Recent advances on ecological effects of microplastics on soil environment

The mass production and wide application of plastics and their derivatives have led to the release of a large number of discarded plastic products into the natural environment, where they continue to accumulate due to their low recycling rate and long durability. These large pieces of plastic will gradually break into microplastics (<5 mm), which are highly persistent organic pollutants and attract worldwide attention due to their small particle size and potential threats to the ecosystem. Compared with the aquatic system, terrestrial systems such as soils, as sinks for microplastics, are more susceptible to plastic pollution. In this article, we comprehensively summarized the occurrence and sources of microplastics in terrestrial soil, and reviewed the eco-toxicological effects of microplastics in soil ecosystems, in terms of physical and chemical properties of soil, soil nutrient cycling, soil flora and fauna. The influence of microplastics on soil microbial community, and particularly the microbial community on the surface of microplastics, were examined in detail. The compound effects of microplastics and other pollutants, e.g., heavy metals and antibiotics, were addressed. Future challenges of research on microplastics include development of new techniques and standardization for the extraction and qualitative and quantitative analysis of microplastics in soils, toxic effects of microplastics at microbial or even molecular levels, the contribution of microplastics to antibiotic resistance genes migration, and unraveling microorganisms for the degradation of microplastics. This work provides as a better understanding of the occurrence, distribution and potential ecological risks of microplastics in terrestrial soil ecosystems.