Magnetic properties and correlation with heavy metals in urban street dust: a case study from the city of Lanzhou, China

We report results obtained from magnetic and geochemical measurements of 71 street dust samples from four distinct districts (residential, commercial and industrial) in Lanzhou, an industrial city in China. Magnetic properties and the concentrations of 17 elements (As, Ba, Bi, Cr, Cu, Mn, Ni, Pb, Ti, Zn, Fe, Si, Na, Mg, K, Ca, Al) are reported for each sample. Ferrimagnetic mineral concentrations are generally high in Lanzhou street dust, mainly due to grains above Stable Single Domain size. The highest concentrations of magnetic materials and heavy metals are in dusts from the two main industrial districts, Xigu and Chengguan. In the least polluted Anning district, some samples have magnetic properties more probably derived from arid areas to the north of the city. The two main industrial areas also show some differences in magnetic mineral assemblages suggesting that magnetic properties and magnetic-metal correlations may be of use in ascribing heavy metal contamination to distinct sources. Geochemical studies and the significant positive correlation between magnetic concentrations and those for Fe, As, Cu, Mn, Ni, Pb and Zn confirm that much of the heavy metal contamination in the study area is linked to combustion derived particulate emissions. The results confirm that a combined magnetic and geochemical approach can provide useful information on the types, levels and sources of heavy metals in street dust.