Spatio-temporal distribution and ecological risks of microplastics in surface water and sediments of Bangshi River

This study investigates the spatio-temporal distribution, characteristics, and ecological risks of microplastics (MPs) in the surface water and sediments of the Bangshi River, which is exposed to intense urban and industrial pressures. Surface water and sediment samples were collected from 10 sites during the pre-monsoon and monsoon seasons. MPs were isolated through chemical digestion and density separation, morphologically characterised by stereomicroscopy, and polymer types identified using FTIR spectroscopy. MP concentrations ranged from 0.07–0.19 MPs/L in water and 120–360 MPs/kg in sediments. Fibres were dominant (≈50% in water, up to 87% in sediments), with black, blue, and transparent particles common in water, and red and black more prevalent in sediments. Smaller MPs (100–1500 µm) were most abundant. Polyethylene (PE) and polypropylene (PP) dominated in water, while polystyrene (PS) and polyvinyl chloride (PVC) prevailed in sediments. PHI classified both matrices in hazard category V (extreme danger), and PERI revealed severe risks, especially in sediments (PERI = 7219.30), despite a low PLI. MP levels were higher near urban/industrial areas, with sediments showing significant monsoon increases. Overall, results highlight urgent ecological threats and provide baseline data for targeted MP pollution management in Bangladesh.