UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

DATE: December 3, 2014 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: Metolachlor and S-Metolachlor. Recommended Environmental Degradates to 

Include in Drinking Water Assessment. 

PC Code: 108800 (S-Metolachlor); DP Barcode: 424250 

1 08801 (Metolachlor) 

Decision No.: 491501 Registration Nos.: 100-815, 11603-43, 19713-539, 

60063-17 

Petition No.: NA Regulatory Action: Registration Review 

Case No.: 0001 Risk Assessment Type: NA 

TXRNo.: NA CAS No.: 87392-12-9,5 1218-45-2 

MRIDNo.: NA 40 CFR: §180.368 

FROM: Susan 

Risk Assessmen

V. Hummel

t Branch 

, Senior 

4 

Chemist ~ 1) ~ 

Health Effects Division (7509P) 

THROUGH: Christine Olinger, ROCKS ; / / ~ / 

Health Effects Division (7509P}_;,c.. ' ~ ~ 

TO: Steven Snyderman, Chemical Review Manager 

Risk Management and Implementation Branch 3 

Pesticide Re-Evaluation Division (7508P) 

I. MATERIAL REVIEWED: 

The herbicides metolachlor and S-metolachlor are registered on a number of crops and are 

undergoing registration review. EFED asked HED for guidance on including the metolachlor 

degradates in the drinking water assessment. EFED flagged four major degradates of metolachlor 

for the drinking water assessment: metolachlor oxanilic acid (metolachlor-OA; CGA-51202), 

metolachlor ethane sulfonic acid (metolachlor ESA; CGA-354743), CGA40172, and CGA771 02. See Table l for structures of metolachlor and its degradation products. 
II. CONCLUSIONS: 

Four major degradates of metolachlor were identified by the EFED chemical team for the 

drinking water assessment: metolachlor oxanilic acid (metolachlor-OA; CGA -51202), 

metolachlor ethane sulfonic acid (metolachlor ESA; CGA-354 743), CGA-40 172, and CGA50720. CGA40172, and CGA-50720 were not considered as residues of concern in previous 

drinking water assessments. The ROCKS members recommended excluding the metolachlorESA from the drinking water assessment since the sulfonic acid is likely to be significantly less 

toxic than the parent compound. The ROCKS members also recommended including the 

degradates CGA-40 172 and CGA-50720, in addition to metolachlor-OA, based on the structural 

similarity to parent metolachlor. It should be noted that the concern for CGA-40172 is 

diminished due to the presence of the carboxylic acid moiety, however, there is insufficient 

information to exclude from the drinking water assessment. Therefore, the ROCKS 

recommended the following degradates as residues of concern for drinking water; parent 

metolachlor, metolachlor-OA, CGA40172, and CGA-50720. 

Individuals in Attendance: 

ROCKS: Ed Scollon, Christine Olinger, Ray Kent 

EFED: Chris Koper, Edom Seifu, Meghan Radtke 

HED: Sue Hummel (via phone), Jessica Kidwell 

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Table 1. Metolachlor/S-Metolachlor and Its Environmental Degradates 

Code Name/ Chemical Name Chemical Structure Study Type I MRID I Maximum Formation 

Synonym (% Apptied) 

Parent 

Metolachlor CAS Name: 

(CGA-24705) (R)2-Chloro-N-(2-ethyl-6- CH; 

methylphenyl)-N-(2-methoxy-1- I 

methylethyl) acetamide 0 

H;C-< l CAS Number: 051218-45-2 

Molecular Weight: 283.80 

Parent structure shown for reference g/mol H;C N-(_ 

Chemical Formula: Cl 

CtsH22N02CI Q\_- CH, 

SMILES: 

CCC!=CC=CC(=C1N(C(C)CO 

C)C(=O)CCI)C 

S-MetoEachlor CAS Name: I ! 

(CGA-77102) (S)-2-Chloro-N-(2-ethyl-6-

methylphenyl)-N-(2-methoxy-1-

:~N~~···( methylethyl) acetamide 

CAS Number: 087392-12-9 

Molecular Weight: 283.80 Parent structure shown for reference 

g/mol 

Chemical Formula: 

CtsHzzNOzCI ~ 

I 

SMILES: ~ CCC 1 =CC=CC(=C 1 N([C@ 

@H](C)COC)C(=O)CCI)C 
Code Name/ Chemical Name Chemical Structure Study Type MRID Maximum Formation 

Synonym (%Applied) 

