Repeated Exposure to Near-Ambient PM_2.5 Decreases Pulmonary Function: Controlled Human Exposure Study

Epidemiologic studies have provided evidence of health effects over cumulative days of PM_2.5 exposure in observational settings; however, there have been no controlled exposure studies in humans over consecutive days. To assess the effects of near-ambient PM_2.5 exposure on pulmonary function and exercise tolerance, a randomized, double-blind controlled exposure study was conducted among healthy human volunteers (n = 17). Exposure consisted of 4 h of intermittent exercise for 3 consecutive days to clean air and 35 μg/m³ of PM_2.5 separated by a minimum of 2 weeks. Spirometry was measured at baseline, postexposure (+0 h), and 20 h (+20 h) after each day of exposure. PM_2.5 exposure reduced lung function, with reductions after Day 2 and Day 3. At Day 1 + 0 h, FEV1 was unchanged (-0.9%, 95% CI: -2.1, 0.3), and at Day 1 + 20 h, FEV1 was unchanged (-1.2%, 95% CI: -2.4, 0.1). At Day 2 + 0 h, FEV1 was reduced by 1.9% (95% CI: -3.1, -0.7). This decrement persisted into Day 2 + 20 h, with FEV1 reduced by 1.7% (95% CI: -3.3, -0.2). At Day 3 + 0 h, FEV1 showed a similar reduction of 1.8% (95% CI: -3.5, -0.1). This decrement persisted into Day 3 + 20 h, with FEV1 down by 1.7% (95% CI: -3.2, -0.1). PM_2.5 exposure reduced exercise output on both Day 2 (-2.0 W, 95% CI: -2.86, -1.08) and Day 3 (-2.4 W, 95% CI: -3.18, -1.61). Lung function and exercise output displayed modification by sex; males showed greater decrements in lung function at Day 3 + 20 h, and females had greater losses in exercise output after Day 3. In conclusion, near-ambient PM_2.5 exposure elicits pulmonary function deficits, sustained after multiple days of exposure and persisting at least 20 h after cessation of exposure. PM_2.5 exposure decreases exercise output.