INCREASED CADMIUM AVAILABILITY TO CROPS ON A SEWAGE-SLUDGE AMENDED SOIL

Analysis of spatial distribution of sewage-sludge born cadmium on the experimental plot revealed positive correlation of total cadmium and o rganic matter. Soil pH fluctuated randomly on the field. 'Bioavailable ' concentrations, as determined by NH4-acetate extraction, were closel y correlated to the total cadmium levels, and only negligible effects of pH and/or organic matter fluctuations were recorded. Desorption mod el using modified Freundlich isotherm was applied to predict risks of cadmium solubilization at different conditions. Simulations revealed t hat the organic matter content within the ranges found at the experime ntal field cannot support a proper immobilization of cadmium at pH-ran ge observed at the field. The phenomenon was explained by ineffective care for the soil in the past.