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 >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.