Quantifying the noncarcinogenic and carcinogenic risks resulting from the inhalation of PM2.5-bound metals: A multicity analysis and implications for public health

Toxic metals in PM_2.5 represent a growing public health concern because of their potential health effects. Ambient PM_2.5 samples were collected from five provinces around Bangkok from December 2020 to December 2021. The concentrations of PM_2.5 and metals (arsenic, cadmium, chromium, cobalt, nickel, lead, and vanadium) were analyzed. The noncarcinogenic and carcinogenic risks were evaluated via Monte Carlo simulations in four age groups (0 to <6, 6 to <12, 12 to <18, 18-70 years), with a dataset comprising 2282 heavy metal assays within the particulate matter. Significantly higher PM_2.5 concentrations were detected in provinces with higher factory densities, as well as higher concentrations during haze periods than during non-haze periods. The HI values for all age groups and provinces were lower than 1, indicating acceptable noncarcinogenic risks. The carcinogenic risks from PM_2.5-bound metals varied between 7.08×10^-7 and 4.29×10^-6, indicating increased cancer risks, for preschool children and adults. Cancer risk was highest in industrial areas, followed by areas with dense traffic, and lowest in agricultural areas. The results indicated that Thailand's current air quality regulations, which primarily provide only lead limits, are insufficient considering the high carcinogenic potential of other metals. The Monte Carlo simulation results confirmed that lowering Thailand's 24-h PM_2.5 standard from 37.5 to either 25 or 15 µg m^-3, as specified in the 2021 World Health Organization guidelines, would decrease cancer risk by 9.63-43.18 %.