Carbofuran-degrading bacteria from previously treated field soils.

Laboratory incubation studies were made on soils collected from five field sites with different histories of treatment with carbofuran. All soils treated earlier with carbofuran degraded the compound more rapidly than untreated samples of the same soils. Reduced rates of degradation in the presence of chloramphenicol imply that soil bacteria are primarily responsible for the breakdown of carbofuran in these soils. Sixty-eight bacteria, capable of degrading carbofuran as the sole source of carbon and nitrogen, were isolated from liquid cultures of treated soils. The concentration of carbofuran in the liquid medium used for isolation and subsequent culture of carbofuran-degrading isolates appeared to affect the stability of their ability to degrade. Similar types of carbofuran-degrading bacteria were isolated from different soils and several different types were isolated from one soil. All carbofuran-degrading isolates were Gram-negative, aerobic rods which hydrolysed the insecticide to carbofuran phenol. They were separated into four groups on the basis of a limited number of phenotypic characters. There was a good correlation between the phenotype of carbofuran-degrading isolates and the stability of their ability to degrade. Fourteen isolates were placed in phenotypic group I and 13 of these did not degrade carbofuran after one subculture in liquid medium. Phenotypic groups II, III and IV consisted of 54 isolates in total (3, 46 and 5 isolates respectively) and 52 of these retained their ability to degrade carbofuran when subcultured.

Characterization of a carbofuran-degrading bacterium and investigation of the role of plasmids in catabolism of the insecticide carbofuran.

A bacterium capable of using the carbamate insecticide carbofuran as a sole source of carbon and energy, was isolated from soil. The ability to catabolise carbofuran phenol, produced by cleavage of the carbamate ester linkage of the insecticide, was lost at very high frequency when the bacterium was grown in the absence of carbofuran. Plasmid analyses together with curing and mating experiments indicated that the presence of a large plasmid (pIH3, greater than 199 kb) was required for the degradation of carbofuran phenol.

Insecticide residues in commercially-grown quick-maturing carrots.

Commercially-grown quick-maturing carrots which had been treated with insecticides to protect them from damage by carrot fly were analysed for residues of carbofuran (4 samples), disulfoton (17 samples) or phorate (20 samples). Intervals between treatment and harvest ranged from 10 to 35 wk. None of the carbofuran-treated carrots, and only two of the phorate-treated crops, contained greater than 0.1 mg/kg-1. Eleven of those treated with disulfoton contained greater than 0.1 mg/kg-1 but only one exceeded the Codex maximum residue limit of 0.5 mg/kg-1.