SEDIMENT-BOUND HEAVY METALS IN HIMALAYAN STRETCH OF GANGA

Abstract

Analysing the sediment quality of rivers is vital while assessing the quality of rivers. The sediments of river Ganga in the Himalayan region are assessed for different heavy metals - Cd, Cr, Cu, Ni, Pb and Zn at 7 different locations. The concentrations of Al and Fe, two of the conservative metals were also analysed for comparison. The sediments collected were sieved, to classify them into 8 different sizes - 0-75μm, 75-150μm, 150- 200μm, 200-250μm, 250-300μm, 300-450μm, 450-600μm and >600μm. The concentration of heavy metals are found for each of these particle size. The concentration of all the metals except Al and Fe showed an increase as we moved from Gomukh to Rishikesh. In general, the order of the metal concentration in the study area was Al > Fe > Cr > Zn > Pb > Ni > Cu > Cd. It was also observed that the concentration of heavy metals was also dependent on particle size as a strong negative correlation was found between particle size and concentration. A strong positive correlation also existed between various metals like Al-Fe, Cr-Pb, Zn-Cu, Zn-Cd, Cu-Cd and Ni-Cd indicating a common source for these metals. Various factors like Contamination Factor and Metal Enrichment Factor showed that the sediments at the downstream locations i.e. Chinyalisaur, Devaprayag and Rishikesh were contaminated and enriched with many toxic metals. Geo-accumulation index showed that the sediments of Chinyalisaur were uncontaminated to moderately contaminated with Pb and Ni and moderately contaminated with Cd; the sediments of Devaprayag were moderately contaminated with Pb and Cd and the sediments of Rishikesh were uncontaminated to moderately contaminated with Cu and Ni, moderately contaminated with Pb and moderately to strongly contaminated with Cd. Other indices such as Sediment Pollution Index and Pollution Load Index revealed that the sediments of Chinyalisaur, Devaprayag and Rishikesh were polluted to different degrees. Most of the pollution in these centres are mainly attributed to anthropogenic sources as human activities in these areas have been on a rise since the past few decades. The increased concentration and increasing relative mobility of metals with respect to distance from origin also confirms the addition and higher ecotoxicological effects to the aquatic system in the Himalayan stretch of River Ganga.