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The study was conducted to investigate the concentrations, distributions, sources and potential ecological risk of heavy metals in surface sediments from the Old Brahmaputra River. Sediment samples were collected from ve sampling stations and analyzed with inductively coupled plasma mass spectrometer (ICP-MS). The results showed that mean concentrations (mg/kg) of heavy metals were in order of Ni (58.82) Cr (32.45) Pb (21.04) Cu (14.24) Cd (3.81) As (2.02). In terms of spatial variation, sedimentary metals differed substantially, and the bulk of metal distribution and abundance can be traced back to man. Element-speci c environmental indices exposed that the ecological risks trailed the downward direction as Cd Ni Pb As Cu Cr. The contamination factor (CF), enrichment factor (EF) and geoaccumulation index (Igeo) exposed all cases a modest level of contamination except Cd, which has a signi cant level of contamination. Only, Ni and Cd were found high ecological risk for aquatic life, based on the sediment quality guidelines.Low to moderate ecological risk was suggested by the prospective ecological risk factor and potential ecological risk. The river sediments were mostly uncontaminated to mildly contaminated, posing a minimal ecological risk. The study concluded that the Old Brahmaputra River is subjected to anthropogenic disturbances for the aquatic environment. In this regards, proper management initiatives and regular monitoring should be carried out immediately by Department of Environment (DoE) to maintain sound and healthy aquatic environment of the River.

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