Health risk implications of potentially toxic metals in street dust and surface soil of Tehran, Iran

Abstract

In this study a total of 30 street dusts and 10 surface soils were collected in the central district of Tehran and analyzed for major potentially toxic metals. Street dust was found to be greatly enriched in Sb, Pb, Cu and Zn and moderately enriched in Cr, Mn, Mo and Ni. Contamination of Cu, Sb, Pb and Zn was clearly related to anthropogenic sources such as brake wear, tire dust, road abrasion and fossil fuel combustion. Spatial distribution of pollution load index in street dust suggested that industries located south-west of the city intensify street dust pollution. Microscopic studies revealed six dominant group of morphological structures in calculation of the exposurethe street dusts and surface soils, with respect to different geogenic and anthropogenic sources. The BCR (the European Community Bureau of Reference) sequential extraction results showed that Sb, Ni, Mo, As and Cr bonded to silicates and sulfide minerals were highly resistant to dissolution. In contrast, Zn, Cd, and Mn were mostly associated with the exchangeable phase and thus would be easily mobilized in the environment. Cu was the most abundant metal in the reducible fraction, indicating its adsorption to iron and manganese oxy-hydroxides. Pb was equally extracted from exchangeable and reducible fractions. Anthropogenic sources related to traffic apparently play a small role in Cr, Ni and Mo contamination and dispersed them as bioavailable forms but with reduced mobility and bioavailablity due to high potential of complexation and adsorption to organic matter and iron and manganese oxy-hydroxides. Calculated Hazard Index (HI) suggests ingestion as the most important pathway for the majority of PTMs in children and dermal contact as the main exposure route for Cr, Cd and Sb for adults. The HIs and fractionation pattern of elements revealed Pb as the sole element that bears potential health risk in street dust and surface soil.