Current status and comparative risk assessment of microplastic pollution in surface water and sediment from the Black Sea coastline using geospatial analysis

This study presents the first comprehensive and multifaceted assessment of microplastic (MP) contamination and site-specific ecological risk along the Central Black Sea coastline (Samsun Province), a region subject to intense and multifaceted anthropogenic pressures in a semi-enclosed marine basin. Surface seawater MP abundances ranged from 630 to 1600 particles/L in 2020-290-2850 particles/L in 2021, with station S1 consistently exhibiting the highest concentrations (1600-2850 particles/L), indicating a approximately 78 % average annual increase. Coastal sediments showed even greater contamination, rising from 6500 to 13700 particles/kg (dry wt.) in 2020-6100-32400 particles/kg in 2021, with station S6 recording the maximum value (>3-fold increase). Fibers dominated both matrices (>68 %), with polypropylene (PE-PP, >27 %), polyethylene terephthalate (PET, >56 %), polyvinyl chloride (PVC, >9 %), and polystyrene (PS, >2 %) identified as the primary polymers via ATR-FTIR. The Polymer Hazard Index (PHI) values revealed Category III (high risk) at most stations. Although MP levels in seawater are relatively low compared to other global marine environments, sediments pose a significant ecological threat, primarily as critical long-term sinks for highly hazardous polymers. These findings reveal that Türkiye's Black Sea coast is a previously unrecognized hub of high-risk microplastic accumulation and highlight the urgent need for region-specific monitoring and mitigation strategies in semi-enclosed seas subject to intense human pressure.