COLLOID-ASSISTED TRANSPORT OF TRACE-METALS IN ROADSIDE SOILS RECEIVING DEICING SALTS

Calcium magnesium acetate (CMA) is an alternative to NaCl for deicing highways. It has been shown to be an effective, biodegradeable deicing salt that is less corrosive than Cl salts and less toxic to aquatic l ife. There has been some concern, however, that CMA may increase the m obility of trace metals from roadside soils. A calcareous roadside soi l was leached with solutions of the deicing salts NaCl and CMA followe d by deionized water to evaluate the potential for trace metal mobiliz ation. Elevated concentrations of Cu, Pb, Ni, Cr, Fe, and organic matt er were found in the deionized water leachate following the NaCl leach ing. Ultrafiltration and dialysis tubing were used to separate dissolv ed matter from colloidal (1000 molecular weight cutoff) and to determi ne if the trace metals were preferentially sorbed to small organic mol ecules and Fe oxides. Under high salinity, there was little evidence o f colloid-assisted transport. Under low salinity, dispersion and mobil ization of colloidal-sized particles occurred. Effluent Cu, Pb, and Ni concentrations were correlated with organic colloid concentrations, w hile Cr was correlated with Fe-oxide concentrations. Evidence for both Fe-organic matter colloidal complexes and Fe-oxide mobilization was f ound. These findings suggest that roadside soils impacted by NaCl from deicing operations could be contributing trace metals to groundwater via colloid-assisted transport.