Role of raw feedstock and biochar amendments on sorption-desorption and leaching potential of three 3H- and 14C-labelled pesticides in soils

The pesticide behavior in soils can be easily affected by biochar addition. However, studies on the effects of raw feedstock and biochar are scarce. The objective of this study was to evaluate the effect of amending soils from three Midwestern U.S. states, with biochar produced from soybean residues, sugarcane bagasse, and wood chips (grape) as well as raw feedstock on the sorption-desorption and leaching potential of the pesticides aminocyclopyrachlor, metolachlor, and imidacloprid. Soil was amended at 10% (w w(-1)), and sorption-desorption studies were performed using the batch equilibration method. Following the determination of the sorption coefficient (K-oc) values, the groundwater ubiquity score (GUS) indices for these pesticides were calculated. The highest pesticide sorption in all unamended soils followed the order imidacloprid (K-d = 0.79-1.66 L Kg(-1)) > metolachlor (K-d = 0.54-0.61 L Kg(-1)) > aminocyclopyrachlor (K-d = 0.12-0.23 L Kg(-1)). Biochar has the potential to decrease metolachlor and imidacloprid availability in soil through increased sorption, while the availability of aminocyclopyrachlor differed between the use of raw feedstock and biochar. Biochar derived from wood chips had the highest impact on pesticide behavior. We confirmed that aminocyclopyrachlor, metolachlor, and imidacloprid would leach easily in the three unamended soils, as illustrated by the GUS index.