Impacts of subway air particles on healthy adults: a randomized controlled trial in a Chinese city

Subway systems reduce traffic congestion, air pollution, and carbon dioxide emissions in cities but the impacts of subway air pollution on the health of subway users remain obscure. We conducted a randomized controlled trial involving 83 healthy adults, with 80 included in the final analysis, randomly grouped to spend 2 h daily for 5 consecutive days either in an office or on a subway platform. The fine (PM_2.5) and thoracic (PM₁₀) particles concentrations, temperature, and humidity were monitored. Measurements of health parameters were assessed, including lung function and levels of fractional exhaled nitric oxide (FeNO), inflammatory and oxidative stress biomarkers, and metabolites in serum.

The subway platform exhibited significantly high pollutant levels, with mean PM_2.5 and PM₁₀ concentrations of 193.4 ± 39.4 µg/m³ and 311.5 ± 64.3 µg/m³ respectively. After the 5-day subway exposure, significant declines were observed in lung-function index values, including forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC), maximal voluntary ventilation (MVV) and peak expiratory flow rate (PEFR) as well as serum levels of glutathione peroxidase (GPX)-1 (p < 0.05). Conversely, somatosensory symptom scores, FeNO levels, and serum levels of tumor necrosis factor (TNF)-α and interleukin (IL)-8 were strongly elevated (p < 0.05). Results indicated increased arsenic and cobalt and decreased selenium in urine after the subway exposure (p < 0.05). Finally, the subway exposure was associated with disruptions in seven metabolic pathways and nine metabolites, particularly the depletion of L-cysteine, pretyrosine and O-acetyl-L-serine.

This study provides the first evidence that repeated exposure to subway airborne particles is associated with reduced lung function and increased respiratory and systemic inflammation in healthy adults. Our results underscore the need to develop strategies to mitigate exposure risks, ultimately protecting public health in urban environments.