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Metolachlor Degradates

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Synonyms: Metolachlor ESA, Metolachlor OA, Metolachlor ethane sulfonic acid, Metolachlor oxanilic acid
Contaminant Type: Chemical

Metolachlor is a synthetic organic compound of the chloroacetanelide class of herbicides. For information on metolachlor, go to Find a Contaminant. Metolachlor is not regulated by USEPA in drinking water, but is an unregulated chemical drinking water contaminant listed on the USEPA's Contaminant Candidate Lists (CCL) 1, 2 and 3. [529, 620]

The primary method of metolachlor degradation is microbial activity. [529] Therefore metolachlor degrades much faster in soil than in water, implying lower concentrations of the parent herbicide in ground water than in surface water. Four degradates have been identified, but the most commonly detected are metolachlor ethane sulfonic acid (ESA) and metolachlor oxanilic acid (OA). ESA and OA are more soluble than the parent herbicide and more resistant to microbial degradation than the parent, implying ESA and OA would be detected more frequently and at higher concentrations than their parent. [561] Other reported degradates are 2-ethyl-6-methylaniline and 2-[(2-ethyl-6-methylphenyl)-amino]-1-propanol. [558]

USEPA reported that the ESA and OA degradates were less toxic than the parent herbicide. [561] The PAN Pesticides Database lists no known health effects for any of the four degradates. [558]

Metolachlor degradates are not regulated by USEPA in drinking water, but are unregulated chemical drinking water contaminants listed on the USEPA's Contaminant Candidate Lists 1, 2 and 3 [529, 620]

A Wisconsin study of municipal wells reported no detections of the parent herbicide metolachlor, but 39 percent detections of ESA averaging 1.3 ug/L and 35 percent detections of OA averaging 0.57 ug/L. [529] A Georgia study of surface waters reported no detections of the parent herbicide, but 74 percent detections of ESA with a maximum of 1.47 ug/L and 61 percent detections of OA with a 0.28 ug/L maximum. [562] An Ohio study of a treated drinking water using a reservoir in an agricultural area reported the parent in the 0.01 to 0.5 ug/L range, ESA in the 0.1 to 1 ug/L range, and OA in the 0.1 to 0.5 ug/L range. [563]

CAS numbers for ESA and OA are, respectively, 171118-09-5 and 152019-73-3.

Date of Literature Search: March 2007



529 USEPA; 2006; Regulatory Determinations Support Document for Selected Contaminants from the Second Drinking Water Contaminant Candidate List (CCL2); Regulatory Determinations Support Document for Selected Contaminants from the Second Drinking Water Contaminant Candidate List (CCL2); EPA Report 815-D-06-007. Chapter 13 pp. 1-29. Office of Ground Water and Drinking Water, U.S. Environmental Protection Agency, Washington, DC.
558 Pesticide Action Network North America; 2007; Pesticide Action Network (PAN) Pesticides Database; http://www.pesticideinfo.org/Index.html; As posted on August 24, 2007. Pesticide Action Network North America, San Francisco, CA.
561 USEPA; 2003; S-Metolachlor; Pesticide Tolerances, Final Rule; Federal Register; 68:182:54827, September 19, 2003.
562 Pittman, J. and Berndt, M.; 2003; Occurrence of herbicide degradation compounds in streams and ground water in agricultural areas of southern Georgia; Georgia Water Resources Conference; Presented at Athens, GA, April 2003.
563 Funk, J., Reutter, D. and Rowe, G.; 2003; Pesticides and Pesticide Degradates in the East Fork Little Miami River and Harsha Lake, Southwestern Ohio 1999-2000; Water-Resources Investigations Report 03-4216, U.S. Geological Survey; WRIR 03-4216
620 USEPA Office of Ground Water and Drinking Water; 2008; Contaminant Candidate List 3 (CCL3); USEPA Office of Ground Water and Drinking Water; http://www/epa.gov/OGWDW/ccl/ccl3.html



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