalofop is scheduled for 

a common mechanism determination and a decision is made, the Agency would not a priori

assume a common mechanism of toxicity exists for quizalofop and other substances. 

Data Requirements. No new data are required. 

Tolerances and International Harmonization. Permanent and time-limited tolerances for 

quizalofop from the most recent CFR are provided in the table below along with international 

tolerances. The Codex Alimentarius Commission has not established Maximum Residue Limits 

(MRLs) for residues of quizalofop in/on various raw agricultural and processed commodities. 

Canada and Mexico have established MRLs for quizalofop. US tolerances and MRLs on raw 

agricultural commodities from these countries do not appear to have been harmonized. However, 

meat, milk, poultry and egg tolerances with the exception of milk, fat have been harmonized 

between Canada and the US. The residue definitions appear to be the same for raw agricultural 

commodities, but slightly different for animal commodities.

51
Quizalofop 

US Canada Mexico Codex

Residue Definition: 

Combined residues of the herbicide quizalofop 

(2-[4-(6-chloroquinoxalin-2-yl 

oxy)phenoxy]propanoic acid) and quizalofop 

ethyl (ethyl-2-[4-(6-chloroquinoxalin-2-yl 

oxy)phenoxy]propanoate), all expressed as 

quizalofop ethyl 

40CFR.180.441 

ethyl (RS) 2-[4-(6-

chloroquinoxalin-2-yloxy) 

phenoxy] 

propionate, including the 

acid metabolites of 

(RS)2-[4-(6- 

chloroquinoxalin-2-yloxy) 

phenoxy] 

propanoic acid, all 

expressed as quizalofopethyl 

quizalofop none 

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg) 

Bean, dry 0.4 0.15 1

Bean, succulent 0.25 

Beet, sugar, roots 0.1 

Beet, sugar, tops 0.5 

Cowpea, forage 3.0 

Cowpea, hay 3.0 

Pea, dry 0.25 

Pea, field, hay 3.0 

Pea, field, vines 3.0 

Pea, succulent 0.3 0.05 

(dry or succulent not 

specified) 

Potato - 0.3 

Soybean flour 0.5 

Soybean, hulls 0.02 

Soybean, meal 0.5 

Soybean, soapstock 1.0 

Soybean 0.05 0.05 0.05 

Residue Definition: 

Combined residues of the herbicide 

quizalofop (2-[4-(6-chloroquinoxalin2-yl oxy)phenoxy]propanoic acid), 

quizalop-ethyl (ethyl-2-[4-(6-

chloroquinoxalin-2-yl 

oxy)phenoxy]propanoate), and 

quizalofop-methyl (methyl 2-[4-(6-

chloroquinoxalin-2-yloxy)phenoxy]propanoate, all 

expressed as quizalofop ethyl 

As above As above none 

Commodity Tolerance (ppm) 

/Maximum Residue Limit (mg/kg) 

0.05 0.05 

52
US Canada Mexico Codex

Cattle, meat 0.02 0.02 

Cattle, meat byproducts 0.05 0.05 

Egg 0.02 0.02 

Goat, fat 0.05 0.05 

Goat, meat 0.02 0.02 

Goat, meat byproducts 0.05 0.05 

Hog, fat 0.05 0.05 

Hog, meat 0.02 0.02 

Hog, meat byproducts 0.05 0.05 

Horse, fat 0.05 0.05 

Horse, meat 0.02 0.02 

Horse, meat byproducts 0.05 0.05 

Milk 0.01 0.01 

Milk, fat 0.25 0.05 

Poultry, fat 0.05 0.05 

Poultry, meat 0.02 0.02 

Poultry, meat byproducts 0.05 0.05 

Sheep, fat 0.05 0.05 

Sheep, meat 0.02 0.02 

Sheep, meat byproducts 0.05 0.05 

Residue Definition: 

