Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND

 POLLUTION PREVENTION

MEMORANDUM

Date: 17-November-2011

SUBJECT: Quizalofop-P-ethyl. Petition for Registration of New Use on Corn (PP#1F7822)

and Sorghum Grain, and Rapeseed Subgroup 20A, Except Flaxseed (PP#0E7802). 

Summary of Analytical Chemistry and Residue Data.

PC Codes: 128711 (quizalofop-ethyl) and 128709 

(quizalofop-P-ethyl)

DP Barcode: 395630

Decision No.: 441518 and 443799 Registration No.: 352-541 and 352-542

Petition No.: 1F7822 and 0E7802 Regulatory Action: Tolerance Petition

Risk Assessment Type: N/A Case No.: NA

TXR No.: N/A CAS No.: 100646-51-3

MRID No.: See MRID Summary Table 40 CFR: §180.441

FROM: Ideliz Negrón-Encarnación, Ph.D., Chemist

 Risk Assessment Branch V (HED; 7509P)

 

THROUGH: William Donovan, Ph.D., Chemist

Michael Metzger, Branch Chief

Risk Assessment Branch V (HED; 7509P)

TO: Laura Nollen, Risk Manager

Risk Management Division (RM 5; 7508 P)

and

Mindy Ondish, Risk Manager 

Risk Management Division (RM 25; 7508P)

Note: This DER was originally prepared under contract by Versar, Inc. (6850 Versar Center, Springfield, VA 22151; submitted 

8/05/11). The DER has been reviewed by the Health Effects Division (HED) and revised to reflect current Office of Pesticide 

Programs (OPP) policies.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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MRID Summary Table

MRID No. Study Type Comments

48310101 860.1300 (field corn metabolism study) New DER; 48310101.der (860.1300)

48260704 860.1500 (corn field trials)

860.1520 (corn processing study)

New DER; 48260704.der1-quizalofop (860.1500)

New DER; 48260704.der2-quizalofop (860.1520)

48273601 860.1500 (sorghum field trials)

860.1520 (sorghum processing study)

New DER; 48273601.der1-quizalofop (860.1500)

New DER; 48273601.der2-quizalofop (860.1520)

Executive Summary

Quizalofop ethyl is a selective herbicide currently registered for the control of annual and 

perennial grasses on noncrop and on crop land areas. The technical quizalofop ethyl is a mixture 

of R- and S-enantiomers. The pesticide active isomer is the R-enantiomer (quizalofop-P-ethyl) 

which is the active ingredient (ai) in DuPontTM Assure®II herbicide (EPA Reg. No. 352-541). 

The 0.88 lb ai/gal emulsifiable concentrate (EC) formulation of DuPontTM Assure II®herbicide is 

registered to E.I. du Pont de Nemours and Company for use on canola, crambe, cotton, crops 

grown for seed, eucalyptus, dry beans (including Chickpea), dry and succulent peas, flax, hybrid 

poplar plantings, lentils, mint (spearmint and peppermint), pineapple, ryegrass grown for seed, 

snap beans, soybeans, sugar beets, sunflowers, and noncrop areas. This summary document 

covers two petitions, one for new uses in field corn (PP#1F7822) and the other for new uses in 

sorghum and the rapeseed subgroup 20A (PP#0E7802). 

E.I. du Pont de Nemours & Company (Dupont) is proposing to amend the label of Assure® II 

herbicide to include uses on herbicide-tolerant field corn containing the aryloxyalkanoate 

dioxygenase-1 gene (DAS-40278-9) and in propagation of corn seed containing DAS-40278-9. 

The proposed uses are postemergence applications to field and seed corn containing the 

quizalofop-resistant trait at a maximum seasonal rate of 0.083 lb ai/A. The proposed preharvest 

interval (PHI) is 30 days for forage; a PHI for corn grain or stover is not specified. Applications 

must include either a crop oil concentrate or a non-ionic surfactant. Dupont is applying for 

registration, but Dow Agrosciences LLC has provided the residue studies.

The Interregional Research Project No. 4 (IR-4) is proposing to amend the label of Assure® II 

herbicide to include uses on sorghum grain containing the DuPontTM INZENTM AII Herbicide 

Tolerance Trait and on rapeseed subgroup 20A, except flaxseed [borage, crambe, gold of 

pleasure (Camelina), cuphea, echium, hare’s ear mustard, lesquerella, lunaria, meadowfoam, 

milkweed, mustard seed, oil radish, poppy seed, rapeseed (canola), sesame, and sweet rocket]. 

The proposed uses are postemergence applications to sorghum at a maximum seasonal rate of 

0.138 lb ai/A, and postemergence applications to rapeseed subgroup 20A at a maximum seasonal 

rate of 0.124 lb ai/A. The proposed preharvest intervals (PHIs) are 30 days for sorghum forage, 

45 days for sorghum grain and stover, and 60 days for rapeseed subgroup 20A.

Under PP#1F7822, Dupont is proposing the establishment of permanent tolerances for combined 

residues of the herbicide quizalofop-P-ethyl (ethyl-2-[4-(6-chloroquinoxalin-2-yl

oxy)phenoxy]propanoate), including its metabolites and degradates in/on the following raw 

agricultural commodities:
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Corn, forage ................................................................0.01 ppm

Corn, grain ..................................................................0.01 ppm

Corn, stover.................................................................0.03 ppm

Under PP#0E7802, IR-4 is proposing the establishment of permanent tolerances for 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-ethyl(ethyl-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 in/on the following raw agricultural commodities:

Gold of Pleasure, seed...................................................1.0 ppm

Gold of Pleasure, meal..................................................1.5 ppm

Borage, seed..................................................................1.0 ppm

Crambe, seed.................................................................1.0 ppm

Crambe, meal ................................................................1.5 ppm

Cuphea, seed .................................................................1.0 ppm

Echium, seed.................................................................1.0 ppm

Hare’s ear mustard, seed...............................................1.0 ppm

Lesquerella, seed...........................................................1.0 ppm

Lunaria, seed.................................................................1.0 ppm

Meadowfoam, seed .......................................................1.0 ppm

Milkweed, seed ............................................................1.0 ppm

Mustard, seed ................................................................1.0 ppm

Oil Radish, seed ............................................................1.0 ppm

Poppy, seed ...................................................................1.0 ppm

Rapeseed .......................................................................1.0 ppm

Sesame, seed .................................................................1.0 ppm

Sweet Rocket, seed .......................................................1.0 ppm

Sorghum, grain..............................................................0.2 ppm

Sorghum, forage............................................................0.2 ppm

Sorghum, stover..........................................................0.35 ppm

Sorghum, aspirated grain ..............................................1.0 ppm

Under PP# 0E7802, IR-4 is also proposing to amend quizalofop ethyl tolerance expressions 

under 40 CFR part 180.441. Currently, tolerances for the combined residues of quizalofop ethyl 

and quizalofop, expressed as quizalofop ethyl, are established under §180.441(a)(1) in/on 

commodities including dry and succulent beans and peas, cowpea forage and hay, field pea vines 

and hay, soybean commodities, and sugar beet roots and tops; tolerance levels range from 0.02 

ppm for soybean hulls to 3.0 ppm for the forage/vines and hay of cowpea and field pea. Under 

§180.441(a)(2), tolerances for combined residues of quizalofop ethyl, quizalofop, and quizalofop 

methyl, expressed as quizalofop ethyl, have been established in eggs, milk, milk fat, and the fat, 

meat, and meat byproducts of cattle, goat, hog, horse, poultry, and sheep, at 0.01-0.25 ppm. 

Under §180.441(a)(3), tolerances for the combined residues of quizalofop-P-ethyl ester, acid 

metabolite quizalofop-P, and the S-enantiomers of the ester and the acid, expressed as 

quizalofop-P-ethyl ester, have been established in/on barley commodities, sugar beet molasses, 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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canola meal and seed, cotton seed, flaxseed, lentil seed, peppermint and spearmint tops, 

sunflower seed, and wheat commodities at 0.05-2.0 ppm. Time-limited tolerances which expired 

6/14/99 were established under §180.441(a)(4) for combined residues of quizalofop-P-ethyl

ester, acid metabolite quizalofop-P, and the S-enantiomers of the ester and the acid, expressed as 

quizalofop-P-ethyl ester, in/on sugar beet commodities, crop group 6, and crop subgroup 7A. A 

tolerance with regional registration has been established for combined residues of quizalofop-Pethyl ester, acid metabolite quizalofop-P, and the S-enantiomers of the ester and the acid, 

expressed as quizalofop-P-ethyl ester, in/on pineapple. 

The nature of residue in plants is adequately described in previously submitted plant metabolism 

studies with soybean, cotton, tomatoes, potatoes, and sugar beets. In addition, plant metabolism 

studies were submitted with this petition to describe the nature of residue in genetically modified 

corn containing the AAD-1 gene (Event 278). In the corn metabolism study, the parent 

quizalofop ethyl ester was not identified in forage and was not conclusively identified in fodder; 

however, radioactivity did elute in the region of quizalofop ethyl ester in fodder. Quizalofop 

acid accounted for 0.7% TRR in forage and 0.9-1.1% TRR in fodder. No other metabolites were 

identified. In forage and fodder, respectively, polar unknowns at 2.0-2.6 minutes were 9.8-

12.1% TRR and 2.1-13.8% TRR, polar unknowns at 2.6-3.0 minutes were 2.2-4.5% TRR and 

4.7-17.0% TRR, and unknowns eluting at 13.2-13.5 minutes were tracked ≤4.6% TRR and 

≤6.1% TRR. Characterization of nonextractable residues in fodder indicated that incorporation 

into pectin and lignin accounted for 1.3% and 5.8% TRR, respectively. Following acid detergent 

fiber (ADF) isolation/hydrolysis, remaining residues in fodder were characterized as 

hemicellulose or as cellulose, accounting for 1.7-3.7% TRR. Based on the results of the 

metabolism study with AAD-1 corn (Event 278), the petitioner proposed that the metabolism of 

quizalofop-P-ethyl ester proceeds from the ester to the acid, the active form. Metabolism 

continues through incorporation of the radiolabeled carbon into natural plant constituents, such 

as lignin and cellulose.

HED has determined that the residues of concern (ROC) in plant commodities are quizalofop-Pethyl, its acid metabolite quizalofop-P, and the S -enantiomers of both compounds, each 

expressed as quizalofop-P-ethyl. Overall, the metabolism studies indicate that quizalofop ethyl 

does not accumulate but is rapidly hydrolyzed at the ethyl ester to form the quizalofop acid. The 

acid then undergoes cleavage of the enol ether linkage between the phenyl and quinoxalinyl rings 

in the acid, and/or cleavage of the ether linkage between the isopropanoic group and the phenyl 

ring to form phenols. The phenols conjugate with plant sugars; some hydroxylation or further 

cleavage of the phenols occurs. Metabolism studies with soybeans demonstrated that the 

racemic mixture of quizalofop ethyl and the R-enantiomer, quizalofop-P-ethyl, have nearly

identical pathways.

The qualitative nature of the residue in livestock is adequately understood based on metabolism 

studies with goats and poultry. The studies indicated that quizalofop ethyl is metabolized in 

livestock via hydrolysis to quizalofop acid which then undergoes methylation to form quizalofop 

methyl ester. No phenols were detected in either goat or hen commodities, indicating that 

cleavage of the ether linkages of quizalofop does not occur. The ROC in livestock commodities 

are quizalofop ethyl, quizalofop-methyl, and quizalofop acid.
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HED previously concluded that the existing high performance liquid chromatography/ultra violet 

(HPLC/UV) method used for tolerance enforcement of soybean commodities (Method AMR153-83, Revision 3) or newer method LAN-1 would not be adequate for the enforcement of 

tolerances in/on barley, flax, sunflower, or wheat commodities. The petitioner did not include 

any validation data reflecting analysis of barley, flax, sunflower, or wheat commodities using the 

current enforcement method, and the extraction procedures of the methods used for data 

collection in the studies submitted with the previous petition differ significantly from the 

extraction procedures of the existing enforcement method. By translation the current 

enforcement method would not be adequate for the enforcement of tolerances in/on corn

commodities. However, the petitioner submitted an analytical method amendment report for the 

determination of residues in sunflower seed, meal and oil which is currently under review by 

HED and will be addressed in a separate residue chemistry chapter.

In conjunction with a previous petition (PP#0F6076; DP#266204, S. Oonnithan, 7/24/2006), 

HED concluded that sufficient data are available to support the use of the HPLC data-collection 

method, Morse Method Meth-147 (used for barley and wheat), for enforcement purposes, 

pending petition method validation (PMV). The method involves hydrolysis of samples with 

methanolic potassium hydroxide (KOH) to convert quizalofop-P-ethyl and quizalofop-P residues 

to 2-methoxy-6-chloroquinoxaline (MeCHQ). Residues of MeCHQ are partitioned into hexane, 

and the extract is cleaned up by gel permeation chromatography (GPC) prior to analysis by

HPLC using fluorescence detection. The validated limit of quantitation (LOQ) is 0.05 ppm for 

all matrices. The method was forwarded to the BEAD's Analytical Chemistry Branch (ACB) for 

PMV (DP#330973, S. Oonnithan, 7/24/2006); however, the PMV results are not available. 

Subsequently, Morse Method Meth-147 has been re-evaluated using “SOP for Reviewing 

Tolerance Methods”, SOP Number:ACB-019, which is the current procedure for determining if a 

method is suitable for tolerance enforcement. After reviewing Morse Method Meth-147 against 

the Tolerance Method Validation (TMV) Review Checklist, the analytical method data appear to 

satisfy the requirements, provided the solvent exchange modification made by the ILV

laboratory is incorporated into the final method. A TMV by ACB will not be necessary.

Adequate methods are available for the enforcement of tolerances in/on livestock commodities. 

HPLC/UV Method AMR-627-86 is available for the determination of residues of quizalofop 

ethyl, quizalofop acid, and quizalofop-methyl in livestock tissues, and HPLC/UV Method AMR515-86 (Revision A) is available for determination of residues of quizalofop ethyl, quizalofop 

acid, and quizalofop-methyl in milk. Methods AMR-627-86 and AMR-515-86 have undergone 

PMV and have been forwarded to FDA for publication in the Pesticide Analytical Manual 

(PAM) Volume II. In addition, HPLC/UV Methods AMR-846-87, AMR-845-87, and AMR623-86 are available for the determination of residues of quizalofop ethyl, quizalofop acid, and 

quizalofop-methyl in livestock fat, cream, and eggs, respectively. Methods AMR-846-87, AMR845-87, and AMR-623-86 have been forwarded to the FDA for publication in PAM Volume II as 

letter methods. 

Multiresidue method data for quizalofop ethyl are available; quizalofop ethyl is completely 

recovered using Multiresidue Methods Section 302 (Luke Method; Protocol D). No data are 

available pertaining to recovery of quizalofop acid or quizalofop-methyl using the multiresidue 

methods.
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The storage duration of the samples of the submitted crop field trial studies with sorghum are 

supported by adequate storage stability data of the residues of concern. However, storage 

stability data for quizalofop P-ethyl and quizalofop acid in/on field corn and processed 

commodities are not currently available. The petitioner indicated that a storage stability study is 

in progress. Storage stability data for quizalofop ethyl and quizalofop in/on various matrices, 

including cotton, soybean, and wheat commodities, have been submitted previously. The 

available wheat storage stability data are tentatively considered adequate to support submitted 

crop field trial on corn. Storage stability data were not provided for the corn processed 

commodities and are required to support the processing studies. When the storage stability study

on corn is submitted, the adequacy of the storage stability data will be re-evaluated.

Adequate ruminant and poultry feeding studies were submitted previously. These studies 

indicate that tolerances are needed for livestock commodities to support the current and proposed 

uses of quizalofop-P-ethyl. The maximum reasonable dietary burdens (MRDBs) of quizalofopP-ethyl to livestock have been re-calculated using the registered and proposed uses. Based on 

the calculated MRDBs, the established tolerances are adequate for all livestock commodities.

The submitted residue data for field corn commodities (forage, grain, and stover) are tentatively 

considered to be adequate, pending submission of storage stability data demonstrating the 

stability of quizalofop-P-ethyl and quizalofop acid in/on field corn forage, grain, and stover. The 

number and locations of crop field trials are in accordance with OCSPP Guideline 860.1500.

The field trials reflect the proposed use pattern. The maximum total quizalofop-P-ethyl residues 

[sum of quizalofop-P-ethyl and quizalofop acid residues (as parent equivalents)] were <0.02 ppm 

in/on forage and grain and <0.022 ppm in/on stover. Using the OECD MRL calculator, the 

recommended tolerances are 0.02, 0.02, and 0.03 ppm in/on corn forage, grain, and stover, 

respectively. The forage and grain recommendations are higher than the tolerance levels

proposed by the petitioner and the stover recommendation is identical to the tolerance level 

proposed by the petitioner.

Adequate processing data for corn have been submitted, pending submission of storage stability

data demonstrating the stability of quizalofop-P-ethyl and quizalofop acid in/on field corn 

processed commodities. Tolerances for the processed commodities of corn are not needed for 

the purpose of this petition based on the results of processing trials which showed that residues 

of quizalofop-P-ethyl and quizalofop acid (as parent equivalents) were <LOQ in/on field corn 

grain RAC (treatment at ~2x the proposed maximum seasonal rate), and in field corn processed 

commodities (starch, refined oil (wet and dry milling), meal, grits, flour, and AGF). The 

registrant explained that phytotoxicity concerns preclude corn processing studies at higher 

treatment rates.

