Particulate matter and black carbon exposure in Seoul subway: Implications for human health risk

Air pollution and the associated health risks to humans caused by exposure to particle matter in enclosed subway systems are currently concerns. This research first time investigated the substantial health hazards (cancerous, non-cancerous, relative risk, and excess mortality rates associated with all-cause, cardiovascular, and respiratory mortality) posed by metals and black carbon (BC) bound to particulate matter (PM10, PM2.5) within subway systems. The Seoul subway system has been found to show notably higher levels of PM (2–1.5 times) and BC (2.3–1.3 times) compared to outdoor environments. Inhalation of PM-containing trace metals such as Cr, Ni, Cd, Pb, and BC significantly contributes to cancer risk, irrespective of age or PM type. The risk of developing inhalation-related cancer due to PM10 and PM2.5-bound metals is notably higher (1.2–2 times) within the subway environment compared to outdoors. Inhalation cancer risk levels (ICR_BC) associated with PM-bound BC are 1.8 times greater at subway stations compared to outdoor stations, with a strong association (1.93–1.98 times) with PM2.5-bound BC compared to PM10. Notably, PM levels in subway stations have a considerable impact on relative mortality risk, with approximately 1.98 times the observed increase in mortality attributed to PM2.5-bound BC. The trace metals and BC bound to PM that contribute to human health risks might originate from vehicle emissions. This includes both surface and underground transportation systems. These findings underscore the significance of addressing air quality within subway systems to mitigate health risks.