Updated 23 February 2016

Radon is a silent killer. Could it be in your home?

Radon is a dangerous radioactive gas that can cause lung cancer. It has no smell, colour or taste and it can seep into your home from the ground, via water and building materials. Why is SA's government not alerting the public to the dangers and just how worried should we be? Health24 takes a closer look.


When we're in our homes, we imagine that we're safe from environmental pollutants. But this may not be the case if invisible, odourless and tasteless radon gas is silently seeping into it.

What is radon and how does it affect us?

Radon is a naturally occurring radioactive gas that is produced from the natural decay of the elements uranium, thorium, and radium in rocks and soil.

Because it's a gas, radon escapes easily from the ground (or water) into the air where its radioactive particles diffuse into the air and enter our homes.

It is invisible, odourless, tasteless and the extremely long half-life of uranium allows it to remain radioactive for millions of years.

While it's mostly found in mine tailing dumps or waste, it is also found in areas where houses are built on soil rich in the elements uranium, thorium, and radium.

Radon dissolves into ground water and can be released into the air when the water is used or when it's released from water obtained from wells. It is also found in building materials such as bricks and mortar.

Radon levels can be higher in homes that are poorly ventilated or well insulated and tightly-sealed, and basements and ground floors typically have the highest radon levels because of their closeness to the ground.

Worldwide, radon causes a million deaths from lung cancer every decade.

The link between radon exposure and lung cancer

Long-term exposure to radon is tied to lung cancer (the only cancer proven to be associated with inhaling radon). When inhaled, radon particles can release radiation that damages surrounding lung tissue and enters the bloodstream.

If you are a smoker, and your house has elevated levels of radon in it, you have an even greater risk of developing lung cancer. In the US, radon is the nation's second leading cause of lung cancer. reports that smoking indoors may also attract airborne radon particles, which could further explain the link between smoking and lung cancer.

"As we breathe, the particles are deposited on the cells lining the airways, where they can damage DNA and may lead to lung cancer in later life," explains Prof Michael Herbst, Head of Health at the Cancer Association of South Africa.

Radon was classified as a human carcinogen by the International Agency for Research on Cancer in 1988 (IARC 1988) after several studies found that miners exposed occupationally to radon, usually at high concentrations, demonstrated a notably increased risk of lung cancer.

Although long-term exposure to radon can lead to lung cancer, tobacco smoking is a much more significant contributor, noted Herbst.

“The majority of radon-related cancer deaths occur among smokers. However, it is estimated that more than 10 percent of radon-related cancer deaths occur among non-smokers.”

According to the World Health Organisation (WHO) smokers are estimated to be 25 times more at risk from radon than non-smokers in the US.

The WHO further warns that radon exposure is a major and growing public health threat in homes.

A WHO Handbook on Indoor Radon: A Public Health Perspective recommends that countries adopt reference levels of the gas of 100 Becquerel per cubic metre (Bq/m3) and not exceeding 300 Bq/m3.

For radon gas, this is interpreted as one atom disintegrating per second, per cubic meter of air through radioactive decay, explains Dr Rian Strydom, technical adviser to the National Nuclear Regulator in South Africa and who has been working independently in the radon field since 1984.

The US Environmental Protection Agency has put it plainly, stating, any radon exposure has some risk of causing lung cancer, meaning there are no 'safe levels' of exposure.

Download: The WHO radon handbook

Dr Strydom pointed out that other international institutions like the International Commission on Radiological Protection (ICRP) recommend 200 to 600 Bq/m3, while the US EPA recommends a minimum level of 150 Bq/m3 as action levels.

“If these levels exist on an annual average basis, action to remediate the situation is recommended”, he said.

In 2005 the WHO conducted a survey on indoor radon among 192 member countries. Health24 contacted the WHO representative in South Africa to inquire whether our country participated in the survey and their response was "I do not think SA was part of the project".

