Alpha particle radioactivity from indoor radon decay products and pulmonary function among chronic obstructive pulmonary disease patients

Background and aim: Radionuclides attached to particulate matter (PM), referred to as particle radioactivity (PR), are mainly from radon decay and continue to emit radiation after inhalation. Decay products that emit α-radiation have the greatest potential of pulmonary damage due to high energy transfer to surrounding tissues. Methods: Our study included 143 patients (90% male, mean age±SD=72.8±8.2 years) with chronic obstructive pulmonary disease (COPD) in Eastern Massachusetts, USA who were not current smokers. Up to four one-week long seasonal indoor samples of PM ≤2.5 µg/m3 (PM2.5) were collected for each patient (n=467), followed by spirometry pre- and post-bronchodilator (BD). α-activity was measured on archived sampling-date-matched ambient and indoor PM2.5 Teflon filter samples (α-PR), which represents the decay of 210Pb, the longest-lived radionuclide (t1/2=22 years), to 210Po. Indoor/ambient sulfur ratio in the filter samples was used as a measure of air infiltration. Exposure surrogates indicating greater exposure to radon decay products from an indoor source were derived: indoor/ambient α-PR and high indoor α-PR (>median) with low air infiltration (<median sulfur ratio). We fitted generalized additive mixed models adjusted for meteorological variables, seasonality, and patient characteristics. PM2.5 mass was additionally adjusted for as sensitivity analysis. Results: An interquartile range increase in indoor/ambient α-PR was associated with a -8.9 (-24.2, 6.3) mL and a -7.7 (-31.6, 16.2) mL reduction in average post-BD forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC), respectively. The greatest effects were found for homes with high indoor PR and low air infiltration compared to others, a -26.9 (95% CI: -61.4, 7.7) mL reduction in post-BD FEV1 and a -75.4 (95% CI: -128.6, -22.2) mL reduction in post-BD FVC. Associations remained after PM2.5 adjustment. Conclusions: Indoor sources of α-PR from radon decay products may reduce pulmonary function in COPD patients. Keywords: air pollution, radiation, pulmonary function