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.

Polyester microfiber and natural organic matter impact microbial communities, carbon-degraded enzymes, and carbon accumulation in a clayey soil.

Microplastics can alter microbial communities and enzymatic activities in soils. However, the influences of microplastics on soil carbon cycling which driven by microbial communities remain largely unknown. In this study, we investigated the effects of polyester microfiber (PMF) and natural organic matter（OM）on soil microbial communities, carbon-degraded enzymes, and carbon accumulation through an incubation experiment. Our results showed that the addition of PMF increased the activities of soil cellulase and laccase but did not impact soil bacterial and fungal communities too much. However, the addition of OM largely altered soil microbial communities and the activities of carbon-degraded enzymes, then mitigated the PMF effects on the activities of soil cellulase and laccase. On the other hand, greater alpha diversity of bacterial community attached on PMF was observed than those in the surrounding soils. The interaction of PMF and OM increased the richness of bacterial community in soils and on PMF. More importantly, we observed that the accumulation of natural organic carbon in soils reduced with increasing PMF. Thus, our results provide valuable insights into the effects of microplastics on soil organic carbon dynamics and microbial communities, and further work is required to clarify the biochemical processes at the surface of microplastics.