Desorption kinetics of cadmium from soils using M ammonium nitrate and M ammonium chloride

The bioavailability and, hence, potential toxicity of a trace metal ion in the soil depends on its concentration in the soil solution and on the soil' s ability to release the trace metal ions from the solid phase to replenish those removed from the soil solution by plants. Voluminous literature is a vailable on the sorption characteristics of heavy metals by soils. However, study of desorption of heavy metals, particularly cadmium (Cd) from soils has not received much attention. The present study reports the kinetic data of desorption of Cd by M ammonium nitrate (NH4NO3) and M ammonium chloride (NH4Cl) from the Luseland and Jedburgh soils of Saskatchewan, Canada, with contrasting Cd-availability characteristics, preadsorbed with different am ounts of Cd. The desorption kinetics were described best using the paraboli c diffusion mathematical model. The overall diffusion coefficient of Cd rel ease by M NH4Cl, obtained using the parabolic diffusion model for the desor ption kinetics, from the Luseland soil was 2.5-14.8 times higher than that of the Jedburgh soil, depending on the initial amount of Cd preadsorbed. Th e lower the amount of initial Cd preadsorbed, the greater was the differenc e in the rate of Cd released between the two soils. The rate constant of Cd desorption by MNH4Cl from the Luseland soil was 14.8 times higher than tha t from the Jedburgh soil, when no Cd was preadsorbed onto the soil. The rat e constants obtained from the desorption kinetics of the two soils reflect very well the Cd availability index and grain Cd content of the durum wheat crops, Kyle and Areola grown in the two soils. The results highlight the i mportance of Cd desorption kinetics in elucidating the availability of Cd i n the soils.