Microplastic contamination, comparative retention efficiency, and ecological hazard in saltmarsh, mangrove, sandy, and muddy habitats along the northern Bay of Bengal coast

Understanding the role of coastal habitats as microplastic "sinks" and estimating associated ecological risks are crucial due to the unique biodiversity and socioeconomic importance of these ecosystems. This study was the first to assess microplastic (MP) retention efficiency in the sediments of four coastal habitat types (saltmarsh, mangrove, mudflat and sandflat) along the northern Bay of Bengal coast, focusing on morpho-chemical attributes, accumulation patterns, and associated ecological risks. Univariate and multivariate statistical analyses (ANOVA, ANOSIM, and nMDS) were applied to examine variations in MP abundance and retention patterns across coastal habitats.The analysis unveiled the presence of MPs across all habitats, with retention trends of saltmarsh > mangrove > mudflat > sandflat. The higher accumulation of MPs in saltmarshes suggested they might serve to reduce the spread of MPs from land to ocean, thereby mitigating their negative impacts.The average MP accumulation was 35.14 ± 19.19 items/kg of sediment, with the highest concentrations in vegetated sediments (mangrove and saltmarsh), showing significant habitat variation (p < 0.05). Vegetation played a key role in MP movement, distribution, and accumulation, with fibers (85 %) being the most prevalent form, followed by films (11 %), fragments (2.5 %), and foams (1.3 %). MPs <0.5 mm were predominant (83 %), suggesting that coastal habitats are effective in trapping smaller MPs. FTIR analysis identified PE (36.67 %), PET (16.67 %), SBR (13 %), Cellulose (13.33 %), PP (11.67 %), and PS (8.33 %) across habitats. The Pollution Load Index (PLI) indicated high MP pollution, while the Contamination Factor (CF) showed a moderate pollution level. The Pollution Hazard Index (PHI) revealed a category II hazard, highlighting significant threats to coastal ecosystems. The results supports vegetation promotion to limit MP spread and the development of targeted pollution management and mitigation strategies. • Microplastics renetion pattern was: saltmarsh > mangrove > mudflat > sandflat. • Vegetated habitats > non-vegetated offered possible mitigation of spread. • Smaller size (<0.5 mm) and fibers were dominant. • PE was the most prevalent (36.67 %) polymer of all observed microplastics. • PHI and PLI indicated moderate MPs pollution in different coastal habitats.