Use of sequential extraction to evaluate zinc and copper in a soil amended with sewage sludge and inorganic metal salts

The addition of sewage sludge to soils, especially those from industrial and mining cities, results in increased metal concentrations in the top soil because the metals are not easily leachable. A four-step sequential extraction procedure was used on a granitic sandy silty loam soil amended with sewage sludge and two rates of soluble salts of Zn and Cu. The extraction scheme was designed to identify exchangeable, Fe-Mn oxides bound, organically bound, and residual metal fractions. The extraction scheme clearly showed the differences in the distribution of the metals in the soil in response to sewage sludge and metal salt addition. The majority of native Zn occurred in the residual form (53%) and most native Cu occurred in the residual (45%) and organic (30%) forms. Addition of soluble salts, and to a limited extent sewage sludge, resulted in large increases in exchangeable Zn. The residual fraction of both metals gradually decreased with metal loading because the added metals went into the more reactive forms. (C) 1998 Elsevier Science B.V. All rights reserved.