The submitted residue data for sorghum commodities (forage, grain, and stover) are adequate to 

satisfy data requirements. The sorghum field trials reflected the maximum proposed application 

rates and the proposed PHIs. The maximum total quizalofop-P-ethyl residues [sum of 

quizalofop-P-ethyl and quizalofop acid residues (as parent equivalents)] were <0.180 ppm in/on 

forage, <0.158 ppm in/on grain, and <0.266 ppm in/on stover. Using the OECD MRL calculator, 

the recommended tolerances are 0.20, 0.20, and 0.30 ppm in/on sorghum forage, grain, and 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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stover, respectively. These recommendations are identical to the tolerance levels proposed by 

the petitioner for sorghum forage and grain. The tolerance level recommendation for sorghum 

stover is slightly lower than the level (0.35 ppm) proposed by the petitioner.

No residue data were submitted to support the proposed use on mustard seed and other members 

of the rapeseed subgroup 20A, except flaxseed. The available field trial data for canola seed, the 

representative crop of the rapeseed subgroup 20A, may be translated to support the proposed 

uses on mustard seed and other members of the rapeseed subgroup 20A, except flaxseed. These 

data are adequate to fulfill data requirements and reflect ~0.8-1.5x the maximum proposed 

seasonal application rate for the EC formulation with 38- to 74-day PHI. The data for 0.8x and 

1.5x was analyzed to recommend a tolerance that may support use of the 0.88 lb ai/gal EC 

formulation.

Adequate processing data for sorghum have been submitted. The processing data indicate that 

total quizalofop-P-ethyl residues concentrate in sorghum AGF. Based on the processing factor, 

3.4x, and the HAFT for sorghum grain, 0.149 ppm, expected residues in sorghum AGF 

following treatment at 1x would be 0.507 ppm. Because this value is greater than the 

recommended 0.2-ppm tolerance for sorghum grain, a tolerance is needed for total quizalofop-Pethyl residues in/on sorghum, grain, aspirated grain fractions. A tolerance of 1.0 ppm would be 

appropriate. 

No new processing data were submitted in support of the label amendment request to expand the 

use of quizalofop on rapeseed meal that would cover the rapeseed subgroup 20A, except 

flaxseed). Acceptable processing data were previously submitted and reviewed for canola seed, 

the representative crop of subgroup 20A, under PP# 5F4545/FAP# 6H5737 (DP#s 220476, 

220478, and 220480, F. Griffith, 2/21/96). Based on the available canola processing data, a 

tolerance for canola meal was established at 1.5 ppm; a tolerance was not required for refined oil. 

The canola processing data was used to recommend a tolerance for the rapeseed, meal of 2.0 

ppm by adjusting for the proposed application rate. 

The available confined/field rotational crop data indicate that a 120-day plant back interval (PBI) 

is required for all crops other than those with registered uses.

No Codex MRLs have been established for residues of quizalofop ethyl. Canadian MRLs have 

been established for residues of quizalofop ethyl and quizalofop in/on flax, oriental mustard 

seeds (condiment type and oil seed type), and rapeseeds (canola), the only crops included in the 

subject petition, at 0.05 ppm. No Mexican MRLs have been established for any of the requested 

crops. 
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Regulatory Recommendations and Residue Chemistry Deficiencies

HED has examined the residue chemistry database for quizalofop ethyl. Pending submission of 

the items requested below, there are no residue chemistry issues that would preclude granting 

registration for the proposed uses on corn, sorghum and rapeseed, subgroup 20A (except 

flaxseed) and the establishment of tolerances for combined residues of quizalofop-P-ethyl, 

quizalofop-P, and the S-enantiomers of these compounds, all expressed as quizalofop ethyl, as 

follows: 

Corn, forage ................................................................0.02 ppm

Corn, grain ..................................................................0.02 ppm

Corn, stover.................................................................0.03 ppm

Rapeseed, subgroup 20A, except flaxseed....................1.5 ppm

Rapeseed, subgroup 20A, meal, except flaxseed..........2.0 ppm

Sorghum, grain, grain .................................................0.20 ppm

Sorghum, forage..........................................................0.20 ppm

Sorghum, stover..........................................................0.30 ppm

Sorghum, grain, aspirated grain fractions.....................1.0 ppm

A human health risk assessment is forthcoming.

860.1200 Directions for Use

The following changes are recommended in the draft label of Assure®II herbicide: 

• The application rate on the supplemental label for field corn and sorghum is 

presented in terms of “oz product/A.” The label should be amended to read “fl. 

oz product/A”.

• The proposed grazing restrictions are impractical for field corn and sorghum and 

should be removed from the product label.

• The supplemental label for field corn should specify the PHI for corn grain and 

stover, and the concentration of either crop oil concentrate or nonionic surfactant.

These parameters should reflect those used in the crop field trials.

860.1340 Residue Analytical Methods

• After reviewing Morse Method Meth-147 against the Tolerance Method 

Validation (TMV) Review Checklist, provided the solvent exchange modification 

made by the ILV laboratory is incorporated into the final method, the analytical 

method data satisfy the requirements. A TMV by ACB will not be necessary.
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860.1380 Storage Stability

• Storage stability data for quizalofop P-ethyl and quizalofop acid in/on field corn 

and processed commodities are not currently available; the petitioner indicated 

that a storage stability study is in progress. The available wheat storage stability

data are tentatively considered adequate to support submitted crop field trial on 

corn. Storage stability data were not provided for the corn processed 

commodities and are required to support the processing studies. When the storage 

stability study on corn is submitted, the adequacy of the storage stability data will 

be re-evaluated.

860.1550 Proposed Tolerances

• The proposed tolerance level for corn forage and grain is 0.01 ppm. However, by 

using the OECD calculator the appropriate tolerance level for corn forage and 

grain is 0.02 ppm. A revised tolerance should be proposed.

• The petitioner proposed separate tolerances in/on the individual commodities of 

the rapeseed subgroup 20A, except flaxseed [borage seed, crambe seed, gold of 

pleasure seed, cuphea seed, echium seed, hare’s ear mustard seed, lesquerella 

seed, lunaria seed, meadowfoam seed, milkweed seed, mustard seed, oil radish 

seed, poppy seed, rapeseed, sesame seed, and sweet rocket seed] at 1.0 ppm. The 

recommended tolerance differs since the residues levels were scaled to reflect the 

proposed use pattern and a tolerance was estimated by using the OECD 

calculator. Therefore, for the proposed use pattern a subgroup tolerance in/on 

rapeseed subgroup 20A, except flaxseed should be proposed at 1.5 ppm. Also, a 

tolerance of 2.0 ppm is recommended for rapeseed, subgroup 20A, meal, except 

flaxseed.

• The proposed tolerance level for sorghum stover is 0.35 ppm. However, by using 

the OECD calculator the appropriate tolerance level for sorghum stover is 0.3 

ppm. A revised tolerance should be proposed. 

• The proposed tolerances should be revised to reflect the correct commodity 

definitions as specified Table 12.
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Background

Dupont has submitted a label amendment for Assure® II herbicide (EPA Reg. No. 352-541) to 

include uses on corn seed containing DAS-40278-9 and field corn containing DAS-40278-9. 

The Interregional Research Project No. 4 (IR-4) is proposing to amend the label of Assure® II 

herbicide to include uses on the rapeseed subgroup 20A, except flaxseed, and sorghum grain 

containing the DuPontTM INZENTM AII Herbicide Tolerance Trait (native trait). Assure®

herbicide contains quizalofop-P-ethyl as the sole ai, which is an R-enantiomer of quizalofop 

ethyl. Chemically, quizalofop ethyl is a racemic mixture containing R- and S-enantiomers and 

the former is the pesticide active component. Quizalofop ethyl is a selective preplant, pre- and 

postemergence herbicide registered for the control of annual and perennial grasses on noncrop 

and on crop land areas.

The chemical structure of quizalofop-P-ethyl and its major breakdown products are presented in 

Table 1 and its physicochemical properties are presented in Table 2.

Table 1. Quizalofop-P-ethyl Nomenclature.

Chemical structure

Common name Quizalofop-P-ethyl

IUPAC name ethyl (R)-2-[4-((6-chloroquinoxalin-2-yl)oxy)phenoxy]propanoate

CAS name (2R)-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid, ethyl ester

CAS registry number 100646-51-3

End-use product (EP) 0.88 lb ai/gal EC formulation (EPA Reg. No. 352-541)

Chemical structure of 

the R-enantiomer of 

quizalofop-P acid

(2R)-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid

Chemical structure of 

quizalofop-methyl

methyl 2-[4-(6-chloroquinoxalin-2-yl-oxy)phenoxy]propanoate

Chemical structure of 

the S-enantiomer of 

quizalofop ethyl

(2S)-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid, ethyl ester

N

Cl N

O

O

CH3

O

O

CH3

N

Cl N

O

O

CH3

OH

O

N

Cl N

O

O

CH3

O

O

CH3

N

Cl N

O

O

O

O

CH3

CH3
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Table 1. Quizalofop-P-ethyl Nomenclature.

Chemical structure of 

the S-enantiomer of 

quizalofop-P acid

(2S)-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid

Table 2. Physicochemical Properties of the Technical Grade Test Compound - Quizalofop-P-ethyl.

Parameter Value Reference

Melting point 76.0-77.0 C (pure form)

CB Nos. 5852 & 

5853, 3/29/90, W. 

Hazel

pH 6.6 (1% aqueous slurry)

Density 1.35 g/cm3

at 20 C (pure form)

Water solubility 0.4 ppm (20 C)

Solvent solubility Solvents

acetone

benzene

carbon disulfide

chloroform

cyclohexanone

dichloromethane

dimethyl sulfoxide

ethanol

n-hexane

methanol

tetrahydrofuran

toluene

xylene

g/L at 20 oC

650

680

660

1350

440

1970

200

22

5

22

1160

430

360

Vapor pressure 8.3 x 10-10 mm Hg (20 C)

Dissociation constant, pKa Not applicable

Octanol/water partition coefficient log POW = 4.66

UV/visible absorption spectrum Not available

860.1200 Directions for Use

The petitioner has submitted a draft specimen supplemental labeling for the 0.88 lb ai/gal EC 

formulation of quizalofop-P-ethyl (Assure® II Herbicide; EPA Reg. No. 352-541). Dupont is 

proposing a label amendment for this product to add new uses on field corn containing DAS40278-9 and propagation of corn seed containing DAS-40278-9. The currently registered EPA

label, dated 4/14/2010, was obtained from PPLS. The currently registered uses include canola, 

crambe, cotton, crops grown for seed, eucalyptus, dry beans (including Chickpea), dry and 

succulent peas, flax, hybrid poplar plantings, lentils, mint (spearmint and peppermint), pineapple, 

ryegrass grown for seed, snap beans, soybeans, sugar beets, sunflowers, and noncrop areas. The 

use patterns for the proposed new uses are presented in Table 3.

N

Cl N

O

O

OH

O

CH3
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 12 of 55

Table 3. Summary of Directions for Use of Quizalofop-P-ethyl Formulation.

1

Applic. Timing, 

Type, and Equip.

Form.

[EPA Reg. 

No.]

Applic. 

Rate 

(lb ai/A)

Max. No. 

Applic. 

per 

Season

Max. 

Seasonal 

Applic. Rate

(lb ai/A)

RTI 

(days)

PHI 

(days)

Use Directions and 

Limitations

Field Corn containing DAS-40278-9

Postemergence, 

Broadcast foliar

application by 

ground

0.88 lb

ai/gal EC

[352-541]

0.034-

0.083 2 0.083 NS2 30 (forage)3

For use in propagation of 

corn seed containing DAS40278-9 and quizalofoptolerant field corn 

containing DAS-40278-9. 

Applications may be made 

to emerged corn that is at 

the V2 through V6 stage of 

development. 

Applications must include 

either a crop oil 

concentrate or a non-ionic 

surfactant. Aerial 

application is prohibited.

The grazing of livestock 

on treated corn or 

harvesting forage within 

30 days of application is 

prohibited.

Sorghum, grain containing the DuPontTM INZENTM AII Herbicide Tolerance Trait

Postemergence, 

Broadcast 

application by 

ground or air

0.88 lb

ai/gal EC

[352-541]

0.034-

0.083 2 0.138 NS2

30 

(forage)4

45 (grain 

and 

stover)

Applications must include 

either a crop oil 

concentrate or a non-ionic 

surfactant.

Rapeseed Subgroup 20A, Except Flaxseed

[includes Borage, Crambe, Cuphea, Echium, Gold of Pleasure (Camelina), Hare’s ear mustard, Lesquerella, 

Lunaria, Meadowfoam, Milkweed, Mustard seed, Oil Radish, Poppy seed, Rapeseed (Canola), Sesame, and 

Sweet Rocket]

Postemergence, 

Broadcast 

application by 

ground or air

0.88 lb

ai/gal EC

[352-541]

NS NS 0.124 7 60

Applications must include 

either a crop oil 

concentrate or a non-ionic

surfactant.

1 General use directions, restrictions, and precautions were obtained from the currently registered label for Assure® 

II Herbicide (EPA Reg. No. 352-541), dated April 14, 2010

2 NS = Not specified

3 The supplemental labeling indicates that a 30-day PHI is proposed for forage; a PHI for corn grain or stover is not 

specified. The currently registered label indicates that the grazing of livestock in treated areas or feeding of forage, 

hay, or straw from the treated crops to livestock is prohibited. 

4 Under Section B, “The Amount, Frequency and Time of Application of Quizalofop-Ethyl Use in Sorghum Grain”, 

the petitioner indicates that forage may be harvested 30 (±2) days following one broadcast application; however, the 

supplemental labeling provided in Section B indicates that a 45-day PHI between grazing or feeding of treated grain, 

forage, fodder, straw, or hay to livestock must be maintained.

5 The Section 3 label describes the crop rotation restrictions as required.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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For field corn, applications are to be made using ground equipment, in a minimum of 10 gal/A in 

nonarid areas or 15 gal/A in arid areas. Aerial application or application through any type of 

irrigation system is prohibited. The grazing of livestock on treated corn or harvesting forage 

within 30 days of application is prohibited. Tank-mix applications may be made with broadleaf 

herbicides, insecticides, and fungicides. Tank mix products should be registered for use on the 

specific crop and the most restrictive label directions are to be followed. The label specifies a 

PBI of 120 days for crops not registered for treatment with quizalofop ethyl. The use of either 

crop oil concentrate or nonionic surfactant is recommended in the supplemental label but the 

concentration is not specified.

For sorghum, applications are to be made using ground equipment, in a minimum of 10 gal/A in 

nonarid areas or 15 gal/A in arid areas, or aerial equipment, in a minimum of 3 gal/A in nonarid 

areas or 5 gal/A in arid areas. Application through any type of irrigation system is prohibited. 

The grazing of livestock in treated areas or feeding of forage, hay, or straw from the treated

crops to livestock within 45 days of application is prohibited. Tank-mix applications may be 

made with broadleaf herbicides, insecticides, and fungicides. Tank mix products should be 

registered for use on the specific crop and the most restrictive label directions are to be followed. 

The label specifies a PBI of 120 days for crops not registered for treatment with quizalofop ethyl. 

A crop oil concentrate (1% v/v) is the preferred adjuvant recommended in the label but the

alternative use of a non ionic surfactant (0.25% v/v) is also permitted.

Conclusions. The proposed use patterns for the 0.88 lb ai/gal EC formulation (Assure® II 

Herbicide; EPA Reg. No. 352-541) are adequate to allow evaluation of the residue data 

submitted in support of this petition. The following label amendments are recommended for 

clarity and to conform to the field trial data submitted on the proposed crops.

1. The application rate on the supplemental label for field corn and sorghum is presented in 

terms of “oz product/A.” The label should be amended to read “fl. oz product/A”. 

2. The proposed grazing restrictions are impractical for field corn and sorghum and should 

be removed from the product label.

860.1300 Nature of the Residue – Plants

DER References: 48310101.der (AAD-1 field corn metabolism)

Residue Chemistry Memo DP#s 196041, 196043, 205430, 205432, 206200, 206201 and 212620-212622, F. 

Griffith, 3/30/1995; PP#3F4268

Residue Chemistry Memo DP# 182751, J. Stokes, 7/15/1993

Residue Chemistry Memo DP#s 160972 and 166083, J. Stokes, 3/4/1992; PP#1F3951

Residue Chemistry Memo DP# none, CB. No. 1127, M. Firestone, 9/25/1985; PP#5F3252

The qualitative nature of the residue in plants is adequately understood based on a previously 

submitted plant metabolism studies with soybean, cotton, tomatoes, potatoes, and sugar beets. 

The metabolism studies indicate that quizalofop ethyl does not accumulate but is rapidly

hydrolyzed at the ethyl ester to form quizalofop acid. The acid then undergoes cleavage of the 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 14 of 55

enol ether linkage between the phenyl and quinoxalinyl rings and/or cleavage of the ether linkage 

between the isopropanoic group and the phenyl ring to form phenols. Metabolism studies with 

soybeans demonstrated that the racemic mixture of quizalofop ethyl and the resolved Renantiomer, quizalofop-P-ethyl have nearly identical pathways (DP# 182751, J. Stokes, 7/15/93). 

The ROC in plant commodities are quizalofop-P-ethyl, quizalofop-P (acid metabolite), and Senantiomers of both the parent and acid, each expressed in terms of quizalofop-P-ethyl.

