Elemental composition of urban street dusts and their dissolution characteristics in various aqueous media

Street dust serves as an important archive for environmental contamination in industrialized countries. Heavy metals which are found in street dust such as Cd, Cu, Ni, Pb, and Zn cause pollution in different environmental media. This study was carried out to characterize the composition of different elements embedded in street dusts and to investigate their leaching behavior in the presence of different aqueous media. Samples of street dusts were collected on a weekly basis for 6 months from three different locations in Singapore, viz. residential, commercial and industrial areas, and processed in the laboratory to determine the concentration of 13 elements (Al, As, Co, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, and Zn). Concentrations showed considerable variations between sites, and within the same site over a period of time. Dust samples collected from the industrial area were of serious concern as they comprise elevated concentrations of most of the potentially toxic metals such as Cd, Cr, Cu, Pb, and Zn. The surface morphology and presence of different elements in street dust samples were confirmed using SEM/EDX analysis. The enrichment factor, used to describe the chemical characteristics of street dusts, revealed that most of the elements have anthropogenic origin. Of the different media used in dissolution of elements from street dusts, the river water and acidified deionized (DI) water (0.01 M HNO3) were found to promote significant leaching of most of the elements. With the aid of dissolution kinetic data, the rate constants of dissolution of various elements were determined.