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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND

POLLUTION PREVENTON

MEMORANDUM

Date: August 7, 2013

SUBJECT: S-Metolachlor, PP#2F8115. Petition for the Amendment of Permanent 

Tolerances for Residues of S-Metolachlor on Corn, field, forage; Corn, sweet, 

forage; and Corn, stover. Summary of Analytical Chemistry and Residue Data.

PC Code: 108800 DP Barcode: D407466, D413850

Decision No.: 471357 Registration No.: 100-818

Petition No.: 2F8115 Regulatory Action: Petition, no amended use

Risk Assessment Type: NA Case No.: 0001

TXR No.: NA CAS No.: 87392-12-9

MRID No.: 48932501, 49186501 40 CFR: 180.368 (a)(2)

FROM: Susan V. Hummel, Senior Chemist

Risk Assessment Branch 4, Health Effects Division, 7509P

THROUGH: Thurston G. Morton, Senior Chemist

Risk Assessment Branch 4, Health Effects Division, 7509P

TO: Michael Walsh & Kathryn V. Montague, PM#23

Fungicides Branch, Registration Division, 7505P

Executive Summary

S-Metolachlor (an isomer enriched form of metolachlor) is a selective, chloroacetanilide 

herbicide that is applied to a variety of crops as a preplant, preplant incorporated, preemergence, 

or postemergence application, primarily for the control of grass weeds. S-Metolachlor is 

registered to Syngenta Crop Protection, Inc. for use on a wide variety of crops including: corn, 

cotton, grasses grown for seed, legume vegetables, peanuts, potatoes, safflower, sorghum, 

sunflower, and tomatoes. 

Pesticide petition #2F8115 was submitted to amend the established tolerances for the herbicide 

S-metolachlor in or on corn, field, forage; corn, sweet, forage; and corn, stover to 20 ppm; 40 

ppm; and 40 ppm, respectively. A tolerance for combined residues (free and bound) of Smetolachlor, its R-enantiomer and its metabolites, determined as the derivatives, 2-[2-ethyl-6-
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methylphenyl)amino]-1-propanol and 4-(2-ethyl-6-methylphenyl)-2-hydroxy-5-methyl-3-

morpholinone is currently established under 40 CFR 180.368 on corn, field, forage; corn, sweet, 

forage; and corn, stover at 6.0 ppm. In connection with PP#2F8115, a residue study was 

submitted with S-metolachlor treated field corn, field corn/simulated sweet corn, sweet corn and 

popcorn. A safener was used in the study. The use pattern used was the currently registered use 

pattern for Dual II Magnum (EPA Reg. No 100-818). Residues of S-metolachlor in some 

samples of forage and stover exceeded the current tolerances.

The nature of S-metolachlor residues in crops and livestock is understood based on adequate 

crop and livestock metabolism studies with metolachlor and S-metolachlor. For both Smetolachlor and metolachlor, the residues of concern in crop and livestock commodities include 

the parent compound (both R and S-enantiomers) and its metabolites, determined as the 

derivatives CGA-37913 and CGA-49751. Following recommendations made in the revised 

Tolerance Reassessment Eligibility Decision (TRED) for Metolachlor and S-Metolachlor (DP# 

292881, 8/15/03, S. Kinard), tolerances for metolachlor and S-metolachlor have been separated. 

Permanent tolerances for combined S-metolachlor residues have been established for crop 

commodities ranging from 0.10 ppm in/on a variety of crop commodities to 20 ppm in/on peanut 

hay [40 CFR §180.368(a)(2)]. Permanent tolerances for indirect or inadvertent residues of Smetolachlor have also been established for non-grass animal feeds (Group 18), and the forage, 

hay, grain and straw of small cereal grains (barley, buckwheat, millet, oats, rice, rye and wheat), 

at levels ranging 0.10 ppm in/on grains to 1.0 ppm in/on non-grass animal feeds [40 CFR 

§180.368(d)(2)].

Adequate methodology is available for enforcing the current tolerances. The Pesticide 

Analytical Manual (PAM), Vol. II, lists a gas chromatography method with nitrogen phosphorus 

detection (GC/NPD) for determining residues in/on crop commodities (Method I) and a GC 

method with mass selective detection (GC/MSD) for determining residues in livestock 

commodities (Method II). These methods determine residues of metolachlor and its metabolites 

as either CGA-37913 or CGA-49751 following acid hydrolysis. 

Syngenta has proposed an enantiomer-specific high performance liquid chromatography method 

with triple quadrupole mass spectrometric detection (LC/MS/MS) for the enforcement of the 

proposed tolerances, Method 1848-01, which has been previously reviewed by HED (DP# 

296904, 4/17/06, R. Loranger). The method uses a chiral HPLC column to separate out the Senantiomers (SYN506357 and SYN508500) of the hydrolysis products CGA-37913 and CGA49751, respectively. HED concluded that the method is not appropriate for enforcement 

purposes because it does not determine residues of the R-isomers of metolachlor and its 

metabolites, which are included in the tolerance expression. The S:R ratio in the active 

ingredient is 88:12; therefore, there is potential for residues of the R-isomers of metolachlor and 

its metabolites in crop commodities. The method could be adapted for enforcement by 

measuring both the S- and the R-enantiomers and monitoring 2 ion transitions per analyte. 

Residue data from the current field trial studies were obtained using LC/MS/MS Analytical 

Method No. ENC-5/99, with modifications found in EPL-BAS Study Number 110S50 (MRID 

49186501). A complete description of the method was not included in the submission, nor in 

MRID 49186501. Briefly, a subsample of each corn matrix was refluxed for 16 hours in 6N 
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hydrochloric acid. After cooling and filtering, an aliquot was diluted with water, basified, and 

partitioned into dichloromethane (DCM). Partitioning was repeated, and the DCM fractions 

were combined and concentrated; methanol was added and the sample was again concentrated. 

Each sample was then diluted to a final volume with methanol:water (17:83, v:v) for analysis by

LC/MS/MS in the positive ionization mode, using a reverse phase column (Luna C18). MS/MS 

detection of CGA-37913 and CGA-49751 monitored the ion transitions from m/z 194→136 and 

m/z 250→204, respectively. [The reviewer noted that the incorrect ion transitions were noted in 

the report; these have been corrected here, and were confirmed via email by the petitioner.] All 

residue levels of the metabolites were converted to parent equivalents using molecular weight 

factors of 1.47 and 1.14 for CGA-37913 and CGA-49751, respectively. The limits of 

quantitation (LOQs, based on the LLMVs) were 0.03 and 0.05 ppm for CGA-37913 and CGA49751, respectively, in all corn matrices. The petitioner used the LLMVs as the limits for 

reporting residues. The method was validated prior to and in conjunction with the analysis of 

field trial samples.

Adequate data are available on the recovery of metolachlor through Multiresidue Method Testing 

Protocols. The FDA PESTDATA database indicates that metolachlor is completely recovered 

through Method 302, PAM Vol. I (3rd ed., revised 10/97).

