Assessment of microplastic pollution on coasts in anthropogenic areas using ecological risk indices

Microplastics (MPs) are common pollutants in coastal habitats and pose a significant threat to marine ecosystems. However, studies that integrate seasonal variability, physicochemical characteristics, and multiple ecological risk indicators along the southern coast of the Marmara Sea remain limited. This study presents the first comprehensive assessments of MP pollution in the coastal sediments of Gemlik Gulf by integrating seasonal variability, MP characteristics, and 10 complementary indices of pollution, ecological risk, and diversity. Analyses were performed on sediment samples collected seasonally from five beaches in Bursa Province, Türkiye. Pollution levels (CFI, PLI, CMPI, and MPPI), ecological risk (PHI, PERI, and ESI), and diversity indices (Shannon, Pielou, and Simpson) were calculated to assess MP pollution loads and potential ecological risks. MP abundances showed significant seasonal but not spatial variations, peaking in winter (226 ± 109 MP kg^-1), followed by spring (160 ± 31 MP kg^-1), summer (95 ± 25 MP kg^-1), and autumn (75 ± 28 MP kg^-1). Fibers predominated at most beaches (35-44%), whereas fragments dominated others (39-57%). MPs were predominantly black (28.0%) and white (23.3%), with the 0.5-1 mm fraction comprising 35-39% of the total. Major polymers were polypropylene (PP, 28.6%), polyamide (PA, 19.9%), and polyvinyl chloride (PVC, 10.5%). PERI and PHI indicated potential ecological risks corresponding to the "Very High" and "Extremely Dangerous" categories. These findings highlight the need for management strategies to mitigate MP pollution.