Street dust is one of the most important carriers of heavy metals (HMs) originating from natural and anthropogenic sources. The main purpose of the work was to identify which of Fe-bearing phases bind HMs in street dust. Magnetic parameters of the Fe-bearing components, mainly magnetically strong iron oxides, are used to assess the level of HM pollution. Chemical sequential extraction combined with magnetic methods (magnetic susceptibility, magnetization, remanent magnetization) allowed determining the metal-bearing fractions and identifying the iron forms that are mostly associated with traffic-related HMs. The use of Mössbauer spectrometry (MS) supplemented by magnetic methods (thermomagnetic curves and psarameters of hysteresis loops) enabled precise identification and characterization of iron-containing minerals. The classification of HMs into five chemical fractions differing in mobility and bioaccessibility revealed that iron is most abundant (over 95%) in the residual fraction followed by the reducible fraction. HMs were present in reducible fraction in the following order: Pb>Zn>Mn>Cr>Ni>Fe>Cu, while they bound to the residual fraction in the following order: Fe>Ni>Cr>Mn>Pb>Cu>Zn. The signature of the anthropogenic origin of street dust is the presence of strongly nonstoichiometric and defected grains of magnetite and their porous surface. Magnetite also occurs as an admixture with maghemite, and with a significant proportion of hematite. A distinctive feature of street dust is the presence of metallic iron and iron carbides. Magnetic methods are efficient in the screening test to determine the level of HM pollution, while MS helps to identify the iron-bearing minerals through the detection of iron.
Keywords: Chemical fractionation; Heavy metals; Magnetic methods; Mössbauer spectrometry; Street dust.
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