75 Countries responded and 45 of those indicated that they had some radon-related activities in their country. 

Responding to the new evidence from the case-control studies on residential radon and lung cancer risk, and in an effort to reduce the rate of lung cancer around the world, the WHO launched the three-year International Radon Project in 2005.

The aim is to help countries increase awareness, collect data and encourage action to reduce radon-related risks. In 2009 the WHO concluded that radon causes up to 15% of lung cancers worldwide.

Map: World Map of National Residential Radon Levels provides an overview of residential radon levels by continent and by country, where the data is available. The map compares the radon levels measured by Becquerel per cubic meter (Bq/m3), a measurement of radon in the air, between countries and continents, ranging from low levels of radon at 7 Bq/m3 to high levels at 184 Bq/m3. Source: McLaughlin Centre, Canada

radon exposure map

How radon enters your home

Radon flows from the soil into the air and also into homes from the soil beneath homes. It can seep through:

- Cracks in floors
- Drains
- Sump pumps
- Exposed soil
- Construction joints and
- Loose-fitting pipes

Your chances of getting lung cancer from radon depend mostly on:

- How much radon is in your home
- The amount of time you spend in your home and how long you've lived there
- Whether you are a smoker or have ever smoked

According to research by the United States' National Academy of Sciences (NAS), a private, non-profit society of scholars, outside air contains very low levels of radon, but it builds up to higher concentrations indoors when it is unable to disperse.

"The most direct way to assess the risks posed by radon in homes is to measure radon exposures among people who have lung cancer and compare them with exposures among people who have not developed lung cancer," the study noted.

The radon level in SA

In South Africa, actual figures on the impact of radon on lung cancer are not available.

However, clinical metal toxicologist Carin Smit told Health24 the average occupant of a house on the West or East Rand will most certainly have a heightened chance of developing cancers because of their exposure levels to radon and other radionuclide particles, which can be described as unstable atoms that form chemical elements that radioactively decay and result in the emission of nuclear radiation.

Referring to a countrywide study of 2 000 homes by South Africa's Atomic Energy Corporation (AEC), Strydom said indoor radon concentration for the West Rand and East Rand appeared higher than average levels, which was in the order of 50 Bq/m3.

To put that into perspective: this study puts levels at 60 Bq/m3 in USA, 35Bq/m3 in UK, 50Bq/m3 in Germany and 100Bq/m3 in Nordic countries.

“In this study, the West Rand and East Rand indicated higher than average levels e.g. 77 Bq/m3 in Krugersdorp and 92 Bq/m3 in Randfontein. However, these areas also indicated a higher than average background radon level, and the increased indoor levels should not arbitrarily be assigned to mining operations in these areas.”

Table: Indoor radon concentrations in South African homes, Strydom et al, 2002. 

radon exposure south africa

The government also came under scathing attack from Smit. "In South Africa the creation of public awareness by government has been criminally low."

She said the Irish government, at the very least, tries to inform the public about radon by publishing educational material and how to minimise its health impacts on one’s family.

"We show no such pro-active governmental vigilance or attempts at information in South Africa," charged Smit.

Government needs to act

"The onus truly weighs heavily on the shoulders of government to compile a similar information plan and strategies as seen, for example, in Ireland to both warn and prepare its citizens".

Smit said there seems to only be academic interest in radon distribution and exposure in South Africa.

"I would urge authorities to look much more closely at the issue of mining closure and the rehabilitation of such mining activities to curtail the huge environmental and health impacts of radionuclides and especially in this context of radon."

Strydom said in compliance with nuclear regulations, all mining companies submit public radiological impact assessments, including the radon exposure pathway, to the National Nuclear Regulator (NNR), who regulates radiation levels, including radon testing in the country.

“I was personally involved in many of these investigations and the perceived high radon impact is not evident from the results from any of the sites. Increased radon impact occurs only within very short range of tailings impoundments, which are the sources of radon. Values approaching the action level of 200 (or even 150) Bq/m3 were never found,” said Strydom.

