EVALUATION OF METAL LOADINGS AND BIOAVAILABILITY IN AIR, WATER AND SOIL ALONG TWO HIGHWAYS OF BRITISH COLUMBIA, CANADA HUMBERTO F. PRECIADO and LORETTA. Y. LI ∗ Department of Civil Engineering, University of British Columbia, Vancouver, Canada ( ∗ author for correspondence, e-mail: lli@civil.ubc.ca) (Received 17 August 2005; accepted 12 December 2005) Abstract. A comprehensive multi-media monitoring field investigation, which included: atmo- spheric, storm-water runoff, road sediment and soil samples, was carried out at two highway sites in Vancouver, Canada, focused on Cu, Fe, Pb, Mn, and Zn, due to their prevalence in most highway environments, both locally and worldwide. Metal potential bioavailability was evaluated through se- quential extraction in the case of particulates and via exchange with a chelating resin for highway runoff. Road sediment showed in most cases a close resemblance with runoff and atmospheric metal concentrations (Fe> Zn> Mn> Cu> Pb), suggesting that road sediment is a useful indicator of current metal loadings and a key factor influencing the quality of urban watersheds. Metals showed increasing bioavailability with decreasing particle size in all samples. Thus, bioavailability was low in roaddust and roadside soils, intermediate in dustfall, and highest in atmospheric suspended particulates and runoff. Speciation analyses in different environmental media suggested that Zn is a metal of future potential concern. Zinc was second in concentration to Fe in most dust, air and water samples, and exhibited the highest mobility and potential bioavailability. Keywords: bioavailability, highway, soils, runoff, dustfall, metals, atmospheric 1. Introduction The highway system is a potential source of a wide variety of contaminants to the surrounding environment through natural mechanisms such as atmospheric dust deposition or the hydrologic cycle (Kobriger and Geinopolos, 1984), affecting the quality of air, runoff and soil. Anthropogenic pollutants from traffic activities, atmo- spheric deposition, engine exhaust, roadway degradation, and highway maintenance (Sansalone et al., 1995) include heavy metals, suspended solids, micro-organics, oils and chlorides. Metals include Pb and Ni from gasoline, Zn from tires, Cu from brake linings, and Mn from moving metal parts and gasoline additives (Young et al., 1996). Heavy metals are the contaminants of greatest concern due to their toxic- ity (Hathhorn and Yonge, 1996). Although the use of leaded gasoline has been suspended in North America and most industrialized nations, lead continues to be used in approximately 74 countries, especially in sub-Saharan Africa, the Middle East and Asia (Hodes et al., 2003). Even with major future changes in automotive manufacturing, such as substitution of metal by plastic, graphite or other materials and reduction in car dimensions, it can be assumed that heavy metals will persist Water, Air, and Soil Pollution (2006) 172: 81–108 DOI: 10.1007/s11270-005-9063-0 C  Springer 2006