HEAVY-METALS IN THE ENVIRONMENT - TRACE-METAL SOLUBILITY IN SOILS AND WATERS RECEIVING DEICING SALTS

Laboratory batch incubation studies were carried out to determine the effects of aerobic and anaerobic conditions on the solubility of trace metals in soils and waters treated with the deicing salts calcium magnesium acetate (CMA) and NaCl. The concentrations of trace metals were, in general, not controlled by equilibrium reactions but rather by the relative rates of several simultaneous and sequential reactions. In three soils from CA, NJ, and MI, and water treated with CMA the production of HCO3 from acetate decomposition initially increased the solution concentration of Pb and Zn as PbCO30 and ZnCO30 . Eventually, supersaturation with respect to calcite occurred and the concentrations of Cu, Cd, Zn, V, and Cr decreased because of coprecipitation with the calcite. The precipitation of pyromorphite [Pb-5(PO4)Cl] was suspected based on elevated saturation indexes for this mineral. At low redox conditions, the solubilization of Fe- and Mn-oxides increased the concentration of the trace metals that were adsorbed or coprecipitated with these phases. Supersaturation with respect to MnCO3, FeCO3, and VO(OH)(2) occurred under low redox conditions. The rate constant for acetate decomposition under anaerobic conditions was 18 times lower than the rate constant for aerobic decomposition. This suggests that if a soil received a high loading of CMA, low Ct conditions could occur and CMA might leach to groundwater. There is evidence that the use of CMA could result in Pb and Zn mobilization as neutral ion pairs with carbonate.