Smit was adamant though that with more than 6 000 abandoned mines in the country, surface uranium tailings and radon are wreaking havoc and causing health concerns, which are, in most cases quite devastating, she claimed.

"Uranium reclamation for mining tailings is big business in South Africa. I cannot foresee that the South African government is anywhere near ready for holding mining bosses and conglomerates responsible for irresponsible and dangerous mining closures".

She added that if one understands the radioactive behaviours of uranium and its progeny correctly, then one needs to factor in that the exposure is never static.

Image: How radon enters your house. Source: Natural Resources Canada

how radon enters house

South Africa's own Chernobyl?

Elaborating on this, Smit explained that the accident at Chernobyl on April 26 in 1986 in the Ukraine affected many countries as winds carried the impact and spread it like a blanket across Europe and the world.

"It took a mere 6 days for the first air-filters in Glasnevin in Ireland to record the radioactive plume that drifted over from Chernobyl," she said.

"I contend that South Africa has its own toxic plume generated every day by past and present mining activity; and that this is a constant source of radon exposure spreading out over thousands of kilometres and affecting most, if not all of our country."

Strydom did not share these sentiments.

He said no elevated radon concentrations were found in all the investigations, except very close (within 100 m) from mine tailings.

“It was found, in all cases, that the radon concentration contributed by the tailings sources decreased to insignificant levels within a km from the source.  Natural background radon is by far the overwhelming contributor to indoor radon,” he claimed.

Radon is soluble in water

The radon in your home can also come from your water supply.

Smit cautioned that radon transfer happens very rapidly and across great distances in hydrological systems, which poses an ingestion risk.  

However, research has shown that your risk of lung cancer from breathing radon in air is much larger than your risk of stomach cancer from swallowing water with radon in it, according to the Environmental Protection Agency (EPA) of the USA. 

It further noted that most of the risk from radon in water comes from radon released into the air when water is used for showering and other household activities.

The EPA also indicated that radon in your home’s water is not usually a problem when its source is surface water, compared to when the source is ground water.

This is the problem facing South Africans, according to Smit who said: "South African underground water compartments, like the Central, East and West compartments, as well as the Swartkrans Groundwater compartment, have been so badly contaminated with acid mine drainage (AMD) that South Africans face not only an airborne radiological threat from radon as a gas, but also in soluble form as a water-borne threat.”

Strydom again differed in his views on this.

“Radon escaping from water has been shown to be a very small component of the radon inhalation dose. Radon ingested with water does not have a dose conversion coefficient and does not contribute to radiological exposure.”

Is the NNR failing the public?

The NNR told Health24 it ensures that the impact on the public from authorised mining activities is kept to safe levels. It does this by requiring mines to conduct public safety assessments, which include the assessment of radon concentration in the environment and the resulting dose to members of the public.

“However, radon that may be from the underlying geological formation or historical radiological contamination or building material containing naturally occurring radioactive material in existing residential areas have not been under regulatory control,” it said.

Smit proceeded to point out two matters that greatly concern her and which she claims shows how the NNR defaults in its task to protect the public:

“Radioactive tailings, which include mining residue, rocks, gravel, etc. are dumped above ground and these tailings are stacked, releasing radon into the atmosphere through the use of such and other mined residues, for urban development projects and housing.”

She said the NNR’s endorsement appears on the signage of mining companies indicating compliance with Act 47 of 1999, where rocks, gravel and sand is sold for building materials. “These will outgas into homes in perpetuity,” claimed Smit.

"The actual tailings residue and rocks/gravel from mining make their way right into our houses, factories, and our everyday living environments, without any consideration of the ongoing health impacts."

Taking a different view once more, Strydom noted that nuclear regulations prohibit the uncontrolled use of mine residues for building developments.

“The regulations set a radioactive content limit of 0.5 Bq/g, below which level the material may be safely used. This limit value is in complete agreement with international practices, and to question it is to question the integrity of the international radiation protection community," he said.

