Mobility of heavy metals in poorly developed carbonate soils in the Mediterranean region

The sorption and mobility of trace metals in calcareous soils (calcaric Fluvisols) were studied in experimental columns using nine soil samples extracted from Ap and AC horizons, under laboratory conditions. A contaminating solution with six heavy metals at identical concentrations (350 mg kg− 1 for each metal) was used to saturate the soil columns, and after the contamination assay two successive washes with de-ionized water were performed. Sorption rates were high for all the metals, higher than 90%. However, competition between metals resulted in greater retention of Cr, Cu and Pb than Ni, Zn and Cd. The data on mobility showed that Cr and Pb (values of Kd 5.6 × 104 and 8.1 × 104, respectively) were the least mobile metals, Cu and Zn had intermediate values (values of Kd 6.9 × 103 and 4.8 × 103, respectively), and Ni and Cd were the most mobile (values of Kd 8.2 × 102 and 7.2 × 102, respectively).The mineralogy of the soil constituents was the main factor determining the retention of the metals applied. The differences observed between the soil samples, in both the retention and liberation phases, could not be linked to the properties used to characterize them.