FRACTIONATION OF RESIDUAL CADMIUM, COPPER, NICKEL, LEAD, AND ZINC IN PREVIOUSLY SLUDGE-AMENDED SOIL

The fractionation of heavy metals in previously sludge-amended soil is important to evaluate their behavior in the environment in terms of m obility and availability to crop plants. A surface soil that received two types of sludges at two different rates, plus fertilizer only and no treatment (control), having been fallow for nine years, was used in this study. The contents of cadmium (Cd), copper (Cu), nickel (Ni), l ead (Pb), and zinc (Zn) fractions in previously sludge-amended soils w ere governed by the total content of these metals in the sludges appli ed and by the rate of sludge application. The contents of these metals were higher for soils that received the Chicago sludge as compared to that receiving the Huntsville sludge. Furthermore, soils that receive d 20 Mg/ha/yr of sludge for five years generally had higher levels of these metals than those receiving a single dose at the 100 Mg/ha appli cation rate. The percentage of the total content in the water soluble and exchangeable forms was very low (less than or equal to 1%) regardl ess of sludge application. The application of sludges tended to reduce the residual fraction and to increase the organic and carbonate fract ions. Overall, the predominant forms of the metals in the sludges were as the Cd-, Ni-, Pb-, and Zn-carbonate and Cu-organic fractions.