AAD-1 Field Corn

Dow AgroSciences submitted a study investigating the metabolism of [U14C-phenyl]-quizalofop 

ethyl ester (PH label; specific activity 25.5 mCi/mmol) and [14C]-quizalofop ethyl ester -

quinoxaline (QU label; specific activity 32.8 mCi/mmol) in quizalofop-tolerant field corn. The 

field corn seed used in the study was genetically modified AAD-1 corn (Event DAS-40278-9, 

also known as Event 278). The modification makes the corn resistant to both 2,4-D and “fop” 

grass herbicides including quizalofop and haloxyfop.

The radiolabeled test substance was formulated as an emulsifiable concentrate (EC) and applied 

to field-grown quizalofop-tolerant corn as a single broadcast foliar application at the V6 growth 

stage at a rate of 0.09 lb ai/A (101-104 g ai/ha). Samples of forage were harvested at a 

preharvest interval (PHI) of 48 days and samples of grain, cob, and fodder were harvested at a 

PHI of 72 days. The in-life phase of the study was conducted by Research For Hire (Porterville, 

CA), and the analytical phase of the study was conducted by ABC Laboratories (Columbia, 

MO).

Total radioactive residues (TRR) determined by combustion/LSC in PH-labeled and QU-labeled 

samples, respectively, were 0.007 and 0.122 ppm in forage, 0.004 and 0.005 ppm in grain, 0.002 

ppm in cobs (both labels), and 0.260 and 0.353 ppm in fodder. Due to the low TRR levels, 

samples of cob, grain, and PH-labeled forage were not further analyzed.

Extraction with ACN/water (replicates 1 & 2) or methanol/water (replicates 3 & 4) released the 

majority of the radioactivity from all replicate samples of forage and fodder: 50-52% TRR from 

forage (QU label) and 43-52% TRR from fodder (both labels). Subsequent extraction with 

methanol/10 N NaOH released an additional ~11-13% TRR from replicate 3 & 4 samples of 

forage (QU label) and fodder (both labels). Subsequent extraction with ACN/1 N HCL

(replicates 1 & 2) or 1 N HCl (replicates 3 & 4) released an additional 16-21% TRR from all 

replicate samples of forage (QU label) and 20-29% TRR from all replicate samples of fodder 

(both labels). Nonextractable residues in all replicates following these extraction procedures 

were 14-33% TRR in QU-labeled forage (0.017-0.041 ppm), 24-29% TRR (0.063-0.101 ppm) in 

fodder (both labels, replicates 1 & 2), and 11-15% TRR (0.029-0.052 ppm) in fodder (both 

labels, replicates 3 & 4). The nonextractable residues were not further analyzed, except for 

replicates 3 & 4 of QU-labeled fodder. The distribution of the nonextractable residues of QUlabeled fodder (replicates 3 & 4) into natural components including pectin, lignin, hemicellulose, 

and cellulose was investigated by a series of extraction/hydrolysis procedures. Nonextractable 

residues remaining following these procedures accounted for 0.8% TRR (0.003 ppm) in fodder 

(QU label). These procedures adequately extracted the majority of the residues from field corn 

matrices. Accountabilities were 93-102% for forage and fodder (replicates 1 & 2) and 89-102% 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 15 of 55

for forage and fodder (replicates 3 & 4).

Residues were identified and quantitated in corn forage and fodder by high performance liquid 

chromatography (HPLC) following purification of extracts by solid phase extraction (SPE). 

Initial HPLC analysis of extracts was completed within 2.0-2.1 months of harvest and final 

HPLC analysis of repeated extracts was completed within 6.1-6.9 months of harvest. Because 

quantitation of residues and initial residue identifications were completed within ~4-6 months of 

harvest, no storage stability data are required to support the study.

The parent, quizalofop ethyl ester, was not identified in forage (QU label, all replicates) and was 

not conclusively identified in fodder; however, radioactivity did elute in the region of quizalofop 

ethyl ester in fodder (both labels, replicates 3 & 4) at 0.4-1.4% TRR (0.001-0.004 ppm). 

Quizalofop acid accounted for 0.7% TRR (0.001 ppm) in forage (QU label, 1 & 2 replicates) and 

0.9-1.1% TRR (0.003 ppm) in fodder (both labels, replicates 3 & 4). No other metabolites were 

identified. Polar unknowns at 2.0-2.6 minutes were 9.8-12.1% TRR (0.012-0.015 ppm) in forage 

(QU label, all replicates) and 2.1-13.8% TRR (0.006-0.048 ppm) in fodder (both labels, all 

replicates). Polar unknowns at 2.6-3.0 minutes were 2.2-4.5% TRR (0.002-0.005 ppm) in forage 

(QU label, all replicates) and 4.7-17.0% TRR (0.017-0.043 ppm) in fodder (both labels, all 

replicates). Unknowns eluting at 13.2-13.5 minutes were tracked and accounted for ≤4.6% TRR 

in forage and ≤6.1% TRR in fodder.

Characterization of nonextractable residues indicated that incorporation into pectin and lignin 

accounted for 1.3% and 5.8% TRR, respectively, in fodder (QU label, 3 & 4 replicates). 

Following acid detergent fiber (ADF) isolation/hydrolysis, remaining residues in fodder were 

characterized as hemicellulose or as cellulose, accounting for 1.7-3.7% TRR.

The forage and fodder methanol/water extracts (replicates 3 & 4) were also subjected to acid 

hydrolysis procedures and analyzed by HPLC. Quizalofop acid accounted for 1.4% TRR (0.002 

ppm) in QU-labeled forage and 0.3% TRR (0.001 ppm) in PH-labeled fodder (replicates 3 & 4). 

The acid hydrolyzed methanol/water extract of forage and fodder contained multiple, polar, low 

level metabolites. Some of the nonpolar peaks in the methanol/water extract SPE eluents were 

not observed in the acid hydrolyzed samples; however, multiple peaks remained, including 

several polar components. The petitioner reported that no common moieties were formed via 

acid hydrolysis, which indicated that the multiple, low level components in the original extract 

were not related and not easily cleaved sugar conjugates.

Based on the results of the metabolism study with AAD-1 corn (Event 278), the petitioner 

proposed that the metabolism of quizalofop-P-ethyl ester proceeds from the ester to the acid, the 

active form. Metabolism continues through incorporation of the radiolabeled carbon into natural 

plant constituents, such as lignin and cellulose.

860.1300 Nature of the Residue - Livestock

Residue Chemistry Memo DP# none, CB Nos. 2806, 2810, & 2811, G. Otakie, 12/18/1987; PP#5F3252
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 16 of 55

The nature of the residue in livestock is adequately understood based on metabolism studies with 

goats and poultry. The studies indicate that quizalofop ethyl is metabolized in livestock via 

hydrolysis to quizalofop acid which then undergoes methylation to form quizalofop methyl ester. 

No phenols were detected in either the goat or hen matrices, indicating that cleavage of the ether 

linkages of quizalofop does not occur. In hens, quizalofop-P acid is utilized in fatty chain 

elongation to form quizalofop-pentanoic acid. The ROC in livestock commodities are 

quizalofop-P-ethyl, quizalofop-methyl, and quizalofop-P, each expressed in terms of quizalofopP-ethyl.

860.1340 Residue Analytical Methods – Plant Commodities

Residue Chemistry Memo DP# 266204, S. Oonnithan, 7/24/2006; PP# 0F6076

Residue Chemistry Memo DP# 330973, S. Oonnithan, 7/24/2006; PP# 0F6076 (PMV Request)

Residue Chemistry Memo DP# 219639, F. Griffith, 10/11/1995

Data Collection Method for Field Corn Commodities:

Samples from the submitted crop field trials and processing study on field corn were analyzed 

for residues of quizalofop-P-ethyl and quizalofop acid using an LC/MS/MS method detailed in 

the study.

Briefly, samples were extracted with methanol:water (90:10, v:v) and centrifuged. An aliquot of 

the extract was mixed with water:formic acid (99.9:0.1, v:v), filtered, and analyzed by on-line 

solid-phase extraction (SPE) and LC/MS/MS. The reported LOQ (determined as the lower limit 

of method validation) was 0.01 ppm, and the limit of detection (LOD) was 0.003 ppm for 

quizalofop-P-ethyl and quizalofop acid in all matrices.

The LC/MS/MS method used to analyze field corn samples from the submitted crop field trials 

and processing study for residues of quizalofop-P-ethyl and quizalofop acid is adequate for data 

collection based on acceptable concurrent method recovery data. Concurrent method recoveries 

were generally within the acceptable range of 70-120% from field corn grain, forage and stover

fortified with quizalofop-P-ethyl and quizalofop acid at 0.01-1.0 ppm, with the exception of 

quizalofop acid recoveries in corn stover at the 1.0 ppm fortification level which were above 

120% in the majority of the samples (117-138%) and a mean recovery of 127%. In processed 

commodities, concurrent method recoveries were also generally within the acceptable range of 

70-120%, with the exception of quizalofop acid recoveries in refined oil at both the 0.01 and 1.0 

ppm fortification levels which were above 120% in about half the samples (95-143%) and mean 

recoveries of 112% and 121%, respectively. Fortification levels were adequate to bracket 

residues found in treated samples.

Data Collection Method for Sorghum Commodities:

Samples from the submitted crop field trials and processing study on sorghum were analyzed for 

residues of quizalofop-P-ethyl and quizalofop acid using an LC/MS/MS method ("Working 

Method for Quizalofop P-Ethyl and Quizalofop Acid [Forage]) modified from the method in Du 

Pont Study No. AMR-1854-90.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 17 of 55

Briefly, samples were extracted twice with acetonitrile (ACN):1% acetic acid (3:1, v:v) and the 

combined extracts diluted to volume. An aliquot of the extract was concentrated then the pH 

adjusted to 5 with ammonium acetate. The extract was incubated with cellulase and βglucoidase and the pH adjusted to 3 with glacial acetic acid. Cleanup of the extract was done 

through a Strata-X solid-phase extraction (SPE) cartridge, followed by elution with methanol 

(quizalofop acid) and ACN (quizalofop-P-ethyl). The fractions were combined and diluted for 

analysis by LC/MS/MS.

The LLMV for quizalofop-P-ethyl and quizalofop acid was 0.05 ppm for sorghum forage, grain, 

stover, and AGF. The petitioner used the LLMV as the LOQ for reporting residue results. The 

LOD for quizalofop-P-ethyl was determined to be 0.0062, 0.0033, 0.0053, and 0.0068 ppm, 

respectively, in/on sorghum forage, grain, stover, and AGF, and the LOD for quizalofop acid 

was determined to be 0.0072, 0.0075, 0.0058, and 0.0058 ppm, respectively, in/on sorghum 

forage, grain, stover, and AGF.

The LC/MS/MS method used to analyze sorghum samples from the submitted crop field trials 

and processing study for residues of quizalofop-P-ethyl and quizalofop acid is adequate for data 

collection based on acceptable method validation and concurrent method recovery data. Method 

verification and concurrent method recoveries were within the acceptable range of 70-120% in 

sorghum forage, grain, and stover fortified with quizalofop-P-ethyl and quizalofop acid at 0.05-

0.5 ppm. Method verification and concurrent method recoveries were within the acceptable 

range of 70-120% from sorghum aspirated grain fractions (AGF) fortified with quizalofop-Pethyl at 0.5 and 1.0 ppm, and quizalofop acid at 0.05, 0.5 and 1.0 ppm. However, they were 

outside the acceptable range of 70-120% for quizalofop-P-ethyl at 0.05 ppm with mean 

recoveries of 59% and 66%. Fortification levels were adequate to bracket residues found in 

treated samples.

Enforcement methods:

DuPont Method AMR-153-83, Revision 3: In conjunction with a previous petition 

(PP#0F6076; DP#266204, S. Oonnithan, 7/24/2006), the petitioner proposed the existing 

enforcement method, “Determination of Residues of DPX-Y6202, DPX-Y6202 Acid, and DPXY6202 Acid Conjugates in Soybeans and Soybeans Fractions” (DuPont Method AMR-153-83, 

Revision 3, January 1987; MRID 40322410; PP# 5F3252, 12/18/87, G. Otakie), for the 

enforcement of tolerances for quizalofop-P-ethyl residues in/on barley, flax, sunflower, and 

wheat commodities. This method involves extraction of samples, other than oil, with acetone 

and water acidified with glacial acetic acid. Oil samples are mixed with hexane, and residues are 

extracted into acetonitrile. The extracts are adjusted to pH 5 using base or buffer and then a 

mixture of -glucosidase and cellulase enzymes are used to convert any quizalofop conjugates to 

quizalofop. Residues of quizalofop ethyl and quizalofop are then extracted from the aqueous 

phase using chloroform. Liquid chromatography is used to separate quizalofop from quizalofop 

ethyl, and quizalofop residues are methylated. Residues of quizalofop ethyl and quizalofopmethyl are determined by HPLC/UV. The LOQ is 0.05 ppm.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 18 of 55

This method has been validated by ACB and submitted to FDA for publication in PAM Vol. II; 

however, the method was accepted for the soybean tolerance only. ACB noted that the 

complexity of the method may require an analyst to perform several practice runs. It was 

concluded that additional methodology development work would be necessary if tolerances were 

proposed for other crops (PP# 3F3252, 6/27/88, G. Otakie). However, the petitioner submitted 

an analytical method amendment report (MRID 47910506) for the determination of residues in 

sunflower seed, meal and oil which is currently under review by HED and will be discussed in a 

separate residue chemistry chapter.

LAN-1: E.I. du Pont de Nemours has since submitted a different, less complex method, referred 

to as LAN-1. The method involves extraction of samples with acetonitrile/1% acetic acid, 

hydrolysis of extracts with a mixture of cellulase and -glucosidase, and further hydrolysis with 

esterase. Residues are partitioned into acetonitrile/dichloromethane, concentrated, and 

transferred into acetonitrile and phosphate buffer. After HPLC column cleanup, extracts are 

analyzed by HPLC/UV. The LOQ is 0.05 ppm (PP# 3F4268, F. Griffith, 3/30/95).

The LAN-1 method was forwarded to ACB for PMV; ACB examined the method and identified 

several deficiencies which needed addressing before the PMV is finalized (D219639, 10/11/95, 

F. Griffith). 

No validation data for the current enforcement method (AMR-153-83), or the newer method 

(LAN-1), have been submitted for the crop commodities (barley, flax, sunflower, and wheat 

commodities) proposed in the previous petition.

Morse Method Meth-147: In conjunction with a previous petition (PP#0F6076; DP#266204, S. 

Oonnithan, 7/24/2006), the petitioner also submitted sufficient data to support the use of an 

HPLC data-collection method, Morse Method Meth-147 (used for barley and wheat), for 

enforcement purposes, pending petition method validation (PMV). The method involves

hydrolysis of samples with methanolic potassium hydroxide (KOH) to convert quizalofop-Pethyl and quizalofop-P residues to 2-methoxy-6-chloroquinoxaline (MeCHQ). Residues of 

MeCHQ are partitioned into hexane, and the extract is cleaned up by gel permeation 

chromatography (GPC) prior to analysis by HPLC using fluorescence detection. The validated 

LOQ is 0.05 ppm for all matrices. The method was forwarded to the BEAD's Analytical 

Chemistry Branch (ACB) for PMV (DP# 330973, 7/24/2006, S. Oonnithan).

A successful independent laboratory validation (ILV) trial was conducted using samples of 

wheat straw fortified with quizalofop-P-ethyl and quizalofop-P at 0.05, 0.10, and 6.5 ppm each. 

The first and second ILV trials failed due to problems in the final evaporation step in the method. 

The ILV laboratory contacted Morse Laboratories after the second trial to discuss the final 

evaporation step of the method. The ILV laboratory tried a different solvent exchange procedure 

for this final step, and the third trial was successful. The laboratory reported that, other than the 

solvent exchange modification, the method was followed as written with minor modifications in 

the type of equipment used and the volumes of solvents used to elute residues from the GPC and 

SPE columns.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 19 of 55

No radiovalidation data were submitted for the method. Because the extraction procedures of the 

method are relatively rigorous, no radiovalidation data will be required to support the method.

Conclusions. HED previously concluded that the existing high performance liquid 

chromatography/ultra violet (HPLC/UV) method used for tolerance enforcement of soybean 

commodities (Method AMR-153-83, Revision 3) or newer method LAN-1 would not be 

adequate for the enforcement of tolerances in/on barley, flax, sunflower, or wheat commodities. 

The petitioner did not include any validation data reflecting analysis of barley, flax, sunflower, 

or wheat commodities using the current enforcement method, and the extraction procedures of 

the methods used for data collection in the studies submitted with the previous petition differ 

significantly from the extraction procedures of the existing enforcement method. By translation 

the current enforcement method would not be adequate for the enforcement of tolerances in/on 

field corn commodities. However, the petitioner submitted an analytical method amendment 

report for the determination of residues in sunflower seed, meal and oil by using the Morse 

method Meth-147 which is currently under review by HED and will be discussed in a separate 

residue chemistry chapter. 

HED also previously concluded that sufficient data are available to support the use of the HPLC 

data-collection method, Morse Method Meth-147 (used for barley and wheat), for enforcement 

purposes, pending petition method validation (PMV). The method was forwarded to the BEAD's 

Analytical Chemistry Branch (ACB) for PMV (DP#330973, S. Oonnithan, 7/24/2006); however, 

the PMV results are not available. Subsequently, Morse Method Meth-147 has been reevaluated using “SOP for Reviewing Tolerance Methods”, SOP Number:ACB-019, the current 

procedure for determining if a method is suitable for tolerance enforcement. After reviewing 

Morse Method Meth-147 against the Tolerance Method Validation (TMV) Review Checklist, 

provided the solvent exchange modification made by the ILV laboratory is incorporated into the 

final method, the analytical method data appear to satisfy the requirements. A TMV by ACB 

will not be necessary. 