Adequate concurrent storage stability data were submitted to support the sample storage 

conditions and durations from the submitted field trial and processing studies. These data 

indicate that the metolachlor derivatives CGA-49751 and CGA-37913 and/or S-metolachlor 

derivatives SYN506357 and SYN508500 are stable during frozen storage for at least 2 years on 

corn commodities.

Although there are livestock feedstuffs associated with the current petition, the proposed uses 

impact the diet for beef cattle, but not dairy cattle. The tolerance is based on the dietary burden 

of S-metolachlor to dairy cattle. Therefore, no changes to the existing tolerances for livestock 

commodities are needed.

The tolerance proposals are adequate. Adequate field trial data have been submitted with the 

current petition to support the requested tolerances. Geographic representation was adequate. 

An adequate analytical method was used for the analysis. The data were properly supported by

storage stability data.

An adequate confined rotational crop study is available, although additional information 

pertaining to the study remains outstanding. The residues of concern in rotated crops are the 

same as in the primary crops, S-metolachlor, its R-enantiomer, and its metabolites determined as 

CGA-37913 and CGA-49751. Adequate field rotational crop data have been submitted 

previously which support the existing rotational crop restrictions on the labels for EPA Reg. Nos. 

100-816 and 100-818.

Regulatory Recommendations and Residue Chemistry Deficiencies

HED has examined the residue chemistry database for S-metolachlor. Pending submission of 

analytical standards and a revised Section F, there are no residue chemistry issues that would 
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preclude setting of the recommended tolerances for S-metolachlor on corn forage and stover, as 

indicated in Table 8. No change in the current registration for S-metolachlor is requested.

A deficiency remains with regard to the confined rotational crop study.

A human health risk assessment is forthcoming.

860.1850 Confined Accumulation in Rotational Crops

 To support the confined rotational crop study submitted under MRID 41470601, the 

additional data required by HED (DP# 207842, 10/12/94, S. Hummel) must be submitted; 

additional data were required characterizing the 14C-residues in plants, along with 

information on the percentage of the 14C-residues measured by the current enforcement 

method; sample storage conditions and intervals and supporting storage stability data 

were also required. These data requirements were reiterated in the Metolachlor TRED 

(DP# 292881, 8/15/03, S. Kinard).

Background

The chemical structure and nomenclature of S-metolachlor and its regulated hydrolytic 

derivatives are presented in Table 1, and the physicochemical properties of S-metolachlor are 

presented in Table 2. 

Table 1. Nomenclature of S-Metolachlor and its Regulated Hydrolytic Derivatives.

Parent compound

Common name 1S-Metolachlor

Company experimental name CGA-77102

IUPAC name (S)-2-chloro-N-(2-ethyl-6-methyl-phenyl)-N-(2-metonym-1-methyl-ethyl)-

acetamide

CAS name 2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(1S)2-methoxy-1-methylethyl]-

acetamide

CAS registry number 87392-12-9

End-use product (EP) Dual Magnum® Herbicide (7.62 lb/gal EC; EPA Reg. No. 100-816) and 

Dual II Magnum® Herbicide (7.64 lb/gal EC; EPA Reg. No. 100-818)

Regulated residue

Common name None

H3C

CH3

N

O

CH3

Cl

H C3

O

H C3

NH

CH3

HO

CH3
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Table 1. Nomenclature of S-Metolachlor and its Regulated Hydrolytic Derivatives.

Company experimental names CGA-37913

SYN506357 (S-enantiomer of CGA 37913)

Chemical name 2-[(2-ethyl-6-methylphenyl) amino]-1-propanol

CAS registry number 61520-53-4

82508-08-5 (S-enantiomer)

Regulated residue

Common name None

Company experimental names CGA-49751

SYN508500 (S-enantiomer of CGA 49751)

Chemical name 4-(2-ethyl-6-methylphenyl)-2-hydroxy-5-methyl-3-morpholinone

CAS registry number 61520-54-5

Table 2. Physicochemical Properties of S-Metolachlor.

Parameter Value Reference

Melting point/range Not applicable, liquid at room temperature MRID 47121701 

(DP#s 332846, etc., 

10/21/08, D. 

McNeilly)

pH 7.8 at 25 oC (1% aqueous dispersion)

Density 1.117 g/cm3at 20 oC

Water solubility (25°C) 0.48 g/L

Solvent solubility (mg/L at 25°C) Completely miscible with methanol, acetone, toluene, 

n-octanol, n-hexane, ethyl acetate, and dichloromethane.

Vapor pressure at 25°C 2.8 x 10-5 mm Hg

Dissociation constant (pKa) No dissociation constant in pH range 2-12

Octanol/water partition coefficient 

Log(KOW)

3.05 at 25 oC

UV/visible absorption spectrum Neutral: 534 L/mol•cm @ 266.4 nm

443 L/mol•cm @ 274.4 nm

Acidic: 534 L/mol•cm @ 266.4 nm

444 L/mol•cm @ 274.4 nm

Basic: 531 L/mol•cm @ 266.4 nm

411 L/mol•cm @ 274.4 nm

860.1200 Directions for Use

The petitioner provided a text listing of proposed uses in Section B of the petition, already 

registered on the label for Dual II Magnum® (EPA Reg. No. 100-818), a 7.64 lb/gal EC 

formulation. This use summary is based on Section B of the petition.

H C3

CH3

N

O

O

OH

H C3
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Table 3. Summary of Current Directions for Use of S-Metolachlor.1

Applic. Timing; 

Type; and Equip.

(minimum volume)

Formulation

[EPA Reg. 

No.]

Applic. 

Rate

(lb ai/A)

Max. No. 

Applic. per 

Season

Max. Seasonal 

Applic. Rate

(lb ai/A)

PHI

(days)

Corn

Fall Application for 

Spring Control/ 

Early Preplant

Broadcast

7.62 lb/gal 

EC

[100-818]

1.6 – 1.9 NS 3.7 NS

Preplant 

Incorporated or 

Preemergence

Broadcast

0.95-1.9 NS 3.7 NS

Postemergence or 

Layby Broadcast Up to 1.9 NS 3.7 NS

Use higher rates on fine or >2,5-3% organic matter soils. Split application may be used. Ground application 

minimum 5 GPA; aerial application minimum 2 GPA. Do not use Dual II Magnum on peat or muck soils. Do not 

graze or feed forage from treated areas for 30 days following application. Do not harvest sweet corn ears for 60 

days following application.

The proposed uses specify that lower rates should be used on relatively coarse textured soils and 

higher rates should be used on fine textured soils. 

Conclusions. The registered use directions are adequate to allow for evaluation of the submitted 

residue data relative to the current uses. The registered uses are generally supported by the 

submitted field trial data. 

