Review on migration, transformation and ecological impacts of microplastics in soil

As a type of emerging pollutant, microplastics exist widely in soil and continue to migrate and transform. Recently, the potential threats of microplastics to soil health and ecological environment have attracted extensive concern. Here, this review discussed the various sources and distribution, and then highlighted the migration, transformation, and ecological impacts of microplastics in soil. Microplastics mainly entered soil through mulch degradation, application of organic fertilizer, and plastic landfill, and their distribution in soil systems showed significant spatial differences. Abiotic and biotic processes, especially leaching and bioturbation, accelerate the vertical and horizontal migration of microplastics in soil systems, thus expanding their pollution range. Mechanical wear, oxidation process and biological factors are the main driving forces for the physical, chemical, and biological transformations of microplastics in soil. Furthermore, soil structure, nutrient cycling, and microbial community were affected by microplastics, which depend on the shape, polymer type, size, and concentration of the microplastics. Based on the present review, we further propose several critical challenges and directions for improving the knowledge on migration simulation, microbial degradation, and ecological impacts of microplastics in the soil systems. This review would help to better understanding the environmental behavior of microplastics in soil and its potential risks to soil health.