Occurrence and ecological risk of microplastics in soils and sediments in the Inner Mongolian Yellow River Basin: An analysis based on functional zoning

Microplastics (MPs) pollution in the Inner Mongolian Yellow River Basin (IMYRB) of China was investigated through 34 soil/sediment samples. The results showed MPs were widely distributed in the region, with a total mean abundance of 5503 ± 1502 n/kg dry weight (dw) in soils and 2059 ± 1188 n/kg dw in sediments. MPs were predominantly 1-2 mm transparent fibers, composed mainly of polypropylene (PP) and polyethylene (PE). Spatial analysis revealed the highest MP abundance in soils of Baotou (6108 n/kg dw) and peak MPs contamination in sediments near Hohhot (2543 n/kg dw). By functional zones, sewage outlets (6133 n/kg dw) and industrial areas (5800 n/kg dw) were major sinks for soil MPs, while wetland fishponds contained the highest sediment MPs (2533 n/kg dw). Agricultural soils dominated by film-shaped MPs (>23 %), industrial areas by fragments, and wetland fishponds by fibers. Polymer composition varied, with elevated polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) in industrial soils, and higher polystyrene (PS) content in wetland sediments. Ecological risk assessment indicated ultrahigh risk in industrial soils and medium risk in wetland sediments, primarily due to toxic PVC/PMMA. These findings provide essential baseline data for ecological risk control of MPs across river basin in northern China.