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Microplastic pollution and ecological risks in the wet season: Potential effects on bacterial communities and nitrogen cycling in a coastal watershed of Southeast China
Summary
Scientists studying a river system in Southeast China found tiny plastic particles (microplastics) in the water, with higher amounts near cities and areas with more human activity. These plastics were linked to changes in the natural bacteria living in the river, including bacteria that help process nitrogen and keep water systems healthy—meaning plastic pollution might be quietly disrupting the ecosystems that filter and clean the water we ultimately rely on.
Microplastics (MPs) are emerging contaminants in freshwater ecosystems, posing ecological risks via physical presence and biological interactions. MP pollution, ecological risks, and potential impacts on bacterial communities were assessed during wet season in the Minjiang River Watershed, a coastal watershed in Southeast China. Average MP concentrations (0.3-5.0 mm) were 0.22 ± 0.12, 0.17 ± 0.05, and 0.48 ± 0.27 n/L in tributaries, midstream, and downstream, respectively. MPs were predominantly composed of fibers, transparent and black particles, and PET, with the 0.3-1.0 mm size fraction being the most abundant. Urban section exhibited higher MP concentrations, whereas tributaries showed greater variability, likely reflecting heterogeneous sources. Socioeconomic factors were positively correlated with MP concentration and diversity, while NH-N, NO-N, pH, and conductivity were identified as key water chemistry parameters associated with MP distribution. Dams appeared to reduce upstream MP transport, whereas high-flow operations may release previously retained MPs. Ecological risk indices (PLI, PERI, and MPERI) indicated minor to high risks. MPs were significantly associated with dominant bacterial taxa, including Proteobacteria, Verrucomicrobia, Nitrospirota, Burkholderiaceae, and Pseudomonadaceae, as well as some predicted nitrogen-cycling genes (e.g., hao, pmoA-amoA, pmoB-amoB, pmoC-amoC, and hcp), suggesting potential shifts in community structure and function. This study highlights the importance of microbial ecology in MP risk assessments and informs river management and mitigation strategies.