Fractionation studies on the sediment samples provide valuable information on the nature of the metals bound to the sediments. Thirty three sediment samples of River Adyar were collected during two seasons and speciation study was carried out. The industrial and domestic effluents are directed into the river course at many points in the middle and lower of the Adyar River. 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 was estimated and the results reveal the extent of risk associated with the heavy metals in the sediments in various stations. The results of speciation shows that Cu and Ni falls in the high risk category at
certain stations of the middle and lower part of the river. Except Cr, Fe and Zn, all other heavy metals studied show medium risk with regard to RAC. The effect of monsoon on the concentration of the metals in various fractions had been studied and the significance of seasonal effect is determined using t-test.