Effects of irrigation on the fate of microplastics in typical agricultural soil and freshwater environments in the upper irrigation area of the Yellow River

Agricultural activities are among the most significant sources of microplastics (MPs) in water. However, few studies have explored the effect of irrigation on the fate of MPs in agricultural systems. This study investigated the distribution of MPs in agricultural soil, surface water, and sediment of adjacent rivers, as well as the "MP communities" in various environments before and after irrigation in a typical agricultural irrigation area of the Yellow River. MPs were detected in all of the examined sites. The number of MPs in surface water and sediment increased after irrigation, whereas those in the surface soil of croplands decreased. In the vertical direction, irrigation accelerated the migration of MPs (< 100 µm) deep into the soil. The vertical mobility of fibers in soil was faster than that of other types of MPs. Moreover, irrigation decreased the correlation between soil properties and MPs in soils. MP community analysis indicated that irrigation enhanced the differences between MP communities among adjacent environments. Collectively, our findings confirmed that river water irrigation caused secondary MP pollution in the soil environment and accelerated MP pollution in deep soil. Therefore, this study provides a theoretical basis for the development of strategies for MP pollution control in agricultural soil.