The color of urban dust as an indicator of heavy metal pollution

Introduction: Urban dust contains heavy metals (HMs) that pose a risk to human health. Objective: To evaluate the color of urban dust as an indicator of HM pollution.  Materials and methods: Color and HMs (Ba, Cr, Cu, Pb, Mn, Ni, V and Zn) were measured in 455 dust samples, and redness and saturation rates were calculated. Based on color, groups of samples were formed using cluster analysis. Multiple regression analysis between HMs and indices by color groups was performed, as well as a Kruskal-Wallis analysis of HMs by color groups. Results and discussion: Urban dust samples were classified as dark grayish brown (I), dark gray (II), dark olive brown (III), very dark gray (IV), grayish brown (V) and black (VI). Multiple linear regressions between color indices and HMs showed high and significant correlation (P < 0.05) in groups I, II, III and IV. Urban dust HMs were generally found in the order Zn > Mn > Ba > Pb > Cu > Cr > Ni > V. Also, Cr, Cu, Ni, Pb and Zn showed significant differences (P < 0.05) among the color groups; the samples from very dark gray to black were the most polluted, and those of dark grayish brown had lower HM contents.  Conclusions: Urban dust color is an indicator of heavy metal pollution in Mexico City.