Spatial and chemical patterns of size fractionated road dust collected in a megacitiy

Abstract

A study was undertaken to investigate the content of 15 elements in size classified street dust. Samples were collected in the megacity of Buenos Aires during two months at 15 sites grouped in five zones with different urban characteristics and traffic profile. Samples were sieved in four fractions (A < 37 mm, 37 < B < 50 mm, 50 < C < 75 mm and 75 < D < 100 mm) before elemental analysis. X-ray powder diffraction (XRD) was selected to detect major components namely, minerals, silicate glass and gypsum. Individual mineral dust particle were analyzed by a scanning electron microscopy and energy dispersive X ray analysis (SEM-EDX) showing that sulphur tended to reside on the particles surface, while Al, Ca, Mg, K, Fe and Si belonged to the lattice. Major, minor and trace elements (Al, As, Ca, Cd, Cu, Fe, Mg, Mn, Mo, Ni, Pb, S, Sb, Sn, and Zn) content was quantified by inductively coupled plasma optical emission spectrometry (ICP OES) in the four particle size ranges. Geological elements, Fe (28e43 mg g 1 ) > Al (13e40 mg g 1 ) >> Ca (1.7e6.9 mg g 1 ) > Mg (2.5e5.8 mg g 1 ) together with S (0.2e1.7 mg g 1 ) exhibited the highest concentrations and the lowest variability. The mean concentrations of anthropogenic elements ranged from 5.4 (Ni) to 1530 (Zn) mg g 1 and significant spatial variability was observed in the order: Cd > S > Sb > Sn > As > Ni > Mo. Cluster analysis allowed differentiating two groups, one composed by elements of both geological and anthropogenic origin (Cu, Fe, Ni and Sn) and another one composed by typical traffic related elements (Cd, Mn, Pb, S, Sb and Zn).