Adsorption and desorption of native and added cadmium in relation to properties of some alluvial soils in Punjab

The adsorption and desorption of cadmium (Cd) in relation to soil properties were examined on twenty-four surface soils collected from different locations in Punjab. Soils varying widely in physico-chemical properties such as CEC, clay content, calcium carbonate content, organic matter stock, EC and pH. Diethylenetriamine pentaacetic acid extractable Cd of the experimental soils ranged from 0.024 to 0.054 μg Cd g⁻¹ soil while the total soil Cd varied from 0.9 to 2.25 μg Cd g⁻¹ soil. For Cd adsorption soil samples were shaken with 0.01M Ca(NO3)2 containing 20 mg Cd mL⁻¹ till an equilibrium was attained. Desorption of Cd was carried out by repeated washing of the soils with cadmium-free 0.01M Ca(NO3)2 solution. The amount of cadmium adsorbed varied from 267.5 to 446.3 μg Cd g⁻¹ soil, which represented 53.5 to 89.3% of the initially added cadmium. Cadmium adsorption was significantly correlated with CEC, % clay content, EC, CaCO3 content and soil pH. The linear multiple regression explained 41% of the total variation in cadmium adsorption in terms of CEC, whereas CEC, pH and organic matter together predicted 73% of variation in cadmium adsorption. Adsorbed cadmium was significantly and negatively correlated with cumulative cadmium desorbed and % cadmium desorbed. Desorption of native soil cadmium was negligible. The amount and pattern of desorption varied with the soil properties. About 12.6 to 41.2% of adsorbed cadmium could be desorbed back into the soil solution after six consecutive desorption runs. The per cent cadmium desorbed was significantly and negatively correlated with pH, EC, CaCO3, CEC and clay content. Calcium carbonate, CEC and pH together explained 69% of variation of per cent cadmium desorption.