Trace metal concentration in the waters of rivers and ponds in a valley filled intermontane basin in the eastern Himalayas

Concentrations of trace elements (Fe, Mn, Cr, Ni, Co, Zn and Cu) were determined for the waters of rivers and ponds in a valley filled intermontane basin of Imphal valley in the eastern Himalayas. It shows that the average concentrations of all the trace elements except Fe and Cr are well under permissible limits set by BIS (1991) and WHO (1993) for drinking purposes. Average concentration of Fe at twelve locations and Cr at one location are above their respective permissible limits. Fe and Cr concentration in the study area is mainly contributed by the leaching from the Disang shales. Seasonal rainfall dilutes the concentration of Fe but Cr gets enriched in both the rivers and ponds. Most of the trace elements show southward increasing trend in their concentration. The occurrence of sediments derived from the ophiohte belt in the eastern part of the basin is responsible for some of the trace metal concentrations in the water. Contributions could be also made from the agricultural use of pesticides and herbicides and other anthropogenic activities.