Human pulmonary cytotoxicity of vehicular derived PM2.5: A study from three characterized tunnels

The increasing number of motor vehicles has given rise to widespread public concern regarding their pollutants emission and according health effects. This study investigated the emission characteristics and chemical composition of PM2.5 in three tunnels in Xiamen, China (the Wucun Tunnel, Xianyue Mount Tunnel, and Wenxing Tunnel). This study also assessed the cytotoxic effects of PM2.5 on human lung epithelial cells and identified the primary chemical components that contribute to such cytotoxicity. Of the three tunnels, the Wucun Tunnel had the highest levels of PM2.5 emissions, which were primarily contributed by diesel vehicles. Carbonaceous compounds and metals, which originate from vehicle-exhaust, brake, and tire-wear emissions, were the predominant constituents of PM2.5 in all three tunnels. Higher concentrations of high molecular weight polycyclic aromatic hydrocarbons (PAHs) were associated vehicle traffic. Dose-dependent increases in oxidative and inflammatory biomarkers, such as superoxide dismutase, reactive oxygen species, tumor necrosis factor-α, and interleukin-6 (IL-6), were identified. The Wucun Tunnel exhibited a higher capacity for radical generation, whereas the Wenxing Tunnel and Xianyue Mount Tunnel exhibited higher capacities for IL-6 generation. Organic carbon, elemental carbon, specific metals (i.e., Ti, Mg, Fe, Cu, Mo, and Sb), and specific PAHs (i.e., benzo[b]phenanthrene, dibenz[a,h]anthracene, benzo[a]anthracene, chrysene, and benzo[a]pyrene) were highly correlated with bioreactivity. These findings advance elucidate the pulmonary health effects of vehicular emissions and provide effective suggestions for improving air quality and safeguarding human health in tunnels and road environments.