Heavy metal contamination of river sediments in Vietnam

There are two rivers in Hanoi City, Vietnam, the To Lich and Kim Nguu rivers, which are the main sources of irrigation water for suburban agricultural land and feed water sources for fish farming ponds. Industrial wastewater that has been discharged into the rivers has degraded the quality of sediments in the river system. The present study showed that sediments in the To Lich and Kim Nguu rivers are heavily polluted with heavy metals. Metal concentrations in sediments appear to be closely related to the type of manufacturing plants located along the rivers. The heavy metals were bound with sediment particles in fractions such as the exchangeable, carbonate, oxide, organic matter and residual fraction. Total heavy metal concentration in the sediment was correlated with organic matter content for copper, lead and nickel while no correlation was found for cadmium, zinc and chromium. Ethylene diamine tetra-acetic acid caused high heavy metal leachability in comparison with water, acetic acid and nitric acid. Average potential leachability decreased in the order: cadmium > nickel > chromium > copper = zinc > lead. The leachability exhibited a tendency of decreasing with increasing organic matter for heavy metals other than chromium and zinc. To reduce the pollutants discharged from plants, countermeasures by the government and the technological improvement of wastewater treatment in manufacturing processes are needed.