Cross-enhancement of carbofuran biodegradation in soil samples previously treated with carbamate pesticides

Laboratory incubation experiments were carried out to estimate the risk of enhanced carbofuran biodegradation in soil following previous treatments with various carbamate compounds. Two soils with different sensitivities to the enhanced degradation phenomenon were used. In the Montardon soil, prior treatments with 15 N-methylcarbamates led to an enhanced rate of [14C-carbonyl]carbofuran degradation and an increase in the number of carbofuran-degrading microorganisms; prior treatment with formetanate and pirimicarb had no enhancing effect. In the Dijon soil, prior treatment with six N-methylcarbamates, chlorpropham or aldicarb had no apparent effect on the subsequent rate of carbofuran degradation and carbofuran-degrading microorganisms were not detected in any of the prior treated samples. Chloroform fumigation of previously untreated and carbofuran treated soil showed that carbofuran degradation in the Montardon soil was mainly due to biological activity, whereas abiotic activity represented a third of the total degradation in Dijon soil. Treatment of both soils with cycloheximide and chloramphenicol led to a decrease in the rate of carbofuran degradation, but streptomycin had a limited effect on the degradation rate. Further studies are needed to characterize the carbofuran-degrading microorganisms which are present in soil after prior treatments with various N-methylcarbamate pesticides.