Local redistribution and partial extraction of heavy metals in bottom sediments of an estuary

Abstract

In order to clarify the mechanism of heavy metal pollution in bottom sediments, we analysed water pollutants and discussed the relationship between water flow and concentration distribution of Cl −, SS and COD in water and heavy metals in sediments of Kojima bay and Japanese estuaries. We also investigated the chemical and physical forms of the heavy metals Pb, Cd, Cu, Zn, Mn and Fe. The average concentration of these water pollutants increased along the waterway from the upper stream to the estuary. No tendency towards an increase in the concentrations was found along the waterway in the bay. However, the concentrations clearly changed due to tidal currents. The local redistribution of heavy metals in sediments seemed to be determined by the principal tidal current. The partitioning rate of heavy metals extracted by 1 m ammonium acetate and 0·2 m ammonium oxyalate was less than 20% except for cadmium. From this result, it is suggested that the release of heavy metals from sediments to overflowing water is a little under the normal environmental condition in sea water.