What is radon?
Radon is a colourless and odourless gas and has been cited to be responsible for half of the natural radiation to which humans will be exposed to (Lorenzo-González et al., 2019). Specifically, Radon-222 stands as the most prevalent naturally-occurring isotope, as well as the most health significant to humans (Schwela & Kotzias, 2005). In general, these gaseous radon isotopes occur as a result of the natural radioactive decay of uranium-containing minerals found in bedrock, surficial materials, and groundwater (Missimer et al., 2019).
The prevalence of radon has proved to be problematic as the gas escapes easily from rocks and soils into the air, and subsequently tends to accumulate within enclosed indoor spaces such as houses and buildings (World Health Organisation [WHO], 2023).
Harmful effects of radon exposure
To date, radon is one of the 19 environmental carcinogens recognized by the WHO, and the International Agency for Research on Cancer has also similarly classified radon and its progeny as carcinogenic to humans (Li et al., 2020).
- Lung cancer
Radon atoms can spontaneously decay or change into other atoms – resulting in a process known as radon progeny. These atoms can then attach themselves to dust particles present in indoor air, which can stick to the inner lining of the lung upon inhalation (National Research Council (US), 1999). The radiation emitted from the deposited radioactive particles can result in severe DNA damage (Riudavets et al., 2022), prompting cells to repair rapidly whilst introducing genetic errors in what has been termed as “genomic instability” (Stanley et al., 2019), thereby leading to lung cancer.
Radon currently stands as the overall second leading cause of lung cancer (US Environmental Protection Agency, 2023), and has been found to synergistic effects with cigarette smoke, leading to the increase of lung cancer risks in smokers (Kim & Ha, 2018). However, another alarming discovery is the fact that residential radon exposure has been found to be the leading cause of lung cancer in individuals who have never smoked before (Lorenzo-González et al., 2019).
2. Childhood leukemia
Ngoc et al. (2023) posit that children who grew up in homes with significant radon concentrations faced a much greater risk of developing childhood leukemia. Currently, researchers hypothesise that a small amount of radon is delivered to the bone marrow upon radon inhalation, which can then interfere with the development of leukocytes, thereby increasing the risk of leukemia (Tong et al., 2012).
Residential radon exposure
Fig. 1: Sources of radon gas within residential homes (Source: Centres for Disease Control and Prevention, 2022)
The concentration of residential radon depends on numerous factors:
| Factors | Examples |
| Housing factors | · Housing type
· Decoration materials · Building materials · Fuel used · Domestic water |
| Environmental conditions | · Temperature
· Humidity · Atmospheric pressure |
| Time factors | · Seasonality
· Daytime/Nighttime |
| Ventilation capacity | · Ventilation of indoor/outdoor air |
Table 1: Factors that affect the concentration of residential radon (Source: Li et al., 2020)
While outdoor radon concentrations do not pose health risks to humans, human-made buildings have been found to artificially concentrate radon gas, amplifying radon exposure experienced by occupants. To elaborate, outdoor radon concentrations usually average around 5 Bq/m3-15 Bq/m3, which is significantly lower than the average of 142 Bq/m3 found in North American residential homes build after 1992 (Reddy et al., 2022).
These observations are further supported by a Canadian-based study, which discovered that newer residential buildings contain higher mean radon levels compared to older ones, along with higher occupancy rates within these newer buildings:
Fig. 2: Graph illustrating rising mean radon levels amongst newer residential buildings, along with increasing occupancy rates (Source: Simms et al., 2021)
It is crucial to note that high radon exposure concentrations are prevalent phenomenon across regions, with countries such as South Korea similarly higher residential radon concentrations in houses built between 2011 and 2014 than those built between 1989 and 2009 (Kim & Ha, 2018). Indoor radon levels have also been recorded to be significantly higher during colder seasons due to closed windows and doors, resulting in an increased accumulation of radon within enclosed areas (Baltrėnas et al., 2020). As such, this might suggest that regions which experience cold temperatures might have populations which are at a higher risk of increased radon exposure and its repercussions.
References
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CDC. (2022, December 22). Radon in the Home. Centers for Disease Control and Prevention. https://www.cdc.gov/radon/radon-facts.html
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