Alachlor

Alachlor was introduced by Monsanto in 1969 under the trade name Lasso and became one of the best-selling herbicides in the United States for control of annual grasses and broadleaf weeds in corn and soybean production [1]. Its use peaked in the 1980s with tens of millions of pounds applied annually. EPA's Special Review in 1986 found that alachlor caused nasal turbinate tumors and stomach tumors in rats and mice, leading to classification as a probable carcinogen and a maximum contaminant level (MCL) in drinking water of 2 µg/L [2]. Despite these findings, EPA retained the registration because of the agricultural importance of alachlor and the limited human epidemiological evidence [1]. Alachlor is mobile and persistent in groundwater — it is among the most frequently detected pesticides in Midwest agricultural groundwater monitoring [2].

Drinking water from Midwestern groundwater sources is the primary community exposure pathway [1]. Agricultural workers applying alachlor to corn and soybean fields face dermal and inhalation exposure [2]. Rural private well users in corn-soybean production areas face the most significant drinking water exposure [1].

Alachlor undergoes hepatic CYP450 metabolism to reactive chloroacetanilide intermediates that alkylate DNA and proteins [1]. Nasal turbinate carcinomas and forestomach tumors were induced in rodents — these are unusual tumor sites suggesting direct tissue contact [2]. EPA B2 probable carcinogen classification and SDWA regulation reflect this evidence. The compound also affects the thyroid in exposed rodents [1].

Rural well users in Midwestern corn and soybean production areas — the heartland of alachlor application [1]. Agricultural workers applying alachlor [2].

1. Test your private well annually for alachlor if you live in Midwestern agricultural areas — EPA MCL is 2 µg/L [1]. 2. Activated carbon block or reverse osmosis filtration removes alachlor from drinking water [2]. 3. Agricultural workers should use PPE during application [1].