Application of a dermal self-exposure model to worker reentry.

The dermal toxicity of five commonly used organophosphate insecticides was investigated with a mouse intermittent self-exposure model. Blood cholinesterases were monitored on d -3 and -1 before exposure and for 4--6 d during exposure to foliar residues. Responses were much greater in unmuzzled than in muzzled animals due to oral contamination. After two 10-h exposures, muzzled mice showed log-linear cholinesterase responses across a wide range of foliar pesticide concentrations. Foliar pesticide levels that caused 50% depression in plasma or red blood cell cholinesterase were determined with log-probit dose-response analysis. The greatest cholinesterase responses for both emulsifiable concentrate and encapsulated formulations were found with diazinon, followed by parathion and methyl parathion. Azinphos-methyl and mevinphos produced no significant responses in muzzled mice at maximal foliar concentrations. Symptomatology, food consumption, and body weight provided less sensitive indicators of response than cholinesterases. No consistent relation existed between the mouse intermittent self-exposure toxicities and mouse dermal LD50 values. Use of data from acutely exposed animals to predict the hazard of intermittent foliar exposure appears inadvisable.