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Biomonitoring Summary


CAS No. 34256-82-1

General Information

Acetochlor is a chloroacetanilide type herbicide with restricted usage for preemergent control of grasses and broadleaf weeds on agricultural crop land, mainly corn. It is absorbed by plants and inhibits plant protein synthesis. Acetochlor is microbiologically degraded, remains in soils for up to 3 months, and has been detected in watersheds of agricultural lands (Battaglin et al., 2000; Hladik et al., 2005; Kolpin et al., 2000). Acetochlor degrades in water to acetochlor sulfonic acid and acetochlor oxanilic acid. Plants can degrade acetochlor to 2-ethyl-6-methylaniline, 2-hydroxyethyl-6-methylaniline, and hydroxymethyl ethyl aniline (U.S.EPA, 2006). Acetochlor is moderately toxic to fish and honey bees.

General population exposure to acetochlor may occur through diet or drinking water. Estimated human intakes of acetochlor have been below recommended limits (U.S.EPA, 2006). In animals, a major pathway for acetochlor metabolism involves mercapturate conjugation, but other pathways occur, including one that produces 2-methyl-6-ethylaniline and its reactive metabolite, the latter which may account for some observed tumor effects (Coleman et al., 2000; Davison et al., 1994; Feng and Wratten, 1989; Jefferies et al., 1998). People exposed to acetochlor will excrete acetochlor mercapturate in their urine; however, this metabolite is not a marker of exposure to most plant metabolites or environmental degradates, which are often more prevalent in the environment.

Human health effects from acetochlor at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Acetochlor has low acute toxicity. Acetochlor has not shown developmental or fetal toxicity in chronic animal studies, but it produced testicular atrophy, renal injury, and neurologic movement abnormalities (U.S.EPA 2000, 2006). Acetochlor is not mutagenic, and it is unlikely to be genotoxic at relevant doses (Ashby et al., 1996). However, in some species and at doses above maximum tolerated doses, animals have demonstrated tumors of the lung, nasal epithelia, and thyroid (U.S.EPA, 2000, 2006). U.S.EPA considers acetochlor likely to be carcinogenic in humans; NTP and IARC do not have ratings regarding human carcinogenicity. Additional information about external exposure (i.e., environmental levels) is available from U.S. EPA at:

Biomonitoring Information

Urinary levels of acetochlor mercapturate reflect recent exposure. Urinary levels of acetochlor mercapturate were generally not detectable in the NHANES 2001-2002 subsample (CDC, 2009). Acetochlor mercapturate was measured in the urine of farmers actively spraying the pesticide and the geometric mean was 8.0 µg/L (Curwin et al., 2005). Urinary acetochlor mercapturate levels of 0.5 to 449 µg/L were measured in commercial applicators within 24 hours following its application (Barr et al., 2007).

Finding measurable amounts of acetochlor mercapturate in the urine does not imply that the levels of acetochlor mercapturate cause an adverse health effect. Biomonitoring studies on levels of acetochlor mercapturate provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of acetochlor than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.


Ashby J, Kier L, Wilson AG, Green T, Lefevre PA, Tinwell H, et al. Evaluation of the potential carcinogenicity and genetic toxicity to humans of the herbicide acetochlor. Hum Exp Toxicol 1996;15(9):702-35.

Barr DB, Hines CJ, Olsson AO, Deddens JA, Bravo R, Striley CA, et al. Identification of human urinary metabolites of acetochlor in exposed herbicide applicators by high performance liquid chromatography-tandem mass spectrometry. J Expo Sci Environ Epidemiol 2007;17(6):559-66.

Battaglin WA, Furlong ET, Burkhardt MR, Peter CJ. Occurrence of sulfonylurea, sulfonamide, imidazolinone, and other herbicides in rivers, reservoirs and ground water in the Midwestern United States, 1998. Sci Total Environ 2000;248(2-3):123-33.

Centers for Disease Control and Prevention (CDC). Fourth National Report on Human Exposure to Environmental Chemicals. Atlanta (GA). 2009. [online] Available at URL: 10/15/12

Coleman S, Linderman R, Hodgson E, Rose RL. Comparative metabolism of chloroacetamide herbicides and selected metabolites in human and rat liver microsomes. Environ Health Perspect 2000;108(12):1151-7.

Curwin BD, Hein MJ, Sanderson WT, Barr DB, Heederik D, Reynolds SJ, Ward EM, Alavanja MC. Urinary and hand wipe pesticide levels among farmers and nonfarmers in Iowa. J Expo Anal Environ Epidemiol 2005;15(6):500-8.

Davison KL, Larsen GL, Feil VJ. Comparative metabolism and elimination of acetanilide compounds by rat. Xenobiotica 1994;24(10):1003-12.

Feng PCC, Wratten SJ. In vitro transformation of chloroacetanilide herbicides by rat liver enzymes: A comparative study of metolachlor and alachlor. J Agri Food Chem 1989;37(4):1088-93.

Hladik ML, Hsiao JJ, Roberts AL. Are neutral chloroacetamide herbicide degradates of potential environmental concern? Analysis and occurrence in the upper Chesapeake Bay. Environ Sci Technol 2005;39(17):6561-74.

Jefferies PR, Quistad GB, Casida JE. Dialkylquinonimines validated as in vivo metabolites of alachlor, acetochlor, and metolachlor herbicides in rats. Chem Res Toxicol 1998;11(4):353-9.

Kolpin DW, Thurman EM, Linhart SM. Finding minimal herbicide concentrations in ground water? Try looking for their degradates. Sci Total Environ 2000;248(2-3):115-22.

U.S. Environmental Protection Agency (U.S. EPA). Acetochlor (Harness) Pesticide Petition Filing 1/00. Federal Register: January 24, 2000, Volume 65, Number 15, pages 3682-3690. Available at URL(non U.S.EPA): 10/15/12

U.S. Environmental Protection Agency (U.S. EPA). Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision (TRED) for Acetochlor. March 2006. EPA 738-R-00-009. Available at URL: 10/15/12

Whyatt RM, Barr DB, Camann DE, Kinney PL, Barr JR, Andrews HF, et al. Contemporary-use pesticides in personal air samples during pregnancy and blood samples at delivery among urban minority mothers and newborns. Environ Health Perspect 2003;111(5):749-56. The U.S. Government's Official Web PortalDepartment of Health and Human Services
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