Chloramben

Chloramben (3-amino-2,5-dichlorobenzoic acid), sold under the trade name Amiben, was developed by Amchem Products in the late 1950s and registered in 1960 as a selective pre-emergent herbicide for use in soybeans, peanuts, corn, and numerous other crops and gardens. [1] It works by inhibiting cell division in germinating weed seedlings, preventing root and shoot elongation before the weed emerges from the soil. As a substituted benzoic acid, it is water-soluble and moves readily through soil — a property that makes it both effective as a soil-applied herbicide and a potential groundwater contaminant in high-use areas. Following the standard carcinogenicity testing required under FIFRA reregistration, animal bioassays found evidence of increased liver tumor incidence in mice, leading to the EPA's Group C classification (possible human carcinogen) and later its listing as a probable carcinogen under older guidelines. [2] Chloramben was voluntarily canceled for many food uses in the United States in the 1990s–2000s as the registrant chose not to fund the complete data package required for reregistration under stricter modern FIFRA standards. It is currently registered for limited ornamental and non-food uses. [3]

Agricultural workers who applied chloramben to soybeans and other crops were the primary occupationally exposed population during its period of peak use. Dermal exposure during mixing and loading was the dominant route. Dietary exposure from food residues was a secondary pathway for the general public. Groundwater contamination in high-use agricultural areas provided a drinking water exposure pathway. Current exposures are limited given the restricted registration.

The liver tumor findings in rodent bioassays (the basis for the carcinogen classification) are consistent with chloramben's metabolism to reactive intermediates capable of hepatic DNA adduct formation. [2] Acute toxicity is relatively low — chloramben is only mildly toxic in standard acute toxicology studies. The environmental concern is groundwater contamination given its relatively high water solubility and soil mobility. Aquatic toxicity to plants (phytotoxicity) is significant.

Former agricultural workers who applied chloramben through the 1970s–1990s, and current workers in the limited ornamental horticulture sector where it may still be registered, represent the at-risk population. People with private wells in historically treated soybean-growing regions may have historical groundwater exposures.

1. Check current registration status in your state — many food uses are canceled and the compound may not be legally applicable to crops. 2. Former applicators should inform their physicians of past occupational exposure for appropriate cancer surveillance. 3. Private well owners in former high-use soybean areas can test their wells for chloramben. 4. If applying to ornamental gardens, wear gloves and eye protection, observe re-entry intervals.