Influence of reducing conditions on metallic elements released from various contaminated soil samples.

The redox conditions of soil may have significant consequences for the mobility of metallic elements (ME), but unlike pH, very few studies have investigated this parameter. A procedure was established to study the solubilization of ME from soil samples in various reducing conditions using a batch method and sodium ascorbate solutions. The change in redox potential from +410 to +10 mV was studied from four contaminated soil samples (designated A-D) of different origins and compositions. The results showed that ME mobilization greatly increased with decreasing redox potential within a limited and very sensitive range. Depending on the soil sample studied, various sensitive ranges of potentials were obtained (A, 220-345 mV; B, 280-365 mV; C, 260-360 mV; and D, 240-380 mV), and the induced percentages of ME mobilization varied (i.e., maximal values for Zn: A, 45%; B, 59%; C, 53%; and D, 58%). The results could be explained by the combined effect of potential and pH decrease on ME-carrying phases; in particular, Fe and Mn (oxy)hydroxides.