Comprehensive survey of household radon gas levels and risk factors in southern Alberta

Abstract

Background: The inhalation of naturally occurring radon (222Rn) gas from indoor air exposes lung tissue to α-particle bombardment, a highly mutagenic form of ionizing radiation that damages DNA and increases the lifetime risk of lung cancer. We analyzed household radon concentrations and risk factors in southern Alberta, including Calgary, the third-largest Canadian metropolis.

Methods: A total of 2382 residential homes (2018 in Calgary and 364 in surrounding townships) from an area encompassing 82% of the southern Alberta population were tested for radon, per Health Canada guidelines, for at least 90 days (median 103 d) between 2013 and 2016. Participants also provided home metrics (construction year, build type, foundation type, and floor and room of deployment of the radon detector) via an online survey. Homes that were subsequently remediated were retested to determine the efficacy of radon reduction techniques in the region.

Results: The average indoor air radon level was 126 Bq/m3, which equates to an effective absorbed radiation dose of 3.2 mSv/yr. A total of 1135 homes (47.6%) had levels of 100 Bq/m3 or higher, and 295 homes (12.4%) had levels of 200 Bq/m3 or higher; the range was less than 15 Bq/m3 to 3441 Bq/m3. Homes built in 1992 or later had radon levels 31.5% higher, on average, than older homes (mean 142 Bq/m3 v. 108 Bq/m3). For 90 homes with an average radon level of 575 Bq/m3 before mitigation, radon suppression successfully reduced levels to an average of 32.5 Bq/m3.

Interpretation: Our findings show that radon exposure is a genuine public health concern in southern Alberta, suggest that modern building practices are associated with increased indoor air radon accumulation, legitimatize efforts to understand the consequences of radon exposure to the public, and suggest that radon testing and mitigation are likely to be impactful cancer prevention strategies.

Figure 1

Indoor air radon concentrations by postal code district in the greater Calgary metropolitan region. Darker-coloured circles indicate multiple overlapping readings. High radon concentrations were documented almost universally across the region.

Figure 2

Average indoor air radon concentrations by subdivision of the greater Calgary metropolitan area and proportion of homes with readings of ≤ 99 Bq/m3, 100-200 Bq/m3 and > 200 Bq/m3 for the 4 quadrants of Calgary and the surrounding towns. Max = maximum observed radon reading in area.

Figure 3

Average indoor air radon concentrations by home features. Box plots show minimum/maximum spread and mean of radon concentrations within home descriptor groupings (*p ≤ 0.001, Bonferroni post hoc testing on one-way analyses of variance).

Figure 4

A: Indoor air radon measured in homes built before 1992 and in those built between 1992 and 2016. B: Home age distribution for homes in our study (red line) and for a random sampling of homes listed for sale in 2016 in the same region (black line). C: Reported square footage of homes constructed between 1940 and 2016, indicating individual home sizes (red dots) and averages across decades.

Figure 5

Pre- and postmitigation indoor air radon concentrations for all homes with initial readings of 200 Bq/m3 or higher.