In large industrialized cities, tons of particles containing heavy metals are released into the environment and accumulate on street surfaces. Such particles cause a potential risk to human health due to their composition and size. The heavy metal contamination levels, main emission sources, and human health risks were identified in 482 samples of street dust. Heavy metal concentrations were obtained by microwave-assisted acid digestion and ICP-OES. The results indicated that street dust in Mexico City is contaminated mainly with Pb, Zn, and Cu, according to the contamination factor and the geoaccumulation index. The pollution load index of the street dust was made with the concentrations of Pb, Zn, Cu, Cr, and Ni. The main sources of Pb, Zn, Cu, and Cr are anthropic, probably due to vehicular traffic. The highest levels of Cr and Pb in urban dust represent a health risk for children. Contamination limits were proposed for heavy metals in street dust of Mexico City. These limits might be useful to generate and apply public policies to decrease anthropic emissions of the heavy metals studied, particularly Cr and Pb.

The composition of urban dust can affect the health of urban populations, making it necessary to study its elemental composition and its sources. Our objectives were: a) to identify the main emission sources of heavy metals, and b) to evaluate the influence of land use and road type on the elemental composition of urban dust. 100 samples of urban dust taken in San Luis Potosí were analyzed using FRX. Descriptive statistics, Pearson's correlations coefficient, kriging interpolations, and analysis of variance were applied to the data. Cu and Zn were spatially associated with a metallurgical complex and, to a lesser extent, with an industrial park; Ca with fluorite and limestone industries, and Si with the surrounding soils. The highest concentrations of Cu, Zn, and Ca were found in mixed and industrial land uses. On the contrary, the highest concentrations of "natural elements" (Al, K, Si, Rb, and Y) were found in developable land and residential areas. The highest contents of Ca were found in secondary and primary roads. The conclusions were: a) the metallurgical complex is the main source of Cu and Zn, and b) the highest concentrations of Cu, Zn, and Ca were found in mixed and industrial land uses.

Heavy metals in street dust represent a risk to the human health due to their toxicity, persistence and bioaccumulation. Using the US Environmental Protection Agency (USEPA) assessment, here, we review the human health risks of such dust worldwide. The street dust in such cities is contaminated by As, Cd, Cr, Cu, Hg, Mn Ni, Pb and Zn beyond the median levels of the world soil background values. Among these elements, the median values of the hazard risk indices (non-carcinogenic risk) are highest for As, Cr and Pb and the median values of the risk indices (carcinogenic risk) for As are in the tolerable risk range for children and adults and in the case of Pb, the median value of the carcinogenic risk indices are also in the tolerable range for children. We emphasize that the level of heavy metals in street dust pose a considerable risk to the human health and require monitoring and approaches to reduce such toxic levels.

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