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Characteristics of Microplastic Pollution in the Water and Sediments of the Suzhou River, Shanghai, China
Summary
A systematic survey of Shanghai's Suzhou River—a densely urbanized waterway—found that microplastic concentrations in the water averaged about 2 particles per liter, while sediments contained roughly 940 particles per kilogram, indicating the riverbed acts as a significant microplastic sink. Fibers and fragments made up the majority of particles, with polyethylene terephthalate (PET) and polypropylene (PP) as the dominant polymers. Heavy metals including chromium, copper, and zinc were detected on microplastic surfaces, raising concern that plastics act as vectors carrying toxic metals through the urban river system into downstream coastal waters.
As an early cradle of China’s plastics industry and a typical megacity, Shanghai’s urban rivers face increasingly severe microplastic pollution. This study selected the Suzhou River, known as Shanghai’s “mother river,” as its research subject. It systematically investigated the pollution characteristics of microplastics in the water and sediments, as well as the heavy metals carried on their surfaces. The abundance, shape, particle size, color, and polymer composition of microplastics were analyzed. SEM–EDS was employed for semiquantitative analysis of surface-bound heavy metals on microplastics. Results: The average microplastic abundance in the Suzhou River water was 2.18 ± 0.76 n·L−1, whereas the average microplastic abundance in the sediments was 939.29 ± 401.26 n·kg−1, indicating a relatively high pollution level in the sediments. Microplastics predominantly comprise fragments, fibers, and films, with polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) as the primary polymer types. EDS analysis detected 11 heavy metals on microplastic surfaces: Ti, Cr, Fe, Zn, Ga, As, Cd, In, Sn, Hg, and Pb. Critically, fragmented MPs were the primary carriers of multiple heavy metals, containing up to 7 different elements in sediments, including toxic Pb and Hg. Compared to water bodies, the metal spectrum loaded in sediments is more complex. It highlights their role as long-term reservoirs for co-pollutants. These findings demonstrate that MPs, especially fragments accumulated in sediments, may serve as significant vectors for the persistent storage and potential bioaccessible transfer of toxic heavy metals in urban aquatic ecosystems, posing a distinct long-term ecological risk that complicates sediment remediation efforts.