Combined residues of the herbicide 

quizalofop-p ethyl ester [ethyl ( R )-(2-[4-

((6-chloroquinoxalin-2-

yl)oxy)phenoxy)propanoate], and its acid 

metabolite quizalofop-p [ R -(2-(4-((6-

quinoxalin-2-yl)oxy)phenoxy)propanoic 

acid], and the S enantiomers of both the 

ester and the acid, all expressed as 

quizalofop-p-ethyl ester

As above As above none 

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg) 

Barley, grain 0.05 

Barley, hay 0.05 

Barley, straw 0.05 

Beet, sugar, molasses 0.2 

Canola, meal 1.5 

Canola, seed 1.0 0.05 

Cotton, undelinted seed 0.1 0.05 

Flax, seed 0.05 0.05 

Lentil, seed 0.05 0.05 

Peppermint, tops 2.0 

Spearmint, tops 2.0 

Sunflower, seed 1.9 

Wheat, forage 0.05 

Wheat, grain 0.05 

Wheat, hay 0.05 

Wheat, straw 0.05 

53
US Canada Mexico Codex

Beet, sugar root (time limited 

06/14/1999) 

0.1 0.2 

(top or bottom not 

specified) 

Beet, sugar, tops (time limited 

06/14/1999) 

0.5 

Vegetable, foliage of legume, except 

soybean, subgroup 7A (time limited 

06/14/1999) 

3.0 

Vegetable, legume, group 6 (time 

limited 06/14/1999) 

0.25 

Pineapple (Regional registration) 0.1 

1

 Interim Marketing Authorization, including adzuki beans, dry beans, dry lima beans, kidney beans, mung beans, 

navy beans, and pinto beans. 

Considerations

In preparation of this problem formulation document for quizalofop-ethyl in support of 

registration review the following has been considered: 

• Search for and review of the most current human health risk assessments, including 

occupational/residential and dietary assessments conducted for new uses, Section 18 

Emergency Exemptions, and Special Local Needs (24Cs) using internal Lotus Notes 

databases 

• Review of the most recent decisions regarding hazard characterization, the adequacy and 

completeness of the toxicity database, the FQPA Safety Factor neurotoxicity, thyroid and 

immune system effects, and cancer issues to ensure their reflection in the most recent risk 

assessments 

• Search of the OPPIN database to identify data submitted that have not been reviewed or 

included in the most current risk assessments 

• Review E Jackets to clarify the status of a use 

• Review of the most current labels to ensure all current registrations have been included in 

the most recent risk assessments 

• Conduct a search of the general literature for information on quizalofop-ethyl not 

captured in current risk assessments 

• Review of labeled uses and use information from BEAD 

• Review of tolerances listed in Part 140 of the Code of Federal Regulations (CFR) Section 

180.441 

• Review of Codex Alimentarius and Canadian and Mexican MRLs to identify tolerance 

harmonization issues 

• Determine if most recent risk assessments reflect current policies 

• Review of poisoning incidents 

54
Reference Memoranda: 

Burnam, William, May 5, 1995, Accession No. 412-04-0141, Quizalofop-p Ethyl Ester’s Cancer 

Classification. 

Donald, J., Reproductive and Cancer Hazard Assessment Section (RCHAS), Office of 

Environmental Health hazard Assessment (OEHHA), California Environmental Protection 

Agency (CAL/EPA), September 1999, “Evidence on Developmental and Reproductive Toxicity 

of Quizalofop-Ethyl”, DRAFT. 

Hawkins, M., D342226, July 31, 2007, “Review of Quizalofop Incident Reports”. 

HED SOP 2002.01 Standard Operating Procedure – Waiver Criteria for Multiple-Exposure 

Inhalation Toxicity Studies. August 15, 2002. 

Johnson, H., D306061, August 2, 2004, “ARIA Risk Assessment: Quizalofop-ethyl Human 

Health Risk Assessment for Tolerance Renewal on Expired Tolerances”. 

Knizner, S., D236729 & D243535, February 25, 1998, “PP#5F4545 and PP#6E4652 Quizalofopp-ethyl: Petitions for Tolerances for Canola and Mint”. 

Oonnithan, S., D310869, August 10, 2006, “Quizalofop-p-ethyl: Human Health Risk Assessment 

for New Uses on Barley, Flax, Sunflower, and Wheat”. 

