Characteristics and health risk assessments of fine particulate matter at the overground and underground subway sites in Chengdu

Fine particulate matter (PM2.5) associated with toxic components in the subway system is likely to lead to various diseases, which has raised public concern, but it has not been explored deeply. Therefore, this study aimed to reveal the characteristics and health effects of the PM2.5 in the subway system. The PM2.5 samples were collected from ticket counters, platforms, and carriages in the overground and underground subway systems in Chengdu, and the composition of PM2.5 at different sites was detected. The pollution degree of toxic elements in PM2.5 and the health risks were evaluated. The results showed that the concentrations of PM2.5, some elements (e.g., arsenic, barium, chromium, copper, iron, manganese, nickel, and antimony), and total carbon at the underground sites were higher than those at the corresponding overground sites, respectively. The pollution extent at underground sites was more severe than that at overground sites according to pollution load index. The subway workers had potential non-carcinogenic risks. The total cancer risks for subway workers were at a moderate level, and for passengers were at a low level in most conditions. The contributions of arsenic to the hazard index and total cancer risk were 74.22%–81.5% and 79.4%–85.3%, respectively. Overall, underground platforms and carriages were the locations with the highest health risks for subway workers and passengers respectively. Subway workers faced higher health risks than passengers and arsenic was identified as the predominant risk element. These results provide basic data for future subway air quality improvement.