The Color and Magnetic Properties of Urban Dust to Identify Contaminated Samples by Heavy Metals in Mexico City Metropolitan Area

Particles from gasoline-powered vehicle combustion often contain dark or black magnetic iron oxides. This work evaluates color variations and heavy metal concentrations in urban dust by separating magnetic particles. We used a high-power magnet to separate the magnetic particles of 30 urban dust samples from the Metropolitan Zone of the Valley of Mexico. In this way, we obtained three types of dust samples: complete particles (CPs), magnetic particles (MPs), and residual particles (RPs). The change in color with the CIE L*a*b* and RGB systems was estimated, while the concentrations of 18 heavy metals with XRF were measured. Results showed significant color differences between magnetic particles (MPs) and complete (CPs) or residual particles (RPs), with MPs exhibiting darker tones and higher concentrations of Cu, Fe, Mn, and V. The redness and saturation indices may help to identify urban dust samples contaminated with heavy metals and magnetic particles. Magnetism is a method that removes magnetic particles and some heavy metals from urban dust, partially reducing its toxicity.