The persistent impacts of polyester microfibers on soil bio-physical properties following thermal treatment

Soilborne microplastics can persist for decades and their consequences are of growing concern. Therefore, it is important to explore the feasible approaches for eliminating microplastic effects on soil properties. Through an incubation experiment, we evaluate the effects of thermal treatment on physical properties, enzymatic activities and microbial communities in polyester-microfibers contaminated soils. The effects of polyester-microfiber levels (0%, 0.1%, 0.3% and 1.0% of soil dry weight) on soil properties were detected under not heated (PMF), heated (mPMF) and added with natural-organic-matters (OM) following heated (mPMF+OM) conditions. Our results showed that 1.0% mPMF soil had lower bulk density and higher mean weight diameter than 0% mPMF soil, akin to PMF soils. Meanwhile, great volumes of < 30 µm pores in 0.3% and 1.0% mPMF soils were observed than that in 0% mPMF soil. Additionally, the dose-effects of melted polyester-microfiber on soil enzymatic activities and bacterial communities were still observed following thermal treatment, even under the OM added condition. Furthermore, our results demonstrated that polyester microfibers influenced soil microbial communities and functioning via altering specific soil physical properties, regardless of thermal treatment or not. Results of this study should be useful to guide further develop viable methods for remediating soils contaminated with microplastics.