Metabolism of carbaryl and carbofuran by soil-enrichment and bacterial cultures

Abstract

Metabolism of side chain and ring 14 C-labelled carbaryl and carbofuran in a mineral salts medium by soil-enrichment cultures and a Bacillus sp. was studied. A change in the substrate of the medium from carbaryl to carbofuran led to a marked shift in the dominant bacterium from Bacillus sp. to Arthrobacter sp. although carbaryl-enrichment culture was the primary inoculum in both media. Hydrolysis was the major route of microbial degradation of both carbamate insecticides. During carbaryl degradation by enrichment cultures and Bacillus sp., 1-naphthol and 1,4-naphthoquinone accumulated in the medium. Of the three metabolites formed from carbofuran, 3-hydroxycarbofuran and 3-ketocarbofuran were further metabolized rapidly, while carbofuran phenol was resistant to further degradation. Evolution of 14 CO 2 and other gaseous 14 C-labelled products from both side chain and ring labels was negligible. This and slow degradation of the hydrolysis products led to significant accumulation of 14 C in the medium even after prolonged incubation.