From beaches to mangroves: Spatiotemporal mapping and risk profiling of microplastics in coastal Bangladesh

This study examines seasonal and spatial variations in microplastic (MP) contamination, polymer types, and associated ecological risks along the entire coastline of Bangladesh, from the Sundarbans region in the west to Teknaf in the east. Sampling was conducted across eighteen sandy and muddy beaches during the monsoon and winter seasons. MP concentrations are 385 items/100 g dry weight (dw) sediments in winter and 471 items/100 g dw in the monsoon season. MPs were quantified using a stereo microscope, and an FT-IR was used to examine polymer composition. Polypropylene (PP, 30.6%), polyethylene (PE, 29%), and polystyrene (PS, 22.4%) were the predominant polymers encompassing both seasons and locations. The mean pollution load index (PLI_zone) values for winter and monsoon were 2.36 and 2.24, respectively, with polymer hazard index (PHI) values spanning from hazards categories III to V across all sites. The potential ecological risk index (PERI) ranged from Danger to Extreme Danger, underscoring high risk levels for marine flora and fauna in their respective habitats. While MP concentration and load were influenced by season, the hazardous polymer composition remained consistent throughout seasons, posing a high threat and ecotoxicological risks. This study provides important baseline information on MP pollution dynamics across the entire coastal area of Bangladesh, highlighting the need for ongoing monitoring and targeted interventions to mitigate long-term ecological risks in this region.