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

Abstract

The role played by soil constituents in governing temporal trends of metal mobility in calcareous<br />Mediterranean soils deserves special attention due to the particular soil and climate characteristics. Reactions<br />occurring during the aging modify the metal mobility over time, and the rate of metal application and type of<br />soil can be decisive in the outcome of aging reactions in soils. The aim of the present work was to investigate<br />the role that both metal dose and soil constituents play in temporal trends of (potential) metal mobility in soils<br />offering a natural gradient of carbonate and whose remaining soil constituents differed. Soil samples were<br />spiked with a mixture of Cd, Cu, Pb and Zn at two levels and then left aging for 12 months incubation. Metals<br />were extracted at different time intervals (1 day, 1, 3, 6 and 12 months) with one-step extraction methods to<br />estimate immediate metal mobility (NaNO3) and potential metal mobility (diethylene triamine pentaacetic<br />acid –DTPA–). At both levels of contamination, NaNO3-extractable Cd, Cu and Zn concentration values<br />reached equilibrium within the period of incubation. Temporal trend of immediate metal mobility was governed<br />by carbonate fraction for Cd and Cu and by the finest carbonate fraction for Zn. In the case of potential metal<br />mobility, DPTA-extractable metal concentrations did not reach equilibrium within the incubation time. In this<br />case, the combined action of carbonate, organic, Fe-oxide and clay fractions were decisive to define the<br />different temporal trends observed for each metal and level.