Studies on distribution and fractionation of heavy metals in Gomti river sediments-a tributary of the Ganges, India

A hydrochemical study on a 630 km stretch of river Gomti, a tributary of the river Ganges examined the distribution of heavy metals in sediments and the partitioning of their chemical species between five geochemical phases (exchangeable fraction, carbonate fraction, Fe/Mn oxide fraction, and organic fraction) using Tessier's analytical sequential extraction technique. Most fractions in the sediments associated with the carbonate and the exchangeable fractions were between 11 and 30% except in a few cases where it was more than 50%. According to the Risk Assessment Code (RAC), the sediments having 11-30% carbonate and exchangeable fractions are at medium risk. The concentrations of cadmium and lead at mid Lucknow, Pipraghat, Sultanpur U/S and Sulthanpur D/S are between 31 and 50%. They thus pose a high risk to the environment. Since the concentrations of cadmium and lead at Neemsar (Cd 56.79%; Pb 51%) are higher than 50%, the RAC as very high. In most cases, the average metal concentrations were lower than the standard shale values. Various physicochemical parameters such as pH, total solids, total dissolved solids, total suspended solids, COD, BOD, DO, conductivity, chloride, sulphate, phosphate, fluoride, total alkalinity, total hardness, etc. were also reported.