Microplastic Contamination in a Freshwater-Dominated Subtropical Estuary: Multi-Approach Assessment of Spatial Dynamics, Sources and Ecological Hazard

Microplastics (MPs) are a growing environmental concern due to their widespread occurrence, persistence, and ecological impacts. However, data on MP pollution in freshwater-dominated subtropical estuaries, particularly in South Asia, remain scarce. This study aimed to assess the spatial distribution, characteristics, sources, and ecological risks of MP contamination in the Feni River Estuary, Bangladesh. MPs were isolated by density separation, characterized by stereomicroscopy, and Fourier Transform Infrared spectroscopy. MP abundances ranged from 426.66 ± 140.23 to 546.66 ± 136.11 items/m 3 (mean: 468.33 ± 105.76 items/m 3 ), with no statistically significant variation among stations ( p > .05). MPs were dominated by fibers, followed by fragments and films, with minor foams (porous plastics) and microbeads (spherical primary plastics). Polymer characterization identified polyethylene terephthalate (PET, 78%) as the dominant type, with polyethylene (PE), polypropylene (PP), and polystyrene (PS) also detected, reflecting strong consumer plastic inputs and secondary fragmentation processes. Contamination indices (CF) indicated non-negligible pollution, with both the contamination factor (CF, 1 ⩽ CF < 3) and pollution load index (PLI > 1) confirming moderate MP contamination. polymer hazard index (PHI) scores ranged from 0.1 to 9.1, placing polymers into risk categories I (<1) and II (1–10). Notably, PS (9.1), PET (8.6), and PE (7.3) were classified as moderate ecological risks (Category II), whereas PP (0.1) posed a negligible risk (Category I). Multivariate analyses using principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed spatial heterogeneity in MP distribution, influenced by municipal discharge, aquaculture, industrial inputs, and estuarine hydrodynamics.