Soil Aggregates and Organic Carbon Transformation in Response to Microplastics Pollution

Soil microplastic pollution has attracted widespread attention, due to its effects on soil ecosystem. In recent years, many studies on environmental behaviors of soil microplastics were investigated, while systematic review about the responses of soil aggregates and soil organic carbon (SOC) to microplastic pollution is still scarce. Therefore, 131 papers were summarized to explore the source and distribution of microplastics in soils and their effects on soil aggregate stability and SOC transformation. Microplastic abundance in agricultural soils shows generalization and spatial heterogeneity. Microplastics are mainly derived from plastic mulching, organic fertilizers and soil amendments, sewage sludge, discharges from sewage treatment plants, tire wear as well as atmospheric deposition. Microplastics reduce soil aggregates stability directly or indirectly by forming fracture points, reducing soil moisture and particle density, decreasing geometric mean diameter (GMD) and the mean weight diameter (MWD). It's worth noting that microplastics can accelerate the mineralization of SOC by fragmenting soil structure and priming effects. On the one hand, microplastics reduce the stability of soil aggregates, leading to the exposure of SOC and increasing its contact with microbes. On the other hand, microplastics stimulate microbial and enzyme activity and further promoting the mineralization of SOC. This study aims to deepen our understanding of how microplastics affect the soil environment and to provide a scientific basis for the development of soil microplastic pollution treatment strategy.