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Microbial Versus Chemical Degradation of Malathion in Soil¹

ABSTRACT

Chemical and microbiological degradation of malathion was studied in three Mississippi soils (Trinity loam, Freestone sandy loam, and Okolona clay) and their aqueous dilutions. Malathion abatement in all cases was more rapid under non-sterile than under sterile conditions, indicating the involvement of the soil microflora in malathion dissipation. Malathion disappearance under sterile conditions was interpreted as chemical degradation. The magnitude of microbial as compared to chemical degradation seemed to increase with increasing soil organic matter and was directly dependent on soil pH. Microbiological degradation predominated in all three test soils and their aqueous dilutions. The greatest amount of chemical degradation occurred in Okolona clay. Malathion was quite stable under neutral or acid pH conditions, but was susceptible to hydrolysis in the alkaline pH range.

Key Words: organophosphorus insecticides • biodegradation • dissipation in soil

¹ Contribution from the Dept. of Agronomy-Soils, Mississippi Agr. and Forest. Exp. Sta., Mississippi State University, State College, Mississippi 39762. The research was supported in part by the S-62 regional project. Approved for publication by the Director of the Exp. Sta., Journal article no. 2052.

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

Received for publication June 12, 1972.