Magnetic, geochemical and granulometric properties of street dust from Warsaw (Poland)

Abstract

The study presents variations in the magnetic properties and heavy metal concentrations of five granulometric fractions, i.e. 1000–500 μm, 500–250 μm, 250–100 μm, 100–71 μm and <71 μm, for street dust collected at two locations in Warsaw. Combination of grain-size determination, magnetometry, electron microscope observation, mineral composition and chemical analyses was applied as an effective and multidisciplinary approach for the complete characterization of individual fractions of street dust. The magnetic properties of street dust are influenced by its grain size; concentration-dependent magnetic parameters, e.g. magnetic susceptibility, saturation magnetization, saturation remanence and anhysteretic remament magnetization of the finest fraction (d < 0.071 mm) are about three times higher than that of the coarsest fraction (d > 0.5 mm). For all fractions the main magnetic mineral is near stoichiometric magnetite. The dust fractions with grain size <250 μm additionally contain a phase with a Curie point ~770 °C, ascribable to metallic iron. The smallest contribution to the total mass is from the finest size fractions, which contain the highest concentrations of the traffic-related heavy metals. Traffic intensity are well reflected at the two sites studied by the concentration of anthropogenic magnetic particles which are strongly associated with traffic-related heavy metals. Magnetic extracts of the finest dust fraction contain a mixture of spherical magnetic particles and irregular angular particles of iron-oxides with traces of Mg, Al, Na, Ca, K, and Si. Detailed studies preferentially oriented toward to the finest fractions of street dust are a critical issue in terms of potential effects on population health.