Advances in quantifying the drivers of the occurrence, transport, and fate of freshwater microplastics

Freshwater microplastics (MPs) can profoundly impact ecosystem functioning and human health. Understanding the current status of MP occurrence and the network of factors that influence the fate and transport of MPs will help objectively assess the environmental risks of MPs and develop effective pollution control strategies. Bibliometric analysis indicates that the current global distribution of freshwater MP has significant spatiotemporal variability, with concentrations spanning seven orders of magnitude. The analysis of the network of factors highlights the importance of the physicochemical properties of MPs, especially the modification of MPs by degradation and aggregation processes. Both biological and anthropogenic factors have extremely complex and dynamic networks of interactions. Microorganisms alter the properties and transport forces of MPs through colonization and the formation of an eco-corona, plants adsorb and trap MPs while altering hydraulic conditions, and animals influence the activation and long-range transport of MPs through physical carrying, ingestion, and bioturbation. Additionally, urbanization and global climate change participate in the entire process of MP transport, thereby increasing the difficulty of understanding the coupled effects of multiple factors in MP transport and fate. Therefore, further conducting MP surveys at spatiotemporal scales based on standardization of sampling and analysis methods is a prerequisite for building a reliable MP database. While advancing the transport mechanisms studies of MPs and combining multi-field research methods to overcome the complexity of the network of factors need to attract more attention, thereby providing theoretical bases to support the formulation and implementation of MP pollution management and control.