The rotational crop restrictions on the label for EPA Reg. No. 100-816 have been evaluated 

previously (DP#s 332846, etc., 10/21/08, D. McNeilly). It was concluded that the proposed 

restrictions are supported by the available data, provided that that rotational crop directions for 

crops with a 60-day PBI be amended to prohibit a second application of S-metolachlor to any of 

these crops replanted within 60 days of the original application. Since the full label was not 

provided in the current petition, it is unknown if these changes have been made.

860.1300 Nature of the Residue - Plants

The qualitative nature of metolachlor residues in plants is adequately understood based upon the 

adequate corn, potato, and soybean metabolism studies. The metabolism of metolachlor involves 

conjugation with glutathione, breakage of this bond to form the mercaptan, conjugation of the 

mercaptan with glucuronic acid, O-demethylation of the methyl ether, and conjugation of the 

resultant alcohol with a neutral sugar. A minor pathway may involve sugar conjugation of 

metolachlor directly to the corresponding oxo-compounds. Residues of concen in plants include 

metolachlor and its metabolites, determined as the derivatives CGA-37913 and CGA-49751. 

The Agency previously concluded that the residues of concern for S-metolachlor are the same as 

for metolachlor (DP# 226780, 11/15/96, L. Kutney).

The Agency has also reviewed plant metabolism data on S-metolachlor from field tests on 

soybeans and corn, in vitro tests on corn seedlings, and greenhouse tests on seedlings of corn, 
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sorghum, soybeans and peanuts (DP#s 278742 and 279110, 8/15/03, S. Kinard). These data 

support Syngenta’s assertion that the metabolism of S-metolachlor in plants is similar to that for 

the racemic mixture. The data did not address whether there is any conversion of the S-isomers 

of metolachlor or its metabolites to the R-isomer forms; however, HED previously concluded 

that such conversion of isomers in plants is not likely to be significant.

860.1300 Nature of the Residue - Livestock

Adequate studies are available depicting the metabolism of metolachlor in ruminants and 

poultry. Metolachlor is rapidly metabolized and almost totally eliminated in the urine and feces 

of ruminants (goats), non-ruminants (rats), and poultry. Metolachlor per se was not detected in 

any of the excreta or tissues. As in plants, metolachlor residues of concern in livestock 

commodities include metolachlor and its metabolites, determined as the derivatives CGA-37913 

and CGA-49751. The residues of concern for S-metolachlor in livestock are the same as those 

for metolachlor.

The Agency has also reviewed livestock metabolism data on S-metolachlor (DP#s 278742, 

8/15/03, S. Kinard). Data from a goat metabolism study indicated that S-metolachlor was readily 

absorbed and extensively metabolized by goats via glutathione conjugation and/or oxidation 

reactions. Oxidized metabolites were also conjugated with glucuronic acid. Data from a poultry

metabolism study indicated that S-metolachlor was also extensively metabolized via O 

demethylation and subsequent glucuronic acid conjugation or oxidation to dihydroxy or 

carboxylic acid metabolites that may also be conjugated with glucuronic acid.

860.1340 Residue Analytical Methods

Enforcement methods: Adequate methodology is available for enforcing the established and 

recommended tolerances. PAM Vol. II, Pesticide Regulation Section 180.368, lists a GC/NPD 

method (Method I) for determining residues in/on crop commodities and a GC/MSD method 

(Method II) for determining residues in livestock commodities. These methods determine 

residues of metolachlor and its metabolites as either CGA-37913 or CGA-49751 following acid 

hydrolysis.

IR-4 and Syngenta have proposed an LC/MS/MS enantiomer-specific method for the 

enforcement of the proposed tolerances, Method 1848-01. This method has been previously 

reviewed by HED (DP# 296904, 4/17/06, R. Loranger). The method as written uses a chiral 

HPLC column to separate out the S-enantiomers (SYN506357 and SYN508500) of the 

hydrolysis products CGA-37913 and CGA-49751. The method monitors a single ion transition 

per analyte.

Data-gathering methods: Samples of crop commodities from the submitted field trial studies 

were analyzed for residues of metolachlor and its metabolites convertible to the derivatives 

CGA-49751 and CGA-37913 using high performance liquid chromatography with tandem mass 

spectrometric detection (LC/MS/MS) according to Analytical Method No. ENC-5/99, with 
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modifications found in EPL-BAS Study Number 110S50 (MRID 49186501). A complete 

description of the method was not included in the submission.

Briefly, a subsample of each corn matrix was refluxed for 16 hours in 6N hydrochloric acid. 

After cooling and filtering, an aliquot was diluted with water, basified, and partitioned into 

dichloromethane (DCM). Partitioning was repeated, and the DCM fractions were combined and 

concentrated; methanol was added and the sample was again concentrated. Each sample was 

then diluted to a final volume with methanol:water (17:83, v:v) for analysis by LC/MS/MS in the 

positive ionization mode with an APCI interface, using a reverse phase column (Luna C18) and 

gradient elution with acetonitrile:water. MS/MS detection of CGA-37913 and CGA-49751 

monitored the ion transitions from m/z 194.3 → 136.3 and m/z 249.9 → 203.8, respectively. All 

residue levels of the metabolites were converted to parent equivalents using molecular weight 

factors of 1.47 and 1.14 for CGA-37913 and CGA-49751, respectively. The analytical method 

description here was corrected for ion transitions monitored by checking MRID 45555901. The 

method description in the current submission had the ion transitions reversed and rounded m/z to 

integers, and was confirmed by email from Syngenta

The limits of quantitation (LOQs, based on the LLMVs) were 0.03 and 0.05 ppm for CGA37913 and CGA-49751, respectively, in all corn matrices. The petitioner used the LLMVs as the 

limits for reporting residues.

The method was validated prior to and in conjunction with the analysis of field trial samples.

Conclusions. Adequate enforcement methods are available for determining residues in crop and 

livestock commodities. 

The petitioner has proposed the enantiomer-specific LC/MS/MS method, Method No. 1848-01, 

for enforcement purposes. HED concludes that the method is not appropriate for enforcement 

purposes because it does not determine residues of the R-isomers which are included in the 

tolerance expression. The S:R ratio in the active ingredient is 88:12; therefore, there is potential 

for residues of the R-isomers of metolachlor and its metabolites in crop commodities. The 

method could be adapted for enforcement by changing the method to measure both the S- and the 

R-enantiomers, and upgraded to include two ion transitions per analyte.

860.1360 Multiresidue Methods

Adequate data are available on the recovery of metolachlor through Multiresidue Method Testing 

Protocols. The FDA PESTDATA database indicates that metolachlor is completely recovered 

through Method 302, PAM Vol. I (3rd ed., revised 10/97).

