Discriminating sources of chemical elements in urban street dust using multivariate statistical techniques and lead isotopic analysis

The chemical composition and possible sources of street dust are not common to all urban environments, but vary according to the peculiarities of each city. Concentrations of major (Na, Mg, Al, K, Ca, Fe and Si) and trace elements (Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, P, S, Cl, Br, Rb, Sr, Ba, La, Hf, Pb, Ce and Zr) were measured on both 49 street dust samples and 19 bedrock samples collected in the city of Xuzhou (China) to (1) assess the contamination status of these elements; (2) discriminate natural and anthropogenic contributions using multivariate statistical techniques and lead isotopic analysis. Medians of trace elements Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Br, Rb, Sr, Ba, La, Hf, Pb, Ce, Zr, P, S and Cl concentrations of the investigated street dusts are 10, 3132, 63, 97, 531, 10, 30, 66, 302, 12, 5, 62, 268, 572, 28, 6.4, 68, 55, 142, 998, 2666, 996 mg/kg, respectively. These values are generally higher than those of bedrock in Xuzhou, especially for S, Zn, Pb, and Ba. Cluster analysis of the results suggest that chemical elements in street dust can be classified into two groups: K, Rb, Si, Zr, Hf, Na, Mn, Co, Al, V, Ga, Ti, Ce, La, Sc (Group I) and Br, S, Ca, Cl, Cr, Cu, Ba, Pb, Ni, P, Mg, Fe, Sr and Zn (Group II), which can be inferred to be tracers of anthropogenic inputs. Discriminant analysis of the 14 variables in Group II indicates that the metal Ba is the most powerful in discriminating between both street dust and bedrock samples. The elements including Cu, Ba, Pb, Ni, P, Fe, Mg, Br, to a lesser extent, Cr, P, S and Cl, were mainly derived from traffic contribution. Pb enrichment in Xuzhou street dust was mainly derived from past vehicular emissions as shown by Pb isotopic signatures (Pb-206/Pb-207 = 1.1641-1.1708, Pb-208/Pb-207 = 2.4518-2.4587).