Transformation Products 

Metolachlor CAS Name: Aqueous Photolysis 40430202 3.54 

Oxanilic Acid/ [(2-ethyl-6-methylphenyl) (2- 11.3 (day 48) Metolachlor-OA methoxy-1-methylethy1) amino] Aerobic Soil Metabolism 45499606 

(CGA-51202) oxo-acetic acid c; T

1

l Aerobic Soil Metabolism 43928936 10.3 (day 21, met) 

Molecula r Weight: 389.06 10.9 (day 21, S-met) 

g/mol r ~ 1

/es • al . 0 • ~ Aerobic Soil Metabolism 3 130980 1 28.09 (day 90) 

A-B ' Anaerobic Soil 31309801 23.33 (day 29) - CO • COOl 

Metabolism A-8 

el•s 

Terrestrial Field 3.0% of applied SDissipation 45848001 metolachlor at 93 days 

in 0-15 em soil depth. 

Metolachlor CAS Name: 

ethane sulfonic Not assigned I found 2-((2- Aerobic Soil Metabolism 45499606 acid/ ethyl-6-methylphenyl)(2- 11.6 ( day 33) 

Metolachlor- methoxy-1-methylethyl)amino )-

ESA 2-oxoethanesulfonic acid 10.7 (day 60, met) I 

(CGA-354743) http://sitem.herts.ac.uk/aeru/iupa 

Aerobic Soil Metabolism 43928936 12.4 (day 60, S-met) CH2CH3 c/103l.htm I 

o2.8% of applied S- I 

Molecular Weight: N/COC H2SOji 329 g/mol metolachlor at 93 days I 

""-cHCH20CH3 

Terrestrial Field 45848001 

in 0- 15 em soil depth 

Dissipation 

"'-cH3 JHJ ~-- I 

Page 4 of7 
CGA-41507 CAS Name: Aerobic Aquatic 41185701 Not assigned 3.34 (day 29) 

CH ~H, . Metabolism 

Mole~ular Weight: 157 g/mol o-'

1CHCH,OCH, 

N\ Anaerobic Aquatic 41 185701 4.85 (12 months) 

CCH, Metabolism 

C1H1 II 

0 

Aerobic Aquatic CGA-40172 CAS Name: 1.13 

Not 41185701 assigned (not reported) Metabolism 

~ Anaerobic Aquatic 5.64 (12 months) Molecular Weight: 346.03 CH-CH-O-CH 41185701 

g/mol Metabolism 'I ~ / a a N' - ~-OH 

II Aerobic Soil Metabolism 45499606 

I 0 11.6 (day 19) 

ll.3 (day 48) 

CGA-41638 CAS Name: 

Not assigned (not reported) 

~ Aqueous Photolysis 40430202 3.63 

Molecular Weight: 346.o3 /CH-CH1-0H Aerobic Soil Metabolism 31309801 'I ~ 2.06 (day 90) g/mol A-B 

- N' C-CH1CI 

Anaerobic Soil 31309801 I g Metabolism A-B 

8.30 (day 60) 

Page 5 of7 
CGA-50720 CAS Name: Aerobic Aquatic 41185701 Not assigned (not reported) Metabo 1.17 lism 

al 

Molecular Weight: 346.03 Q-<:.=o. Aqueous Photolysis 40430202 3.20 glmol 

Aerobic Soil Metabolism 3130980 1 

A-B 14.85 (day 272) 

el•s Anaerobic Soil 31309801 

Metabolism A-B 7.34 (day 60) 

CGA-37913 o-CH ~H, 

' / CHCH,OH Anaerobic Aquatic N, 41 185701 Metabolism 4.28 (6 months) H 

CaHs 

Page 6 of7 
CGA-37735 Aerobic Soil Metabolism 31309801 1.27 (day 30) 

r}'H 

A-B 

I 

H\ 1.25 (day 29) 

CCH 10H Anaerobic Soil 3 1309801 

CIHI II Metabolism A-B 

0 

CGA-13656 31309801 - Aerobic Soil Metabolism 1.02 (day I) A-B 

'I N~ - 'C-CHJ:I Anaerobic Soil 31309801 1.46 (day 29) 

u Metabolism A-B 

0 

CGA-46129 

. CH ~Hs Q-' CHCOOH I 

N\ Aqueous Photolysis 40430202 

3.42 

CCH 10H 

C2H1 U 

0 

CGA-46127 

q:>r~~ Aerobic Aquatic 

Metabolism 41 185701 1.54 

" Anaerobic Aquatic 41185701 co-o-t2 -s-or3 Metabolism 

~l·J 4.69 (12 months) 

Note: Bold values denote major e 10%) degradates. L____ __ --·--·-··-·--

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