The SA National Nuclear Regulator (NNR) has conceded that South Africa is not immune to a dangerous gas known as radon, but it added that the levels of the gas in our homes are not a cause for alarm.
But what makes this gas so dangerous? Radon is an invisible, tasteless and scentless gas that is believed to increase the risk of lung cancer, which is a leading killer of cancer deaths in South Africans.
"Long-term exposure to radon can lead to lung cancer, which is the only cancer proven to be associated with inhaling radon," said health specialist at the Cancer Association of South Africa, Professor Michael Herbst.
He added that there had been a suggestion of increased risk of leukaemia associated with radon exposure in adults and children; however the evidence was not conclusive.
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.
In the US, radon is the nation's second leading cause of lung cancer. Worldwide, radon causes a million deaths from lung cancer every decade.
"Radon occurs naturally and everyone is exposed to it to some extent," Dr Rian Strydom told Health24.
Strydom, who has been working independently in the radon field since 1984, said although inhalation of radon increased the risk of contracting lung cancer, there were no certain short-term effect of exposure to the gas.
"Remember that radon raises the risk of lung cancer, and it is impossible to identify radon directly as the cause of the cancer. The effect is not clearly seen."
He noted that this aspect was controversial and the subject of international research effort. However, Professor Herbst said: "Scientists agree that radon causes lung cancer in humans."
He said recent research had focused on specifying the effect of residential radon on lung cancer risk. "In these studies, scientists measure radon levels in the homes of people who have lung cancer and compare them to the levels of radon in the homes of people who have not developed lung cancer."
How radon enters the body
Strydom explained that radon is formed through the decay of uranium. "Radon decays to a series of radioactive atoms called radon daughter products. These are metal atoms that attach themselves to aerosol particles in the air e.g cigarette smoke."
After inhalation of the particles, he said, these atoms adhere to the respiratory tract, especially in the deep lung area, where they subsequently decay radioactively.
"This means that they eject high energy alpha rays directly into the lung cells, causing radiation damage to the cell DNA. The cells repair the damage, but it becomes irreparable if the exposure is chronic, e.g through a lifetime. The damaged DNA is the start of cancer."
How radon enters our homes
Radon is found in small quantities in all rocks and soil and is also present in air, water and building materials like bricks and mortar.
Strydom said when uranium occurs in e.g. soil, the radon atoms formed in the soil pores diffuse to the surface of the soil and escapes into the atmosphere.
"From there, the gas may penetrate into homes through natural ventilation. Radon will also intrude into a home from the subsoil on which the house is built, permeating through the floor slab and floor openings."
In America and Europe people regularly test their houses for radon exposure, but this is not the case in South Africa.
Image: How radon enters your house. Source: Natural Resources Canada.
The only government body to regulate radiation levels in the country is the NNR, however, their concern and the regulations are aimed at protection against radiation that occurs as a result of human intervention such as mining.
The NNR told Health24 in an emailed response to questions that in several countries abroad it is a legislative requirement to have the radon measured and if need be, mitigated to levels that is considered safe.
"In many of these [countries], the by-laws of certain municipalities also require that new houses that are built, must conform to certain radon levels and be certified safe in a certain range. This also includes houses that are being sold 'second hand' which must conform to a certain value."
It said it was not yet a legislative requirement in South Africa for houses to be tested for radon; however, it added that plans are afoot to change this. "The country is on initial stages of setting up a regulatory framework for radon in dwellings."
Where are the radon hot spots in SA?
The NNR further admitted to Health24 that the identification of the geographical or geological areas which are classified as radon prone areas had not been done for the country.
"Increased levels of radon are expected to increase in certain geological formations, but the actual situation for the country is still to be established."
It noted that some studies indicated that there was a slight increase in radon background in areas where there were mining activities, where uranium or associated radionuclides occured in the ore or the waste products.
Strydom pointed out though that while regions with uranium deposits or base-rock containing uranium were generally prone to higher radon concentrations, this factor could be overshadowed by the soil type or the natural ventilation of the house.
"Mining and groundwork activities may result in elevated concentrations if the house is very near to the activities (< 100m) although this has not been shown unequivocally. The effect is highly dependent on weather conditions and season."
The NNR claimed that there were mitigating circumstances that decreased radon levels significantly in our homes and workplaces. These, it said, were good ventilation habits and fair weather throughout most of the year.
"It has been proven that ventilation of an area with high radon can significantly decrease the radon and therefore the risk," it said.
"In countries which experience extensive winters and cold bouts of weather, houses are well built and insulated from the outside, so if any radon come into the house, through ground, the soil or crawl space, not much can be flushed out from normal ventilation processes. But in South Africa, the air is circulated through normal ventilation processes unlike double glazed windows and sealed houses which leads to radon accumulation."
The World Health Organisation (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.
What about radon levels?
The WHO Handbook on indoor radon recommends that countries adopt reference levels of the gas of 100 Becquerel per cubic metre (BQ/m3) and not exceeding 300 Bq/m3.
"At the typical action level of 200 Bq/m3, non-smokers have a risk of about 1% (one person in hundred) to get lung cancer. At a 4 times lower level, the risk reduces to 0.3%. In the case of smokers, the corresponding risk values are about 10 times higher," Strydom said.
These risk estimates, he said, wee only true if people were exposed to the levels on average for their entire life.
The NNR added that draft regulations of South Africa had set a reference level of 300 Bq/m3 which could not be exceeded.
"This upper value is yet to be implemented when the regulatory framework for radon in dwellings is finalised for South Africa."
The regulator said this reference level was in line with the International Commission on Radiological Protection (ICRP), the WHO and IAEA recommendations.
Is your kitchen top a health hazard?
There have also been claims that some kitchen counter tops made from granite could also be emitting radon.
The NNR pointed out that only radon on the outermost part of granitic areas had the possibility of escaping the rock.
"There have been studies around the world to test the hypothesis of the kitchen counter top increasing the radon activity concentrations in homes. The conclusion of some studies conducted is that kitchen counter tops do not emit significant amounts of radon that could become of concern from a radiation safety perspective, more so that radon is easily dissipated since South African homes are normally well ventilated."
Strydom further explained that most granites contained uranium, which was the radioactive "mother" of radon. He said radon atoms were formed in the granite rock and diffused through the rock material to the surface.
"If the granite is dense and unfractured, the radon atoms decay before they can reach the surface and are not emitted. Therefore, some kitchen tops may emit radon, but the resulting levels of radon in the house depend on many factors, mostly ventilation, and cannot simply be determined by radon gas measurement.
"It is possible to predict levels, but this is a complex exercise of radioanalysis and mathematical modelling," he added.
How can people test for radon in their homes?
Testing is the only way to know if a person's home has elevated radon levels, said Professor Herbst.
"Short-term detectors measure radon levels for 2 days to 90 days, depending on the device. Long-term tests determine the average concentration for more than 90 days.”
Herbst said, since radon levels could vary from day to day and month to month, a long-term test was a better indicator of the average radon level. "Both tests are relatively easy to use and inexpensive."
Strydom indicated that radon levels in homes could easily be measured by using a Passive Radon Gas Monitor from PARC RGM.
He said this comprisesd a plastic dome-like device which was exposed in the home for a period of one to two months. After exposure, the device was dispatched back to the company who then performed a read-out of the radon concentration and provides a report.
Health24 has been informed that a committee, made up of the NNR, Medical Research Council, the University of Witwatersrand and Parc RGM, is looking into a study where 2 000 homes in mining towns in South Africa will be tested for Radon exposure.
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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.