Baseline assessment of sedimentary heavy metals and ecological risks in the high-siltation Gorai River, Bangladesh

The Gorai River, the largest distributary of the Ganges in Bangladesh, experiences high sedimentation and increasing anthropogenic pressure, raising concerns about heavy metal accumulation. This study examined the spatial distribution, pollution status, source apportionment, and ecological risks of 10 heavy metals in surface sediments collected from 22 sampling points along the Gorai River using a grab sampling method. The mean concentrations (mg/kg) followed the order: Mn (367.0) > Cr (23.97) > Ni (21.97) > Cu (18.66) > Co (9.55) > Pb (7.65) > As (5.41) > Se (0.187) > Cd (0.088) > Hg (0.0146), with Mn, Cu, and Ni exceeding the Toxicity Reference Values. Pollution indices including contamination factor (CF), enrichment factor (EF), and the pollutant load index indicated minimal pollution (CF < 6, EF < 5, PLI < 1). Nevertheless, EF for Se reached 6.93, and Cd showed elevated potential ecological risks (Er > 40). The overall Risk Indices indicated low pollution risks. Non-carcinogenic health risks were negligible, though children showed relatively higher sensitivity to As and Cr exposure. Ni represented relatively higher carcinogenic risks for children. The source apportionment analyses collectively indicated that most heavy metals (As, Pb, Cd, Co, Ni, Cr, Cu, Se) suggest mixed geogenic and anthropogenic origins. In contrast, Hg showed a distinct source signature, indicating localized contamination. These findings provide important baseline data for sediment quality assessment, management and long-term monitoring of the Gorai River system.