Trace element dynamics and ecological risk indices in coastal sediments along the southeastern Bangladesh

Bangladesh's southeastern estuaries are increasingly contaminated with trace metals from industrial effluents, aquaculture waste, and maritime activities. This study evaluates ecotoxicological risks and contamination levels of potentially toxic elements (PTEs) in sediments at five locations: Matamuhuri, Moheshkhali, Bakkhali, Naf River, and St. Martin's Island. Sediment quality was analyzed using geochemical indices, including Contamination Factor (CF), Degree of Contamination (C_d, mC_d), Geo-accumulation Index (I_geo), Pollution Load Index (PLI), and Potential Ecological Risk (PER), and compared with sediment quality guidelines (SQGs). The results show significant regional variability, with Bakkhali and Moheshkhali having high to extremely high pollution loads (PLI > 2), I_geo values for Cd (>2.16), Cr (>1.36), Cu (>1.20), and Ni (>1.58), and values exceeding the ecological risk threshold (>300). St. Martin's Island and the Naf River, on the other hand, demonstrate very low levels of pollution (PLI <0.77), I_geo values for Cd (<0.05), Cr (<-0.58), Cu (<-1.29), and Ni (<0.89), and (PER<91.87) and ecological concern. Multivariate analyses (Pearson correlation, PCA, and HCA) reveal familiar anthropogenic sources linking Cu, Zn, Pb, and Cr. Recommendations include recognizing Bakkhali and Moheshkhali as pollution hotspots for regulatory actions and supporting sustainable development by contributing to global sustainable development initiatives, particularly SDG 6, SDG 13, SDG 14, and SDG 15, and addressing regional coastal pollution management.