Dry-season screening assessment of microplastics and potentially toxic elements contamination in a tropical Estuary

Bangladesh’s river systems carry microplastics (MPs) and potentially toxic elements (PTEs). The underexplored Rupsha River, near the Sundarbans, was studied for MPs and PTEs. Surface water and sediment samples from four urban sites were analyzed: MPs via stereomicroscopy and ImageJ, PTEs (As, Cd, Cr, Pb) by atomic absorption spectrophotometry. Relative pollution risks were evaluated using the Pollution Load Index, Ecological Risk Index, and Principal Component Analysis to understand potential contamination patterns. Significant spatial variation was observed, with Site 3 identified as a pollution hotspot featuring 283.33±23.33 particles/L in water and 11.47±0.66 particles/g in sediment. MPs were predominantly black, smaller than 0.5 mm, and consisted mostly of fragments and fibers. Cd and Pb were the primary drivers of degradation; Cd reached “very high” ecological risk levels at two sites, and the Heavy Metal Pollution Index exceeded the critical threshold of 100 at all stations. Multivariate analysis revealed a spatial occurrence of MP abundance and PTE concentrations (i.e., As, Cr, and Cd), potentially indicating shared sources in industrial effluents and urban runoff. Therefore, the Rupsha River is significantly contaminated with MPs and PTEs, threatening the local aquatic environment. This study highlights the urgent need for targeted pollution control and stricter industrial effluent regulations.