Metal geochemical and mineral magnetic characterization of the <2.5 μm fraction of urban soils in Xuzhou (China).

The concentrations of metals (Pb, Cu, Zn, Co, Ni, Fe and Mn) in the <2.5 μm fraction of surface soils (0-5 cm) from highly industrialized areas in Xuzhou (China) were determined. All analyzed metals with the exception of Mn and Co in the present study showed elevated concentrations in the <2.5 μm fraction of soils compared to background concentrations, particularly for Zn. Metal enrichment was positively correlated with carbonate complexation constants (but not bulk solubility products) as well as the first stability constants of metal-citrate, likely suggesting that both metal-organic complexation and/or precipitation of carbonate surfaces that subsequently adsorb metals are likely responsible for these metal enrichment on these samples. Sequential extraction analysis shows the metals Pb, Cu, Zn, Co and Mn were largely associated with the reducible fraction, whereas Ni was largely associated with the oxidisable fraction. Manganese is the only metal showing significant association with the exchangeable fraction (up to 33 %), suggesting that it may be the most susceptible metal to mobilization. Mineral magnetic analysis indicates that ferrimagnetic SSD + SP (stable single domain + superparamagnetic) minerals dominated the <2.5 μm fraction of Xuzhou surface soils. Lead, Cu and Zn were found to show significant correlations with χlf ( p < 0.01), suggesting that magnetic technique might be beneficially used as a rapid and inexpensive method to estimate these metal contaminations in the <2.5 μm fraction of surface soils. [ABSTRACT FROM AUTHOR]