Particle radioactivity from radon decay products and reduced pulmonary function among chronic obstructive pulmonary disease patients

Background: Radon (²²²Rn) decay products can attach to particles in the air, be inhaled, and potentially cause airway damage.

Research question: Is short-term exposure to particle radioactivity (PR) attributable to radon decay products emitted from particulate matter ≤2.5 μm in diameter (PM_2.5) associated with pulmonary function in chronic obstructive pulmonary disease (COPD) patients?

Study design and methods: In this cohort study, 142 elderly, predominantly male patients with COPD from Eastern Massachusetts each had up to 4 one-week long seasonal assessments of indoor (home) and ambient (central site) PR and PM_2.5 over the course of a year (467 assessments). Ambient and indoor PR were measured as α-activity on archived PM_2.5 filter samples. Ratios of indoor/ambient PR were calculated, with higher ratios representing PR from an indoor source of radon decay. We also considered a measure of outside air infiltration that could dilute the concentrations of indoor radon decay products, the indoor/ambient ratio of sulfur concentrations in PM_2.5 filter samples. Spirometry pre- and post-bronchodilator (BD) forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) were conducted following sampling. Generalized additive mixed models were adjusted for meteorologic variables, seasonality, and individual-level determinants of pulmonary function. We additionally adjusted for indoor PM_2.5 and black carbon (BC).

Results: PR exposure metrics indicating radon decay product exposure from an indoor source were associated with a reduction in FEV₁ and FVC. Patients in homes with high indoor PR (≥median) and low air infiltration (<median) compared to others had a -26.9 (95% CI: -61.4, 7.7) mL and -75.4 (95% CI: -128.6, -22.2) mL reduction in post-BD FEV₁ and FVC, respectively. These associations remained similar after PM_2.5 and BC adjustment.

Interpretation: Our findings raise concern about the harmful effects of PR exposures attributable to residential radon on pulmonary function in patients with COPD.