Diagnosis of heavy metals in urban dust during the COVID- 19 pandemic in a tourist city from Mexico

Particle emissions from vehicular traffic are one of the main sources of heavy metals in cities. During the COVID- 19 pandemic, mobility was reduced, which created the opportunity to measure baseline heavy metal pollution in cities. Citizens took urban dust samples at 25 sites inside and outside their homes, with four repetitions; 159 urban dust samples were analyzed. The elements analyzed with FRX equipment in triplicate were Mn, Ni, Cu, Pb, Rb, Sr, Y, Zn, K, Ca, Ti, Cr, Fe, Zr, Nb, Sn, Sb, V and Ag. The contamination factor and health risk indices were calculated, and the most contaminated sites were geographically identified. The highest average values for the contamination factor were those of copper, vanadium, and zinc. The other metals presented moderate contamination. The extreme contamination cases with values higher than CF > 6 were Cu indoors, Mn outdoors, Pb indoors, and Ni, V, and Zn in both cases. The health risk index, no danger was observed in adults and children. However, sites 2 and 6, located in the east and southeast of the city, were the most contaminated outdoors, while indoors, they were sites 1 and 20 in the southwest and west, respectively. The results of this study carried out under low mobility conditions allowed the identification of two possible background levels for heavy metals: (a) the first decile and (b) the median value of the concentrations of Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sn, V and Zn, for tourist cities and industrial cities in karst areas.