Biomonitoring Summary
Alachlor
CAS No. 15972-60-8
General Information
Alachlor is a chloroacetanilide type herbicide with restricted usage for preemergent control of grasses and broadleaf weeds on agricultural cropland, including corn, soybeans, peanuts and other crops, and on non-crop land for general weed control. Since the late 1980s alachlor use has been declining. In 1993-1995, about 20-25% of the U.S. corn cropland was treated with alachlor.It is absorbed by plants and inhibits plant protein synthesis. Alachlor has a soil half-life of a few weeks. It is both metabolized in plants and degraded microbiologically in agricultural soils into as many as 19 metabolites and degradates. Alachlor and its degradates are leachable from agricultural soils and have been detected in watersheds of agricultural land including ground and surface waters (Battaglin et al., 2000; Hladik et al., 2005; Kolpin et al., 2000; USGS, 1999 and 2007; WHO, 2003). Alachlor is highly toxic to freshwater fish and slightly toxic to birds and some invertebrates, but shows little bioaccumulation.
General population exposure to alachlor may occur through consumption of contaminated food or drinking water. Estimated human intakes have been below recommended limits (U.S.EPA, 1998). Because it can be absorbed through skin, the dermal exposure route is potentially significant for applicators, formulators, and field workers. In animal studies, alachlor is quickly absorbed after oral doses and mostly excreted as metabolites within a week (IPCS, 1996; U.S.EPA, 1998; WHO, 2003). In animals, mercapturate conjugates were predominant metabolites, but another metabolic pathway can produce 2,6-diethylaniline and its reactive metabolite; the latter may account for some observed tumor effects (Davison et al., 1994; Feng and Wratten, 1989; Jefferies et al., 1998). People exposed to alachlor will excrete alachlor mercapturate in their urine (Driskell et al., 1996), but 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 alachlor at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Alachlor has low potential for acute toxicity. In chronic animal testing, alachlor has demonstrated hepatotoxicity, hemosiderosis, and uveal degeneration, but has not shown developmental or reproductive toxicity in mammalian systems (U.S.EPA, 1998; WHO, 2003). Alachlor itself is not considered mutagenic, though positive genotoxic results are reported for several metabolites of alachlor (Brown et al., 1988; Hill et al., 1997; Tessier and Clark, 1995; U.S.EPA, 1998). Animal carcinogenicity studies have demonstrated tumors of the nasal turbinates, stomach, and thyroid only at either maximum tolerated doses or related to species-specific pathways (Heydens et al., 1999; IPCS, 1996; U.S.EPA, 1998; WHO, 2003). U.S.EPA considers alachlor to be a probable human carcinogen at high doses, but not likely at low doses. NTP and IARC do not have ratings regarding human carcinogenicity. Addit
ional information about is available from U.S. EPA at:https://www.epa.gov/pesticides/external icon.
Biomonitoring Information
Urinary levels of alachlor mercapturate reflect recent exposure. Urinary levels of alachlor mercapturate were generally not detectable in the NHANES 1999-2000 subsample (CDC, 2009). In a study of applicators and workers exposed to alachlor, mean values of urinary concentrations of alachlor metabolites, as measured through conversion to deethylamine, ranged from 0.1 to 1.1 mg/L at various collection times (Sanderson et al., 1995). Hines et al. (2003) showed that 2.2% of a reference population had detectable alachlor equivalents by immunoassay in their urine, whereas 60% of applicators had detectable amounts.
Finding measurable amounts of alachlor mercapturate in the urine does not imply that the levels of alachlor mercapturate cause an adverse health effect. Biomonitoring studies on levels of alachlor mercapturate provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of alachlor than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
References
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Driskell WJ, Hill RH Jr, Shealy DB, Hull RD, Hines CJ. Identification of a major human urinary metabolite of alachlor by LC-MS/MS. Bull Environ Contam Toxicol 1996;56(6):853-9.
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U.S. Geological Survey (USGS). The Quality of Our Nation’s Waters
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