PM2.5-bound trace metals in an urban area of Northern Mexico during the COVID-19 pandemic: characterization, sources, and health risk

Abstract

A field study was carried out in the Metropolitan Area of Monterrey (MAM), the second most populated city in Mexico, characterized by increasing urbanization, high traffic density, and intense industrial activity. These characteristics commonly present high concentrations of air pollutants leading to the degradation of air quality. PM2.5 was analyzed for heavy metals at two urban sites located within the MAM (Juarez and San Bernabe) in order to determine sources, health risk, morphology, and elemental content during the COVID-19 pandemic (autumn 2020 and spring 2021). Twenty-four-hour samples of PM2.5 were collected at each site during 30-day periods using high-volume equipment. Gravimetric concentrations and 11 metals were measured (Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Ni, Cr, and Pb) by different analytical techniques (flame atomic absorption spectroscopy, graphite furnace atomic absorption spectroscopy, and inductively coupled plasma optical emission spectroscopy). Selected samples were analyzed by scanning electron microscopy-energy-disperse spectroscopy in order to characterize their morphology and elemental content. PM2.5 concentrations exceeded the Mexican standard and WHO guidelines in Juarez during spring 2021. Cu, Cd, and Co were highly enriched by anthropogenic sources, and Ni, K, Cr, and Pb had a moderate enrichment. Mg, Mn, and Ca were of crustal origin. Bivariate statistics and PCA confirmed that alkaline metals originated from crustal sources and that the main sources of trace metals included traffic emissions, resuspension from soil/road dust, steel industry, smelting, and non-exhaust emissions at both sites. Lifetime cancer risk coefficients did not exceed the permissible levels established by EPA and WHO, implying that local residents are not at risk of developing cancer. Non-carcinogenic risk coefficients revealed that there is a possible risk of suffering cardiovascular and respiratory diseases due to inhalation of cobalt at the study sites.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11869-023-01372-7.

Seasonal and Diurnal Variations of BTEX in Ambient Air from a Site Impacted by the Oil Industry in Southeast Mexico

Atmospheric concentrations of BTEX were measured in an urban site located in the vicinity of an oil storage-distribution facility in Paraiso, Tabasco, Mexico. Samples were collected during two seasons (nortes 2018 and dry 2019). The relative abundance of BTEX mean concentrations was: toluene (5.24 µg m^-3) > ethylbenzene (3.92 µg m^-3) > m, p-xylene (3.89 µg m^-3) > benzene (2.43 µg m^-3). BTEX concentrations had a clear diurnal and seasonal pattern, showing higher levels during the dry season due to differences in wind conditions, rainfall patterns and temperature. Statistical analysis showed significant positive correlations among BTEX, indicating that these compounds had common sources. Interspecies ratios revealed that BTEX were originated from sources beyond vehicular traffic and that they were influenced by the transport of local air masses. The assessment of lifetime cancer risk showed that the population in the study area is at possible risk of developing cancer.