TemporalTrends ofMetal Extractability in Calcareous soilsAffected by Soil Constituents andMetal Contamination Levels

The role played by soil constituents in governing temporal trends of metal mobility in calcareousMediterranean soils deserves special attention due to the particular soil and climate characteristics. Reactionsoccurring during the aging modify the metal mobility over time, and the rate of metal application and type ofsoil can be decisive in the outcome of aging reactions in soils. The aim of the present work was to investigatethe role that both metal dose and soil constituents play in temporal trends of (potential) metal mobility in soilsoffering a natural gradient of carbonate and whose remaining soil constituents differed. Soil samples werespiked with a mixture of Cd, Cu, Pb and Zn at two levels and then left aging for 12 months incubation. Metalswere extracted at different time intervals (1 day, 1, 3, 6 and 12 months) with one-step extraction methods toestimate immediate metal mobility (NaNO3) and potential metal mobility (diethylene triamine pentaaceticacid –DTPA–). At both levels of contamination, NaNO3-extractable Cd, Cu and Zn concentration valuesreached equilibrium within the period of incubation. Temporal trend of immediate metal mobility was governedby carbonate fraction for Cd and Cu and by the finest carbonate fraction for Zn. In the case of potential metalmobility, DPTA-extractable metal concentrations did not reach equilibrium within the incubation time. In thiscase, the combined action of carbonate, organic, Fe-oxide and clay fractions were decisive to define thedifferent temporal trends observed for each metal and level.