Soil biodegradation of carbofuran and furathiocarb following soil pretreatment with these pesticides

Abstract A field application level (9 μg·g −1 ) of carbofuran was completely hydrolyzed within 1 to 3 days in a loamy sand soil pretreated with the same level of carbofuran, while <5% of the carbofuran was hydrolyzed in control soil not pretreated. The number of microbial carbofuran‐hydrolyzers was substantially greater in loamy sand soil treated twice with a field application level (9 μg·g −1 ) of carbofuran than in untreated soil. Also, carbofuran‐adapted soil showed no significant change in the number of carbofuran‐hydrolyzers during the period of rapid degradation. Inorganic nitrogen, at a typical fertilization level, appeared to slightly stimulate the enhanced degradation of carbofuran in the pretreated soil. Soil pretreated with an application level hydrolyzed 65% of a residue level (8 ng·g −1 ) within two days, but virtually none of the remaining carbofuran was hydrolyzed thereafter. A microbial biomass carbon experiment with a sandy loam soil indicated that only 0.2% of the applied carbonyl‐C could be attributed to biomass. Soil pretreated with a residue level did not show rapid degradation of the same level or a field application level, although the field application level was degraded slightly faster in this soil than in soil not pretreated. Soil pretreated with a field application level of carbofuran or furathiocarb also rapidly hydrolyzed the same level of furathiocarb, but furathiocarb is probably converted into carbofuran before hydrolysis.