The influence of single topical application of dichlorvos on blood esterases and toxicity in male calves.

The effect of dichlorvos on inducing changes in blood esterase activities and systemic toxicity was investigated following single topical applications of 1, 3 or 6% dichlorvos concentrations to male calves. Dichlorvos at 1% concentration did not produce any signs of toxicity, whereas 3 and 6% concentrations induced mild to severe toxicity characteristic of anticholinesterase poisoning. Dichlorvos at all concentrations significantly inhibited erythrocyte cholinesterase (25-75%), plasma cholinesterase (30-85%), and serum carboxylesterase (15-51%) activities in male calves. The dose-dependent inhibition was maximum 12 h after insecticide exposure. The extent of inactivation of blood esterases was not correlated with the severity of toxicity. Inhibition of blood cholinesterases by the 6% dichlorvos was still present 21 d after the dichlorvos exposure.