Effects of biochar on the fate and toxicity of herbicide fenoxaprop-ethyl in soil

Biochar, as a soil amendment in agriculture, has attracted considerable attention. In the study, the fate and toxicity of the herbicide fenoxaprop-ethyl were evaluated in soils with and without 5% rice husk biochar amendment. Fenoxaprop-ethyl and metabolite fenoxaprop degradation followed first-order kinetics in the two soils. Fenoxaprop-ethyl decreased fast with half-lives less than 2 days. Large amounts of fenoxaprop formed and remained in the control soil. However, fenoxaprop was much lower in the biochar-amended soil with reduction over 85% on the 35th day. The estimated half-lives of fenoxaprop were 56.9 and 1.5 days in the control and biochar-amended soils, respectively. Biochar restrained the formation and promoted the dissipation of fenoxaprop. Biological indicator earthworms (Eisenia fetida) were used in a 14-day acute toxicity test. Fenoxaprop-ethyl showed low toxicity to earthworms with LC(50) value of 322.9 µg g(−1). Biochar amendment was non-toxic to earthworms and effectively reduced the toxicity. The results suggested that the application of biochar may reduce the risks of fenoxaprop-ethyl in the soil environment.