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

Metabolism of side chain and ring 14C-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 14CO2 and other gaseous 14C-labelled products from both side chain and ring labels was negligible. This and slow degradation of the hydrolysis products led to significant accumulation of 14C in the medium even after prolonged incubation.