Colloid‐Assisted Transport of Trace Metals in Roadside Soils Receiving Deicing Salts

Abstract

AbstractCalcium 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 life. There has been some concern, however, that CMA may increase the mobility of trace metals from roadside soils. A calcareous roadside soil was leached with solutions of the deicing salts NaCl and CMA followed by deionized water to evaluate the potential for trace metal mobilization. Elevated concentrations of Cu, Pb, Ni, Cr, Fe, and organic matter were found in the deionized water leachate following the NaCl leaching. Ultrafiltration and dialysis tubing were used to separate dissolved matter from colloidal (1000 molecular weight cutoff) and to determine if the trace metals were preferentially sorbed to small organic molecules and Fe oxides. Under high salinity, there was little evidence of colloid‐assisted transport. Under low salinity, dispersion and mobilization of colloidal‐sized particles occurred. Effluent Cu, Pb, and Ni concentrations were correlated with organic colloid concentrations, while Cr was correlated with Fe‐oxide concentrations. Evidence for both Fe‐organic matter colloidal complexes and Fe‐oxide mobilization was found. These findings suggest that roadside soils impacted by NaCl from deicing operations could be contributing trace metals to groundwater via colloid‐assisted transport.