Efficiency of Four Extraction Methods to Assess the Bioavailability of Oxyfluorfen to Earthworms in Soil Amended with Fresh and Aged Biochar

Due to its high persistence in soil, oxyfluorfen has negative effects on environmental and human health. To reduce soil contamination and impacts on non-target organisms, biochar is introduced into soils to immobilize and sequestrate oxyfluorfen as a remediation practice. Three types of soils common in China were selected and biochar (rice hull, BCR) was added to investigate the desorption and bioavailability of oxyfluorfen after aging BCR for 0, 1, 3, and 6 months. Four chemical extraction methods were used to predict oxyfluorfen bioavailability. Results indicated that after addition of 0.5–2% unaged BCR, the desorption values of oxyfluorfen increased from 64–119 to 176–920 (μg/g)/(mg/L) n in the three soils compared with unamended soil. The bioaccumulation factor (BCF) values of oxyfluorfen in earthworms decreased from 0.80–1.7 to 0.10–1.56 after BCR addition. However, the desorption values decreased from 170–868 to 144–701 (μg/g)/(mg/L) n after aging. The bioavailability of oxyfluorfen in earthworms also increased after the aging treatments, while the BCF was still lower than with unaged BCR. The reduced BCF indicated lower exposure risk of oxyfluorfen to earthworms after amendment with biochar, even after aging 6 months. The bioavailability after extraction by Tenax showed a high linear correlation with uptake in earthworms, even after the 6-month aging treatment (R 2 > 0.80). Consequently, BCR could be a practical method to remediate contaminated soil and the 6h Tenax method could be a sensitive and feasible tool to assess the bioavailability of oxyfluorfen in soil.