Comparison of different methods for assessing heavy metal contamination in street dust of Xianyang City, NW China

Street dust is one of the important indicators that reflect the status of urban environmental pollution. There are many studies of heavy metals contamination of street dust in capital cities; however, little attention has been paid to this kind of study in medium cities, including China. The dust samples were collected in the district of traffic crossroads in Xianyang city, Shaanxi Province. Pb, Cd, Cu, Ni, Zn, Cr and Mn concentrations were determined using atomic absorption spectrometry (AAS). The results indicate that the concentrations of heavy metals are higher than the background values of soils in Shaanxi Province. The contamination level of heavy metals is assessed by potential ecological risk index (E (r)), geoaccumulation index (I (geo)), enrichment factor (EF) and pollution index (Pi). The low I (geo), EF, E (r), Pi and PIn (integrated pollution index) for Mn in street dusts indicate an absence of distinct Mn pollution. The high EF, Pi and PIn of Cu and Zn indicate that there is considerable Cu and Zn pollution. It is suggested that more attention should be paid to heavy metals contamination of Cu and Zn. The assessment results of Pi and PIn suggest that Pb, Ni and Cr present strong pollution; however, their EFs indicate that they cause moderate pollution and their I (geo) indicates that they are unpolluted to moderately polluted. The contamination class value with different assessing methods is of the order: Pi a parts per thousand PIn > EF > I (geo) > E (r).