A Review of the Migration and Transformation of Microplastics in Inland Water Systems

Plastic productions continue to grow, and improper management of plastic wastes has raised increasing concerns. This reflects the need to explore the microplastics in water bodies. Microplastics have been regarded as emerging pollutants in water systems. In recent years, large numbers of studies across the world were conducted to investigate the distribution, behavior and the integrated impacts of microplastics in both the marine environment and the freshwater environment. Compared with the marine environment, the migration and transformation of microplastics in inland water systems seem more informative as they may reach the marine environment as one of their final destinations. Based on the updated literature, this review aims at overviewing the migration and transformation processes/behavior of microplastics in rivers, lakes and reservoirs. As for the migration, the microplastics' fate is from manufacturing, consuming, discarding to migrating and returning to the human society which could form a closed though complicated circle. For transformation, microplastics experience five stages of their fate in inland water systems. These include changing into suspending pieces; ending up deposited as the sediment; resuspending under various changing conditions; ending up via burying into the soil as the part of the riverbed; reaching the marine environment; and being ingested by organisms and also becoming entangled with aquatic plants, etc. It is highly expected that this review can provide a valuable reference for better understanding microplastics' migration and transformation mechanisms and a guide for the future study of microplastics in an inland water environment.