Pollution Characteristics and Ecological Risks of Microplastics in Surface Waters of Coastal Area and Rivers Entering the Sea on Hainan Island
Coastal areas serve as critical ecological interfaces for the migration of terrestrial microplastics (MPs) into the ocean, and characterizing their pollution is essential for integrated coastal management. This study investigated the occurrence, sources, and ecological risks of MPs in surface waters of nearshore areas and river estuaries around Hainan Island, a typical tropical tourist island. MPs abundance ranged from 316.67 to 1300 n·m−3 in seawater and from 400 to 5416.67 n·m−3 in river water. In seawater, the dominant polymer was polyethylene terephthalate, with fibers being the predominant shape, size class 500–1000 μm, and white/transparent color. In river water, polypropylene-ethylene copolymer dominated, also as fibers, but with size class 100–500 μm and white/transparent color. Seawater MP abundance showed a significant positive correlation with tourist numbers, and distribution across functional areas followed: tourism areas > natural areas > aquaculture areas > residential areas. Multiple correspondence analysis identified household plastic waste, laundry wastewater, aquaculture, and fishery products as primary sources of seawater MPs. Principal component analysis indicated homologous characteristics between seawater and river MPs, suggesting rivers are a major pathway for terrestrial MP transport to coastal zones. Ecological risk assessment revealed low pollution loads, with potential ecological risks moderate for seawater and medium-low for river water. Notably, 15% of seawater sampling sites exhibited polymer risk level Ⅳ, primarily driven by polyacrylonitrile's high biological toxicity. These findings provide a scientific basis for developing MP pollution control strategies in Hainan Island.