Chemical fractionation of heavy metals in a soil amended with repeated sewage sludge application

A sequential extraction method (KNO3, NaOH, Na-2-EDTA, HNO3) was used to de termine the soil fraction of Zn, Cd, Cu, Ni, Ph, and Cr in different plots treated with sewage sludges. The sludges were applied to cropland from 1983 to 1991. Soil samples were collected after the Ist and 5th-year of the las t sludge application. Sludge applications increased the INOR-fraction for Z n, Cd, and Cu. Cu was the only element found in the EXCH-fraction. Pb and C r were found mainly in the RES-fraction. Ni was found in the INOR and OM-fr actions. All the metals increased in the more resistant fractions. Sewage s ludge applications changed the metals distribution of the soil and this eff ect has continued for at least 5 years. (C) 1999 Elsevier Science B.V. All rights reserved.