Investigation of the effects and mechanisms of biochar on the 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) is proposed to effectively improve the intercept and resistance to photodegradation ability of biochar on AVM. As a result, when AVM loaded on BC-H2O2, the loss of AVM decreased from 31.81% to 4.11% in the leaching experiment, and the degradation rate decreased from 92.32% to 15.29% under UV light irradiation. In addition, BC-H2O2 showed stable intercept efficiency at both pH 6-9 and 5-35 °C and in the presence of heavy metals, which demonstrated its strong structural stability. Kinetic analysis revealed that hydrogen peroxide modification changed the diffusion of AVM in biochar, and this diffusion process was more consistent with the First-order kinetic model. Moreover, hydrogen peroxide modification effectively reduced the dissolved organic carbon (DOC) content and hydrophilicity of the biochar, which increased the interception of AVM. Furthermore, increasing the content of oxygenated functional groups in the biochar by hydrogen peroxide modification improved 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.