THE CHEMICAL-PHASE CHANGES IN HEAVY-METALS WITH DRYING AND OXIDATION OF THE LAKE-SEDIMENTS

In order to understand the effects of oxidation on heavy metal behavior in sediments, the changes in chemical phase distributions of heavy metals with oxidation of sediments from Lake Teganuma were investigated using a sequential chemical extraction procedure for heavy metals. The exposure of sediments from the lake bottom to atmosphere caused the increase of Eh and the decrease of acid volatile-S in sediments. Most of the cadmium is expected to exist as relatively stable forms such as sulfides in original reduced sediments prior to exposure to the atmosphere. With the oxidation of sediments, Cd in the sulfidic/organic fraction were transformed to forms in the exchangeable and the reducible fractions which are easily dissolved. The chemical phase changes of Cu, Pb and Zn in sediments were less drastic than the case of Cd. Cadmium distinctly affected by the change in redox potential in sediments, and its behavior in the oxidized state is most mobile. Compared to Cd, the behavior of Cu and Pb are not so remarkably affected by the change in redox condition of sediments.