Heavy metals in Xuzhou urban roadside topsoils (China): magnetic characterization and enrichment mechanism

Heavy metal contamination is prevalent in urban areas where soil represents a significant sink. Urban topsoil samples were collected and metal concentrations including Pb, Zn, Cu, Cd, Ni and Co were measured by inductively coupled plasma mass spectrometry. All analyzed metals showed elevated concentrations compared to local background concentrations with the exception of Co. Cadmium was the metal most enriched in the analyzed area, presenting enrichment factor, on average, of 16.5. Mineral magnetic concentration parameters (χlf and SIRM) exhibited significant relationships with Pb, Zn, Cu and Cd, respectively. Zinc, Co and Ni exhibited a substantial build-up in the finest particles (<28 μm). Enrichment was positively correlated with carbonate complexation constants (but not bulk solubility products) and suggests that the dominant mechanism controlling metal enrichment in these samples is a precipitation of carbonate surfaces that subsequently adsorb metals.