860.1380 Storage Stability

Adequate storage stability data are available for crop commodities. Previously submitted data 

(DP# 292881, 8/15/03, S. Kinard) indicate that: CGA-37913 is stable at ≤-10 °C for at least 2 

years in corn (grain and forage), peanut, potato (tubers, wet peel and flakes), soybean (hulls and 

meal) and tomatoes, for at least 29 months in cottonseed oil, and for at least 37 months in 
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cottonseed and corn oil; and CGA-49751 is stable at ≤-10°C for at least 2 years in corn (grain, 

forage, and oil), peanuts, potatoes (tubers, wet peel and flakes), soybeans (hulls and meal) and 

tomatoes, and for at least 37 months in cotton seed and cottonseed oil.

The durations and conditions of samples from the current crop field trials and processing studies 

are presented in Table 4.

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

Processing Studies. 

Matrix Storage Temperature

(°C)

Actual Storage 

Duration

Interval of Demonstrated Storage Stability

Corn commodities 

(grain, K+CWHR, 

forage and stover)

-10 -- -20 116-477 days CGA-49751 and CGA-37913 are stable for up 

to 2 years in/on corn grain, forage, and oil

Conclusions. Adequate storage stability data are available to support the storage durations and 

conditions for samples from the submitted field trial and processing studies. No corrections for 

potential 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

The reregistration requirements for magnitude of the residue in meat, milk, poultry, and eggs are 

fulfilled (DP# 292881, 8/15/03, S. Kinard). Adequate ruminant and poultry feeding studies are 

available for metolachlor, and these data will also support the use of S-metolachlor.

The livestock feedstuffs treated with S-metolachlor in this petition include corn forage and 

stover.

The dietary burdens for livestock to S-metolachlor residues were recently recalculated in 

conjunction with a request to amend use directions for sorghum and soybean (DP#s 332846, etc., 

10/21/08, D. McNeilly). At that time, the dietary burdens were calculated to be 26.2 ppm for 

cattle, 0.51 ppm for poultry, and 0.44 ppm for swine. It was concluded that the established 

tolerances for livestock commodities were adequate to support existing metolachlor uses.

HED has recalculated the reasonable dietary burdens (RDBs) to livestock using the most recent 

guidance (June 2008) and the existing and proposed tolerances for residues of metolachlor in/on 

livestock feedstuffs; see Table 5. The RDBs are 15.9 ppm for beef cattle, 20.2 ppm for dairy

cattle, 0.48 ppm for poultry, and 0.40 ppm for swine. Because these RDBs are less than the 
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dietary burdens that were calculated previously, no changes to the established tolerances for 

livestock commodities are needed to support the proposed uses.

Table 5. Calculation of Dietary Burdens of S-Metolachlor Residues to Livestock.

Feedstuff Type1 % Dry 

Matter2 % Diet2 Tolerance (ppm) Dietary Contribution (ppm)

3

Beef Cattle

Corn, field, forage R 40 15 40.0 15.00

Beet, sugar, molasses CC 75 10 2.0 0.27

Potato, processed waste CC 15 30 0.20 0.40

Sorghum, grain CC 86 40 0.30 0.14

Sunflower, meal PC 92 5 1.0 0.054

TOTAL BURDEN -- -- 100 -- 15.86

Dairy Cattle

Grass forage R 25 45 10 18.0

Corn, sweet, cannery waste CC 30 10 6.0 2.0

Sorghum, grain CC 86 35 0.30 0.12

Sunflower, meal PC 92 10 1.0 0.11

TOTAL BURDEN -- -- 100 -- 20.2

Poultry

Sorghum, grain CC NA 75 0.30 0.23

Sunflower, meal PC NA 25 1.0 0.25

TOTAL BURDEN -- -- 100 -- 0.48

Swine

Corn, field, grain CC NA 5 0.10 0.005

Sorghum, grain CC NA 80 0.30 0.24

Sunflower, meal PC NA 15 1.0 0.15

TOTAL BURDEN -- -- 100 -- 0.40

1

 R: Roughage; CC: Carbohydrate concentrate; PC: Protein concentrate.

2

 OPPTS 860.1000 Table 1 Feedstuffs (June 2008). 

3

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

poultry and swine.

Conclusions. The proposed uses for S-metolachlor will have no significant impact on the dietary

burden of metolachlor to livestock, since corn forage and stover are fed to beef cattle, which had 

a significantly lower dietary burden than dairy cattle. As a result, no changes are required in the 

current tolerances for metolachlor residues in livestock commodities.
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860.1500 Crop Field Trials

48932501.der.docx

The petitioner submitted field trial data in support of the registered uses on field corn, sweet 

corn, and popcorn. Trials were conducted on simulated sweet corn, field corn, and popcorn. The 

treatments included an early treatment, either preplant incorporated, pre-emergence, or early 

post-emergence, plus a layby treatment at either 30” or 40” The results of the field trials are 

summarized in Table 6. 

TABLE 6. Summary of Residue Data from Field Corn, Sweet Corn, and Popcorn Field Trials with 

 S-Metolachlor.

Corn Matrix

Total 

Rate

(lb ai/A)

PHI range 

in days

(Mean ± 

Std. Dev.)

Analyte

Residue Levels, ppm1

n

Sample 

Min.

Sample 

Max. LAFT2 HAFT2 Median Mean Std. Dev.

Treatments 2, 4, 6, and 8: One of Four Types of Soil Surface Treatment + Broadcast OTT

3 Treatment When Corn 

Was About 30 Inches Tall

Forage with ears 

if present

3.9159-

4.1734 

except 

for

2.6539 

in trial 

C01-

0745

28-40

(33 ± 3)

CGA-37913 20 0.04 1.8 0.13 1.28 0.79 0.75 0.34

CGA-49751 20 0.16 6.3 0.48 5.7 2.58 2.74 1.20

Combined Residues 20 0.20 7.5 0.61 7.0 3.42 3.48 1.50

Forage without 

ears

28-47

(36 ± 7)

CGA-37913 12 0.10 2.9 0.20 2.5 0.65 0.96 0.74

CGA-49751 12 0.43 15 0.55 13 2.70 4.13 3.80

Combined Residues 12 0.59 18 0.75 16 3.34 5.09 4.53

K+CWHR 30-54

(42 ± 8)

CGA-37913 12 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 NA

CGA-49751 12 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA

Combined Residues 12 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 NA

Field corn

grain

59-111

(95 ± 15)

CGA-37913 20 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 NA

CGA-49751 20 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA

Combined Residues 20 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 NA

Popcorn grain 77

CGA-37913 1 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 NA

CGA-49751 1 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA

Combined Residues 1 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 NA

Stover of field 

corn, sweet corn, 

and popcorn

47-111

(84 ± 20)

CGA-37913 26 <0.03 2.1 <0.03 1.8 0.55 0.69 0.51

CGA-49751 26 <0.05 8.9 <0.05 8.2 2.18 2.64 2.31

Combined Residues 26 <0.08 11 <0.08 9.9 2.75 3.32 2.81

Treatments 3, 5, 7, and 9: One of Four Types of Soil Surface Treatment + Broadcast OTT

3 Treatment When Corn

Was About 40 Inches Tall

Forage with ears 

if present

3.7915-

4.1612

28-31

(30 ± 1)

