Transport and transformation of microplastics and nanoplastics in the soil environment: A critical review

Soil pollution by microplastics (MPs, 0.1 μm ~ 5 mm) and nanoplastics (NPs, ≤0.1 μm) has drawn much attention in recent years due to its potential ecological and human health risks; however, there are very limited studies and a general lack of consensus regarding the transport and transformation of MPs/NPs in soil environment. This review critically discusses the environmental behaviour of soil MPs/NPs, including the homo‐aggregation or hetero‐aggregation with other particles, sorption of pollutants and the photoaging process. The physicochemical property change of aggregated and aged MPs and its effect on the transport of other pollutants in soil has also been reviewed. Critical factors that affect the fate of MPs/NPs, including the physicochemical properties of MPs/NPs, physicochemical properties of soil and environmental factors, are reviewed to understand the latest progress in the environmental behaviour of soil MPs. Finally, we identify important research gaps, which include standard uniformity of quantification method, transformation mechanism elucidation and long‐term field studies. The review provides an overview of current findings for transport and transformation of MPs/NPs in natural soil environment and gives comments for future work.