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Beyond Particle Counts: Mass-Based Microplastic Risk Assessment in Urban Freshwater Reveals PVC-Dominated Ecological Threats in China’s Qiantang River
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Researchers assessed microplastic pollution in China's Qiantang River using both particle counting and mass-based methods, finding that PVC dominated total microplastic mass despite lower particle counts, and that its high toxicity placed ecological risk at the most severe level requiring urgent regulatory action.
With the advancement of industrialization, microplastic (MP) pollution in urban freshwater systems has become increasingly severe. Although particle counting methods are widely used to characterize MP contamination, the mass-based properties of MPs are often overlooked. This study assessed MP pollution in surface waters of the Qiantang River in eastern China by combining quantitative and mass perspectives using laser direct infrared spectroscopy (LDIR) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). LDIR analysis revealed MP concentrations ranging from 4.8 to 251.2 items L−1, with small-sized MPs (10–50 μm) accounting for 54.2% of the total. Fragments and particles were the dominant morphologies. A total of 11 polymer types were identified, among which polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polystyrene (PS), and polymethyl methacrylate (PMMA) collectively accounted for 85% of the total particle abundance. PET was the most prevalent polymer by count (38.8%), followed by PP (16.1%), PVC (13.8%), and PE (12.1%). Targeted Py-GC/MS analysis of these six polymers showed mass concentrations between 35.72 and 80.74 μg L−1, with PVC (54.8%) and PET (43.71%) dominating the total mass. Despite the diversity in particle counts per polymer types, MP mass was concentrated in a few key polymers, likely due to differences in polymer density and particle volume. By integrating principal component analysis (PCA) and k-means clustering, five major pollution sources were identified: (1) industrial/agricultural/urban sources; (2) packaging/industrial sources; (3) construction materials/textile sources, (4) consumer goods/electronic sources, and (5) packaging/fishery sources. Ecological risk assessment indicated that the high toxicity of PVC led to polymer hazard index (PHI) and potential ecological risk index (PERI) values corresponding to Level V risk, representing a very high ecological threat and underscoring the need for urgent regulatory action. In summary, this dual assessment of MP pollution from both quantitative and mass-based perspectives provides a more comprehensive understanding of MP contamination in urban freshwater systems, offering valuable insights for source identification, risk evaluation, and targeted mitigation strategies.
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