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Distribution and Risk Assessment of Microplastics in the Basin of the Pearl River, China
Summary
Sampling along the entire length of China's Pearl River revealed microplastics throughout, with concentrations highest near the river's origin and estuary and the toxic polymer PMMA dominant in upstream sections. Rivers act as highways carrying land-based plastic pollution to the ocean, and the presence of highly toxic PMMA raises ecological risk concerns even where overall particle counts appear relatively low.
Microplastics (MPs) pollution is one of the most pressing environmental problems. Rivers are important conduits for land-sea transport of materials and greatly influence the behaviour of MPs into the ocean. The Pearl River is the second largest river in China in terms of water flow and has a prosperous transport industry. Meanwhile, a large amount of MPs are transported into the South China Sea through the Pearl River. We collected water samples from the origin to the estuary of the Pearl River and studied the abundance, characteristics, ecological risks, and possible impacting factors of MPs. The results showed that the abundance of MPs in the surface water of the Pearl River Basin ranged from 0.7 to 4.5 items/L, and the distribution of abundance showed the order of: origin > estuary > downstream > midstream > upstream. MPs with sizes of 1–1000 µm were the most widely distributed, and fragments and fibers were the most prevalent MPs. The distribution of MPs showed strong spatial heterogeneity, with Polymethyl methacrylate (PMMA) dominating at the origin and upstream, polyethylene terephthalate (PET) dominating in the midstream, while polyethylene (PE) was most abundant in the downstream and estuary of the Pearl River Basin. Compared with the literature data, the concentration of MPs in the Pearl River Basin was overall low, and the pollution load index indicates that the Pearl River is at a low pollution level. However, the highly toxic PMMA could lead to significant ecological risks in the Pearl River, especially at the origin and upstream watersheds. Natural factors such as hydrological conditions, gravity, and topography can affect the migration trajectory of this MPs. Reservoirs and the concave banks of curved rivers may become new"sinks"for MPs.