We note that the method descriptions did not address the issue of determination of the Senantiomers of quizalofop ethyl and quizalofop. Because the KOH hydrolysis step would 

convert both the R- and S-enantiomers of quizalofop ethyl and quizalofop acid to the 

intermediate MeCHQ, all reported results for total quizalofop-P-ethyl residues would include 

residues of both the R- and S-enantiomers of quizalofop ethyl and quizalofop acid. This was 

specified in the analytical method amendment report for sunflowers which is under review by

HED.

HED notes that the Morse Method Meth-147 is appropriate for tolerance enforcement since is 

considered adequate for barley and wheat, a preliminary review of the validation data for 

sunflowers suggests that it is also adequate for oily seeds, and it is considered less complex than 

method AMR-153-86. Therefore, the proposed tolerance expression for plants, which is based 

on measurement of MeCHQ, is considered adequate.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 20 of 55

860.1340 Residue Analytical Methods – Livestock Commodities

Residue Chemistry Memo DP# None, G. Otakie, 6/27/1988; PP#3F3252

Adequate methods are available for the enforcement of tolerances in livestock commodities (PP# 

3F3252, 6/27/88, G. Otakie). A HPLC/UV Method (AMR-627-86, MRID 40322403) is 

available for the determination of residues of quizalofop ethyl, quizalofop, and quizalofopmethyl in livestock tissues. Another HPLC/UV Method (AMR-515-86, Revision A; MRID 

40322408) is available for determination of residues of quizalofop ethyl, quizalofop, and 

quizalofop-methyl in milk. Methods AMR-627-86 and AMR-515-86 have undergone PMV and 

have been forwarded to FDA for publication in PAM Volume II. In addition, HPLC/UV 

Methods AMR-846-87 (MRID 40322405), AMR-845-87 (MRID 40322409), and AMR-623-86 

(MRID 40322404) are available for the determination of residues of quizalofop ethyl, 

quizalofop, and quizalofop-methyl in livestock fat, cream, and eggs, respectively. Methods 

AMR-846-87, AMR-845-87, and AMR-623-86 have been forwarded to FDA for publication in 

PAM Volume II as letter methods. The methods involve extraction of samples with acetonitrile, 

methanol, acidified acetone, or acidified acetone/hexane (depending on the matrix), treatment of 

the extract with enzymes (lipase and esterase) to disassociate the fat and to convert residues of 

quizalofop ethyl and quizalofop-methyl to quizalofop. Quizalofop residues are then partitioned 

into chloroform for analysis by HPLC/UV. Residue results are reported in terms of residues of 

quizalofop. The reported LOQs are 0.02 ppm for muscle and 0.05 ppm for liver, kidney, cream, 

and fat; based on validation data, the LOQ for egg and milk is 0.01 ppm.

860.1360 Multiresidue Methods

No multiresidue method data were submitted with the current petition; however, multiresidue 

method data for quizalofop ethyl have been submitted previously. According to the Pesticide 

Analytical Manual (PAM) Volume 1, Appendix II (FDA PESTDATA database dated 10/99), 

quizalofop ethyl is completely recovered using Multiresidue Methods Section 302 (Luke 

Method; Protocol D). The database did not contain any information pertaining to the recovery of 

quizalofop acid or quizalofop-methyl using the multiresidue methods.

It’s important to emphasize that multiresidue methods used for enforcement need to be validated 

considering the residues of concern, in this case quizalofop ethyl and the metabolites quizalofop 

acid and quizalofop-methyl. The latter being considered for livestock commodities only.

860.1380 Storage Stability

Residue Chemistry Memo DP# None, G. Otakie, 12/18/1987; PP#5F3252

Residue Chemistry Memo DP#s 220215-17, F. Griffith, 2/13/1996; PP#s 3F42681/5H5720

Residue Chemistry Memo DP# 266204, S. Oonnithan, 7/24/2006; PP# 0F6076

The storage durations and conditions of samples from the field corn and sorghum crop field trials

and processing studies submitted to support this petition are presented in Table 4.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Table 4. Summary of Storage Conditions and Durations of Samples from Crop Field Trial and Processing Studies. 

Matrix Storage 

Temperature 

(°C)

Actual Storage Duration1Interval of Demonstrated Storage Stability

Corn, field, early forage Frozen at field 

sites

Approximately 

-20 at 

analytical lab

335-376 days

(11.0-12.4 months)

Storage stability data for quizalofop P-ethyl 

and quizalofop acid in/on field corn and 

processed commodities are not currently 

available; the petitioner indicated that a storage 

stability study is in progress.

Quizalofop P-ethyl and quizalofop acid in/on 

wheat forage and grain for 12.7 months, wheat 

hay for 11.3 months, and wheat straw for 11.2 

months. 2

Corn, field, forage 314-375 days

(10.3-12.3 months)

Corn, field, grain 253-320 days

(8.3-10.5 months)

Corn, field, stover 272-335 days

(8.9-11.0 months)

Corn, field, grain (RAC)

(prior to processing)

Frozen at field 

sites

< -12

at processing 

facility

Approximately 

-20 

at analytical 

lab

184-199 days

(6.1-6.5 months)

Flour 185-199 days

Grits (6.1-6.5 months)

Meal

Refined oil, wet 171-186 days

(5.8-6.1 months)

Refined oil, dry 171-191 days

(5.6-6.3 months)

Starch 180-194 days

(5.9-6.4 months)

Corn, aspirated grain fractions 175-182 days

(5.8-6.0 months)

Sorghum, forage -20 142-227 days

(4.7-7.5 months)

206 days

Sorghum, stover 109-191 days

(3.6-6.3 months)

188 days

Sorghum, grain 144-224 days

(4.7-7.4 months)

201 days

Sorghum, grain (RAC)

(prior to processing)

-20 116 days

(3.8 months)

201 days

Sorghum, aspirated grain 

fractions

110 days (3.6 months) 101 days

1

 For the processing study duration is from harvest/collection after processing to extraction; interval between extraction and 

analysis was not provided. Samples were processed within 87-136 days of harvest.

2

 PP# 0F6076, DP# 266204, 7/24/2006, S. Oonnithan

A concurrent storage stability study was conducted to support the storage durations and 

conditions of samples from the submitted sorghum field trials and processing study. These data 

demonstrate that residues of quizalofop-P-ethyl and quizalofop acid are stable when stored 

frozen for up to 206 days (6.7 months) in/on fortified sorghum forage, 201 days (6.6 months) 

in/on fortified sorghum grain, 188 days (6.1 months) in/on fortified sorghum stover, and 101 

days (3.3 months) in/on fortified AGF.

Storage stability data for quizalofop P-ethyl and quizalofop acid in/on field corn and processed 

commodities are not currently available; the petitioner indicated that a storage stability study is 

in progress. Storage stability data for quizalofop ethyl and quizalofop in/on various matrices, 

including cotton, soybean, and wheat commodities, have been submitted previously. Adequate 

storage stability data are available for soybean seed indicating that residues of quizalofop ethyl 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 22 of 55

and quizalofop are stable under frozen storage for up to 48 and 36 months, respectively (PP# 

5F3252, 12/18/87, G. Otakie). In addition, data are available indicating that residues of 

quizalofop are relatively stable in/on cotton seed, meal, and oil stored frozen for up to 28 months 

(PP# 3F42681/5H5720; DP#s 220215-17, F. Griffith, 2/13/96). Since the parent ethyl ester 

hydrolyzes rapidly to quizalofop after application, HED concludes that separate storage stability

data for quizalofop ethyl/quizalofop-P-ethyl in cotton commodities are not necessary. Adequate 

storage stability data are available for wheat commodities indicating that residues of quizalofopP-ethyl and quizalofop-P are stable during frozen storage for up to 12.7 months in/on wheat 

forage and grain, 11.3 months in/on wheat hay, and 11.2 months in/on wheat straw (PP# 0F6076, 

DP# 266204, 7/24/2006, S. Oonnithan).

Conclusions. The available wheat storage stability data are tentatively considered adequate to 

support submitted crop field trial on corn. Storage stability data were not provided for the corn 

processed commodities and are required to support the processing studies. When the storage 

stability study on corn is submitted, the adequacy of the storage stability data will be reevaluated. The submitted concurrent storage stability data for sorghum forage, stover, grain, and 

aspirated grain fractions are adequate to support the sorghum crop field trials. The data indicate 

that there are no storage stability issues and no corrections for decline during storage are needed.

860.1400 Water, Fish, and Irrigated Crops

There are no proposed uses that are relevant to this guideline topic.

860.1460 Food Handling

There are no proposed uses that are relevant to this guideline topic.

860.1480 Meat, Milk, Poultry, and Eggs

Residue Chemistry Memo DP# 266204, S. Oonnithan, 7/24/2006; PP# 0F6076

Residue Chemistry Memo DP#s 160972 and 166083, J. Stokes, 3/4/1992; PP#1F3951

Residue Chemistry Memo DP# None, G. Otakie, 12/18/1987; PP#5F3252

The livestock feedstuffs included in the current petitions are field corn (forage/silage, stover, 

grain, aspirated grain fractions, and milled byproducts) and sorghum (forage/silage, stover, grain, 

and aspirated grain fractions). The potential dietary exposure of livestock to quizalofop-P-ethyl

residues, considering both proposed and registered uses of quizalofop-P-ethyl, was calculated 

using recent Agency guidance on calculating dietary exposure from “reasonably balanced” 

livestock diets (ChemSAC draft memo, 6/2008). The dietary burden is reproduced below in 

Table 5.

The maximum reasonable dietary burdens are estimated to be: 0.382 ppm for beef cattle, 2.455 

ppm for dairy cattle, 0.625 ppm for poultry, and 0.463 ppm for swine.
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Table 5. Calculation of Dietary Burdens of Quizalofop-P-ethyl Residues to Livestock.

Feedstuff Type1 % Dry 

Matter1 % Diet1 Recommended Tolerance (ppm)

Dietary Contribution 

(ppm)

2

Beef Cattle

Sorghum, forage/silage R 35 15 0.20 0.086

Sorghum, grain CC 86 40 0.20 0.093

Aspirated grain fractions CC 85 5 1.0 0.059

Sugar beet, molasses CC 75 10 0.20 0.027

Barley, grain CC 88 25 0.05 0.014

Sunflower, meal PC 92 5 1.9 0.103

TOTAL BURDEN -- -- 100 -- 0.382

Dairy Cattle

Cowpea, forage R 30 20 3.0 2.0

Sorghum, forage/silage R 35 25 0.20 0.143

Sorghum, grain CC 86 45 0.20 0.105

Sunflower, meal PC 92 10 1.9 0.207

TOTAL BURDEN -- -- 100 -- 2.455

Poultry

Sorghum, grain CC 86 75 0.20 0.150

Sunflower, meal PC 92 25 1.9 0.475

TOTAL BURDEN -- -- 100 -- 0.625

Swine

Sorghum, grain CC 86 80 0.20 0.160

Barley, grain CC 88 5 0.05 0.003

Canola, meal PC 88 15 2.0 0.300

TOTAL BURDEN -- -- 100 -- 0.463

1 Table 1 (OCSPP Guideline 860.1000), ChemSAC memo dated June 30, 2008. 

2 Contribution = ([tolerance /% DM] X % diet) for beef and dairy cattle; contribution = ([tolerance] X % diet) for 

poultry and swine.

Ruminants

Dietary burdens of 2.70 and 2.72 ppm were previously calculated for beef and dairy cattle, 

respectively, in support of proposed uses on barley grain, hay, and straw; flax meal; sunflower 

meal; and wheat forage, grain, hay, straw, aspirated grain fractions, and milled byproducts (DP# 

266204, S. Oonnithan, 7/24/2006). A dairy cattle feeding study was submitted previously (PP# 

F3951, 12/18/87, G. Otakie, and PP# F3951, 3/4/92, J. Stokes). In the study, three groups of 

three lactating dairy cows (plus a control group) were fed quizalofop ethyl ester at 0.1, 0.5, and 

5.0 ppm in the diet for 28 consecutive days. These levels corresponded to 0.04x, 0.19x, and 1.9x 

the calculated maximum theoretical dietary burden to beef and dairy cattle. After re-calculating

a “reasonably balanced” dietary burden, these levels correspond to 0.3x, 1.3x, and 13x the 

maximum reasonable dietary burden (MRDB) to beef cattle, 0.04x, 0.20x, and 2.0x the MRDB

to dairy cattle, 0.2x, 1.1x and 10x the MRDB to swine. Milk was collected daily, and a subsample was divided into skim milk and cream. Two cows from each group were sacrificed after 

28 days, and samples of fat, skeletal muscle, liver, and kidney were collected and analyzed. The 

remaining cow in each test group was used to measure depuration, and was sacrificed 7 days 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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after dosing finished. The methods used for analysis converted residues of quizalofop ethyl and 

quizalofop-methyl to quizalofop; therefore, all reported residue results were expressed in terms 

of quizalofop. Quizalofop residues in whole milk, skim milk, and cream from the control, and 

the 0.1- and 0.5-ppm dose groups were <0.01 ppm (<0.05 ppm in cream). In samples from the 5-

ppm dose group, quizalofop residues ranged 0.01-0.02 ppm in whole milk, reaching a plateau on 

the fourth day of dosing. Quizalofop residues were found to partition into the cream samples 

from this group, with residues reaching plateaus of 0.26, 0.28, and 0.31 ppm after 2, 3, and 4 

weeks of dosing, respectively. Quizalofop residues were <0.02 ppm in skeletal muscle, and 

<0.05 ppm in liver, kidney, and fat samples from all three dose groups, with the exception of one 

kidney sample from the 5-ppm dose group which had quizalofop residues of 0.05 ppm.

Conclusions. The available feeding study data indicate that the established tolerances for 

combined residues of quizalofop ethyl and its metabolites quizalofop and quizalofop-methyl in 

the fat, meat, and meat byproducts of cattle, goat, hog, horse, and sheep at 0.05 ppm for fat and 

meat byproducts and 0.02 ppm for meat are adequate and do not need to be revised based on the 

requested uses of quizalofop-P-ethyl. Based on whole milk residues being 0.02 ppm at 2x

feeding level, the established tolerance of 0.01 ppm for milk is still adequate. Based on the 

maximum residues in milk of 0.02 ppm at a 2x dosing rate and an assumed 25x concentration 

factor for milk fat, expected residues at a 1x dosing rate would be 0.25 ppm; the established 

tolerance of 0.25 ppm for milk fat remains adequate.

Poultry

A poultry feeding study has been submitted and reviewed (PP#F3951, 12/18/87, G. Otakie). 

Three groups of 20 hens per group (plus one control group) were dosed with quizalofop ethyl at 

0.1, 0.5, and 5 ppm in the diet for 28 consecutive days; each dose group was subdivided into four 

subsets of five birds each. These levels correspond to 0.20x, 1x, and 10x previously calculated 

maximum theoretical dietary burden. After re-calculation, these levels correspond to 0.16x, 

0.8x, and 8x the maximum reasonable dietary burden to poultry. Eggs were collected daily. 

After 28 days, 15 of the hens in each test group were sacrificed, and samples of fat, liver, kidney, 

breast and thigh muscles were collected and analyzed; tissues from each test group subset were 

pooled prior to analysis. The remaining five hens in each test group were used to measure 

depuration, and were sacrificed 7 days after dosing finished. The methods used for analysis 

converted residues of quizalofop ethyl and quizalofop-methyl to quizalofop; therefore, all 

reported residue results were expressed in terms of quizalofop. Quizalofop residues were <0.05 

ppm in liver samples and <0.02 ppm in breast and thigh muscle samples from all dose groups, 

and were <0.05 ppm in kidney and fat samples from the 0.1- and 0.5-ppm dose groups. In 

samples from the 5-ppm dose group, quizalofop residues were 0.09 ppm in one pooled kidney

sample, 0.05 and 0.06 ppm in two fat samples, and were <0.05 ppm in the other kidney and fat 

samples. In eggs, residues were <0.02 ppm in all samples from all dose groups with the 

exception of one sample from the 5-ppm dose group which had quantifiable residues at 0.02 

ppm. 

Conclusions. The available feeding study data indicate that the established tolerances for 

combined residues of quizalofop ethyl and its metabolites quizalofop and quizalofop-methyl in 

egg at 0.02 ppm and the fat, meat, and meat byproducts of poultry at 0.05 ppm for fat and meat 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 25 of 55

byproducts and 0.02 ppm for meat are adequate and do not need to be revised based on the 

requested uses of quizalofop-P-ethyl.

860.1500 Crop Field Trials

Residue Chemistry Memo DP# 266204, S. Oonnithan, 7/24/2006; PP# 0F6076 (flax)

Residue Chemistry Memo DP#s 220476, 220478, 220480, F. Griffith, 2/21/1996; PP#5F4545/FAP#6H5737 

(canola)

Field Corn

DER References: 48260704.de1-quizalofop (AAD-1 field corn)

To support the use of quizalofop-P-ethyl (0.88 lb ai/gal EC formulation) on AAD-1 field corn

containing DAS-40278-9, Dow Agrosciences has submitted field trial data for these 

commodities. The results from these field trials are discussed below and summarized in Table 6. 

