Fractionation of heavy metals in bottom sediments in Chahnimeh 1, Zabol, Iran.

In the present study, 180 sediment samples were collected from the Chahnimeh 1 reservoir to investigate the concentration of metal and sequential extraction. Five geochemical phases (exchangeable fraction, carbonate fraction, Fe/Mn oxide fraction, organic fraction and residual fraction) for the determination of the speciation of heavy metals (Zn, Fe, Cd, Pb, Mn, Ni) as proposed by Tessier was applied to sediments collected from Chahnimeh 1. Results were obtained for nickel and cadmium, as over 40 % of metal was present in the exchangeable phase and bound to carbonate. According to the risk assessment code (RAC), sediments that have 31 to 50 % carbonate and exchangeable fraction are high risk. Similar results were obtained for zinc and lead. The major fraction of the two metals (63 % of the total concentration for lead and 85 % of the total concentration for zinc) occurred in the residual phase and fraction-bound hydrous Fe-Mn oxides. The risk assessment showed moderate risk for lead and no risk for zinc. This indicates that the Igeo and IPOLL used in the present investigation showed no pollution to moderate pollution in terms of metals in sediments.