Oonnithan, S., D266205, August 10, 2006, Quizalofop-p-ethyl: “Occupational Risk Assessment 

for the Proposed Uses on Barley, Flax, Sunflower, and Wheat”. 

Personal communication (letter) from Robert J. Taylor, PM, Registration Division, OPP to Marie 

M. Chubb, du Pont de Nemours & Company RE: toxic profiles of quizalofop-ethyl and 

quizalofop-p-ethyl (undated). 

Quest, J., TXR 0052709, February 6, 1987, “Peer Review of Assure”. 

Rowland, J., TXR 012373, October 24, 1997, “Quizalofop-ethyl: Report of the Hazard 

Identification Assessment Review Committee (HIARC)”. 

55
IV. Glossary of Terms and Abbreviations 

ai Active Ingredient 

AR Anticipated Residue 

CFR Code of Federal Regulations 

cPAD Chronic Population Adjusted Dose 

CSF Confidential Statement of Formula 

CSFII USDA Continuing Surveys for Food Intake by Individuals 

DCI Data Call-In 

DEEM Dietary Exposure Evaluation Model 

DFR Dislodgeable Foliar Residue 

DNT Developmental Neurotoxicity 

DWLOC Drinking Water Level of Comparison 

EC Emulsifiable Concentrate Formulation 

EDWC Estimated Drinking Water Concentration 

EEC Estimated Environmental Concentration 

EPA Environmental Protection Agency 

EUP End-Use Product 

FDA Food and Drug Administration 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FFDCA Federal Food, Drug, and Cosmetic Act 

FQPA Food Quality Protection Act 

FOB Functional Observation Battery 

GENEEC Tier I Surface Water Computer Model 

IR Index Reservoir 

LC50 Median Lethal Concentration. A statistically derived concentration of a substance that 

can be expected to cause death in 50% of test animals. It is usually expressed as the 

weight of substance per weight or volume of water, air or feed, e.g., mg/l, mg/kg or ppm. 

LD50 Median Lethal Dose. A statistically derived single dose that can be expected to cause 

death in 50% of the test animals when administered by the route indicated (oral, dermal, 

inhalation). It is expressed as a weight of substance per unit weight of animal, e.g., 

mg/kg. 

LOC Level of Concern 

LOAEL Lowest Observed Adverse Effect Level 

μg/g Micrograms Per Gram 

μg/L Micrograms Per Liter 

mg/kg/day Milligram Per Kilogram Per Day 

mg/L Milligrams Per Liter 

MOE Margin of Exposure 

MRID Master Record Identification (number). EPA's system of recording and tracking 

submitted studies. 

MUP Manufacturing-Use Product 

NA Not Applicable 

NAWQA USGS National Ambient Water Quality Assessment 

NPDES National Pollutant Discharge Elimination System 

NR Not Required 

NOAEL No Observed Adverse Effect Level 

OPP EPA Office of Pesticide Programs 

OPPTS EPA Office of Prevention, Pesticides and Toxic Substances 

PAD Population Adjusted Dose 

PCA Percent Crop Area 

PDP USDA Pesticide Data Program 

PHED Pesticide Handler's Exposure Data 

PHI Preharvest Interval 

56
ppb Parts Per Billion 

PPE Personal Protective Equipment 

ppm Parts Per Million 

PRZM/EXAMS Tier II Surface Water Computer Model 

Q1* The Carcinogenic Potential of a Compound, Quantified by the EPA's Cancer Risk Model 

RAC Raw Agriculture Commodity 

RED Reregistration Eligibility Decision 

REI Restricted Entry Interval 

RfD Reference Dose 

RQ Risk Quotient 

SCI-GROW Tier I Ground Water Computer Model 

SAP Science Advisory Panel 

SF Safety Factor 

SLN Special Local Need (Registrations Under Section 24©) of FIFRA) 

TGAI Technical Grade Active Ingredient 

USDA United States Department of Agriculture 

UF Uncertainty Factor 

WPS Worker Protection Standard

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