Copper distribution among physical and chemical fractions in a former vineyard soil

The Copper (Cu) contamination of vineyard soils due to the heavy use of copper-based fungicides is a well known problem (Probst et al., 2008; Fernãndez-Calviño, 2008). Since Cu is scarcely mobile in soils, it tends to accumulate in surface horizons (Pietrzak and McPhail, 2004) even after land use change (FERNÃNDEZ- CALVIÑO, 2008). This Cu accumulation is well beyond the natural background concentrations of metal normally found in soils (22-55 mg kg-1 depending on the nature of the parent material) (Baker and Senft, 1995). Adsorption is a key process responsible for accumulation of heavy metals in soil and regulates their concentration in solution, which is also influenced by inorganic and organic ligands (Bradl, 2004; Violante et al., 2008). Cu in soils may occur in several forms that are partitioned between the solution and the solid phases. Cu bioavailability and phytotoxic- ity is closely related to its distribution in different chemical forms. Exchangeable Cu may be readily mobilized to the soil solution, with negative effects for plants and soil organisms. On the other hand, Cu phytoavailability can be reduced by Cu binding to soil organic mat- ter (Bolan and Duraisamy, 2003). Cu distribution in the different chemical forms depends on several soil properties, such as pH, redox potential, cation exchange capacity (CEC), texture, soil organic matter (SOM), as well as Mn and Fe oxides content (McLaren et al., 1983; Sims, 1986). Cu fractionation studies have shown that this metal exists in soils predominantly as organically bound, in residual, precipitated, or acid-soluble form (Berti and Jacobs, 1996; Alva et al., 2000). The most important interfaces involved in Cu adsorption in soils are Fe and Mn oxides, SOM, sulfides and carbonates (Jenne, 1968).