Metal distribution in road dust samples collected in an urban area close to a petrochemical plant at Gela, Sicily

Eight samples of road dust were collected from three different localities (industrial, urban, peripheral) of the town of Gela (Italy) to characterize their chemical composition and to assess (a) the influence of the petrochemical plant and the urban traffic on the trace element content in different grain-size fractions of street dust and (b) the solid-phase speciation of the analysed metal using sequential extraction. The samples were sieved into six particle size ranges: 500–250, 250–125, 125–63, 63–40, 40–20 and <20 μm and then analysed for 15 trace elements by ICP-MS. Sequential extraction of metals was performed on each subsample. A principal component analysis was also carried out to define the possible origin of metals in dusts. A comparison was made between the trace metal concentrations in road dust and those in main local outcropping rocks. The obtained results, indicate, that the road dust samples contain non-soil-derived elements, whose primary contributors appear to be vehicular traffic and the nearby petrochemical plant. Traffic appears to be responsible for the high levels of Ba, Cu, Cr, Mo, Pb, Sb and Zn. High concentrations of Ni, V and, partly, Ba and Cr were associated with emissions from the petrochemical plant. With respect to the local background, Sb was the most highly enriched trace element in the road dusts. Results of sequential extraction analysis show that most metals are mainly distributed in the non-residual fractions and particularly in the organic/sulphide and Fe–Mn oxides fractions. They also point to superficial adsorption as an important transfer mechanism of trace metals from their sources to the environment.