Investigation of Effects and Mechanisms of Biochar on Long-term Residual Action of Avermectin

Avermectin (AVM) is a widely used pesticide, but its susceptibility to loss and photodegradation make it economically and ecologically costly. As a commonly used adsorbent and soil amendment, biochar may be an effective solution to this problem. In this study, a facile hydrogen peroxide modification of biochar (BC-H₂O₂) has been proposed to effectively improve its interception capacity and photodegradation resistance of AVM on biochar. As a result, when AVM is loaded on BC-H₂O₂, the loss rate of AVM decreases from 31.81% to 4.11% in leaching experiment, and the degradation rate decreases from 92.32% to 15.29% under UV light irradiation. In addition, BC-H₂O₂ shows stable interception efficiency at both pH 6−9 and 5−35 °C, and in the presence of heavy metals, which demonstrates its strong structural stability. Kinetic analysis reveals that hydrogen peroxide modification changes the diffusion of AVM in biochar, and this diffusion process was more consistent with the first-order kinetic model. Moreover, hydrogen peroxide modification effectively reduces the dissolved organic carbon content and hydrophilicity of biochar, which increases the interception of AVM. Furthermore, increasing the content of oxygenated functional groups in the biochar by hydrogen peroxide modification improves the binding capacity of AVM to the biochar, thus decreasing the AVM photodegradation rate. This study offers a new approach to promote the efficiency of pesticides by loading on the modified biochar.