Microplastic characterization, transport and ecological risk across functional zones of China's largest tropical...

Microplastics (MP) are widespread contaminants in coastal and marine systems. Hainan Province, China's largest tropical island, was the first provincial-level jurisdiction to ban disposable plastics, yet its MP burden and the policy's effect remain poorly quantified. This study examined the distribution, sources and ecological risk of MP in surface water and sediments across industrial-residential, agricultural and aquaculture zones on Hainan Island. A total of 47 samples (31 surface-water, 16 sediment) were collected from 33 sites during the early wet season in July 2024 and characterized by μ-FTIR spectroscopy. MP were detected in all surface-water samples (2419 ± 1840 items m^-3) and in 94% of sediment samples (91 ± 58 items kg^-1 dry weight). Different functional zones exhibited distinct polymer compositions and morphological characteristics, consistent with inputs from domestic discharge, agriculture and aquaculture. Compared with pre-ban datasets, the proportion of polyethylene in the polymer pool decreased, a shift tentatively linked to the 2020 plastic ban. Spearman analysis linked surface-water MP to port throughput, tourism and water-quality variables, and sediment MP to settlement proximity and local economic activity. The compositional contrast between riverine and marine waters in the aquaculture zone indicates that direct sea-based inputs have been underestimated. Combined Pollution Load, Polymer Hazard and Ecological Shape Indices indicated low-to-moderate index-based risk, with hotspots at industrial-port sites dominated by polyvinyl chloride and polyurethane.