In this work, sampling was carried out in the urban area of Madrid to analyze the content of total heavy metals (Zn, Pb, Cu, Cr, Ni, and Cd) in the street dust. Contamination was evaluated using various indices, such as the Contamination Factor (CF), Enrichment Factor (EF), Geo-accumulation Index (Igeo), Potential Ecological Risk Index (RI), Pollution Load Index (PLI), the Human Health Index Hazard Index (HI), and Cancer Risk (CR). Pollution indices were related to traffic density and color. Traffic density was the factor that most influenced the values of the pollution indexes, but no significant differences were found with the color of street dust. The concentration of heavy metals in the urban dust of Madrid had the following sequence: Zn (895) > Cu (411) > Pb (290) > Cr (100) > Ni (42) > Cd (1.25 mg kg⁻¹). The pollution levels were high or very high in Pb, Zn, and Cd regarding the environmental pollution indexes. Ingestion was the main route of exposure to heavy metals contained in street dust. The CR for adults and children is less than 1 × 10⁻⁶, which means that there is no risk for the population. However, the HI was 10 times higher in children than in adults.

In the present work, a sampling grid of the urban core of the city of Murcia (South East Spain) was designed in order to analyze street dust, focusing on the contents of the heavy metals Cd, Cr, Cu, Ni, Pb, and Zn and their relationships with the color of the sample, the traffic pattern, and the location where they were sampled (sidewalks, ledges, and roads). The characterization of the samples was carried out by X-ray diffraction and scanning electron microscopy, whereas the heavy metals were extracted by acid digestion and determined by inductively coupled plasma mass spectrometry. The concentration (mg/kg) in urban dust of the city of Murcia was highest for Zn (653), followed by Cu (201) > Pb (177) > Cr (117) > Ni (51) >> Cd (0.5). The color expounded statistically significant differences with regard to the heavy metals, including the pollutant load. The same pattern was found when the classification variable was the traffic intensity, except in the case of Ni. The areas with a higher risk of contamination by heavy metals in the urban dust are the ledges of narrow city center streets with moderate traffic, where Zn and Pb seem to accumulate most greatly.