Effects of microplastics on soil environmental behavior of fosthiazate

【Objective】 This study aimed to investigate the effects of different microplastics on the soil environmental behaviors of fosthiazate， including adsorption， degradation， mobility， and leaching， providing a theoretical basis for risk assessment of fosthiazate in soil environment with microplastics. 【Method】 Under laboratory simulated conditions， the soil supplemented with polyamide （PA）， polyethylene （PE）， polymethyl methacrylate （PMMA）， and polypropylene （PP） at a mass fraction of 2.5% was taken as treatment groups， and soil without microplastics was taken as blank control （CK）. The fosthiazate content in soil was determined. Through adsorption kinetics and isothermal adsorption experiments， the effects of microplastics on fosthiazate adsorption ability were investigated； through degradation， mobility， and leaching experiments， the effects of microplastics on environmental behaviors of fosthiazate， including degradation， mobility， and leaching， were investigated. 【Result】 The adsorption kinetics and isothermal adsorption experiments showed that the fosthiazate adsorption rates in CK， PMMA， PE， PP， and PA treatment groups were 39.40%， 49.10%， 50.35%， 66.13%， and 74.45% respectively， while the fosthiazate adsorption ability of four microplastics ranked as： PA > PP > PE > PMMA. From the adsorption coefficient K_F and K_L， supplementing microplastics could enhance fosthia-zate adsorption ability， with PA and PP showing strong adsorption ability. Degradation， mobility， and leaching experiments showed that the degradation half-life of fosthiazate in soil of CK was 22.36 d， and the half-life of fosthiazate in PA and PP treatment groups was 63.01 and 43.32 d respectively， showing significant extensions compared to CK （P<0.05， the same below）； the retention factor values （R_f） of fosthiazate in soil of CK， PE， PMMA， PA， and PP treatment groups were 0.23， 0.19， 0.18， 0.12， and 0.09 respectively， while compared to CK， R_f values of fosthiazate in soil of PA and PP treatment groups were significantly reduced. Fosthiazate was detected in three soil layers of CK， PE， and PMMA treatment groups； fosthiazate was detected in 0-10 cm soil layer in PA treatment group， and fosthiazate was detected in 0-10 cm and 10-20 cm soil layers in PP treatment group. 【Conclusion】 Supplementing four microplastics （PA， PE， PMMA， and PP） can strengthen fosthiazate adsorption ability of soil， with PP and PA showing strong adsorption ability； after supplementing PP and PA， degradation half-life of fosthiazate in soil significantly extends， with mobility and leaching ability being obviously inhibited， demonstrating that degradation， migration， and leaching ability of fosthiazate in soil with microplastics are negatively correlated with its adsorption ability.