Indoor and Outdoor Heavy Metal Contamination in the City of Morelia, Mexico: A Case of Citizen Science During the COVID-19 Pandemic

Abstract

Heavy metal contamination of street dust in the city of Morelia is well-documented; however, contamination of indoor dust remains largely unexplored, despite people spending most of their time indoors. Given the mobility restrictions during the COVID-19 pandemic, it was necessary to engage citizens in science; a total of 480 samples (60 houses, 4 weeks, two locations: indoor and outdoor) were collected by citizens, and general information was recorded in an app developed for this research. Heavy metal concentrations were measured by x-ray fluorescence. Contamination factor, pollution load index, and human health risk assessment were carried out. Contamination was moderate for Cu, Mn, Ni, Pb, and Zr and high for Zn. Contamination action limits were proposed based on local background values. Indoor concentrations of Cu (90 mg/kg), Pb (45 mg/kg), and Zn (731 mg/kg) were higher than outdoor concentrations, while outdoor concentrations of Fe (34217 mg/kg), Mn (838 mg/kg), and Sr (399 mg/kg) were higher than indoors. Mn, Fe, and Pb had the highest hazard indices (> 0.1) for children’s health; ailments can be expected due to Mn and Pb exposure to indoor and outdoor dust. In addition, the extreme values of Cu, Ni, and Zn were also higher than 0.1 and, therefore, these extreme values posed a risk to children’s health, both indoors and outdoors. This research was made possible through citizen science, and now, citizen participation is also essential for managing polluted dust exposure.