Presence and fate of heavy metals and roads maintenance salts in sweep sand and roadside environment

Abstract

A wide range of roads maintenance salts and heavy metals emissions from vehicles may potentially contribute to contaminant loads in urban environment. The ability of sand sediments particles to act as emission accumulative media for heavy metals micropollu-tants, thereby providing environmental benefits in addition to surface water protection, have not been fully explored. This paper investigates the sources, presence and potential fate of a selection of heavy metals (Pb, Ni, Cr, Cu, Mn, Zn) in on-site mobilization by deicing salts. All of the investigated compounds are listed under the European Water Framework Directive as either "Priority Substances" or "Priority Hazardous Substances". Environmental modeling indicates that heavy metals removal during treatment is likely to be predominantly due to liquid/solid phase adsorption, with only minor contributions to the soluble phase. Many roads maintenance salts are resistant to biodegradation and as the majority of automated street sweeping periodically discharge small particles to the municipal drainage system, stormwater treatment is unlikely to act as a comprehensive heavy metals emission barrier. Hence, it is important to ensure that other source control options (e.g. eco-labeling, substance substitution, and regulatory controls) for roads deicing items continue to be pursued, in order that heavy metals emissions from these sources are effectively reduced and/or phased out as required under the demands of the European Water Framework Directive.