Characteristics of Heavy Metal Distribution in Bottom Mud of Urban Rivers

Abstract

In order to clarify the distribution pattern of heavy metals contained in the bottom mud of urban rivers, the metals were fractionated by extraction with 2N CH₃COONH₄ and 0.5N HCl. The total metal content was determined after the decomposition with HNO₃-H₂O₂. A part of the Cu, Zn, and Cd in the bottom mud of urban rivers was extracted with 2N CH₃COONH₄, but the Pb, Ni and Cr were unextractable. This result indicated that the forms of metals in bottom mud differed from one another. The metal content increased in the lower reaches of the urban river, and the amount of the increased metals was approximately equal to those of the metals extracted with 0.5N HCl. The increase of metals downstream was also correlated to the grain size and the organic matter content of bottom mud. These results suggested that a significant part of the metals in the bottom mud of urban rivers were weakly bound to fine grain size sand and organic matter.