CGA-37913 20 0.09 2.2 0.11 1.9 0.91 0.95 0.55

CGA-49751 20 0.21 11 0.26 10.4 2.88 3.67 2.56

Combined Residues 20 0.29 13 0.36 12 3.80 4.62 3.06

Forage without 

ears

21-42

(32 ± 6)

CGA-37913 12 <0.03 4.7 <0.04 4.3 1.09 1.66 1.34

CGA-49751 12 <0.05 24 <0.07 22 4.68 7.28 6.54

Combined Residues 12 <0.08 29 <0.10 26 5.75 8.90 7.83

K+CWHR 21-48

(35 ± 8)

CGA-37913 12 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 NA

CGA-49751 12 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA

Combined Residues 12 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 NA

Field corn

grain

51-101

(88 ± 16)

CGA-37913 20 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 NA

CGA-49751 20 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA

Combined Residues 20 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 NA
Page 12 of 20

TABLE 6. Summary of Residue Data from Field Corn, Sweet Corn, and Popcorn Field Trials with 

 S-Metolachlor.

Corn Matrix

Total 

Rate

(lb ai/A)

PHI range 

in days

(Mean ± 

Std. Dev.)

Analyte

Residue Levels, ppm1

n

Sample 

Min.

Sample 

Max. LAFT2 HAFT2 Median Mean Std. Dev.

Popcorn grain 72

CGA-37913 1 <0.03 <0.03 <0.03 <0.03 <0.03 <0.03 NA

CGA-49751 1 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 NA

Combined Residues 1 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 NA

Stover of field 

corn, sweet corn, 

and popcorn

44-101

(77 ± 20)

CGA-37913 26 0.03 5.1 0.04 4.7 0.97 1.38 1.24

CGA-49751 26 <0.05 23 <0.05 21 3.63 5.33 5.35

Combined Residues 26 <0.08 28 <0.09 26 4.52 6.72 6.61

Syngenta has submitted field trial data for S-metolachlor on field corn, sweet corn, and popcorn. 

A total of 20 crop field trials on field corn were conducted in the United States during the 2010 

growing season in North American Free Trade Agreement (NAFTA) Growing Zones 1 (NY), 2 

(VA), 5 (IA, 4 trials; MN; MO, 2 trials; ND, 3 trials; NE, 2 trials; OH, 2 trials), 5A (WI, 3 trials), 

and 6 (TX); at 7 of these trials, samples were also collected at the milk stage to simulate sweet 

corn commodities. A total of 5 crop field trials on sweet corn were conducted in the United 

States during the 2010 growing season in NAFTA Growing Zones 1 (PA), 3 (FL), 10 (CA), 11 

(OR), and 12 (OR). One crop field trial on popcorn was conducted in the United States during 

the 2011 growing season in NAFTA Growing Zone 6. Examination of the field trial records 

indicates that individual Field Research Directors (FRDs) supervised two trials each within 23 

miles or less of each other in IA (2 instances), MO, ND, NE, and OH; and one FRD supervised 3 

trials in one location in WI. (All other trials within individual states were far apart.) For 

purposes of OCSPP 860.1500 data requirements, all of these trials are considered to be separate 

independent trials because of sufficient differences in residue levels for at least one of the corn 

commodities and/or differences between trials in some of the sets regarding crop variety, 

adjuvant class, application spray volume, soil type, and location (distances between the trials).

Each trial consisted of one untreated (control) plot of field corn, sweet corn, or popcorn and plots 

of the same type of corn that were treated with a 7.64 lb ai/gal emulsifiable concentrate (EC) 

formulation of S-metolachlor (Dual II MAGNUM®), which contains 0.375 lb benoxacor/gal as a 

safener. Sufficient plots were treated at each site to accommodate two different treatment 

regimens for each of the commodities to be harvested at that site. The commodities harvested, 

which differed depending on the type of corn, were forage with ears if present, forage without 

ears, kernels plus cob with husk removed (K+CWHR), grain, and stover. Each treated plot was 

sprayed twice, once to the soil around the time of planting (using one of four different methods) 

and once broadcast over-the-top (OTT) of the crop. At each site, one plot received the OTT 

spray when it was about 30 inches tall, and another plot received the OTT spray when it was 

about 40 inches tall. Because the method of application to the soil was held constant at each site, 

the only difference at each site for each commodity was the OTT sprayings applied at two 

different crop heights. Each pair of applications was assigned either an even or odd treatment ID 

number depending on whether the OTT application was at 30 or 40 inches, respectively. In the 

applications to soil in treatments 2 and 3, spray was incorporated into the top few inches of the 

soil before planting (pre-plant incorporated, PPI); in treatments 4 and 5, the soil surface was 

sprayed pre-planting; in treatments 6 and 7, the soil surface was sprayed at the time of planting; 

and in treatments 8 and 9, the soil surface was sprayed after planting but preemergence. In the 
Page 13 of 20

even-numbered treatments, plots received a soil application and a broadcast OTT application of 

the EC formulation each at rates of 1.89-2.11 lb ai/A/application (2.12-2.36 kg ai/ha/application) 

for total application rates of 3.92-4.17 lb ai/A (4.39-4.67 kg ai/ha). At one field corn trial in OH, 

the soil treatment was made at 0.66 lb ai/A for a total rate of 2.65 lb ai/A. In the odd-numbered 

treatments, plots received a soil application and a broadcast OTT application of the EC 

formulation each at rates of 1.83-2.13 lb ai/A/application (2.05-2.39 kg ai/ha/application) for 

total application rates of 3.79-4.16 lb ai/A (4.25-4.66 kg ai/ha). Applications were made in spray

volumes of 1.98-2.08 gal/A of water (18.5-19.5 L/ha) at three trials and in spray volumes of 

7.88-28.42 gal/A of water (73.7-266 L/ha) in the other 23 trials. Although no adjuvant was used 

in most of the soil applications, the OTT application always included a crop oil concentrate 

(COC), a non-ionic surfactant (NIS), or ammonium sulfate (AMS), singly or in combination, as 

an adjuvant. No information was provided as to the types of equipment used for application of 

the test substance.

In the field corn trials, samples of forage with ears (if present) were collected with a target 

preharvest interval (PHI) of 30 ± 3 days, and grain and stover samples were collected at standard 

maturity. At seven of the field corn trials, samples of forage without ears and K+CWHR were 

collected at the milk stage to simulate sweet corn commodities. At the sweet corn trials, samples 

of forage without ears were collected with a target PHI of 30 ± 3 days, and K+CWHR and stover 

were collected at standard maturity. Popcorn grain and stover samples were collected at standard 

maturity. Partly because of differences as to when crop maturity was reached, the PHIs for the 

different commodities varied widely. The target PHI for forage with ears if present was well 

achieved for the odd-numbered treatments; however, other forage samples often had PHIs of 

about 1-2 weeks beyond target. Residue decline was assessed in two trials each (for one evennumbered treatment and one odd-numbered treatment) in field corn commodities (forage with 

ears if present, grain, and stover) and in sweet corn commodities (forage without ears, 

K+CWHR, and stover). In these trials, additional forage samples were collected at PHIs of 19-

21, 25, 35, and 40 days, and additional K+CWHR, grain, and stover samples were collected 

14/15 and 7/8 days before mature harvest and 6-8 and 13/15 days after mature harvest.

