Risk assessment of metal species in sediments of the river Ganga

• Metal speciation study was conducted on river Ganga sediments.
• Sequential Extraction Procedure and Total Acid Digestion mechanism was used.
• pH-metal species relation was studied with Medusa chemical equilibrium software.

The present study deals with the geochemical fractions of nine heavy metals [chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb)] present on the river sediments using sequential extraction process (SEP) and total acid digestion (TAD). This work was conducted on Ganga river sediments at Varanasi. A ten kilometer stretch of the river Ganga from Samne Ghat to Varuna-Ganga confluence was selected to perform this study. Pollution Load Index (PLI) varied from 1.2 to 3. Geo-accumulation index (Igeo) and Risk Assessment Code (RAC) showed higher concern for Cd and Pb whereas Mn, Fe and Ni showed negative accumulation index at all sampling stations. Lead, cadmium, copper and nickel were present significantly in available fraction; however, the Igeo of Ni was found negative at all stations. Various sources of the metal pollution in the city include domestic, industrial and agricultural untreated wastewater draining into the river. Geochemical fractions of the metals–pH relation study, using Medusa Hydra chemical equilibrium software, revealed the presence of different species of metals at different pHs.