Vertical distribution in soil column and dissipation in soil of benzoylurea insecticides diflubenzuron, flufenoxuron and novaluron and effect on the bacterial community.

Benzoylurea insecticides are used for prevention and eradication of household or field pests. However, few studies have investigated their distribution and dissipation in soils and the effects on the soil microbial community. We examined the dissipation and vertical distribution of diflubenzuron, flufenoxuron and novaluron and their effects on bacterial diversity in two soils in Taiwan. The dissipation of the three benzoylureas was concentration dependent. The half-life of 1, 10 and 50 mg kg(-1) concentration was from 3.0 to 45.9, 52.1 to 433.2 and 27.7 to 533.2 d, respectively. The proportion of residual benzoylureas in sterilized soils remained up to 83% at the end of the incubation, which implied that the dissipation was mainly by microorganisms. All three benzoylureas were not detected below 10 cm in soil column experiments. Comparison of initial pesticides concentrations (50 mg kg(-1)), diflubenzuron was detected at <1%. However, flufenoxuron and novaluron remained at >30% and 50% in Pu and Wl soil, respectively after leaching for 70 d. Furthermore, the presence of flufenoxuron and novaluron at 5- to 10-cm depth led to greater change in bacterial community diversity in Pu than Wl soil.