Abstract
The effect of the malathion impurities, isomalathion of O,S,S-trimethyl phosphorodithioate (OSS-Me), on the toxicokinetic behavior of [ methoxy- 14C]malathion in female rats was investigated. Malathion α- and β-monoacids and the diacid were the predominant metabolites in the blood of rats pretreated orally with corn oil followed 4 hr later with radiolabeled malathion. Pretreatment of rats with isomalathion or OSS-Me in corn oil followed by treatment with malathion resulted in a decrease of total radioactive metabolites in the blood. Moreover, a substantial reduction in the level of malathion β-monoacid and malathion diacid was observed in the blood of impurity pretreated animals. These results indicate that the impurities have a stronger effect in inhibiting carboxylesterases which preferentially hydrolyze the β-carboethoxy moiety of malathion. The major malathion metabolites excreted in the urine of pretreated and control rats generally matched those present in the blood. The potentiation of the acute toxicity of malathion by pretreatment with isomalathion or OSS-Me may be explained by the reduction in the rat's capacity to degrade malathion via carboxylesterase-catalyzed hydrolysis of the β-carboethoxy moiety.
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