Abstract: Industrial activity is a significant source of atmospheric emissions, including both criteria pollutants and air toxics. Even in small concentrations, these pollutants can cause or contribute to cancer and other severe health and/or environmental damages. In Mexico, the Tula de Allende region in Hidalgo has been characterized by the presence of various industrial facilities, including an oil refinery, a thermoelectric power plant, several cement factories, lime production plants, among others. This has led to its classification as one of the most polluted areas in the country. However, the risk assessment due to air toxics in the area has been limited. Therefore, the objective of this study is to determine the impact of air toxic emissions by estimating inhalation risks in 2019 to quantify the danger posed by the population’s exposure to such substances. Initially, a prioritization technique was applied to identify industrial facilities posing higher risks based on emissions reported in the Pollutant Release and Transfer Register (RETC, by its initials in Spanish), inhalation unit risk factors, and reference exposure levels approved by the California Office of Environmental Health Hazard Assessment (OEHHA) and the California Air Resources Board (CARB). Subsequently, using the CALPUFF model, concentrations of ait toxics included in the RETC were determined. Cancer risk and non-cancer risk (hazard quotient) were estimated following the methodology of the United States Environmental Protection Agency, at nine sites located within a 6 km radius of emission sources. It was found that eight industries in the region reported air toxic emissions to the RETC during the study year, of which six required a more detailed risk assessment. Simulation of the dispersion of their emissions through CALPUFF revealed that the highest concentrations of nickel, chromium, cadmium, lead, acetaldehyde, and formaldehyde occurred in Bomintzha, a site located south of the refinery and thermoelectric plant. Conversely, the locality west of these establishments recorded the lowest concentrations. Regarding inhalation cancer risk, it was found to exceed the acceptable level (corresponding to 1 x 10- 6 ) for nickel and chromium at all selected receptor sites, as well as for benzene in La Joya and Apaxco, located in the vicinity of the cement factories. Moreover, six out of the nine populations obtained a hazard quotient greater than 1 for nickel, indicating the potential for adverse health effects due to this element. Finally, with the spatial distribution of concentration obtained from CALPUFF, areas with unacceptable cancer risk were identified.

Keywords: Risk assessment, air toxics, Tula.