Distribution, Sources, and Ecological Risk Assessment of Microplastics in the Lower Minjiang River

Microplastics, as a pervasive emerging pollutant, pose a critical threat to freshwater ecosystems and have emerged as a pressing global environmental concern. This study employed methods such as microscopic observation and Raman spectroscopy analysis to characterize the abundance, morphology, and polymer composition of microplastics in surface water and sediments from the lower Minjiang River (Fujian Province, China) in July and November 2024. By integrating socioeconomic indicators with water quality parameters, we dissected the pollution sources, and employed the Pollution Load Index (PLI), Polymer Chemical Toxicity Hazard Index (PHI), and Potential Ecological Risk Index (PERI) to quantify ecological risks in the study area. Findings reveal that the lower Minjiang River exhibits moderate microplastic contamination compared to domestic and international river systems, with mean abundances of 19.90 ± 1.56 n/L (flood-season surface water), 22.87 ± 1.32 n/L (dry-season surface water), and 728.17 ± 20.51 n/kg (dry-season sediments). Spatiotemporal dynamics demonstrate significantly higher microplastic loads in dry-season surface water versus flood-season counterparts, and markedly elevated concentrations in sediments relative to water column, underscoring medium-specific contamination gradients. Microplastic particles predominantly comprised transparent fibrous/fragmentary entities <500 μm, with polymeric constituents dominated by PP and PE. Urbanization-driven wastewater discharge emerged as the primary contamination vector. Notably, PLI assessment confirmed moderate pollution, whereas PHI and PERI analyses indicated elevated risks, with highly toxic polymers, such as PVC and PAN, contributing disproportionately to risk indices.