Spatial distribution, characteristics, polymer composition, and ecological risk of microplastics in marine sediments...

This study investigated the abundance, spatial distribution, physical characteristics, polymer composition, and ecological risks of microplastics in surface sediments collected from 11 marine sites spanning bays, nearshore waters, estuaries, offshore islands, and urbanized tourist areas along Central Vietnam. Microplastics were detected in all samples, with concentrations ranging from 250 to 3217 particles/kg dry sediment. Morphologically, fragments and fibers predominated; fragments were more prevalent in bays, islands, and urban-tourism beaches, reflecting the secondary degradation of larger plastic waste, while fibers predominated in fishing port areas and textile processing zones. The size distribution showed that small MPs (50-300 μm) were dominant, with the 50-100 μm and 100-300 μm groups accounting for the majority of the total particles, and virtually no particles >500 μm were recorded. FTIR analysis revealed that polyethylene terephthalate (PET), polyethylene (PE), and fluoropolymers (PTFE) were the dominant polymers, along with numerous others with high hazard levels. The Pollution Load Index (PLI) indicates an overall pollution level of 1, but both the Polymer Hazard Index (PHI) and the Potential Ecological Risk Index (PERI) are at the highest level, highlighting that the ecological risk is primarily driven by polymer toxicity rather than particle count alone. Because density separation used NaCl, the proportions of high-density polymers (PET, PVC, PA) and the PHI/PERI values reported here are conservative estimates. This study provides the first regional baseline dataset for Central Vietnam and offers scientific evidence to support prioritized management and long-term monitoring of plastic pollution in the marine environment.