Trace metal mobility under varying redox conditions: modeling Cd and Zn release

摘要

Metal-contaminated riparian soils can be a source of metal release to surface water. The effects of varying redox conditions on mobility of zinc (Zn) and cadmium (Cd) were measured and modeled. Soil sampled from a riparian Spodosol contaminated with Cd and Zn was incubated in the laboratory under water-saturated conditions. The experiment was performed in a 3×3 factorial design with C-source (plant residue, 2 levels and control) and N amendments (NO3, NH4+, and control) as factors. Carbon was added to accelerate the rate of reducing the redox potential. We postulate that the mobility of Cd and Zn is critically affected by the change in pH, DOC, reductive dissolution of Fe(III) oxides and, potentially, sulphide precipitation on the long term The currently available data only reflect incipient reducing conditions (Eh not below 336 mV) and show hardly any change in soluble Cd and Zn that results from the counteracting effects of increasing soil pH, increasing DOC, and increasing Fe2+ that compete with Cd2+ and Zn2+ sorption. Speciation calculations (WHAM VI) confirm these trends.