“Material containing radioactivity below this limit, can be used safely in all development and housing scenarios. If the limits are exceeded, the operator has to be licensed by the NNR, through which the use scenarios of the material is strictly controlled by NNR inspection and audit, or the use is totally prohibited.”

In addition, Strydom said mining houses who go through the regulatory process as described above, are entitled to make the claim, and use the material accordingly.

He said the material most likely contains less than the 0.5 Bq/g limit, and is therefore safe for public use. “If not, the company runs the risk of committing fraud,” warned Strydom.

No national radon figures for households in SA

The Department of Environment Affairs told Health24 that indoor radon is the major contributor to the natural radiation dose of the general population, however, no average national figures were provided for radon levels in households.

The concentration of radon in a home depends on:

-  the amount of radium, the decay product of uranium and direct progenitor of radon, in the underlying rocks and soils, as well as possibly in the building materials
-  the routes available for its passage into the home and
-  the rate of exchange between indoor and outdoor air

Communications Director Albi Modise said the South African climate seems to favour better ventilation conditions, but he added that it is evident that the cold Highveld winters and lack of central heating result in stagnant indoor conditions for certain months.

He said programmes have been launched to measure radon levels in South African homes in areas where either mine waste or natural granites are known to have high uranium levels. "This includes Soweto and the surrounding rural areas."

Albi cited studies done in the Western Cape and Witwatersrand which showed average indoor concentrations of 20 Bq/m3 and 40 Bq/m3 in two small samples of approximately 70 and 100 houses respectively.

"Correlations between high indoor concentrations and factors such as structural type, geological characteristics and ventilation rate showed that houses with wooden floors are more likely to have high indoor radon concentrations."

Albi also mentioned the AEC study quoted by Smit. He said from the 2 000 residential homes tested in 27 towns, including Soweto, an average of about 63 Bq/m3 was recorded, indicating an approximately log-normal distribution of indoor radon concentrations.

Although people can test their homes, he said there is no simple way of recognising homes with high radon concentrations since many factors such as soil type, geological faults, building features and ventilation can affect the situation.

"Hence radon concentrations can vary between adjacent homes, and can vary within a home from day to day and from hour to hour."

The WHO recommends reducing radon exposure in your house by:

- increasing under-floor ventilation
- installing a radon sump system in the basement or under a solid floor
- avoiding the passage of radon from the basement into living rooms
- sealing floors and walls and
- improving the ventilation of the house

How you can test your home

Radon gas monitors manufacturer, PARC RGM explained to Health24 that it makes use of alpha track detectors to test for radon exposure in homes.

"We can provide test kits for radon tests in dwellings and it is a very simple procedure to test for radon in homes. A set of monitors can be acquired and deployed inside the areas to be measured," said PARC RGM Executive Director Ian Donald.

He said the price for such a test kit is typically over R300 for the recommended 3 monitors. This would include the analysis and reporting of the exposure values.

In old homes radon mitigation will be more expensive than when building a new home, said Donald.

“For new homes radon resistant sheets can be installed with the foundations and flooring making it simple and cost effective,” he said.

The Medical Research Council (MRC) informed Health24 that it is on course to test radon in homes, however, the focus is mainly in mining areas and as such is not expected to provide information on a countrywide average.

Health24 will write a follow-up article that includes what the National Nuclear Regulator will be doing to safeguard South Africa.

Health24 has ordered radon testing kits and will be randomly testing houses across Cape Town, as well as our workplace. Results will only be available in 3 – 4 months, so sign up for our Daily Dose newsletter to receive alerts when these articles are published. Sign up here.

The information in this article has been reviewed by biochemist turned occupational toxicologist, Dr Puleng Matatiele who is with the National Institute for Occupational Health.

Final editing by Health24 editor, Laura van Niekerk.

Watch the video for more on radon:


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