Influence of biochars on plant uptake and dissipation of two pesticides in an agricultural soil.

This study investigated the influence of two types of biochars on the bioavailability of two soil-applied insecticides (chlorpyrifos and fipronil) to Chinese chives ( Allium tuberosum ) and dissipation of the pesticides in the biochar-amended soils. The biochars (BC450 and BC850) prepared from the burning of cotton ( Gossypium spp.) straw chips at two different temperatures (450 and 850 degrees C) were thoroughly mixed into a soil to achieve 0, 0.1, 0.5, and 1% by soil dry weight. Chinese chives were grown for 5 weeks in the biochar-amended soils spiked with 50 mg kg(-1) of each pesticide. The loss of both pesticides in soils decreased significantly with increasing amounts of the biochars in the soil. After 35 days of incubation, 58-68% of the pesticides was lost from the control soil, whereas in the soil amended with 1.0% BC850 only 34% of chlorpyrifos and 32% of fipronil were dissipated. More losses of the pesticides were found in the soils with plants due to plant uptake and enhanced microbial degradation. Despite greater persistence of the two pesticide residues in the biochar-amended soils, plant uptake of the two pesticides from the amended soils decreased markedly with increasing biochar content in the soil. With the amendment of 1% of BC850 in the soil, the total chlorpyrifos and fipronil residues in plant biomass decreased to 19 and 48% of those in the control treatment, respectively. Thus, biochar BC850 was found to be effective in reducing the bioavailability of both pesticides from the soil. Biochar could be applied to sequester pesticide residues in contaminated soils and to reduce plant uptake.