‘‘Spatial distribution, abundance, and risk assessment of microplastics in the surface water of Kaptai Lake: Southeast Asia's largest artificial reservoir’’

• The amount of MPs in surface water was from 13.33 ± 6.67 to 683 ± 70.55 items/m 3 . • PE (36 %) and PET (38.57 %) were the most abundant polymers. • The PHI value, RI, and er indicated serious microplastic contamination. Microplastics (MPs) are ubiquitous in aquatic habitats and have the potential to seriously harm the ecosystem, creatures, and public health. Microplastic pollution in water has garnered attention, but regional microplastic distribution, shape, and risk are unknown. We collected 42 samples from 14 sampling sites in Kaptai Lake to study the spatial variations, causes, transfer, composition profile, and environmental impact of MPs in water. The sampling was done in January 2024 by using a manta trawl having a mesh size of 300 μm. The MPs in water samples were digested, vacuum filtered and quantified using an optical microscope. The number of MPs ranged from 13.33 ± 6.67 to 683 ± 70.55 items/m 3 . Plastic particles were most often transparent (38.07 %) and red (11.01 %). MPs types in water were ordered as follows: Fibers > foams > fragments > lines > films > pellets. According to the analysis in Fourier-transform infrared spectroscopy (FTIR), Polyethylene terephthalate (PET) (38.57 %) and polyethylene (PE) (36 %), with filamentous (33.33 %) and irregular (32.37 %) morphologies, were the most common polymers. Most MPs (83.98 %) were between 0.3 and 1.5 mm, followed by 3–5 mm (8.75 %) and 1.5–3 mm (7.27 %). Scanning electron microscopy (SEM) was employed to examine the surface deformation of different polymer types due to environmental exposure where the PE showed the highest degree of deformity. The polymer hazard index (PHI), the potential ecological risk index (RI), and, the ecological risk factor (E r ) values for Lake water indicate serious MPs risk. The pollution load index (PLI) had very low MP contamination. Household wastewater and fishing may be related to local MPs. This study may provide a MPs contamination baseline in Bangladesh's extensive freshwater ecosystem. The results will enhance knowledge of MPs pollution risk and contamination levels, which could facilitate the development of remediation strategies.