Concentrations and associated health risks of indoor/outdoor PM2.5- bound metallic elements at a subway station in Tianjin city during winter

ObjectiveTo compare the concentrations and to assess the chronic health risks of particulate matter less than 2.5 microns in aerodynamic diameter (PM2.5)-bound metal elements on the platform and in the ambient air of a subway station in Tianjin city during winter. MethodsSeven-day continuous PM2.5 air sampling was conducted in November and December 2023 simultaneously on the platform near the tracks and outside of a subway station that had been in operation for more than 10 years in Tianjin city. The mass concentrations of PM2.5 in the samples were calculated, and the contents of 21 metallic elements in the PM2.5 samples were determined. The health risk assessment model recommended by the United States Environmental Protection Agency (USEPA) was used to assess the health risks of the metallic elements via the respiratory route. ResultsThe mean mass concentration of PM2.5 on the platforms in winter was 246.71 ± 85.55 μg/m3, which was significantly higher than that (112.64 ± 26.26 μg/m3) outside the station during the same period (t = 5.61, P < 0.001). The contents of antimony, manganese, alum, copper, cobalt, aluminum, chromium, lead, nickel, iron, sodium, magnesium, calcium, and zinc in PM2.5 samples collected on the subway platform were all significantly higher than those in PM2.5 samples collected outside the station (all P < 0.05). The combined non-carcinogenic hazard index (HI) of the nine metal elements was greater than 1, indicating that the exposed population may have some non-carcinogenic health risks. Manganese was found to have the highest non-carcinogenic risk (hazard quotient [HQ] = 0.8), followed by antimony (HQ = 0.1). Chromium posed the highest carcinogenic risk (6.05 × 10 – 5) to the exposed population. ConclusionsThe level of metallic element pollution in PM2.5 on a subway platform in Tianjin city is relatively high. The combined effects of several non-carcinogenic metallic elements may pose certain non-carcinogenic risks to the exposed population. The carcinogenic risks of arsenic, nickel, lead, and cadmium to the exposed population are low, and the carcinogenic risk of chromium is still within acceptable limits.