Detection of incipient effects of anticholinesterase insecticides in rats and humans by electromyography and cholinesterase assay

Rats, fed low levels of diazinon (0.5 and 5.0 mg/kg) and parathion (0.1, 0.5 and 1.0 mg/kg) daily for 26 weeks, and agricultural workers chronically exposed to anticholinesterase insecticides, were monitored by electromyographic (EMG) and blood cholinesterase determinations. The two diazinon-fed and the highest parathion-fed groups of rats gained less weight, whereas the lowest parathion-fed group gained more weight than the control; rats fed 0.5 mg/kg parathion daily did not show any difference in weight gain when compared to the control. In addition, the two diazinon-fed groups of rats gained significantly less weight than the three parathion-fed groups. Both erythrocyte acetylcholinesterase (AChE) and plasma cholinesterase (ChE) activities were severely inhibited in the treated groups. However, parathion inhibited ChE much less than diazinon, and slight recovery of both enzymes was evident in the parathion-treated groups. No changes in amplitudes of EMGs were observed in the treated rats. Agricultural workers were examined monthly during one growing season. Although there was high variation in the data, EMG amplitudes and AChE levels were lower in the workers than in persons not exposed to pesticides; ChE levels were statistically different only once. These results have demonstrated that the rat is not suitable for investigating the use of EMG as a method for monitoring exposure to anticholinesterase insecticides, but that EMG (or AChE) may be used to monitor such exposures in humans.