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Acetylcholinesterase Toxicity of Malathion and Its Metabolites¹

ABSTRACT

Malathion, under in vitro laboratory conditions, is readily degraded by an Arthrobacter species to four metabolites—malathion half-ester, malathion dicarboxylic acid, potassium dimethyl phosphorothioate, and potassium dimethyl phosphorodithioate. However, it is not clear whether or not this degradation represents a simultaneous detoxication of the malathion molecule. With this in mind, the relative toxicity of each of the four metabolites to bovine acetylcholinesterase was determined manometrically with the Warburg apparatus. Malathion half-ester retained roughly one-third the enzyme toxicity of unaltered malathion, while the other metabolites showed essentially no enzyme inhibition. It was concluded that while microbial conversion of malathion to malathion halfester may well represent complete malathion degradation, it does not constitute complete insecticide detoxication.

Key Words: malathion • acetylcholinesterase inhibition • detoxication • Arthrobacter

¹ Contribution from the Department of Agronomy-Soils, Miss. Agr. and Forest. Exp. Sta., Miss. State Univ., Mississippi State, Miss. 39762. Part of the Ph.D. dissertation submitted by the senior author. The research was supported in part by the S-62 regional project. Approved for publication by the Director of the Experiment Station, Journal article no. 2520.

² Microbiologist, Gulf Coast Research Laboratory, Ocean Springs, Mississippi, and Professor of Agronomy (Soil Microbiologist), Miss. State Univ., Mississippi State, Miss., respectively.

Received for publication February 28, 1973.