We note that all crop field trials were conducted using a DuPont quizalofop-P-ethyl product 

(Assure II; 0.88 lb ai/gal EC; EPA Reg. No. 352-541).

Table 6. Summary of Per Trial Average Residue Data from Crop Field Trials with Quizalofop-P-ethyl.

Field Corn containing DAS-40278-9

(Proposed Use: 0.083 lb ai/A total application rate, 30-day PHI for forage; plus adjuvant)

Crop matrix Total Applic. 

Rate

(lb ai/A)

PHI 

(days)

Total Quizalofop-P-ethyl Residue Levels (ppm)1

n Sample 

Min.

Sample 

Max.

HAFT 2 Median Mean Std. Dev.

Corn, field, 

early forage

0.078-0.088 32-47 24 <0.02 <0.02 <0.02 0.02 0.02 ---

Corn, field, 

forage

44-83 24 <0.02 <0.02 <0.02 0.02 0.02 ---

Corn, field, 

grain

79-144 25 <0.02 <0.02 <0.02 0.02 0.02 ---

Corn, field, 

stover

79-144 25 <0.02 <0.022 <0.022 0.02 0.02 ---

1 Except for sample min/max, values reflect per trial averages; n = no. of field trials. For calculation of median, mean, and 

standard deviation, the LOQ (0.01 ppm) was used for any results reported as ND (0.003 ppm) or between the LOD and LOQ in 

Table C.3.

2 HAFT = highest-average-field-trial.

Dow AgroSciences LLC has submitted field trial data for quizalofop-P-ethyl on field corn. 

Twenty five field trials were conducted in the United States and Canada during the 2009 growing 

season in the North American Free Trade Agreement (NAFTA) Growing Zones 1 (NJ and PA; 2 

trials), 2 (GA; 2 trials), 5 (IA, IL, IN, KS, MI, MN, MO, NE, OH, and ON; 19 trials), and 6 (OK 

and TX; 2 trials). 

Each trial consisted of one untreated and two treated plots. The treated plots were planted with 

hybrid field corn containing the Aryloxyalkanoate Dioxygenase-1 (AAD-1) gene. Expression of 

the AAD-1 protein, which is encoded by the AAD-1 gene, provides tolerance to quizalofop-P-
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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ethyl. At each site, one treatment plot was planted with seed line Event DAS-40278-9 and the 

other treatment plot was planted with seed line Event DAS-40474-7. Due to limited availability

of the seed from the treated plots, the untreated plots were planted with field corn variety 

Mycogen 2M746 which is a hybrid field corn with a genetic background similar to the seed used 

at the treated plots. The study indicated that the Sponsor discontinued development of AAD-1 

Event DAS-40474-7 seed line; therefore, samples were collected from these plots but were not 

analyzed. 

The Event DAS-40278-9 treated plots received one broadcast foliar application of a 0.88 lb/gal 

emulsifiable concentrate (EC) formulation of quizalofop-P-ethyl (Assure II) at a target rate of 

0.082 lb ai/A. Applications were made using ground equipment in spray volumes of 20-33 

gal/A. A crop oil concentrate (COC) was added to the spray mixture for all applications; except 

for one site (MO-08) in which a non-ionic surfactant (NIS) was used. HED prefers to have at 

least three side-by-side trials with the adjuvants recommended in the label; however, since 

residues with the NIS were below the LLMV, which was also the case for most trials with the 

COC, the three side-by-side trials will not be required. The label should be modified to include 

the concentration of the adjuvant. Three applications of 2,4-D dimethylamine salt (2,4-D DMA; 

Weedar®64 Herbicide) were also made to the field corn with a non-ionic surfactant (NIS). Two 

of the 2,4-D DMA applications were made before the quizalofop-P-ethyl application, including 

one as a pre-emergence application and one approximately 12 days before corn reached the V8 

growth stage or 48 inch height. One 2,4-D DMA application was made ~5 days after the 

quizalofop-P-ethyl application at approximately the V8 growth stage or 48 inch height. Data 

pertaining to 2,4-D DMA are addressed under DP# 384441 (MRDI #48260704). Field corn 

forage was harvested at two preharvest intervals (PHIs), reflecting early harvest before the 

typical growth stage to support a reduced PHI (targeted 40-day PHI) and typical harvest at the 

late-dough to early-dent stage (targeted 60-day PHI); grain and stover were harvested at 

maturity. Based on the application of quizalofop-P-ethyl, PHIs were 32-47 days and 44-83 days 

for forage and 79-144 days for grain and stover. Additional samples of forage, grain, and stover 

were collected from one trial each conducted in GA, MI, and OK at PHIs targeted at ~7 and 14 

days before and after the desired PHI; for forage, the decline PHIs bracketed the second (60-day) 

PHI.

Samples were analyzed for residues of quizalofop-P-ethyl and quizalofop acid using a High 

Pressure Liquid Chromatography/Mass Spectrometry/Mass Spectrometry (LC/MS/MS) method 

detailed in the study. The reported limit of quantitation (LOQ; determined as the lowest limit of 

method validation, LLMV) was 0.01 ppm for quizalofop-P-ethyl and quizalofop acid in all 

matrices. The methods are adequate based on acceptable concurrent recovery data. The 

fortification levels used in concurrent method recovery were adequate to bracket expected 

residue levels.

Samples were stored frozen (approximately -20 °C) from collection to extraction for analysis of 

quizalofop-P-ethyl and quizalofop acid for up to 376 days (12.4 months) for forage, 320 days 

(10.5 months) for grain, and 335 days (11.0 months) for stover. Storage stability data for 

quizalofop-P-ethyl and quizalofop acid in/on field corn are not currently available; the petitioner 

indicated that a storage stability study with quizalofop-P-ethyl and quizalofop acid P in corn 

commodities was initiated in 2010 and will be submitted separately.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Following one foliar broadcast application of quizalofop-P-ethyl with an adjuvant at a total 

seasonal rate of 0.078-0.088 lb ai/A, residues of quizalofop-P-ethyl, quizalofop acid (parent 

equivalents) and total quizalofop-P-ethyl residues (sum of quizalofop-P-ethyl and quizalofop 

acid residues as parent equivalents) were below the LOQ (<0.01 ppm for individual analytes and 

<0.02 ppm for total analytes) in/on early forage (32-to 47-day PHI), forage (44- to 83-day PHI), 

and grain (79- to 144-day PHI). In/on stover (79- to 144-day PHI), residues of quizalofop-Pethyl were <0.01 ppm and residues of quizalofop acid were <0.01 to 0.012 ppm (per trial average 

residues were also <0.01 to 0.012 ppm). Quizalofop acid was only detected above the LOQ 

in/on stover at one field trial. Total quizalofop-P-ethyl residues in/on stover were <0.02 to 0.022 

ppm. 

Residue decline on the three submitted studies (GA-04, MI-11, and OK-22) could not be 

assessed because the residues of quizalofop-P-ethyl and quizalofop acid were <LOQ in/on forage 

and grain samples and <LOQ or near the LOQ in/on the majority of the stover samples.

The results of the field corn crop field trials are presented in Table 6.

Conclusions. The submitted residue data for field corn commodities (forage, grain, and stover) 

are tentatively considered to be adequate, pending submission of storage stability data 

demonstrating the stability of quizalofop-P-ethyl and quizalofop acid in/on field corn forage, 

grain, and stover. The number and locations of crop field trials are in accordance with OCSPP 

Guideline 860.1500. The field trials reflect the proposed use pattern. However, the label should 

be modified to specify the concentration of the adjuvant used in the crop field trials, 1.25% (v/v). 

The residue data were entered into the OECD MRL calculator (March 2011 version) to 

determine the appropriate tolerance levels; see Appendix I. The OECD MRL calculator 

recommends tolerances of 0.02 ppm for corn forage and grain and 0.03 ppm for corn stover for 

total quizalofop-P-ethyl residues [sum of quizalofop-P-ethyl and quizalofop acid residues (as 

parent equivalents)]. The corn forage and grain recommendations are higher than the tolerance 

levels (0.01 ppm) proposed by the petitioner. The corn stover recommendation is identical to the 

tolerance level proposed by the petitioner.

The submitted residue data for field corn are adequate to fulfill data requirements. 

Sorghum

DER References: 48273601.der1 (sorghum)

To support the use of quizalofop-P-ethyl (0.88 lb ai/gal EC formulation) on sorghum, IR-4 has 

submitted field trial data for these commodities. The results from these field trials are discussed 

below and summarized in Table 7. We note that all crop field trials were conducted using a 

DuPont quizalofop-P-ethyl product (Assure II; 0.88 lb ai/gal EC; EPA Reg. No. 352-541).
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 28 of 55

Table 7. Summary of Residue Data from Crop Field Trials with Quizalofop-P-ethyl.

Sorghum grain containing the DuPontTM INZENTM AII Herbicide Tolerance Trait

(Proposed Use: 0.138 lb ai/A total application rate, 30-day PHI for forage and 45-day PHI for grain and stover;

plus adjuvant)

Crop matrix Total Applic. 

Rate

(lb ai/A)

PHI 

(days)

Total Quizalofop-P-ethyl Residue Levels (ppm)

n Min. Max. 1 HAFT 2 Median Mean Std. 

Dev.

Sorghum, 

forage

0.136-0.145 25-32 13 <0.104 <0.180 <0.169 0.104 0.112 0.019

Sorghum, 

grain

29-49 12 <0.104 <0.158 <0.149 0.104 0.111 0.014

Sorghum, 

stover

42-56 13 <0.104 <0.266 <0.212 0.104 0.129 0.040

1 The max value was determined from the individual samples 

2 HAFT = Highest average field trial result.

n = number of field trials

IR-4 has submitted field trial data for quizalofop-P-ethyl on ACCase resistant grain sorghum. 

Thirteen field trials were conducted in the United States during the 2009 growing season in 

Zones 2 (MD and NC; 2 trials), 4 (AR; 1 trial), 5 (KS and NE; 3 trials), 6 (TX; 2 trials), 7 (NE; 1 

trial) and 8 (KS, NM, and TX; 4 trials). 

Each trial consisted of one untreated and one treated plot. Each treated plot received a single 

broadcast or directed foliar application of a 0.88 lb ai/gal emulsifiable concentrate (EC) 

formulation of quizalofop-P-ethyl (Assure II; EPA Reg. No. 352-541) at a target rate of 0.138 lb 

ai/A. Applications were made using ground equipment in spray volumes of 14.9-36.0 gal/A; an 

adjuvant (crop oil concentrate or non-ionic surfactant) was added to the spray mixtures at all trial 

sites. Applications in all trials except one were performed with a crop oil concentrate (1% v/v) 

which is the preferred adjuvant recommended in the label. A non ionic surfactant (0.25% v/v) 

was applied in the remaining trial. HED prefers to have at least three side-by-side trials with the 

adjuvants recommended in the label; however, since the label specifies that the crop oil 

concentrate is the preferred adjuvant and residues with the non ionic surfactant were lower than 

those of with the crops oil concentrate the three side-by-side trials will not be required. Samples 

of forage were harvested at a preharvest interval (PHI) of 25-32 days. Grain and stover were

harvested at 29- to 49-day and 42- to 56-day PHIs, respectively. Additional forage samples were 

collected from trial TX08 at PHIs of 8, 14, 29 and 37 days to generate residue decline data. 

Additional samples were also collected from one trial (KS02) to conduct a processed food and 

feed study; refer to the 860.1520 DER for MRID 48273601 for the study details and results.

Samples of sorghum forage, grain, and stover were analyzed for residues of quizalofop-P-ethyl

and quizalofop acid using an LC/MS/MS method modified from the method in Du Pont Study

No. AMR-1854-90. The lowest level of method validation (LLMV) for quizalofop-P-ethyl and 

quizalofop acid was 0.05 ppm for sorghum forage, grain, and stover. The petitioner used the 

LLMV as the limit of quantitation (LOQ) for reporting residue results. The method is adequate 

based on acceptable method validation and concurrent recovery data. 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Samples were stored frozen (approximately -20 °C) from harvest to analysis for quizalofop-Pethyl and quizalofop acid for up to 227 days (7.5 months) for forage, 224 days (7.4 months) for 

grain, and 191 days (6.3 months) for stover; extracts were stored for up to 3 days prior to 

analysis for all samples. Sample storage conditions and durations are supported by concurrent 

storage stability data. However, zero-day data were not provided with the storage stability study. 

IR-4 is reminded that storage stability studies should always include a zero-day sampling interval 

to establish the residue levels present at the time samples are placed into storage [see OCSPP 

860.1380(d)(6)(i)].

The results of the sorghum crop field trials are presented in Table 6. Following one foliar 

broadcast or direct application of quizalofop-P-ethyl at a total application rate of 0.136-0.145 lb 

ai/A, residues of quizalofop-P-ethyl were <LLMV (0.05 ppm) in/on forage (25- to 32-day PHI), 

grain (29- to 49-day PHI), and stover (42- to 56-day PHI). Residues of quizalofop acid (as 

parent equivalents) were <0.054-0.130 ppm in/on forage, <0.054-0.108 ppm in/on grain and 

<0.054-0.216 ppm in/on stover. Total quizalofop-P-ethyl residues (sum of quizalofop-P-ethyl

and quizalofop acid residues (as parent equivalents)) were <0.104-<0.180, <0.104-<0.158 and 

<0.104-<0.266 ppm in/on forage, grain, and stover, respectively.

The submitted residue decline data indicate that residues of quizalofop acid (as parent 

equivalents) decreased in/on forage with increasing PHI. Residues of quizalofop-P-ethyl in/on 

forage were <LLMV; therefore, residue decline could not be assessed.

Conclusions. The submitted residue data for sorghum commodities (forage, grain, and stover) are 

adequate to satisfy data requirements. Trials were conducted according to the proposed use 

pattern, samples were analyzed for residues of residues of quizalofop-P-ethyl and quizalofop 

acid using an acceptable method, and adequate storage stability data were submitted to support 

the study. The number and location of crop field trials are not in strict accordance with OCSPP 

860.1500. However, geographic representation of data is adequate considering the total number 

of field trials submitted (13 trials were submitted and 12 trials are required for sorghum).

The residue data for sorghum forage, grain, and stover were entered into the OECD MRL

calculator (March 2011 version) to determine appropriate tolerance levels; see Appendix I. The 

OECD MRL calculator recommends tolerances of 0.20, 0.20, and 0.30 ppm for total quizalofopP-ethyl residues [sum of quizalofop-P-ethyl and quizalofop acid residues (as parent equivalents)] 

in/on sorghum forage, grain, and stover, respectively. These recommendations are identical to 

the tolerance levels proposed by the petitioner for sorghum forage and grain. The tolerance level 

recommendation for sorghum stover is slightly lower than the level (0.35 ppm) proposed by the 

petitioner.

Rapeseed Subgroup 20A, Except Flaxseed

IR-4 is proposing use of the 0.88 lb ai/gal EC formulation on mustard seed and other members of 

the rapeseed subgroup 20A, except flaxseed, as postemergence applications at a total seasonal 

application rate of 0.124 lb ai/A. A 60-day PHI is proposed.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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No new residue data were submitted in support of the label amendment request. The petitioner 

has submitted a request to use acceptable field trial data for canola seed, the representative crop 

of subgroup 20A, that were previously reviewed under PP# 5F4545/FAP# 6H5737 (DP#s 

220476, 220478, and 220480, F. Griffith, 2/21/96) in support of the proposed use on members of 

the rapeseed subgroup 20A, except flaxseed. Currently tolerances are established for canola, 

seed at 1.0 ppm and flaxseed at 0.05 ppm. Acceptable field trial data for flaxseed for a different 

use pattern were previously reviewed in conjunction with a previous petition (DP# 266204, S. 

Oonnithan, 7/24/2006).

Table 8. Summary of Residue Data from Crop Field Trials with Quizalofop-P-ethyl.

Rapeseed Subgroup 20A, Except Flaxseed

[includes Borage, Crambe, Cuphea, Echium, Gold of Pleasure (Camelina), Hare’s ear mustard, Lesquerella, 

Lunaria, Meadowfoam, Milkweed, Mustard seed, Oil Radish, Poppy seed, Rapeseed (Canola), Sesame, and 

Sweet Rocket]

(Proposed Use: 0.124 lb ai/A total application rate, 60-day PHI; plus adjuvant)

Canola data available from a previous petition (PP#5F4545/FAP#6H5737; DP#s 220476, 220478, 220480, F. Griffith, 2/21/96)

Crop matrix Total Applic. 

Rate

(lb ai/A)

PHI 

(days)

Total Quizalofop-P-ethyl Residue Levels (ppm)

n Min. Max. HAFT 1 Median Mean Std. 

Dev.

Canola, seed 0.094 38-74 9 <0.05 0.7 0.65 0.12 0.19 0.21

Canola, seed 0.188 38-74 9 <0.05 1.5 1.5 0.25 0.39 0.46

n = number of field trials

A summary of residue data from the canola seed field trials is presented in Table 8. The 

available data reflect nine field trials conducted in 1989. Each trial had a one control plot and 

two test plots. One canola test plot received a single broadcast ground spray at 1.5 oz ai/A 

(0.094 lb ai/A; ~0.8x proposed seasonal application rate) along with the surfactant. The application was postemergence, when the canola was flowering, or at least 4 inches high. The other 

canola plot received a single broadcast ground spray at a rate of 3 oz ai/A (0.188 lb ai/A; ~1.5x 

proposed seasonal application rate) with the surfactant. Both the 0.8x and 1.5x applications were 

done at the same time. One of the MN trials did not produce seed after the Assure® II 

application due to a lack of rain and an early frost. The test sites in TN received the racemic 

Assure® application and the test site in the other four states received Assure® II containing the 

D+ isomer. Neither of these situations affect the validity of the data presented.

