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Acetochlor Structural Formula
Acetochlor Structural Formula
CAS Number: 34256-82-1
Synonyms: Acenit, Harness, Surpass, Top Hand, Trophy
Contaminant Type: Chemical

Acetochlor is a synthetic organic compound of the chloroacetanilide class of herbicides. Its IUPAC name is 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide. It is primarily used for selective pre- and early post-emergent control of broadleaf weeds and annual grasses for corn. Acetochlor was granted a conditional registration by USEPA in 1994 in an effort to significantly reduce the total use of corn herbicides in the United States, including alachlor, metolachlor, atrazine, and 2,4-D. [1441, 1444] In the United States, an estimated 32.3 million pounds of acetochlor is applied to field corn annually. [1442]

Acetochlor enters the water through accidental spills, spraying, leaching from fields via run off, and leaching of groundwater. Peak concentrations of the herbicide are detected in surface waters during the spring, as a result of runoff.

In addition to the goal of reduced herbicide use, the USEPA required an extensive surface water monitoring program intended to limit potential risks to human health and the environment. In the event the time-weighted annual mean concentration (AMC) of acetochlor exceeds 2ug/L, the Acetochlor Registration Partnership (ARP), consisting of Monsato and Dow AgroSciences, would suspend sales. [1444] This threshold was selected by USEPA as a conservative limit based on the maximum contaminant level in effect for alachlor. [1444]

Studies indicate that acetochlor and its degradates, acetochlor ethanesulfonic acid (ESA) and acetochlor oxanilic acid (OXA), are moderately persistent and moderately to very mobile in soil, depending on the characteristics of the soil where it is applied. As a result, there is a relatively high potential for acetochlor residues to reach ground and surface water. Acetochlor does not appear to pose a significant risk of concentrating through the food chain. [1441]

Acetochlor is not regulated by USEPA in drinking water, but is an unregulated chemical drinking water contaminant listed on the USEPA's Contaminant Candidate Lists 1, 2 and 3. [620] USEPA has classified acetochlor as “likely to be carcinogenic to humans” based on tumor incidence in animals, and has determined that acetochlor and alachlor share a common mechanism of toxicity for formation of nasal tumors in rats. [1442, 1444] Both degradates, however, appear to be less toxic than parent compounds in all species tested. [1444]

Date of Literature Search: December 2009

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
1441 USEPA; 1994; Questions and Answers - Conditional Registration of Acetochlor; Questions and Answers - Conditional Registration of Acetochlor; Agency Docket I.D. EPA-HQ-OPP-2007-0725-0004. Prevention, Pesticides and Toxic Substances.
1442 USEPA; 2005; Overview of Acetochlor Risk Assessment; Overview of Acetochlor Risk Assessment; Agency Docket I.D. EPA-HQ-OPP-2005-0227-0003
1444 Hackett, A., Gustafson, D., Moran, S., Hendley, P., van Wesenbeeck, I., Simmons, N., Klein, A., Kronenberg, J., Fuhrman, J., Honegger, J., Hanzas, J., Healy, D. and Stone, C.; 2005; The acetochlor registration partnership surface water monitoring program for four corn herbicides; Journal of Environmental Quality; 34:877