Pollution Characteristics and Ecological Risks of Microplastics in Surface Waters of Coastal Area and Rivers Entering the Sea on Hainan Island

• • Seawater MP abundance ranged from 316.67 to 1300 n·m−3, while river water ranged from 400 to 5416.67 n·m−3, indicating rivers as a significant conduit for terrestrial MPs; this differential informs source mitigation priorities. • • Dominant polymer in seawater was polyethylene terephthalate (PET), whereas river water was dominated by polypropylene-ethylene copolymer (PP-PE); this polymer-specific signature aids in tracing sources and selecting targeted waste management. • • Seawater MP abundance correlated significantly with tourist numbers, with distribution pattern tourism areas > natural areas > aquaculture areas > residential areas; this quantifies tourism's impact, guiding policy for coastal tourism management. • • Ecological risk assessment showed moderate risk in seawater and medium-low in river water, but 15% of seawater sites reached polymer risk level Ⅳ due to polyacrylonitrile's high toxicity; this identifies hotspots requiring urgent intervention.