Novel Approach to Assess the Toxicity of PM2.5 on a Subway Platform Using a Mobile Air-Liquid Interface System and Submerged Exposure.

Subway stations are enclosed environments that can have elevated concentrations of PM2.5 (particulate matter with an aerodynamic diameter of <2.5 μm). These particles are primarily generated by mechanical wear from trains and are therefore rich in transition metals and suspected to affect health upon inhalation. To simulate real-world inhalation scenarios, this study aimed to assess the toxicity of airborne subway PM2.5 using a mobile air-liquid interface (ALI) exposure system directly on the platform, using monoculture (A549) and coculture (A549 + dTHP-1) cell models, alongside laboratory submerged exposures. In ALI exposures, a dose of 0.12 ± 0.07 μg/cm2 could not induce any change in cell viability or inflammatory markers after 24 h of incubation. In submerged experiments, a higher dose was applied than in ALI, inducing a decrease in cell viability in both A549 and dTHP-1 cells. A549 cells exhibited increased IL-6 and TNF-α release at the highest dose (100 μg/mL). In dTHP-1 cells, IL-8 release was significantly elevated even at the lowest dose (10 μg/mL), and all four cytokines (IL-8, IL-6, IL-1β, and TNF-α) were significantly increased at 100 μg/mL. These findings highlight the critical role of exposure conditions in toxicological studies and support the use of both in situ and laboratory-based approaches. Moreover, longer in situ exposures may be necessary to achieve doses comparable to those in a laboratory setup for comparison.