Mobility of Cadmium‐109 and Zinc‐65 in Soil Influenced by Equilibration Time, Temperature, and Organic Matter

Partitioning of 109 Cd and 65 Zn fractions in an alum shale soil as affected by time, temperature, and organic matter was investigated. The soil was extracted sequentially by H 2 0 (F1), 1 M NH 4 OAc at pH 7 (F2), 1 M NH 4 OAc at pH 5 (F3), 0.04 M NH 2 OH HCl (F4), 30% H 2 O 2 (F5), and finally by 7 M HNO 3 (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 109 Cd and 65 Zn. The soil was placed incipiently in temperature controlled climate chambers at 9, 15, and 21°C. Before spiking, the soil was treated with 0 or 4% organic matter. Adsorption of 109 Cd and 65 Zn was rapid, but a subsequent slow diffusion of the metals toward chemisorbed fractions was also evident since the 109 Cd and 65 Zn 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 109 Cd and 65 Zn in the F2 and F3 fractions, whereas the concentrations of these metals increased in the inert fractions. In the organic matter‐treated soil, 109 Cd and 65 Zn were increased significantly in the mobile fractions, with a corresponding reduction of 109 Cd and 65 Zn in the inert fractions. The effect of organic matter was more pronounced at 9°C than at 21°C. The results thus indicate that increasing time and temperature reduce the organic matter‐induced mobilization of 109 Cd and 65 Zn in soil.