THE POSSIBILITY OF ROAD SALT-INDUCED RELEASE OF HEAVY METALS FROM SOIL IN A WATERSHED

Initial results of our aqueous geochemistry study, utilizing ICP-OES analyses, indicate that the enhanced release of heavy metals, including lead, arsenic, nickel, silver, etc., can occur in a salted watershed, based upon the statistically significant correlations observed among metal concentrations measured for a small watershed in Mercer County, New Jersey. Overall, the concentration of sodium in an effluent stream in the studied watershed is positively correlated with the concentrations of most other metals measured during the three-year period data were collected. The major source of sodium in the studied watershed is winter deicing road salt, a situation similar to many urban watersheds throughout the northeastern United States. In moist soil at equilibrium, the concentration ratio of any two cations in the soil pore solution equals their concentration ratio on the surface of soil colloids, as described by the ratio law of Thomas and Gaines. Therefore, when a large influx of sodium, in the form of dissolved deicing salt, enters soil pore waters, Na+ ions will be adsorbed onto the negatively charged sites on the surface of soil colloids, replacing and releasing other cations, including the heavy metals, into the soil pore solutions to maintain the ratio law; hence, sodium from the applied road deicing salt increases the release of heavy metals from the impacted soil. This process might exacerbate, and possibly create, surface water quality issues in regions where large concentrations of heavy metals exist in soils and parent rocks. This research is a follow-up to our previous experimental and field study of sodium retention by soil in watersheds where road-deicing salt (NaCl) was applied on a regular basis during the winter months.