Mature canola seeds were harvested at 38 to 74 days PHI. Samples were promptly frozen and 

remained frozen until preparation and analysis. Samples were analyzed by the residue analytical 

methods which have adequate validation and concurrent recovery data for quizalofop ethyl ester 

and the phenol metabolites. Residues of quizalofop and phenols 2 and 4 were not detected to the 

LOQ of 0.05 ppm in any of the control canola seeds. From the 0.8x application, detectable 

quizalofop residues ranged from < 0.05 ppm (3 trials) to 0.7 ppm, averaging 0.22 ± 0.22 ppm (n 

= 12). The highest average field trial (HAFT) for the 0.8x application is 0.65 ppm. From the 

1.5x application, quizalofop residues ranged < 0.05 ppm (2 trials) to 1.5 ppm, averaging 0.45 ± 

0.44 ppm. No phenol 2 or phenol 4 residues were detected in any of the canola seed samples 

from the 0.8x and 1.5x applications at any of PHIs. 

Based on the available data, a tolerance for canola seed was established at 1.0 ppm. However, 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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since proportionality is observed between the application rate, 0.10 lb ai/A and 0.20 lb ai/A, and 

the average residues, 0.22 ppm and 0.45 ppm, respectively, we adjusted the field trial residue 

data to reflect the residues that may be expected after application of the proposed rate (0.124 lb 

ai/A). The residues originally reported as quizalofop acid equivalents were converted to 

quizalofop-P-ethyl equivalents, adjusted for the application rate, and included in the OECD 

calculator to estimate a tolerance of 1.5 ppm. 

Conclusions. Previously separate tolerances for individual members of a subgroup were required 

in the appropriate section of the CFR entry until the new crop group regulation for the Rapeseed 

Subgroup 20A is published in the Federal Register. Recently, the final rule (75 FR 76284-

76292, December 8, 2010) for the pesticide tolerance crop grouping regulations which allow 

establishment of tolerances for multiple related crops, based on data from a representative set of 

crops, created a new crop group for Oilseed and also established a Rapeseed Subgroup 20A.

The available field trial data for canola seed, the representative crop of the rapeseed subgroup 

20A, may be translated to support the proposed uses on mustard seed and other members of the 

rapeseed subgroup 20A, except flaxseed. These data are adequate to fulfill data requirements 

and reflect ~0.8-1.6x the maximum proposed seasonal application rate for the EC formulation 

with 38- to 74-day PHI. A new tolerance of 1.5 ppm will support use of the 0.88 lb/gal EC 

formulation.

HED, therefore, recommends a tolerance of 1.5 ppm for residues of quizalofop and its 

metabolites, all expressed as quizalofop-P-ethyl in/on rapeseed subgroup 20A, except flaxseed

based on residue data from canola seed. Individual tolerances for each member of the subgroup 

are no longer required because the Rapeseed Subgroup 20A may be published in the Federal 

Register. The petitioner is required to submit a revised Section F to reflect this determination.

860.1520 Processed Food and Feed

Field Corn

DER References: 48260704.de2-quizalofop (AAD-1 field corn)

Dow AgroSciences LLC has submitted a processing study for quizalofop-P-ethyl on hybrid field 

corn containing the inserted aryloxyalkanoate dioxygenase-1 (AAD-1) gene (seed line Event 

DAS-40278-9). Expression of the AAD-1 protein, which is encoded by the AAD-1 gene, 

provides tolerance to quizalofop-P-ethyl. In two trials conducted in GA and NE during the 2009 

growing season, one broadcast foliar application of a 0.88 lb/gal emulsifiable concentrate (EC) 

formulation of quizalofop-P-ethyl (Assure II) was made to field corn at a target rate of 0.164 lb 

ai/A (~2x the proposed maximum seasonal rate). Applications were made using ground 

equipment in spray volumes of 22-31 gal/A with an adjuvant (crop oil concentrate; COC) at both 

trial sites. Three applications of 2,4-D dimethylamine salt (2,4-D DMA; Weedar®64 Herbicide) 

were also made to the field corn with a non-ionic surfactant (NIS). Two of the 2,4-D DMA 

applications were made before the quizalofop-P-ethyl application, including one as a preemergence application and one approximately 12 days before corn reached the V8 growth stage 

or 48 inch height. One 2,4-D DMA application was made ~5 days after the quizalofop-P-ethyl
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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application at approximately the V8 growth stage or 48 inch height. Data pertaining to 2,4-D 

DMA are addressed under DP# 384441 (MRID #48260704). Field corn grain was harvested at 

maturity, 79 days following the quizalofop-P-ethyl application at the GA site and 140 days after 

the quizalofop-P-ethyl application at the NE site. Field corn grain raw agricultural commodity

(RAC) samples were processed into field corn starch, refined oil (wet milling), refined oil (dry

milling), meal, grits, flour, and aspirated grain fractions (AGF) using procedures simulating 

commercial processing.

The maximum theoretical concentration factor for corn is 25x based on separation into 

components in corn oil (OCSPP 860.1520 Tables 1 and 3). An exaggerated rate of at least 5x is 

recommended in the guideline. However, the petitioner noted that the application rate used in 

the study was only 2x that used in the corresponding crop field trials (refer to the 860.1500 DER 

for MRID 42860704) due to concerns over the potential for crop injury. 

Samples of field corn grain RAC and processed commodities were analyzed for residues of 

quizalofop-P-ethyl and quizalofop acid using a High Pressure Liquid Chromatography/Mass 

Spectrometry/Mass Spectrometry (LC/MS/MS) method detailed in the study. The reported limit 

of quantitation (LOQ; determined as the lowest limit of method validation, LLMV) was 0.01 

ppm for quizalofop-P-ethyl and quizalofop acid in all matrices. The methods are adequate based 

on acceptable concurrent recovery data. The fortification levels used in concurrent method 

recovery were adequate to bracket expected residue levels.

Samples were stored frozen (~-20 °C) from harvest/collection to extraction for analysis of 

quizalofop-P-ethyl and quizalofop acid for up to 199 days (6.5 months) in field corn grain, meal, 

grits, and flour; 194 days (6.4 months) in starch, 191 days (6.3 months) in refined oil (dry

milling); 186 days (6.1 months) in refined oil (wet milling); and 182 days (6.0 months) in AGF. 

Storage stability data for quizalofop-P-ethyl and quizalofop acid in/on field corn and processed 

commodities are not currently available; the petitioner indicated that a storage stability study

with quizalofop-P-ethyl and quizalofop acid P in corn commodities was initiated in 2010 and 

will be submitted separately.

A summary of residue data from the field corn processing study is presented in Table 9. 

Residues of quizalofop-P-ethyl and quizalofop acid (as parent equivalents) in/on field corn grain 

RAC were <LOQ (<0.01 ppm) at each trial following one application of quizalofop-P-ethyl at a 

target rate of 0.164 lb ai/A. Processing factors for quizalofop-P-ethyl, quizalofop acid, and total 

quizalofop-P-ethyl in field corn processed commodities (starch, refined oil (wet and dry milling), 

meal, grits, flour, and AGF) could not be calculated because residues were also <LOQ in these 

matrices.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Table 9. Residue Data from Field Corn Processing Study with Quizalofop-P-ethyl.

RAC Processed 

Commodity

Total 

Rate

(lb ai/A)

PHI 

(days)

Residues (ppm) Processing Factor3

Quizalofop. 

P-ethyl

Quizalofop 

acid1

Total 

Quizalofop. 

P-ethyl2

Quizalofop

P-ethyl

Quizalofop 

acid1

Total 

Quizalofop. 

P-ethyl2

Trial GA-03

Field 

Corn

Grain (RAC) 0.164 79 ND

ND

[<0.01]

ND

(0.003)

[<0.01]

<0.02

<0.02

[<0.02]

-- -- --

Grain (from 

the processor 

prior to AGF 

generation)

ND

ND

ND

[<0.01]

ND

ND

ND

[<0.01]

<0.02

<0.02

<0.02

[<0.02]

-- -- --

Grain

(from the 

processor 

after AGF 

generation)

ND

ND

ND

[<0.01]

ND

ND

ND

[<0.01]

<0.02

<0.02

<0.02

[<0.02]

-- -- --

Starch ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC4 NC NC

Refined oil 

(wet milling)

ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Refined oil 

(dry milling)

ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Meal ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Grits ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Flour ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

AGF ND ND <0.02 NC NC NC

Trial NE-14

Field 

Corn

Grain (RAC) 0.163 140 ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

--- --- ---

Grain (from 

the processor 

prior to AGF 

generation)

ND 

(0.004)

ND

[<0.01]

ND, 

(0.005)

ND

[<0.01]

<0.02

<0.02

<0.02

[<0.02]

--- --- ---

Grain

(from the 

processor 

after AGF 

generation)

ND

ND

ND

[<0.01]

ND

ND

ND

[<0.01]

<0.02

<0.02

<0.02

[<0.02]

--- --- ---

Starch ND

(0.005)

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Refined oil 

(wet milling)

ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Refined oil 

(dry milling)

ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Table 9. Residue Data from Field Corn Processing Study with Quizalofop-P-ethyl.

RAC Processed 

Commodity

Total 

Rate

(lb ai/A)

PHI 

(days)

Residues (ppm) Processing Factor3

Quizalofop. 

P-ethyl

Quizalofop 

acid1

Total 

Quizalofop. 

P-ethyl2

Quizalofop

P-ethyl

Quizalofop 

acid1

Total 

Quizalofop. 

P-ethyl2

Meal ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Grits ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

Flour ND

ND

[<0.01]

ND

ND

[<0.01]

<0.02

<0.02

[<0.02]

NC NC NC

AGF ND ND <0.02 NC NC NC

1

 ND = <LOD (<0.003 ppm). The LOQ was 0.01 ppm for each analyte. Residues between the LOD and LOQ are reported in 

parentheses and averages are reported in brackets. When calculating averages, the LOQ was used for values reported as ND or 

between the LOD and LOQ.

2 Quizalofop acid reported as parent equivalent (quizalofop acid result x 1.0814)

3 Total quizalofop-P-ethyl residues = residues of quizalofop-P-ethyl + quizalofop acid (in parent equivalents).

4

 NC = Not calculated. The processing factor could not be calculated because residues were below the LOQ in the RAC and the 

processed fraction.

Conclusions. The submitted processing data for field corn are tentatively considered to be 

adequate, pending submission of storage stability data demonstrating the stability of quizalofopP-ethyl and quizalofop acid in/on field corn grain starch, refined oil, meal, grits, flour, and AGF 

stored frozen for up to 6.0-6.5 months. The results of submitted field corn processing study

show that residues of quizalofop-P-ethyl and quizalofop acid (as parent equivalents) in/on field 

corn grain RAC at each trial were <LOQ (<0.01 ppm) following one application at a target rate 

of 0.164 lb ai/A (~2x the proposed maximum seasonal rate). Processing factors for quizalofopP-ethyl, quizalofop acid, and total quizalofop-P-ethyl in field corn processed commodities 

(starch, refined oil (wet and dry milling), meal, grits, flour, and AGF) could not be calculated 

because residues were also <LOQ in these matrices. The Agency would have preferred the use 

of exaggerated rates in the conduct of the processing study to yield a RAC with quantifiable 

residues; however, the petitioner noted that the application rate used in the study was only 2x due 

to concerns over the potential for crop injury.

Sorghum, Aspirated Grain Fractions

DER References: 48273601.der2 (sorghum)

IR-4 has submitted a processing study for quizalofop-P-ethyl on ACCase resistant grain 

sorghum. In one crop field trial conducted in 2009 in KS, sorghum samples were harvested 48 

days after a single broadcast foliar application of a 0.88 lb/gal emulsifiable concentrate (EC) 

formulation of quizalofop-P-ethyl (Assure II; EPA Reg. No. 352-541) at a rate of 0.139 lb ai/A 

(1x field application rate). The sorghum grain samples were processed into aspirated grain 

fractions (AGF) by GPL Technologies (Navasota, TX). Adequate descriptions were provided of 

the processing procedures, including material balance summaries.

The sorghum grain and AGF samples were analyzed for residues of quizalofop-P-ethyl and 

quizalofop acid using an LC/MS/MS method modified from the method in Du Pont Study No. 

AMR-1854-90. The lowest level of method validation (LLMV) for quizalofop-P-ethyl and 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 35 of 55

quizalofop acid was 0.05 ppm for sorghum grain and AGF. The petitioner used the LLMV as 

the limit of quantitation (LOQ) for reporting residue results. The method is adequate based on 

acceptable method validation and concurrent recovery data. 

Samples were stored frozen (approximately -20 °C) prior to processing and analysis. The 

maximum storage duration for the sorghum grain raw agricultural commodity (RAC) was 116 

days (3.8 months) from harvest to analysis and the maximum storage duration for AGF was 110 

days (3.6 months) from processing to analysis. Sample storage conditions and durations are 

supported by concurrent storage stability data. However, zero-day data were not provided with 

the storage stability study. IR-4 is reminded that storage stability studies should always include a 

zero-day sampling interval to establish the residue levels present at the time samples are placed 

into storage [see OCSPP 860.1380(d)(6)(i)].

Residues of quizalofop-P-ethyl, quizalofop acid (as parent equivalents), and total quizalofop-Pethyl [sum of quizalofop-P-ethyl and quizalofop acid (as parent equivalents)] were <0.05, 0.108, 

and <0.158 ppm, respectively, in/on sorghum grain RAC. The processing data indicate that 

residues of quizalofop acid and total quizalofop-P-ethyl may concentrate (processing factors of 

4.5x and 3.4x, respectively) in AGF. The processing factors for quizalofop-P-ethyl could not be 

calculated because the results in/on the RAC and the processed commodity were less than the 

LLMV.

Table 10. Residue Data from Sorghum Processing Study with Quizalofop-P-ethyl.

RAC Processed 

Commodity

Total 

Rate

(lb ai/A)

PHI 

(days)

Residues (ppm) Processing Factor3

Quizalofop. 

P-ethyl

Quizalofop 

acid1

Total 

Quizalofop. 

P-ethyl2

Quizalofop

P-ethyl

Quizalofop 

acid1

Total 

Quizalofop. 

P-ethyl2

Sorghum Grain (RAC) 0.139 48 <0.05 0.108 <0.158 --- --- ---

AGF <0.05 0.49 <0.54 NC44.5x 3.4x

1 Quizalofop acid reported as parent equivalent (quizalofop acid result x 1.0814)

2 Total quizalofop-P-ethyl residues = residues of quizalofop-P-ethyl + quizalofop acid (in parent equivalents). 

3 Processing factors were calculated using the equation: Processing Factor = [Measured residue for analyte in the processed 

fraction] / [Measured residue for analyte in the RAC prior to processing]. 

4

 NC = Not calculated. The processing factor could not be calculated because residues were below the LLMV in the RAC and 

the processed fraction.

Conclusions. The submitted sorghum processing study is adequate to satisfy data requirements. 

The processing data indicate that total quizalofop-P-ethyl residues concentrate in AGF. Based 

on the processing factor, 3.4x, and the HAFT for sorghum grain, 0.149 ppm, expected residues in 

sorghum AGF following treatment at 1x would be 0.507 ppm. Because this value is greater than 

the recommended 0.2-ppm tolerance for sorghum grain, a tolerance is needed for total 

quizalofop-P-ethyl residues in/on sorghum, grain, aspirated grain fractions. A tolerance of 1.0 

ppm would be appropriate. This recommendation is identical to the tolerance level proposed by 

the petitioner.

Crambe, Meal and Gold of Pleasure, Meal

Residue Chemistry Memo DP#s 220476, 220478, 220480, F. Griffith, 2/21/1996; PP#5F4545/FAP#6H5737 

(canola)

No new processing data were submitted in support of the label amendment request to expand the 

use of quizalofop on members of the rapeseed subgroup 20A, except flaxseed, that may be 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 36 of 55

processed (crambe and gold of pleasure). Acceptable processing data were previously submitted 

and reviewed for canola seed, the representative crop of subgroup 20A, under PP# 5F4545/FAP# 

6H5737 (DP#s 220476, 220478, and 220480, F. Griffith, 2/21/96). Based on the available 

canola processing data, processing factor for canola meal was established as 2.3x; a processing 

factor was not required for refined oil. By using the HAFT (0.65 ppm) and adjusting for the 

application rate (0.806x), a tolerance of 2 ppm is calculated.

Conclusion: HED concludes that the available canola processing data and the established 

processing factor for canola meal may be translated to rapeseed meal. Separate tolerances for 

crambe meal and gold of pleasure meal need are covered by the tolerance recommended (2 ppm)

for rapeseed meal.

860.1650 Submittal of Analytical Reference Standards

Analytical standards from DuPont for quizalofop-P-ethyl (expiration date 8/18/2014), quizalofop

acid (expiration date 12/8/2019), and quizalofop-P-methyl (expiration date 3/28/2018) are 

currently available in the National Pesticide Standards Repository (personal communication with 

Theresa Cole, ACB, 8/2/11).

