Degradation and adsorption of carbendazim and 2‐aminobenzimidazole in soil

Increasing adsorption of [ 14 C]‐labelled carbendazim in soil took place within a few weeks of incubation and was greatest in soil with a high organic matter content. Carbendazim was slowly decomposed in soil, mainly by soil microorganisms. After 250 days of incubation in two unsterilised soils, 13 and 5% respectively of added [ 14 C]‐carbendazim was recovered compared with 70 and 50% respectively from sterile soils; 4–8% of added carbendazim was recovered as 2‐aminobenzimidazole (2‐AB) from both unsterilised and sterile soil. After 270 days' incubation, 33 and 9% of 14 C was recovered as 14 CO 2 from soil supplied with [ 14 C]‐carbendazim (20 and 100 mg/kg) respectively. Degradation started more rapidly when carbendazim was added to soil preincubated with the fungicide but the degradation rate was very low in all cases, indicating that the compound is a poor microbial energy source and that the degradation is a co‐metabolic process. 2‐AB was found as a degradation product although it appeared to be unstable in soil, decomposing rapidly after a lag period of about 3 weeks; small amounts remained in the soil for several months, however, presumably adsorbed on soil particles.