Effects of organophosphate insecticide residue variability on reentry intervals.

A stochastic simulation program was written to study the importance of residue variability in predicting excessive chronic (seasonal) cholinesterase (AChE) inhibition and acute illness among a cohort of agricultural harvesters grouped into crews exposed to AChE-inhibiting insecticides. It was concluded that residue variability can substantially affect the cohort's AChE level only for daily mean AChE inhibitions below 4% per day, increasing end-of-season mean AChE inhibition but actually decreasing the cohort's end-of-season variability. The incidence of acute individual and group (crew) AChE inhibitions in excess of that potentially producing clinical symptoms (assumed herein to be greater than 50% in a day), exhibits a fairly clear boundary as a function of a combination of the residue's mean and deviation. The predicted acute response accurately parallelled reported rates, thus validating the simulation model.