860.1850/860.1900 Confined/Field Accumulation in Rotational Crops

Residue Chemistry Memo DP#s 219672 and 222000, F. Griffith, 1/26/1996; PP#5E4590

Adequate confined rotational crop studies were submitted previously. In the studies, rotational 

crops of red beets, lettuce, wheat, peanuts, and cotton were planted 30 and 62 days following 

treatment of the soil with [phenyl14C]quizalofop ethyl and [quinoxaline14C]quizalofop ethyl. 

Over 50% of the residues in rotational crops were characterized and identified; the studies 

indicate that the metabolic pathway in rotational crops is the same as for primary crops. Total 

quizalofop residues were 0.032-0.104 ppm in rotational crop commodities from the 30-day PBI

and 0.045-0.071 ppm in rotational crop commodities from the 62-day PBI. HED concluded that 

a 120-day PBI is needed for quizalofop-P-ethyl (DP#s 219672 and D222000, 1/26/96, F. 

Griffith).

860.1900 Field Accumulation in Rotational Crops

Because the proposed label includes a 120-day PBI, no field rotational crop studies are needed.

860.1550 Proposed Tolerances

The Agency has previously determined that the ROC in plant commodities are quizalofop-Pethyl, its acid metabolite quizalofop-P, and the S-enantiomers of both compounds, each 

expressed as quizalofop-P-ethyl. The ROC in livestock commodities are quizalofop ethyl, 

quizalofop-methyl, and quizalofop, expressed as quizalofop.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 37 of 55

No Codex MRLs have been established for residues of quizalofop ethyl. Canadian MRLs have 

been established for residues of quizalofop ethyl and quizalofop in/on flax, oriental mustard 

seeds (condiment type and oil seed type), and rapeseeds (canola), the only crops included in the

subject petition, at 0.05 ppm. No Mexican MRLs have been established for any of the requested 

crops. An International Residue Limit status sheet is attached.

Field Corn

An adequate number of field trials at ~1x the proposed use rate are available for corn forage, 

grain, and stover. The OECD MRL calculator (March 2011 version) was utilized for 

determining appropriate tolerance levels for RACs that were treated according to the proposed 

use patterns; see Appendix I for tolerance calculations.

Adequate processing data for corn have been submitted. Tolerances for the processed 

commodities of corn are not needed for the purpose of this petition based on the results of 

processing trials which showed that residues of quizalofop-P-ethyl and quizalofop acid (as parent 

equivalents) were <LOQ in/on field corn grain RAC (treatment at ~2x the proposed maximum 

seasonal rate), and in field corn processed commodities [starch, refined oil (wet and dry milling), 

meal, grits, flour, and AGF]. The petitioner mentions that concerns of phytotoxicity preclude 

corn processing studies at higher rates. 

A summary of the recommended tolerances from the current petition is presented in Table 8. 

The petitioner should submit a revised section F reflecting the recommended tolerances and 

commodity definitions presented in Table 11. These new tolerances should be included in the

revised 40 CFR § 180.441 (a)(1).

Table 11. Tolerance Summary for Quizalofop-P-ethyl.

Commodity Tolerance (ppm) Comments; Correct Commodity 

Definition Proposed Recommended

Corn, forage 0.01 0.02 Corn, field, forage

Corn, grain 0.01 0.02 Corn, field, grain

Corn, stover 0.03 0.03 Corn, field, stover

Sorghum and Rapeseed Subgroup 20A (except flaxseed)

An adequate number of field trials at ~1x the proposed use rate are available for sorghum forage, 

grain, and stover. The OECD MRL calculator (March 2011 version) was utilized for 

determining appropriate tolerance levels for RACs which showed quantifiable residues in/on 

samples that were treated according to the proposed use patterns; see Appendix I for tolerance 

calculations.

Adequate processing data for sorghum have been submitted. The processing data indicate that 

total quizalofop-P-ethyl residues concentrate in sorghum AGF. Based on the processing factor, 

3.4x, and the HAFT for sorghum grain, 0.149 ppm, expected residues in sorghum AGF 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 38 of 55

following treatment at 1x would be 0.507 ppm. Because this value is greater than the 

recommended 0.2-ppm tolerance for sorghum grain, a tolerance is needed for total quizalofop-Pethyl residues in/on sorghum, grain, aspirated grain fractions. A tolerance of 1.0 ppm would be 

appropriate. 

Recently the final rule (75 FR 76284-76292, December 8, 2010) was published for the pesticide 

tolerance crop grouping regulations which allow establishment of tolerances for multiple related 

crops, based on data from a representative set of crops, created a new crop group for Oilseed and 

also established a Rapeseed Subgroup 20A. HED, therefore, tentatively recommends a tolerance 

of 1.5 ppm for residues of quizalofop and its metabolites, all expressed as quizalofop-P-ethyl

in/on rapeseed subgroup 20A, except flaxseed based on available residue data from canola seed. 

Individual tolerances for each member of the subgroup are no longer required. Canola seed is a 

member of crop subgroup 20A. Pending revision of 40 CFR §180.441(a)(3), a separate tolerance 

for canola seed may be removed.

The available canola processing data and the established processing factor for canola meal were

used to calculate a tolerance of 2 ppm for rapeseed meal. Separate tolerances for crambe meal 

and gold of pleasure meal need not be established.

HED recommends the amendment of the tolerances in 40 CFR part 180.441 by combining the 

tables for sections (a)(1) and (a)(3) into one table under section (a)(1), and by removing section 

(a)(3). Also, the tolerance expressions under section (a)(1), (a)(2) and (c) can be modified as 

follows: 

Section (a)(1): “Tolerances are established for residues of the herbicide quizalofop ethyl, 

including its metabolites and degradates, in or on the commodities in the table below. 

Compliance with the tolerance levels specified below is to be determined by measuring only

those quizalofop ethyl residues convertible to 2-methoxy-6-chloroquinoxaline, expressed as the 

stoichiometric equivalent of quizalofop ethyl, in or on the commodity.” 

Section (a)(2): “Tolerances are established for residues of the herbicide quizalofop ethyl, 

including its metabolites and degradates, in or on the commodities in the table below. 

Compliance with the tolerance levels specified below is to be determined by measuring only

those quizalofop ethyl residues convertible to quizalofop (2-[4-(6-chloroquinoxalin-2-yloxy)phenoxy]propanoic acid), expressed as quizalofop, in or on the commodity.”

Section (c): “Tolerances with regional registrations. Tolerances with regional registration are 

established for residues of the herbicide quizalofop ethyl, including its metabolites and 

degradates, in or on the commodities in the table below. Compliance with the tolerance levels 

specified below is to be determined by measuring only those quizalofop ethyl residues 

convertible to 2-methoxy-6-chloroquinoxaline, expressed as the stoichiometric equivalent of 

quizalofop ethyl, in or on the commodity.”

A summary of the recommended tolerances from the current petition is presented in Table 8. 

The petitioner should submit a revised section F reflecting the recommended tolerances and 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 39 of 55

commodity definitions presented in Table 12. These new tolerances should be included in the 

revised 40 CFR § 180.441 (a)(1).

Table 12. Tolerance Summary for Quizalofop-P-ethyl.

Commodity Tolerance (ppm) Comments; Correct Commodity 

Definition Established1

Proposed Recommended

Canola, seed 1.0 -- Removed HED recommends a tolerance of 

1.5 ppm for residues of 

quizalofop and its metabolites, 

all expressed as quizalofop-Pethyl in/on rapeseed subgroup 

20A, except flaxseed, based on 

available residue data from 

canola seed. Individual 

tolerances for each member of 

the subgroup are no longer 

required because the Rapeseed 

Subgroup 20A has been 

published in the Federal Register 

(75 FR 76284-76292, December 

8, 2010).

Gold of Pleasure, seed -- 1.0 Not needed

Borage, seed -- 1.0 Not needed

Crambe, seed -- 1.0 Not needed

Cuphea, seed -- 1.0 Not needed

Echiuim, seed -- 1.0 Not needed

Hare’s ear mustard, seed -- 1.0 Not needed

Lesquerella, seed -- 1.0 Not needed

Lunaria, seed -- 1.0 Not needed

Meadowfoam, seed -- 1.0 Not needed

Milkweed, seed -- 1.0 Not needed

Mustard, seed -- 1.0 Not needed

Oil Radish, seed -- 1.0 Not needed

Poppy, seed -- 1.0 Not needed

Rapeseed -- 1.0 Not needed

Sesame, seed -- 1.0 Not needed

Sweet Rocket, seed -- 1.0 Not needed

Canola, meal 1.5 -- Remove The available canola processing 

data was translated to the 

rapeseed subgroup 20A to 

calculate and propose a tolerance 

for the meal.

Rapeseed, subgroup 20A, meal, 

except flaxseed

Rapeseed, subgroup 20A, except 

flax, meal

2.0

Gold of Pleasure, meal -- 1.5 Not needed

Crambe, meal -- 1.5 Not needed

Sorghum, grain -- 0.2 0.20 Sorghum, grain, grain

Sorghum, forage -- 0.2 0.20 Sorghum, grain, forage

Sorghum, stover -- 0.35 0.30 Sorghum, grain, stover

Sorghum, aspirated grain -- 1.0 1.0 Sorghum, grain, aspirated grain 

fractions

Tolerance that need to be proposed

Rapeseed, subgroup 20A, except 

flaxseed

-- -- 1.5 Canola seed is a member of crop 

subgroup 20A. Pending revision 

of 40 CFR §180.441(a)(3), a 

separate tolerance for canola 

seed may be removed.

Rapeseed, subgroup 20A, except 

flaxseed

1 Under 40 CFR §180.441(a)(3).
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Milk, Meat, Egg and Poultry

Based on the results of the available ruminant feeding study and a re-calculated 1x maximum 

reasonable dietary burdens of 2.455 ppm for dairy cattle, the established tolerances for combined 

residues of quizalofop ethyl and its metabolites quizalofop and quizalofop-methyl in the fat, 

meat, and meat byproducts of cattle, goat, hog, horse, and sheep at 0.05 ppm for fat and meat 

byproducts and 0.02 ppm for meat are adequate and do not need to be revised based on the 

requested uses of quizalofop-P-ethyl. Based on whole milk residues being 0.02 ppm at 2x 

feeding level, the established tolerance of 0.01 ppm for milk is still adequate. Based on the 

maximum residues in milk of 0.02 ppm at a 2x dosing rate and an assumed 25x concentration 

factor for milk fat, expected residues at a 1x dosing rate would be 0.25 ppm; the established 

tolerance of 0.25 ppm for milk fat remains adequate.

The available poultry feeding study data indicate that the established tolerances for combined 

residues of quizalofop ethyl and its metabolites quizalofop and quizalofop-methyl in egg at 0.02 

ppm and the fat, meat, and meat byproducts of poultry at 0.05 ppm for fat and meat byproducts 

and 0.02 ppm for meat are adequate and do not need to be revised based on the requested uses of 

quizalofop-P-ethyl.

Tolerance Expressions

On 27/May/2009 HED established interim guidance on writing tolerance expressions for 

enforcement purposes. In order to add clarity to the language used to establish the coverage of 

the tolerance expression and measurement of the level of the residue in the RACs the text in the 

40 CFR § 180.441 (a)(1) should read: “Tolerances are established for the combined residues of 

the herbicide quizalofop ethyl, including its metabolites and degradates, in or on the 

commodities in the table below. Compliance with the tolerance levels specified below is to be 

determined by measuring only 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.”

For tolerances on meat, milk and poultry, the text in the 40 CFR § 180.441 (a) (2) should read: 

“Tolerances are established for the combined residues of the herbicide quizalofop-P-ethyl, 

including its metabolites and degradates, in or on the commodities in the table below. 

Compliance with the tolerance levels specified below is to be determined by measuring only

quizalofop (2-[4-(6-chloroquinoxalin-2-yl-oxy)phenoxy]propanoic acid), quizalofop ethyl (ethyl2-[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”

In addition, the text in the 40 CFR § 180.441 (a)(3) should read: “Tolerances are established for 

the combined residues of the herbicide quizalofop-P-ethyl, including its metabolites and 

degradates, in or on the commodities in the table below. Compliance with the tolerance levels 

specified below is to be determined by measuring only quizalofop-P-ethyl ester [ethyl (R)-(2-[4-

((6-chloroquinoxalin-2-yl)oxy)phenoxy)propanoate] and its acid metabolite, quizalofop-P [Rethyl(ethyl-2-[4-(6-quinoxalin-2-yl)oxy)phenoxy)propanoic acid], and the S enantiomers of both 
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 41 of 55

the ester and the acid, all expressed as quizalofop-P-ethyl ester.”

References

CB No.: 1127

Subject: PP# 5F3252 [RCB # 1127]. DPX-Y6202 (Assure®) Herbicide on Cotton and 

Soybeans. Evaluation of Analytical Methodology and Residue Data (Accession 

Nos. 073529 and 073547).

From: M. Firestone

To: R. Taylor and Toxicology Branch

Date: 9/25/1985

MRIDs: [Accession Nos. 073529 and 073547]

CB Nos.: 2806, 2806, 2810, and 2811

Subject: PP# 5F3252/FOP # 6H5479 Quizalofop ethyl (Assure®) on Soybeans. 

Amendment Dated August 31, 1987

From: G. Otakie

To: R. Taylor and Toxicology Branch

Date: 12/18/1987

MRIDs: 40322401-40322413, 40336201, and 40337101

CB No.: None

Subject: PP# 3F3252/FAP # 6H5479 Ethyl 2-[4-(6-chloroquinoxalin-2-yl oxy)phenoxy] 

Propanoate (Quizalofop ethyl) on Soybeans, Liver, and Milk - Results from EPA 

Method Validation Dated May 25, 1988

From: G. Otakie

To: R. Taylor

Date: 6/27/1988

MRIDs: None

CB Nos.: 5852 & 5853

Subject: Quizalofop-P-ethyl [D+ isomer]/Assure® II: DuPont registration proposal 

(I.D.Nos. 352-LUE and 352-LUR; Record Nos. 250157 and 250158)

From: W. Hazel

To: R. Taylor

Date: 3/29/1990

MRIDs: 41224001 & 41206101-41206103
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 42 of 55

DP#s: 160972 & 166083

Subject: PP# 1F3951. Quizalofop ethyl ester in/on cottonseed. Evaluation of Analytical 

Method and Residue Data. CBTS #’s 7640, 7641, 8229.

From: J. Stokes

To: R. Taylor and Toxicology Branch

Date: 3/4/1992

MRIDs: 41735401-41735403 & 41919801

DP#: 182751

Subject: Quizalofop-P-ethyl ester. Comparison of the Metabolism of DPX-79376, the R 

Enantiomer, Optically Active Ingredient, and DPX-Y6202, the Racemic Mixture, 

in Soybeans. CB# 10606.

From: J. Stokes

To: R. Taylor

Date: 7/15/1993

MRID: 42643201

DP#s: 196041, 196043, 205430, 205432, 206201, 206200, & 212620-212622

Subject: PP # 3F4268 - Quizalofop-P-ethyl Ester (Assure® II) On The Legume Vegetables 

(Succulent Or Dried) And Foliage Of Legume Vegetables Crop Groups, Sugar 

beet Tops, Roots, Molasses, and Cottonseed. Review of Magnitude of the 

Residue Data and Residue Analytical Method and the February 22, 1995, 

Amendment. [CBTS #s 12699, 12700, 14060, 14061, 14148, 14149, and 15196-

98]

From: F. Griffith

To: R. Taylor and J. Smith

Date: 3/30/1995

MRIDs: 42827501-42827509, 43314001, & 42439101

DP#: 219639

Subject: PP # 3F4268 - Quizalofop-P-ethyl ester (Assure® II) on Legume Vegetables 

(Succulent or Dried) and Foliage of Legume Vegetables Crop Group, Sugar beet 

Tops, Roots, and Molasses, and Cottonseed. Evaluation of the Analytical 

Chemistry Laboratory Prereview of the Tolerance Method Validations for 

Quizalofop-P-ethyl Ester. [CBTS # 16260]

From: F. Griffith

To: R. Taylor and D. Marlow

Dated: 10/11/1995

MRIDs: 43314001 and 42927509
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 43 of 55

DP#s: 219672 and 222000

Subject: PP # 5E4590 - Quizalofop-P-ethyl ester (Assure® II) on Pineapples. Review of 

Magnitude of the Residue Data and Residue Analytical Method. [CBTS # 16279 

and 16681].

From: F. Griffith

To: H. Jamerson and K. Whitby

Dated: 1/26/1996

MRIDs: 43782501

DP#s: 220215, 220216, and 220217

Subject: PP # 3F4268/5H5720 - Quizalofop-P-ethyl ester (Assure® II) on the Legume 

Vegetables (Succulent or Dried) and Foliage of Legume Vegetables Crop Groups, 

Sugar beet Tops, Roots, Molasses, and Cottonseed. Review of the July 27, Sept., 

22 and 26, 1995, Amendments. [CBTS #s 16400, 16401, and 16402].

From: F. Griffith

To: R. Taylor and K. Whitby

Dated: 2/13/96

MRID: 43804101

DP#s: 220476, 220478, and 220480

Subject: PP # 5F4545/FAP # 6H5737 - Quizalofop-P-ethyl Ester (Assure® II) on the 

Foliage Of Legume Vegetables (Except Soybeans) Crop Group, Canola And 

Canola Processed Commodities. Review of Magnitude of the Residue Data and 

Residue Analytical Method. [CBTS #s 16392, 16393, and 16394]

From: F. Griffith

To: R. Taylor and K. Whitby

Date: 2/21/1996

MRIDs: 43695701 and 43695702

DP#: 266204

Subject: Quizalofop-P-ethyl: New Uses on Barley, Wheat, Sunflower, and Flax. 

