Partitioning of heavy metals into mineral and organic fractions in sediments from a reservoir.

Abstract

A sediment core was collected from S Reservoir, which is located in the western part of Okayama Prefecture. The vertical distribution of heavy metals (Fe, Mn, Zn, Ni, Cu and Cd) and fine particles (<37μm) was measured. The heavy metal contents of the sediment core are relatively high in small grain layers. Partitioning of heavy metals into NH2OH HCl soluble, H2O2 soluble and HF soluble fractions has been determined with a selective chemical leaching technique on the sediment samples. The greatest parts of Mn and Cd are contained in the NHOH HCl soluble fraction (mostly iron and manganese oxide and hydroxide coatings on silicate minerals), whereas more than 50% of Fe, Zn, Ni and Cu is present in the HF soluble fraction (silicate lattice). The variations of heavy metal contents in the sediment core are chiefly due to those in NH2OH HCl soluble and HF soluble fractions. Only manganese is significantly enriched in the NH2OH HCl soluble fraction of the settling material collected by the sediment trap near the bottom, probably due to the release of manganese from bottom sediment into overlying water. Manganese oxide and hydroxide reprecipitated under oxic conditions of the bottom water after the release might have been effectively collected by the sediment trap.