Radon is a naturally occurring element (Rn) produced by the radioactive decay of radium. Because of its radioactivity, it is considered a health hazard.
The US Environmental Protection Agency (EPA) classes radon as a carcinogen. It is the leading cause of cancer in non-smokers and the second leading cause in smokers.
In this article, we will look at what radon is, where it comes from, the health implications of radon exposure and how to minimize risks.
Contents of this article:
Here are some key points about radon. More detail and supporting information is in the main article.
- Radon is a naturally occurring radioactive element
- It is a colorless, odorless and tasteless gas
- Radon is found in the atmosphere, but it has a tendency to accumulate in buildings
- Some of the highest recorded levels of radon were found in a town in County Cork, Ireland
- Radon can increase the risk of lung cancer, especially when combined with smoking
- There are a number of ways to reduce radon build-up in the home
- Before appropriate ventilation became mandatory, many miners developed lung cancer from radon exposure
- Simply making your home airtight is not enough to prevent radon from building up
- Radon is heavier and denser than air so often accumulates in basements.
What is radon?
Radon is created by the decay of radium.
Radium decays to produce radon which then emanates from uranium ores, shales, phosphate rock, igneous and metamorphic rocks such as granite, and, to a lesser degree, more common rocks such as limestone.
Radon is a gas at standard temperatures and pressures, in fact, it is one of the most dense substances that remains a gas under normal circumstances.
As a colorless, odorless, tasteless gas, radon is undetectable by human senses alone.
Radon is all around us, but in very small quantities. However, it can pool in buildings. Radon accounts for the majority of most people's exposure to ionizing radiation.
Where is radon found?
Radon tends to enter buildings at their lowest point. It often makes its way in through splits in foundations, cracks in walls, gaps around pipes, cavities inside walls and the water supply. The gas is likely to accumulate in airtight buildings that are insufficiently ventilated.
Levels vary substantially from location to location and, although the half-life of radon is less than 4 days, it can build up in high concentrations, especially in low areas such as basements or mine shafts.
The highest levels of radon in the US are to be found in Iowa and the Appalachian Mountain areas in southeastern Pennsylvania.1 However, it is worth noting that two adjacent homes - indeed, two adjacent rooms - can vary significantly in their levels of radon.
The high levels of radon in Iowa are due to ancient glaciers which ground down granite rocks and deposited them as the rich soil that covers Iowa today.
Some of the highest radon readings ever found were taken in the town of Mallow in County Cork, Ireland.2
Radon has also been found in some spring water and hot springs.3
Health effects of radon
Paradoxically, in the early 20th century, radon was touted by quacks as being beneficial to health. People could pay small sums of money to spend time in a "radiotorium" and be bombarded by radon.
Other companies attempted to add radon to water, but, thankfully for the consumers, radon's short half-life meant that it had disappeared by the time it reached them.
Radon's radioactive and negative health implications were only discovered at a later date.
In the 1940s and 1950s, ventilation systems in mines were not widely implemented. Lung cancer in miners in the Czech Republic, South Australia and Southwestern USA was attributed to radon inhalation. Despite the eventual realization of the hazards, radon-induced lung cancer in miners remained a significant hazard until the 1970s.
It is now known that the inhalation of large quantities of radon causes lung cancer. According to the EPA, radon is the second greatest cause of lung cancer, after smoking.
Radon causes 21,000 lung cancer deaths per year in the US. About 2,900 of those deaths occur in people who have never smoked.4 Similarly, in the UK, radon accounts for around 6% of total lung cancer deaths, making it the second biggest cause after smoking.5
Thorium and uranium decay to produce radium which, in turn, decays to produce radon. Radon itself decays to produce radon progeny.
The radon progeny are a sticky solid substance rather than a gas; they can coat dust particles and are easily inhaled. There is evidence that inhalation of radon progeny can also cause lung cancer.6
Radon risks at home
After smoking, radon is the biggest cause of lung cancer.
There are some difficulties in assessing the exact risks of radon in the home. Most studies have used data from miners who will have had far more exposure to radon than is likely in any building.
The biggest cause of lung cancer is smoking, and this can muddy the waters because even non-smokers may have been exposed to second-hand smoke.
A combination of radon and cigarette smoke could, potentially, be more harmful than either on their own.
Some researchers believe that the risk of cancer from radon without exposure to cigarette smoke is so small as to be almost insignificant.78
Others, however, believe the risks that radon presents to lung health are understated and deserve more attention.
How to minimize radon risks
Some estimate that 1 in 15 US homes have elevated levels of radon. Radon test kits are widely available and are generally cheap or even free.
Radon kits include a collector to be left in the lowest habited room of the house for 2-7 days; this is then sent off to a laboratory for evaluation.
If the radon readings are high, there are a number of ways to deal with the issue. The most common of which are the following:9
- Sub-slab depressurization (soil suction): consisting of a vent pipe system and a fan that pulls radon from under the house and vents it to the outside
- Improving ventilation: it is also important to avoid moving radon from lower floors to the rest of the home
- Radon sump system: a sump is an underfloor cavity into which a pipe is inserted. A fan pulls air and radon up and away from the home
- Positive pressurization: these systems constantly blow fresh filtered air into the home to clear out radon.
It is worth noting that simply making your home airtight has not been proven to limit radon levels unless other measures, like the ones above, have also been implemented.
Although radon is demonstrably carcinogenic, its implications for health at the levels found in the home are still up for debate, with smoking making conclusions difficult to draw. However, it is better to be safe than sorry, and all homes can be adapted if required.
The EPA, American Lung Association and other partners are announcing a strategy for preventing 3,200 lung cancer deaths annually by 2020 through radon exposure reduction strategies. The goal to save these lives will be achieved by reducing high radon levels in five million homes, apartments, schools and childcare centers.
Radon gas is a silent health threat, and Canada needs to align its guidelines for acceptable radon levels with World Health Organization (WHO) limits, argues an editorial in CMAJ.