Spatial Distribution and Source Apportionment of Microplastics in a Typical Urban River: A Case Study of Pingshan River, Shenzhen, China

This study systematically investigated microplastics (MPs) in Pingshan River, Shenzhen—a representative urban river with short channel length, rapid flow, and limited environmental capacity. Surface water and sediment samples from seven sites were analyzed for MP abundance, size, morphology, color, and polymer composition. Results revealed significant MP pollution: surface water abundance ranged from 132 to 423 items/L (mean 311.42 ± 90.78 items/L), while sediment abundance ranged from 334 to 756 items/kg (mean 508.85 ± 151.79 items/kg). Spatial heterogeneity was pronounced, with the highest abundance at a construction-influenced site (Site 6) and the lowest at a less-impacted site (Site 2). MPs were predominantly 300–1000 μm in size. Fibers dominated surface water, while fragments prevailed in sediment. Transparent particles constituted >77% of all MPs. Polymer composition was dominated by polypropylene (PP) and polyethylene (PE). Key factors controlling spatial distribution included proximity to construction/industrial activities, aquatic vegetation cover, and hydrological conditions during the dry season. Polymer hazard risk index (H) classified all sites as Category II (10 ≤ H < 100), indicating low ecological risk despite high abundances. This research provides a scientific foundation for targeted pollution control in urban river systems, emphasizing the need to consider both abundance and polymer-specific toxicity in risk assessment.