Effects of Biodegradable and Nonbiodegradable Microplastics on the Environmental Fate of Chlorantraniliprole and Its Ecotoxicity to Reticulitermes flaviceps

Microplastics (MPs) are widespread emerging pollutants in agricultural soils and frequently co-occur with pesticides. While numerous studies have addressed their combined effects, the impacts of biodegradable versus nonbiodegradable MPs and their particle sizes on pesticide behavior and ecotoxicity remain to be fully clarified. This study investigated the effects of biodegradable poly(butylene succinate) (PBS) and nonbiodegradable polypropylene (PP) MPs on the adsorption and dissipation of chlorantraniliprole (CHL) in soil and its combined toxic effects on Reticulitermes flaviceps . The results showed that the adsorption kinetics of CHL in soil and soil–MP systems fitted well with the pseudo-second-order model, and chemical adsorption dominated the process. PP MPs significantly increased the adsorption capacity of soil for CHL and reduced its dissipation rate, thereby prolonging the half-life of CHL in soil, with finer particles (1000-mesh) showing stronger effects than coarser ones (200-mesh). In contrast, PBS MPs exhibited weaker adsorption toward lipophilic CHL, which accelerated CHL degradation in soil. Toxicity bioassays showed that CHL alone significantly reduced the survival rate of R. flaviceps and induced oxidative stress and metabolic disorders. Coexposure with PP MPs further increased the activities of antioxidant enzymes superoxide dismutase and catalase, inhibited the activities of detoxification enzymes acid phosphatase and alkaline phosphatase, and aggravated the decline in termite survival. However, PBS MPs showed no obvious synergistic toxic effect. These findings demonstrated that MP type and particle size jointly control CHL soil adsorption capacity, degradation half-life, as well as acute lethal toxicity, oxidative stress, and detoxification metabolic disruption in the soil arthropod R. flaviceps . Nonbiodegradable PP MPs increase the persistence and bioaccumulation risk of CHL, while biodegradable PBS MPs pose a lower ecological risk and alleviate the combined toxic effects. This study provides scientific data for assessing the ecological risks of pesticide-MP combined pollution in agricultural soils.