Samples were analyzed for residues of residues of S-metolachlor as CGA-37913 and CGA49751 using high performance liquid chromatography with tandem mass spectrometric detection

(LC/MS/MS) according to Analytical Method No. ENC-5/99, with modifications found in EPLBAS Study Number 110S50 (MRID 49186501). For all matrices, the petitioner used the lowest 

levels of method validation (LLMVs) of 0.03 and 0.05 ppm as the limit for reporting residues of 

CGA-37913 and CGA-49751, respectively. All residue levels were converted to parent 

equivalents using molecular weight factors of 1.47 and 1.14 for CGA-37913 and CGA-49751, 

respectively. The method was adequate for data collection based on acceptable method 

validation and concurrent recovery data. The fortification levels used in the concurrent 

recoveries were adequate to bracket expected residue levels. Method validation and concurrent 

recoveries were corrected, if needed, for apparent residues in controls. No corrections were 

made for control residue levels in the treated samples.

Samples of corn forage with ears if present, forage without ears, K+CWHR, field corn grain, 

popcorn grain, and stover were stored frozen (<-10 °C) from collection to extraction for analysis 

for up to 17.0, 14.7, 14.0, 13.6, 3.8, and 14.6 months, respectively. Samples were analyzed 
Page 14 of 20

within 0-60 days of extraction. Adequate storage stability data are available indicating that CGA37913 is stable at ≤-10 °C for at least 2 years in corn (grain and forage), peanut, potato (tubers, 

wet peel and flakes), soybean (hulls and meal), and tomatoes, and for at least 37 months in corn 

oil, and CGA-49751 is stable at ≤−10 °C for at least 2 years in corn (grain, forage, and oil), 

peanuts, potatoes (tubers, wet peel and flakes), soybeans (hulls and meal) and tomatoes (DP# 

292881, S. Kinard, 8/15/03). These data are adequate to support the storage conditions and 

durations of samples from the submitted field trials. In addition, recovery data for fortified 

samples analyzed concurrently with treated samples are adequate to support the extended storage 

of extracts prior to analysis.

Following two approximately equal applications (one sprayed on the soil and one sprayed OTT 

when the corn was 30 inches tall) of the 7.64 lb ai/gal EC formulation at total rates of 3.92-4.17 

lb ai/A, residues (and per trial averages) of CGA-37913, CGA-49751, and both metabolites 

combined, respectively, were 0.04-1.8 (0.13-1.28), 0.16-6.3 (0.48-5.7), and 0.20-7.5 (0.61-7.0) 

ppm in/on forage with ears if present harvested with a PHI of 28-40 days; 0.10-2.9 (0.20-2.5), 

0.43-15 (0.55-13), and 0.59-18 (0.75-16) in/on forage without ears harvested with a PHI of 28-47 

days; and <0.03-2.1 (<0.03-1.8), <0.05-8.9 (<0.05-8.2), and <0.08-11 (<0.08-9.9) ppm in/on 

stover harvested with a PHI of 47-111 days. No residues at or above the LLMVs of 0.03 and 

0.05 ppm for the two analytes, respectively, were detected in any samples of K+CWHR, field 

corn grain, or popcorn grain harvested with a PHI of 30-54, 59-111, and 77 days, respectively. 

Following two approximately equal applications (one sprayed on the soil and one sprayed OTT 

when the corn was 40 inches tall) of the 7.64 lb ai/gal EC formulation at total rates of 3.79-4.16 

lb ai/A, residues (and per trial averages) of CGA-37913, CGA-49751, and both metabolites 

combined, respectively, were 0.09-2.2 (0.11-1.9), 0.21-11 (0.26-10.4), and 0.29-13 (0.36-12) 

ppm in/on forage with ears if present harvested with a PHI of 28-31 days; <0.03-4.7 (<0.04-4.3), 

<0.05-24 (<0.07-22), and <0.08-29 (<0.10-26) in/on forage without ears harvested with a PHI of 

21-42 days; and 0.03-5.1 (0.04-4.7), <0.05-23 (<0.05-21), and <0.08-28 (<0.09-26) ppm in/on 

stover harvested with a PHI of 44-101 days. No residues at or above the LLMVs of 0.03 and 

0.05 ppm for the two analytes, respectively, were detected in any samples of K+CWHR, field 

corn grain, or popcorn grain harvested with a PHI of 21-48, 51-101, and 72 days, respectively.

In the residue decline study on field corn, the combined residues of CGA-37913 and CGA-49751 

and/or their combined per trial averages in/on forage with ears if present at PHIs of 20, 25, 31, 

35, and 40 days (Treatment 2) were 3.6, 2.9, 2.7, 2.7, and 2.7 ppm, respectively, and, at PHIs of 

21, 25, 30, 35, and 40 days (Treatment 3), they were 13, 10, 12, 11, and 9.9 ppm, respectively,

which demonstrated a slight residue decline with increasing PHIs. The combined residues and/or 

their per trial averages at PHIs of 75, 82, 90, 96, and 103 days (Treatment 2) were 3.3, 1.2, 0.91, 

0.54, and 0.60 ppm in/on stover, respectively, and at PHIs of 64, 71, 79, 87, and 94 days 

(Treatment 3), were 16.5, 16.5, 23, 10, and 8.0 ppm in/on stover, respectively, which 

demonstrated a decline in residues with increasing PHIs. In the residue decline study on sweet 

corn, the combined residues and/or their per trial averages in/on forage without ears at PHIs of 

20, 25, 29, 35, and 40 days (Treatment 4) were 7.6, 2.7, 3.2, 4.5, and 5.7 ppm, respectively, and, 

at PHIs of 19, 25, 30, 35, and 40 days (Treatment 5), they were 10, 8.6, 6.6, 7.7, and 7.2 ppm, 

respectively, which demonstrated a slight decrease in residues with increasing PHIs. The 

combined residues and/or their per trial averages at PHIs of 40, 47, 54, 60, and 67 days 

(Treatment 4) were 5.1, 7.1, 3.8, 7.6, and 10 ppm in/on stover, respectively, and at PHIs of 30, 
Page 15 of 20

37, 44, 50, and 57 days (Treatment 5), were 12, 9.2, 11.8, 11, and 15 ppm in/on stover, 

respectively, which indicated that combined residues remained the same or increased slightly in 

stover with increasing PHIs. Residue decline in K+CWHR and grain could not be evaluated 

because residues of each analyte were below the LLMV at each sampling interval.

