Appraisal of risks from nonoccupational exposure to chlorpyrifos

The toxicological database for chlorpyrifos indicates that humans are not more sensitive than laboratory animals to the toxic effects. Although an oral dose of 1 mg/kg-day resulted in measurable levels of chlorpyrifos in the blood, daily dosing at this level from 9 days to 2 years did not affect brain acetylcholinesterase activity (AChE) in laboratory animals. Developmental toxicity did not occur at doses below maternal toxicity. Most nonoccupational illnesses resulting from entry into areas treated with chlorpyrifos likely stem from odor, rather than the ability of the organophosphate to inhibit AChE. Based on biological monitoring studies, chronic aggregate nonoccupational exposures to chlorpyrifos ranged from 0.0002 mg/kg-day (adults) to 0.0005 mg/kg-day (infants and small children)-1 order of magnitude less than exposures estimated by standard procedures. Other biological monitoring data indicated that cumulative exposure to all organophosphate pesticides ranged from 0.0003 mg/kg-day (adults) to 0.003 mg/kg-day (children). Considering all these factors, the risks of aggregate, nonoccupational exposure to chlorpyrifos have been overstated by more than a 1000-fold.