Microplastic occurrence, source tracking and integrated risk assessment in a linked lake-river system of the Yangtze River Delta.

Microplastics (< 5 mm) pose a growing threat to freshwater ecosystems, yet systematic assessments in inland lake-river networks remain scarce. This study addresses this gap by investigating microplastic contamination across four environmental compartments (surface water, lakeshore soil, borehole groundwater, and well water) in China's Wujiang District and its Yuandang Lake-a system with limited self-purification capacity. The relationship between Wujiang District and Yuandang Lake exemplifies the 'jurisdiction-watershed' dynamic and epitomizes the 'development-conservation' interplay. Key findings reveal: (1) Surface water exhibited the highest microplastic concentration (3.70 ± 0.58 items/L), followed by topsoil (average 214 n/kg). Groundwater showed lower but pervasive contamination. (2) Fibers (50-100 μm, transparent) dominated (> 60%), with polyethylene terephthalate (PET) as the predominant polymer. (3) Textile industries were the primary source of groundwater microplastics, while topsoil contamination correlated with construction waste and agricultural practices. (4) Although the Pollution Load Index (PLI) indicated low risk, the Polymer Hazard Index (PHI) and Potential Ecological Risk Index (PERI) revealed moderate-to-mild risks, highlighting the need for compartment-specific management. Notably, topsoil microplastic levels (up to 1233 n/kg) exceeded those in less disturbed basins and aligned with industrialized systems like Taihu Lake. The multi-compartment assessment underscores the importance of localized industrial and land-use practices, providing a framework for targeted pollution control and ecological risk management. The results offer key data to support collaborative governance in the Yangtze River Delta, especially across the Wujiang-Qingpu boundary, advancing regional sustainability.