Conclusions. The submitted field trial data are adequate to satisfy data requirements. The 

number of field trials and geographic representation is adequate. An adequate analytical method 

was used for the analysis. Adequate storage stability data were available to support the data 

from this study. The trials showed tolerance exceeding residues on forage and stover; that is the 

reason for the submission of the current petition. Residues were non-quantifiable in samples of 

field and pop corn grain, and in sweet corn kernals plus cobs with husks removed (K+CWHR), 

and thus within the currently established tolerances.

860.1520 Processed Food and Feed

MRID 40980705, DEB 4391, R. Quick, 6/14/1989 (Metolachlor Reg. Std. Followup)

D255484, S. Kinard, 8/15/2003 (Res Chem Chapter for TRED)

No processing data for corn commodities were included with the current petition. Processing 

data were previously submitted with MRID 40980705. The data were review in the Metolachlor 

Registration Standard Followup (R. Quick, 6/14/1989). Residues of metolachlor do not 

concentrate in corn or cottonseed processed commodities. This conclusion was extended to Smetolachlor. (D255484, S. Kinard, 8/15/2003).

860.1650 Submittal of Analytical Reference Standards

Analytical standards for the following compounds related to metolachlor are currently available 

in the EPA National Pesticide Standards Repository (personal communication with Theresa 

Cole, 7/23/2013). The metolachlor metabolite CGA-03713 standard must be replaced or 

recertified prior to publication of new tolerances for S-metolachlor.

Table 7. S-Metolachlor Standards in Pesticide Repository

Chemical Name Company Date Recd Date Exp

metolachlor metab. (CGA-037913) Syngenta 4/1/2003 1/31/2013

metolachlor metab. (CGA-49751) Syngenta 9/1/2004 12/31/2014

metolachlor, S- (CGA-37913) Syngenta 5/20/2013 4/30/2015

metolachlor, S- (CGA-77102) Syngenta 1/3/2011 8/31/2015

metolachlor, S- (CGA-77102) Syngenta 8/27/2012 8/31/2015

metolachlor, S- ESA (CGA 380168) Syngenta 1/13/2006 8/31/2014

metolachlor, S- OA (CGA 351916) Syngenta 1/13/2006 8/31/2014
Page 16 of 20

860.1850 Confined Accumulation in Rotational Crops

D207842, 10/12/94, S. Hummel

D292881, 8/15/03, S Kinard

The data requirements for confined accumulation in rotational crops are not fulfilled. A confined 

rotational crop study with [14C]metolachlor was reevaluated by HED (DP# 207842, 10/12/94, S. 

Hummel) after review of rotational crop data was transferred to HED. It was concluded that the 

available study was inadequate but potentially upgradable. Additional data were required 

characterizing the 14C-residues in plants, along with information on the percentage of the 14Cresidues measured by the current enforcement method; sample storage conditions and intervals 

and supporting storage stability data were also required. These data requirements, which were 

reiterated in the Metolachlor TRED (DP# 292881, 8/15/03, S. Kinard), remain outstanding.

A confined rotational crop study using S-metolachlor has also been submitted. The study was 

reviewed by HED (DP# 283235, 8/15/03, S. Kinard) and found to be scientifically adequate. 

Although 14C-residue in the representative rotational crops were adequately identified and 

characterized, the [14C]-S-metolachlor was applied at only 1.45 lb ai/A, which is ~0.4x the 

maximum seasonal use rate for corn. Based on the available data, HED concluded that the 

metabolism of [14C]S-metolachlor in rotational crops is similar to the metabolism observed in the 

primary crops. Metabolism in rotational crops primarily involves two pathways: (i) conjugation 

of the parent molecule with glutathione by substitution of the chlorine, followed by the 

degradation of the glutathione moiety to form a variety of sulfur containing metabolites; and (ii) 

direct oxidation of parent or secondary metabolites, primarily on the chloroacetyl side chain. 

Complete degradation of secondary metabolites either in the soil and/or plants also resulted in 

the incorporation of molecule fragments into natural plant constituents. The residues of concern 

for both metolachlor and S-metolachlor in rotational crops are the same as for primary crops, 

metolachlor and its metabolites, determined as the derivatives CGA-37913 and CGA-49751. 

The deficiency listed in the RED has not been fulfilled. (DP# 283235, 8/15/03, S. Kinard) For 

confined rotational crops, additional information is needed on the percentage of the 14C-residues 

measured by the current enforcement method, supporting storage stability data, and sample 

storage conditions and intervals. With regard to field accumulation in rotational crops, “Residue 

data are required for both metolachlor and S-metolachlor on grain, forage, hay, and straw of 

representative cereal grains (wheat and oats) supporting the 4.5 month plantback interval.”

860.1900 Field Accumulation in Rotational Crops

D292881, 8/15/03, S Kinard

D332846, 10/21/08, D. McNeilly

D296904, 4/17/06, R. Loranger

Field rotational crop data have been submitted previously which are adequate to support the 

existing rotational crop restrictions on the labels for the 7.62 and 7.64 lb/gal EC formulations 

(EPA Reg. Nos. 100-816 and 100-818), provided that the restrictions on the label for EPA Reg. 

No. 100-816 are amended as specified under 860.1200 Directions for Use. In the TRED it was 

concluded that adequate residue data are available to support a PBI of 4 months for non-grass 

animal feeds and the current 1.0-ppm tolerance for rotated non-grass animal feed (DP# 292881, 
Page 17 of 20

8/15/03, S. Kinard); additional data were required to support cereal grain rotational crop 

restrictions. 

In response, field rotational crop data for oats and wheat were submitted which have been 

reviewed by HED (DP#s 332846, etc., 10/21/08, D. McNeilly). Fourteen field trials were 

conducted with wheat and fifteen trials were conducted with oats. In each test, the 7.64 lb/gal 

EC formulation of S-metolachlor was applied to a primary crop of field corn as a PPI application 

at planting at 2.36-2.49 lb ai/A, followed by a second directed application at lay-by at 1.25-1.4 lb 

ai/A, for a total of 3.61-3.83 lb ai/A/season (1x the maximum use rate on corn). Wheat was 

planted ~60 days and oats were planted ~7 months following the last application. 

These field trials were considered sufficient for assessing rotational crop tolerances for small 

grains rotated with corn, which has the highest labeled use rate. Following a final lay-by

application to corn, the wheat field trials reflect a typical plant-back interval (2 months) for small 

grains that can be planted in the fall (barley, oats, rye and wheat), and the oat field trials reflect 

the typical plant-back interval (7 months) for small grains that can be planted the following 

spring (barley, oats, rice, rye and wheat).

It was concluded that the wheat and oat data support tolerances of 0.5 ppm for rotated barley hay

and straw, oat forage, hay and straw, rye forage and straw, and wheat forage, grain and straw, 

and tolerances of 0.1 ppm for the grain of rotated barley, oats, rye and wheat. For rice and 

buckwheat, which would only be rotated to the following spring (7-month PBI), the oat field trial 

data support tolerances of 0.1 ppm for rotated buckwheat grain and rice grain. 

