Pollution, source apportionment and health risk of potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs) in urban street dust of Mashhad, the second largest city of Iran

Street dust samples from industrial, residential and heavy density traffic areas in Mashhad metropolis were collected to study the mineralogy, distribution, accumulation, health risk assessment and probable sources of potentially toxic elements (PTEs) and polycyclic aromatic hydrocarbons (PAHs). Also, the oral bioaccessibility of PTEs using a simple bioaccessibility extraction test (SBET) was investigated. X-ray diffraction analysis of dust samples showed that the mineralogy of dust is dominated by quartz (also alpha-quartz), calcite (also Mg-calcite), and dolomite. Calculation of geoaccumulation index indicated that the dust is much enriched in Hg, Pb, Zn, Cu, Sb and Cd. Combined multivariate statistical and geochemical methods successfully differentiated the anthropogenic PTEs from natural ones. Zn, Hg, Pb and Cu showed high bioaccessibility. Moreover, carcinogenic and non-carcinogenic effects of PTEs due to exposure to urban street dust were assessed for both children and adults. It is found that the total amount of PAHs (Sigma 16 PAHs) varied from 764 to 8986.7 mu g/kg, with the most serious species being 4-ring PAHs. Molecular indices and ring classes indicated that the sources of PAHs were both petrogenic and pyrogenic. The incremental lifetime cancer risks of exposure to dust PAHs for children and adults living in the study area were 7 x 10(-4) and 6.2 x 10(-4) respectively, indicating a high potential carcinogenic risk.