Biological monitoring of human exposure to acephate

Acephate is a water-soluble organophosphate insecticide whose action on insects has been related to its conversion to methamidophos, a very potent anticholinesterase agent which has caused delayed neuropathy in man. Inhalation and skin exposure to acephate was evaluated in four workers engaged in 8-day campaigns with the formulation of the 97%-pure technical product. Before, during, and after exposure, the workers were monitored for the urine content of acephate and methamidophos, and for erythrocyte (AChE) and plasma (PChE) cholinesterase levels. Median air concentrations (8-hr TWA) ranged from 0.278 to 2.170 mg/m3; median total-body skin deposition ranged from 26.1 to 41.9 mg/day. Based on these values, daily workers' absorption of acephate was estimated to be in the order of 10-20 mg. Urinary excretion of unchanged acephate followed a pattern consistent with exposure, showing peak values of excretion during the workshift or in the eight hr after the end of the workshift. The urine levels of unchanged acephate were found to vary from 1 to 10 mg/L. Methamidophos was not detected in any urine sample (detection limit: 30 micrograms/L). High correlation (r = 0.78) was found between skin exposure level and urine acephate elimination. No changes in AChE or PChE were observed for the workers whose urinary concentrations of acephate were 1 or 2 mg/L. One subject who had urinary acephate excretion between 3 and 8 mg/L, showed slightly decreased values of PChE during exposure and of AChE after exposure.