Biodegradation of carbofuran and furathiocarb in soil: effect of pretreatment and microbial growth responses to carbofuran

The rate of degradation of carbofuran was measured in Norfolk loamy sand and Lynchburg sandy loam soils with no known history of pesticide treatment. Degradation was measured by trapping 14CO2 evolved from 14C-carbonyl carbofuran applied to soil in flasks. Loamy sand soil pretreated with 9 μg x g-1 carbofuran completely degraded a second or third application of 9 μg x g-1 within 1-3 days, but <5% was degraded in soil treated for the first time. Nitrogen, applied as 100 μg x g-1 in NH4NO3, very slightly increased the rate of degradation of 9 μg x g-1 carbofuran in the pretreated soils. The rate of degradation of carbofuran in the pretreated soils can be described by 1st order kinetics. However, in the soil pretreated with 9 μg x g-1 carbofuran, the rate of degradation of an 8 ng x g-1 treatment was biphasic, with only 65% rapidly degraded within 2 days. This 14CO2 evolution curve was best described by a two-compartment model for the degradation of low levels of organics in soil