Mobility of cadmium-109 and zinc-65 in soil influenced by equilibration time, temperature, and organic matter

Partitioning of Cd-109 and Zn-65 fractions in an alum shale soil as affected by time, temperature, and organic matter was investigated The sop was extracted sequentially by H2O (FI), 1 M NH4OAc at pH 7 (F2), 1 M NH4OAc at pH 5 (F3), 0.04 M NH2OH HCl (F4), 30% H2O2 (F5), and finally by 7 M HNO3 (F6). Sequential extraction of metals was performed on soil samples collected at time intervals ranging from 0.5 to 8760 h (1 yr) after spiking the soil with Cd-109 and Zn-65. The soil was placed incipiently in temperature controlled climate chambers at 9, 15, and 21 degrees C. Before spiking, the soil was treated with 0 or 4% organic matter. Adsorption of Cd-109 and Zn-65 was rapid, but a subsequent slow diffusion of the metals toward chemisorbed fractions was also evident since the Cd-109 and Zn-65 concentrations decreased in the three mobile fractions (F1-F3) and increased in the inert fractions (F4, F5, F6 and F7) with time. Temperature elevation resulted in decreased concentrations of Cd-109 and Zn-65 in the F2 and F3 fractions, whereas the concentrations of these metals increased in the inert fractions. In the organic matter-treated soil, Cd-109 and Zn-65 were increased significantly in the mobile fractions, with a corresponding reduction of Cd-109 and Zn-65 in the inert fractions. The effect of organic matter was more pronounced at 9 degrees C than at 21 degrees C. The results thus indicate that increasing time and temperature reduce the organic matter-induced mobilization of Cd-109 and Zn-65 in soil.