It was also concluded that 60-day PBIs for root vegetables (subgroup 1B), tuberous and corm 

vegetables (subgroup 1C), bulb vegetables (group 3), leaf petiole vegetables (subgroup 4B) head 

and stem Brassica vegetables (subgroup 5A), fruiting vegetables (group 8), and winter squash are 

acceptable based on the available field trial data supporting the tolerances and uses of 

S-metolachlor on these crops (DP# 296904, 4/17/06, R. Loranger) provided that (i) the 

application to the previous crop was less than or equal to the maximum approved rates for the 

respective crops and crop groups, and (ii) the label directions are amended to prohibit application 

of S-metolachlor to the replanted crops. Although the first condition is met on the current label 

for EPA Reg. No. 100-816, the label directions have not yet been amended to prohibit 

application of S-metolachlor to crops planted at a 60-day PBI. 

860.1550 Proposed Tolerances

The residues of concern in plant and animal commodities include S-metolachlor, its Renantiomer, and its metabolites, determined as the derivatives CGA-37913 and CGA-49751. 

Tolerances for S-metolachlor are currently established [40 CFR §180.368(a)(2) and (d)(2)] for 

the combined residues (free and bound) of S-metolachlor, its R-enantiomer, and its metabolites, 

determined as the derivatives, CGA-37913 and CGA-47951, each expressed as parent 

compound. The text of the current tolerance expression is in accordance with our current 

guidance (S. Knizner, 5/10/2009)
Page 18 of 20

Tolerances are currently established under 40 CFR §180.368 for residues of S-metolachlor, 

including its metabolites and degradates, in or on the commodity(s), as defined. Compliance with 

the tolerance levels specified in the following table below is to be determined by measuring only 

the sum of free and bound S-metolachlor, S-2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-

methoxy-1-methylethyl)acetamide, its R-enantiomer, and its metabolites, determined as the 

derivatives, 2-(2-ethyl-6-methylphenyl)amino-1-propanol and 4-(2-ethyl-6-methylphenyl)-2-

hydroxy-5-methyl-3-morpholinone, calculated as the stoichiometric equivalent of S-metolachlor, 

in or on the commodity.

Table 8. Tolerance Summary for Metolachlor.

Commodity Established/

Proposed Tolerance

(ppm)

Recommended

Tolerance

(ppm)

Comments; 

Correct Commodity Definition

Proposed tolerances under §180.368(a)(2)

Corn, field, forage 20 40

Corn, sweet, forage 40 40

Corn, stover 40 40 Corn, field, stover

Corn, sweet, stover

Corn, pop, stover

A revised Section F is required.

References

DP#: 207842

Subject: Metolachlor (108801) Addendum to RED, Reregistration Case No. 0001. 

Confined Rotational Crop Data (GLN 165-1). CB No. 14435

From: S. Hummel

To: J. Mitchell/W. Waldrop

Dated: 10/12/94

MRID: 41470601

DP#: 226780

Subject: Replacement of Metolachlor Technical (Racemic Metolachlor) with AlphaMetolachlor (formerly called Chiral Metolachlor) Technical; Review of Bridging 

Data.

From: L. Kutney

To: R. Griffin

Dated: 11/15/96

MRIDs: 43928901-43928903, 43928939-43928942
Page 19 of 20

DP#s: 278742 and 279110

Subject: S-Metolachlor. Information Supporting the Assertion That the Metabolism of 

S-Metolachlor Is Essentially the Same as for the Racemic Mixture.

From: S. Kinard

To: S. Kinard

Dated: 8/15/03

MRIDs: 45499603, 45499604, 45499605, 45533103

DP#: 283235

Subject: Sandmeier, P. (2001) Outdoor Confined Accumulation Study on Rotational Crops 

after Bare ground Application of [Phenyl-U-14C] CGA77102: Lab Project 

Number: 99PSA53; 1287-99. Unpublished study prepared by Syngenta Crop 

Protection, Inc. 252 p.

From: S. Kinard

To: N/A (DER)

Dated: 8/15/03

MRID: 45672302

DP#: 292881

Subject: PP#s: 7F04897, 9E06055, 7E04916, 2E06374, 4E04420, 8E05029, and 8E05030. 

Revised Metolachlor and S-metolachlor Residue Chemistry Chapter for the 

Tolerance Reassessment Eligibility Decision (TRED) and Registration for Use on 

Asparagus, Carrots, Cotton, Horseradish, Green Onions, Peppers, Rhubarb, Sugar 

Beet, Sunflower, and Swiss Chard.

From: S. Kinard

To: H. Jamerson

Dated: 8/15/03

MRIDs: 44378401, 44908701, 45544701

DP#: 296904

Subject: PP# 3E6787. S-Metolachlor. Petition for Tolerances on Various Crops, Crop 

Groups, and Livestock Commodities. Summary of Analytical Chemistry and 

Residue Data.

From: R. Loranger

To: B. Madden/S. Jackson

Dated: 4/17/06

MRIDs: 45499609, 45499610, 46046501-46046506

RDI: SHummel: 07/25/2013: RAB4 Chemists 07/25/2013

Attachments: 

International Residue Limit Status sheet

OECD Tolerance/MRL Spreadsheet
Page 20 of 20

Appendix I: International Residue Limits 

S-Metolachlor (PC Code 108800; Date of Request 6/26/13)

Summary of US and International Tolerances and Maximum Residue Limits 

Residue Definition:

US Canada Mexico1 Codex

40 CFR: 180.368 sum of

free and bound S-metolachlor,

S-2-chloro-N-(2-ethyl-6-methylphenyl)-N-

(2-methoxy-1-methylethyl)acetamide, its Renantiomer, and its metabolites, determined as 

the derivatives, 2-(2-ethyl-6-

methylphenyl)amino-1-

propanol and 4-(2-ethyl-6-

methylphenyl)-2-hydroxy-5-

methyl-3-morpholinone

calculated as the

stoichiometric equivalent of

S-metolachlor

2-chloro-N-(2-ethyl-6-

methylphenyl)-N-

[(1S)-2-methoxy-1-

methylethyl)acetamide

and 2-chloro-N-(2-

ethyl-6-

methylphenyl)-N-

[(1R)-2-methoxy-1-

methylethyl)acetamide

, including the 

metabolites 2-[(2-

ethyl-6-

methylphenyl)amino]-

1-propanol and 4-(2-

ethyl-6-

methylphenyl)-2-

hydroxy-5-methyl-3-

morpholinone

None

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg)

US Canada Mexico1 Codex

Corn, field, forage 40 ppm 

Corn, sweet, forage 40 ppm

Corn, stover 40 ppm

Completed by: M. Negussie; 

1 Mexico adopts US tolerances and/or Codex MRLs for its export purposes.