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Abstract

Industrial wastewater, including both domestic and production waster, with high organic matter content, discharged into the To Lich and Kim Nguu Rivers has degraded the quality of sediments in the river system. The present study shows that sediments are heavily polluted with heavy metals (220 to 475 mg/kg for Cu, 260 to 665 mg/kg for Pb, 250 to 535 mg/kg for Zn, 2.5 to 40 mg/kg for Cd, 505 to 655 mg/kg for Cr, and 48 to 165 mg/kg for Ni). Total heavy metal concentration in the sediment was correlated with organic matter content for Cu, Pb and Ni while no correlation was found for Cd, Zn and Cr. The heavy metals were bound with sediment particles through phases such as exchangeable, carbonate, oxide, organic matter and residual. The percentage of each phase was different among metal types; the organic matter and the oxide were predominant for the group of Cu, Pb and Ni and the group of Zn and Cd, respectively, and each phase was almost equal for Cr. The EDTA caused high heavy metal leachability compared to water, acetic acid and nitric acid. Average potential leachability decreased in the order: Cd > Ni > Cr > Cu = Zn > Pb.

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