Heavy metals in urban dust inside and outside homes during the Covid-19 pandemic in Mérida, Yucatán, México

The COVID-19 pandemic caused a decrease in outdoor activities but an increase in indoor ones. Does this situation cause changes in pollution patterns? The objective of this study was to compare heavy metal contamination in indoor and outdoor dust in homes in the city of Mérida, Yucatán. Dust was collected in 51 homes on the weekends of May 2020 during the COVID-19 pandemic when there was a lockdown. Three hundred ninety-six samples were obtained (203 indoors and 193 outdoors on the sidewalk). Heavy metal concentrations were measured in triplicate with a portable XRF Genius 7000 spectrometer from Skyray Instruments. The contamination factor was calculated using a local (decile 1) and a global background value. To identify whether there were differences in indoor and outdoor heavy metal concentrations, mixed linear models were used, and the statistical inference was made using hypothesis tests. The risk to human health was evaluated using the USEPA methodology. Using decile one as background, the contamination factor's median showed moderate contamination for Lead (Pb), Manganese (Mn), Iron (Fe), Calcium (Ca), Strontium (Sr), and Yttrium (Y) indoors and outdoors. Using world concentrations as background, higher Ca, Sr, and Y concentrations were found outdoors, while Copper (Cu), Pb, Titanium (Ti), and Zinc (Zn) concentrations were higher indoors. Pb represented a risk of developing health problems for children inside homes. These studies help design public policies to reduce urban emissions and pollution, implement dust and risk management programs, and conduct citizen cleaning campaigns.