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

Document Type: Original Research Paper

Authors

1 Département deGénie civil et Génie des eaux. Faculté de Sciences. Université Laval. Pavillon Adrien-Pouliot. 1065Avenue de laMédecine. Québec (Québec). G1V 0A6. Canada

2 Departamento de Edafología. Facultad de Farmacia. Universidad Complutense deMadrid. Plaza Ramón yCajal s/n. 28040.Madrid. Spain

Abstract

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

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