Speciation technique for the risk assessment of trace metals in the bed sediments of River Cooum, South India

Abstract

Speciation of sediment samples yields valuable information on the nature of the metals bound to the sediments. Thirty samples of River Cooum sediment were collected during two seasons and a fractionation study was carried out. The middle and lower parts of the Cooum River flow largely through urbanized areas and are grossly polluted by industrial and domestic wastes. To ascertain the extent of heavy metal pollution in the bed sediments of the river, total metal content and speciation were evaluated. The summation of the metal recoveries in the sequential extractions was found to be within ± 10 % of the total metal content. The mobility factor was evaluated which represents the exchangeable and carbonate fractions in the sediments. Risk Assessment Code (RAC) was estimated and the results reveal the extent of risk associated with the heavy metals in the sediments in various stations. The results of the fractionation show that Ni and Pb fall in the high risk category in certain stations in the middle and lower parts of the river. Except for Cr and Fe, all other heavy metals studied show medium risk with regard to RAC. The effect of the monsoon on the concentrations of the metals in various fractions has been evaluated and the significance of seasonal effect was determined using Student’s t-test.