Sequential extraction of copper, nickel, zinc, lead and cadmium from Brazilian oxysols: metal leaching and metal distribution in soil fractions

Abstract

The paper reports a study of the mobility of Cu, Ni, Zn, Pb and Cd through the profiles of tropical soils which received addition of those metals on the surface of soils accommodated in polyvinyl chloride (PVC) columns, separated into seven rings. Leaching tests were conducted by pouring deionized water into soil surface of the top column ring, collecting the leached effluents and analysing the collected extracts for determination of metal concentrations. Soil samples from each column ring were withdrawn and analysed by a sequential extraction method to identify the binding forms of the metals retained in the soil, which correspond to six fractions of metal retained forms in soil. The metal amounts accumulated in leachates varied for each metal and depended on the soil type studied and the horizons where the fraction was located. Compared to the amount of each metal applied to soil surface, only a small proportion reached the rings located at the bottom of the columns. In leachates, only 10% of Cu added to soil surface was found and for the other metals, percentages were even smaller. Texture and organic matter content of soils affected significantly the mobility of heavy metals in the columns. The sequential extraction showed that soluble + exchangeable fraction and organic fraction corresponded to predominant forms of retention of the heavy metals in the soil.