Determination of Heavy Metals Pollution in Traffic dust of Mashhad City, and its Origin by Using " Selective Sequential Extraction" (SSE) Procedure

Traffic dust often contains high concentrations of heavy metals and can influence on environment and human health. In this study, we tried to measure heavy metals in street dusts and soil in the city of Mashhad and sample collections were carried out at the time and location of high traffic. For the purpose of this study, twenty three samples were collected from three main paths that cover the entire city and total concentrations of five heavy metals (Ni, Zn, Pb, Cr, and Cu) were measured. The index of geo-accumulation (Igeo), Pollution index (PI) and integrated pollution index (IPI) were also calculated for the contamination levels of the metals in the city of Mashhad,. The pollution index represent that all samples are highly polluted by Pb (3.688-74.16) and most of the samples are highly polluted by Zn (1.484-7.23). However, Cu (0.678-1.945) and Ni show medium level of pollution in the samples (1.01-1.935). Chromium in all samples show low levels of contamination (0.246-0.772). Possible sources of the pollutants were assessed using Pearson correlation and principal components analysis. The results of this analysis show high concentrations of metals such as lead, copper, zinc and nickel in the soil samples as compared to UCC (Upper Continental Crust). There is a positive correlation between heavy metals of zinc and copper as well as lead and zinc, which indicate the source of these metals, can be fuels as well as powder of shoe brake of vehicles. The results of the sequential extraction procedure also imply that the elements of Ni, Zn and Pb has occurred in unstable phases (F1+F2+F3+F4), indicating their human origin. But the elements such as Cr and Cu are mainly on stable phases (F5), which represents natural origin for these two elements.