Radon synergizes with lung carcinogens such as tobacco smoke to multiply lung cancer risk13,14. However, unlike tobacco use, radon inhalation is not addictive and effective testing and mitigation techniques exist15. Thus, radon exposure represents a readily preventable cause of the most lethal and common cancer type, and is a priority area of public health intervention and cancer prevention. Decaying 222Rn emits alpha particle ionizing radiation, severely damaging DNA in such a way that is almost impossible for our cells to repair without introducing genetic errors16. Such errors trigger ‘genomic instability’, a self-propagating cycle of DNA alteration that drives cancer formation2. Further to this, approximately 1 in 30 adult humans display radiation sensitivity, meaning that (compared to the average) they over-respond to ionizing radiation exposure leading to moderate to severe health effects including morbidities, mortality and/or increased risk of cancer17,18,19,20. The International Agency for Research on Cancer lists radon as a category 1 carcinogen, meaning it is unequivocally known to cause human and animal cancers1. Ionizing radiation such as alpha particle radiation is measured in Becquerels (Bq) that represents one radioactive decay event per second. A 16% increase in relative lifetime risk of lung cancer is measurable per ≥100 Becquerel/m3 (Bq/m3) chronic radon inhalation1,21,22.
Historically, radon exposure is thought to be increased in cold climate regions where populations predominantly occupy closed indoor air environments long periods of the year to avoid adverse meteorological conditions. However, climate change and growing adoption of air conditioning across all regions may alter this 20th century norm. It is estimated that the average North American spends 86.9% of their lives indoors23, meaning that analyzing the modern built environment is crucial for understanding exposure to many carcinogens. There are many regions of high radon potential on Earth, although this does not mean that all buildings in those areas contain unsafe radon levels8,15. Indeed, there are three factors needed to incur hazardous radon exposure: (i) a rich geologic source and pathway (upwards) for radon, (ii) environmental design metrics that actively draw up and concentrate radon and (iii) essential or elective human behaviour that prolongs exposure or increases radon concentrations. These latter two variables are potentially modifiable and are of interest in terms of exposure reduction.
Establishing historic and ongoing radon exposure represents significant ‘exposome’ information, similar to documenting smoking history24. Such information is important for early cancer detection programs, harm reduction25 and is also of interest to define best practice within scenarios such as business licensing, rental leasing, real estate transactions or home inspections. Thus, establishing the contextual (geographic, seasonal and environmental) effectiveness of distinct radon testing method(s) for decision-making is also important. Motivated by this, we measured household radon across a large North American area of high radon potential encompassing ~5.45 million humans spread across 1,313,748 km2. Radon dosimetry data was coupled to geospatial analysis, an interrogation of how built environment metrics and associated behaviours correlate with radon levels and, within a subset of regional buildings, an evaluation of multiple modalities of radon testing.
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