Occurrence, impact factors, and pollution risk assessment of microplastics in a typical semi-arid urban river in northwest China.

Microplastics (MPs) have garnered much attention as emerging pollutants in recent years, but the occurrence characteristics and impact factors of MPs in the semi-arid region remain poorly understood. Thus, this study adopted a method combining sample plot investigation and data analysis to investigate the occurrence of MPs in the surface water and sediment of the Huangshui River in the semi-arid northwest China, and further analyzed the migration pattern, influencing factors and pollution risk assessment of MPs. The results verified that the MPs abundance in surface water and riverbank sediments ranged in 6.2-19.9 items/L and 3.8 × 10-13.4 × 10 items/kg (dry weight), respectively. Among them, particles smaller than 0.5 mm constituted the majority, with polyamide and fluororubber being the predominant polymer types. Fibers (67.94 %) represented the most common shape of MPs, followed by fragments (14.77 %) and granules (13.62 %). Combining multiple anthropogenic impact factors, Mantel test analysis and cluster analysis determined that domestic activities and industry in riverside urban areas contribute significantly to MPs in the Huangshui River, whereas agricultural sources played a relatively minor role. A comprehensive MPs pollution risk assessment, incorporating the MPs abundance, size, shape, color and polymer type, revealed that the Huangshui River basin was at a medium-to-high risk level, with sediment risk level higher than surface water. Each characteristic contributed differently to the MPs pollution risk in the river. This study represented the first systematic research into MPs pollution in the Huangshui River, laying the groundwork for understanding and controlling river MPs pollution in the semi-arid area.