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Predictors of Indoor Radon Concentrations in Pennsylvania, 1989–2013

Background: Radon is the second-leading cause of lung cancer worldwide. Most indoor exposure occurs by diffusion of soil gas. Radon is also found in well water, natural gas and ambient air. Pennsylvania has high indoor radon concentrations; buildings are often tested during real estate transactions with results reported to the Department of Environmental Protection (PADEP).
Objectives: To evaluate predictors of indoor radon concentrations.

Methods: Using first floor and basement indoor radon results reported to the PADEP between 1987-2013, we evaluated associations of radon concentrations (ln-transformed) with geology, water source, building characteristics, season, weather, community socioeconomic status, community type and unconventional natural gas development measures based on drilled and producing wells.

Results: Primary analysis included 866,735 first measurements by building, the large majority from homes. The geologic rock layer on which the building sat was strongly associated with radon concentration (e.g., Axemann Formation, median = 365 Bq/m3, IQR = 167-679 vs. Stockton Formation, median = 93 Bq/m3, IQR = 52-178). In adjusted analysis, buildings using well water had 21% higher concentrations (β = 0.191, 95% CI: 0.184, 0.198). Buildings in cities (vs. townships) had lower concentrations (β = -0.323, 95% CI: -0.333, -0.314). When we included multiple tests per building, concentrations declined with repeated measurements over time. Between 2005-2013, 7469 unconventional wells were drilled in Pennsylvania. Basement radon concentrations fluctuated between 1987-2003, but began an upward trend from 2004-2012 in all county categories (p < 0.001), higher levels in counties with ≥100 drilled wells vs. counties with none, and with highest levels in the Reading Prong.

Conclusions: Geologic unit, well water, community, weather and unconventional natural gas development were associated with indoor radon concentrations. Future studies should include direct environmental measurement of radon, and building features unavailable for this analysis.

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