Summary of Analytical Chemistry and Residue Data.

From: S. Oonnithan

To: J. Tompkins

Dated: 7/24/2006

MRID(s): 44967701-05, 45089201-03, and 45885801-04
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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DP#: 330973

Subject: PP# 0F6076. New Food Uses on Quizalofop-Ethyl on Barley, Flax, Sunflower, 

and Wheat. Request of Petition Method Validation (PMV) of the proposed 

tolerance enforcement methods.

From: S. Oonnithan

To: F. Siegelman

Dated: 7/24/2006

MRID(s): 44967703, 44967704, 45885803, and 45885804
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 45 of 55

International Residue Limits 

Quizalofop-P-ethyl (PC Code 128709; 08/05/2011)

Quizalofop-ethyl (PC Code 128711)

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico2 Codex3

40 CFR 180.441:

Plants (commodities in this action): 

combined residues of the herbicide quizalofopP-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

Livestock: combined residues of the herbicide 

quizalofop (2-[4-(6-chloroquinoxalin-2-yl 

oxy)phenoxy]propanoic acid), quizalop-ethyl 

(ethyl-2-[4-(6-chloroquinoxalin-2-yl 

oxy)phenoxy]propanoate), and quizalofopmethyl (methyl 2-[4-(6-chloroquinoxalin-2-yloxy)phenoxy]propanoate, all expressed as 

quizalofop ethyl

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 quizalofop 

ethyl

None

Commodity1 Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico2 Codex3

Rapeseed, subgroup 20A, except 

flaxseed

1.5 0.05 flax, oriental 

mustard seeds (condiment 

type and oilseed type), 

rapeseeds (canola)

Sorghum, grain 0.20

Corn, field, forage 0.02

Corn, field, grain 0.02

Corn, field, stover 0.03

Completed: M. Negussie; 08/09/2011 and 08/05/2011 (for corn in a separate table)

1

Includes only commodities of interest for this action. Tolerance values should be the HED recommendations and 

not those proposed by the applicant.

2 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.

3 * = absent at the limit of quantitation; Po = postharvest treatment, such as treatment of stored grains. PoP = 

processed postharvest treated commodity, such as processing of treated stored wheat. (fat) = to be measured on the 

fat portion of the sample. MRLs indicated as proposed have not been finalized by the CCPR and the CAC.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 46 of 55

Appendix I. Tolerance Assessment Calculations.

For each of the corn commodities listed below, the OECD MRL calculator (March 2011 

version), was used for calculating recommended tolerances. The statistical goal of the OECD 

MRL calculator is to produce an MRL proposal in the region of the 95th percentile of the 

underlying residues distribution. The average residue values used to calculate the tolerances are 

provided in Table I-1. Residue values represent total residues of quizalofop-P-ethyl and 

quizalofop acid, converted to quizalofop-P-ethyl equivalents.

Table I-1. Residue data used to calculate tolerance for quizalofop-P-ethyl in/on corn commodities.

Regulator: EPA

Chemical: Quizalofop-P-ethyl

Crop: Corn forage Corn grain Corn stover

PHI: 32-47 Days (early harvest) 79-144 Days 79-144 Days

App. Rate: 0.078-0.088 lb ai/A 0.078-0.088 lb ai/A 0.078-0.088 lb ai/A

Submitter: Dow AgroSciences Dow AgroSciences Dow AgroSciences

MRID Citation: MRID 48260704 MRID 48260704 MRID 48260704

Total Quizalofop-P-ethyl Residues

[quizalofop-P-ethyl + quizalofop acid (in parent equivalents); ppm]

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.02

<0.02 <0.02 <0.022

<0.02 <0.02 <0.02

<0.02 <0.02
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Corn forage

The dataset used to establish a tolerance for quizalofop-P-ethyl on corn forage consisted of field 

trial data representing application rates of 0.078-0.088 lb ai/A with a 32- to 47-day PHI (early 

forage). The field trial application rates are within 25% of the proposed maximum label 

application rate; however, the majority of the field trials (22 of 24) were conducted at a PHI up 

to 57% greater than the proposed minimum label PHI. The average residues values used to 

calculate the tolerance are provided in Table I-1. Residue values represent total residues of 

quizalofop-P-ethyl and quizalofop acid, converted to quizalofop-P-ethyl equivalents. For corn

forage, all residues of quizalofop-P-ethyl and quizalofop acid, converted to parent equivalents, 

were below the LLMV. Because >50% of the corn forage dataset is censored, there is high 

uncertainty of MRL estimate.

The quizalofop-P-ethyl-corn forage dataset was entered into the OECD MRL calculator; the 

recommended tolerance is 0.02 ppm for corn forage.

Total Quizalofop-P-ethyl

Corn Forage

U.S. and Canada

1 app at 0.083 lb ai/A

Total number of data (n) 24

Percentage of censored data 100%

Number of non-censored data 0

Lowest residue 0.020

Highest residue 0.020

Median residue 0.020

Mean 0.020

Standard deviation (SD) 0.000

Correction factor for censoring (CF) 0.333

Proposed MRL estimate

- Highest residue 0.020

- Mean + 4 SD 0.020

- CF x 3 Mean 0.020

Unrounded MRL 0.020

Rounded MRL 0.02

High uncertainty of MRL estimate.

[High level of censoring]
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Corn grain

The dataset used to establish a tolerance for quizalofop-P-ethyl on corn grain consisted of field 

trial data representing application rates of 0.078-0.088 lb ai/A with a 79- to 144-day PHI. The 

field trial application rates are within 25% of the proposed maximum label application rate. The 

average residues values used to calculate the tolerance are provided in Table I-1. Residue values 

represent total residues of quizalofop-P-ethyl and quizalofop acid, converted to quizalofop-Pethyl equivalents. For corn grain, all residues of quizalofop-P-ethyl and quizalofop acid, 

converted to parent equivalents, were below the LLMV Because >50% of the corn grain dataset 

is censored, there is high uncertainty of MRL estimate.

The quizalofop-P-ethyl-corn grain dataset was entered into the OECD MRL calculator; the 

recommended tolerance is 0.02 ppm for corn grain.

Total Quizalofop-P-ethyl

Corn Grain

U.S. and Canada

1 app at 0.083 lb ai/A

Total number of data (n) 25

Percentage of censored data 100%

Number of non-censored data 0

Lowest residue 0.020

Highest residue 0.020

Median residue 0.020

Mean 0.020

Standard deviation (SD) 0.000

Correction factor for censoring (CF) 0.333

Proposed MRL estimate

- Highest residue 0.020

- Mean + 4 SD 0.020

- CF x 3 Mean 0.020

Unrounded MRL 0.020

Rounded MRL 0.02

High uncertainty of MRL estimate.

[High level of censoring]
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Corn stover

The dataset used to establish a tolerance for quizalofop-P-ethyl on corn stover consisted of field 

trial data representing application rates of 0.078-0.088 lb ai/A with a 79- to 144-day PHI. The 

field trial application rates are within 25% of the proposed maximum label application rate. The 

average residues values used to calculate the tolerance are provided in Table I-1. Residue values 

represent total residues of quizalofop-P-ethyl and quizalofop acid, converted to quizalofop-Pethyl equivalents. For corn stover, all residues of quizalofop-P-ethyl were below the LLMV and 

all quizalofop acid residues, converted to parent equivalents were below the LLMV except for 

one sample. Because >50% of the corn stover dataset is censored, there is high uncertainty of 

MRL estimate.

The quizalofop-P-ethyl-corn stover dataset was entered into the OECD MRL calculator; the 

recommended tolerance is 0.03 ppm for corn stover.

Total Quizalofop-P-ethyl

Corn Fodder

U.S. and Canada

1 app at 0.083 lb ai/A

Total number of data (n) 25

Percentage of censored data 96%

Number of non-censored data 1

Lowest residue 0.020

Highest residue 0.022

Median residue 0.020

Mean 0.020

Standard deviation (SD) 0.000

Correction factor for censoring (CF) 0.360

Proposed MRL estimate

- Highest residue 0.022

- Mean + 4 SD 0.022

- CF x 3 Mean 0.022

Unrounded MRL 0.022

Rounded MRL 0.03

High uncertainty of MRL estimate.

[High level of censoring]
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Sorghum

For each of the sorghum commodities listed below, the OECD MRL calculator (March 2011 

version), was used for calculating recommended tolerances. The statistical goal of the OECD 

MRL calculator is to produce an MRL proposal in the region of the 95th percentile of the 

underlying residues distribution. The average residues values used to calculate the tolerances are 

provided in Table I-1. Residue values represent total residues of quizalofop-P-ethyl and 

quizalofop acid, converted to quizalofop-P-ethyl equivalents.

Table I-1. Residue data used to calculate tolerance for quizalofop-P-ethyl in/on sorghum commodities.

Regulator: EPA

Chemical: Quizalofop-P-ethyl

Crop: Sorghum forage Sorghum grain Sorghum stover

PHI: 25-32 Days 29-49 Days 42-56 Days

App. Rate: 0.136-0.145 lb ai/A 0.136-0.145 lb ai/A 0.136-0.145 lb ai/A

Submitter: IR-4 IR-4 IR-4

MRID Citation: MRID 48273601 MRID 48273601 MRID 48273601

Total Quizalofop-P-ethyl Residues

[quizalofop-P-ethyl + quizalofop acid (in parent equivalents); ppm]

<0.104 <0.115 <0.119

<0.104 <0.104 <0.104

<0.110 <0.104 <0.171

<0.104 <0.112 <0.104

<0.129 <0.104 <0.132

<0.106 <0.104 <0.104

<0.104 <0.104 <0.104

<0.104 <0.104 <0.204

<0.104 <0.149 <0.108

<0.104 <0.127 <0.104

<0.169 <0.104 <0.212

<0.104 <0.104 <0.104

<0.104 <0.104
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 51 of 55

Sorghum forage

The dataset used to establish a tolerance for quizalofop-P-ethyl on sorghum forage consisted of 

field trial data representing application rates of 0.136-0.145 lb ai/A with a 25- to 32-day PHI. 

The field trial application rates and PHIs are within 25% of the maximum label application rate 

and minimum label PHI, respectively. The average residues values used to calculate the 

tolerance are provided in Table I-1. Residue values represent total residues of quizalofop-P-ethyl

and quizalofop acid, converted to quizalofop-P-ethyl equivalents. For sorghum forage, all 

residues of quizalofop-P-ethyl were below the LLMV and average residues of quizalofop acid, 

converted to parent equivalents, were above the LLMV in 4 of 13 trials. Because >50% of the 

sorghum forage dataset is censored, there is high uncertainty of MRL estimate.

The quizalofop-P-ethyl-sorghum forage dataset was entered into the OECD MRL calculator; the 

recommended tolerance is 0.20 ppm for sorghum forage.

Total number of data (n) 13

Percentage of censored data 69%

Number of non-censored data 4

Lowest residue 0.104

Highest residue 0.169

Median residue 0.104

Mean 0.112

Standard deviation (SD) 0.019

Correction factor for censoring (CF) 0.538

Proposed MRL estimate

- Highest residue 0.169

- Mean + 4 SD 0.186

- CF x 3 Mean 0.180

Unrounded MRL 0.186

Rounded MRL 0.2

 High uncertainty of MRL estimate.

[High level of censoring]

0.136-0.145 lb ai/A

Quizalofop-P-ethyl

Sorghum forage

U.S.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 52 of 55

Sorghum grain

The dataset used to establish a tolerance for quizalofop-P-ethyl on sorghum grain consisted of 

field trial data representing application rates of 0.136-0.145 lb ai/A with a 29- to 49-day PHI. 

The field trial application rates are within 25% of the maximum label application rate. The PHIs 

are within 25% of the minimum label PHI, with the exception of one trial (29-day PHI) that was 

harvested early due to damage caused by birds. This trial was included in the data set because 

residues were not significantly different from the other field trials. The average residues values 

used to calculate the tolerance are provided in Table I-1. Residue values represent total residues 

of quizalofop-P-ethyl and quizalofop acid, converted to quizalofop-P-ethyl equivalents. For 

sorghum grain, all residues of quizalofop-P-ethyl were below the LLMV and average residues of 

quizalofop acid, converted to parent equivalents, were above the LLMV in 4 of 12 trials. 

Because >50% of the sorghum grain dataset is censored, there is high uncertainty of MRL

estimate.

The quizalofop-P-ethyl-sorghum grain dataset was entered into the OECD MRL calculator; the 

recommended tolerance is 0.20 ppm for sorghum grain.

Total number of data (n) 12

Percentage of censored data 67%

Number of non-censored data 4

Lowest residue 0.104

Highest residue 0.149

Median residue 0.104

Mean 0.111

Standard deviation (SD) 0.014

Correction factor for censoring (CF) 0.556

Proposed MRL estimate

- Highest residue 0.149

- Mean + 4 SD 0.166

- CF x 3 Mean 0.185

Unrounded MRL 0.185

Rounded MRL 0.2

 High uncertainty of MRL estimate.

[High level of censoring]

0.136-0.145 lb ai/A

Quizalofop-P-ethyl

Sorghum grain

U.S.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 53 of 55

Sorghum stover

The dataset used to establish a tolerance for quizalofop-P-ethyl on sorghum stover consisted of 

field trial data representing application rates of 0.136-0.145 lb ai/A with a 42- to 56-day PHI. 

The field trial application rates and PHIs are within 25% of the maximum label application rate 

and minimum label PHI, respectively. The average residues values used to calculate the 

tolerance are provided in Table I-1. Residue values represent total residues of quizalofop-P-ethyl

and quizalofop acid, converted to quizalofop-P-ethyl equivalents. For sorghum stover, all 

residues of quizalofop-P-ethyl were below the LLMV and average residues of quizalofop acid, 

converted to parent equivalents, were above the LLMV in 6 of 13 trials. Because >50% of the 

sorghum stover dataset is censored, there is high uncertainty of MRL estimate.

The quizalofop-P-ethyl-sorghum stover dataset was entered into the OECD MRL calculator; the 

recommended tolerance is 0.30 ppm for sorghum stover.

Total number of data (n) 13

Percentage of censored data 54%

Number of non-censored data 6

Lowest residue 0.104

Highest residue 0.212

Median residue 0.104

Mean 0.129

Standard deviation (SD) 0.040

Correction factor for censoring (CF) 0.641

Proposed MRL estimate

- Highest residue 0.212

- Mean + 4 SD 0.289

- CF x 3 Mean 0.247

Unrounded MRL 0.289

Rounded MRL 0.3

 High uncertainty of MRL estimate.

[High level of censoring]

0.136-0.145 lb ai/A

Quizalofop-P-ethyl

Sorghum stover

U.S.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

Page 54 of 55

Rapeseed, subgroup 20A, except flaxseed

The available data for canola reflect nine field trials conducted in 1989 (for residue values refer 

to MRID# 43695701). Each trial had a one control plot and two test plots. The canola test plots 

received either a single broadcast ground spray at 1.5 oz ai/A (0.094 lb ai/A; ~0.8x proposed 

seasonal application rate) or 3 oz ai/A (0.188 lb ai/A; ~1.6x proposed seasonal application rate) 

along with the surfactant. Both the 0.8x and 1.5x applications were done at the same time. 

Mature canola seeds were harvested at 38 to 74 days PHI. 

Based on the available data, a tolerance for canola seed was established at 1.0 ppm. However, 

since proportionality is observed between the application rate, 0.10 lb ai/A and 0.20 lb ai/A, and 

the average residues, 0.22 ppm and 0.45 ppm, respectively, we adjusted the data to reflect the 

residues that may be expected after application at the proposed rate (0.124 lb ai/A). The residues 

originally reported as quizalofop acid equivalents were converted to quizalofop-P-ethyl

equivalents, adjusted for the application rate by using a scaling factor, and included in the OECD 

calculator to estimate a tolerance of 1.5 ppm. HED understand that this new tolerance is more 

consistent with the proposed use pattern. 

Residues for 

0.10 lb ai/A

Scaling

Factor

Scaled

Residues1

Residues for 

0.20 lb ai/A

Scaling 

Factor

Scaled

Residues1

0.120 0.806 0.161 0.180 1.61 0.121

0.081 0.806 0.109 0.250 1.61 0.168

0.050 0.806 0.067 0.050 1.61 0.034

0.125 0.806 0.167 0.510 1.61 0.342

0.050 0.806 0.067 0.084 1.61 0.056

0.050 0.806 0.067 0.050 1.61 0.034

0.310 0.806 0.415 0.600 1.61 0.402

0.210 0.806 0.281 0.280 1.61 0.188

0.700 0.806 0.938 1.500 1.61 1.006

1 Converted to quizalofop-P-ethyl equivalents by multiplying for a conversion factor of 1.08.
Quizalofop-P-ethyl Summary of Analytical Chemistry and Residue Data DP#: 395630

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Quizalofop-P-ethyl

Canola seed

USA

0.10 - 0.20 lb ai/A

Total number of data (n) 18

Percentage of censored data 0%

Number of non-censored data 18

Lowest residue 0.034

Highest residue 1.006

Median residue 0.164

Mean 0.257

Standard deviation (SD) 0.287

Correction factor for censoring (CF) 1.000

Proposed MRL estimate

- Highest residue 1.006

- Mean + 4 SD 1.404

- CF x 3 Mean 0.771

Unrounded MRL 1.404

Rounded MRL 1.5