Carbon Monoxide is a much-publicised invisible killer. But there's another little-known gas that kills 27 times more people, causing the deaths of 1,100 people a year in the UK alone. Worse still, it could be seeping into your home.
Radon is a radioactive, odourless, colourless gas that is naturally present throughout most of the UK and in several other countries across the globe. It is emitted in varying quantities or concentrations from radioactive elements, for example Uranium, that are naturally present in rocks and soils.
Epidemiological studies on the health of miners undertaken by the United States Public Health Service during the 1950s and 1960s established a link between higher concentrations of Radon and incidences of lung cancer.
As Radon is emitted from the ground, it quickly dilutes in the atmosphere into relatively harmless concentrations. But in confined and unventilated spaces in buildings, in basements and in underground mines, it's concentration levels can become dangerously high.
The daughters of Radon
Following more detailed research undertaken in the UK during the 1970s and 1980s, it was recognised that concentrations of Radon in residential dwellings and other buildings could reach concentrations of a sufficiently high level to present a material risk of lung cancer.
It was following this research that the UK government introduced a series of policies and regulative measures for the monitoring, recording and reporting of Radon levels, as well as guidance, relating to the mitigation of Radon levels in buildings. In 1991, UK building regulations first introduced a requirement that Radon protection measures, must be incorporated within the design of new buildings in Radon affected areas. This guidance has been revised since.
Radon itself does not really cause tissue damage. It is the decay products, sometimes referred to as the progeny or daughters of Radon, that do. Radon gas may be inhaled and exhaled with little damaging effect. But the decay products include Radon - 222 (derived from Uranium - 238) and Radon - 220 (also known as Thoron, and derived from Thorium - 232), and other progeny including Polonium-218, 214 and 210, that can.
These isotopes have half lives of between half a second and 138 days. It is the precipitation of isotopes within lung tissue, and their subsequent degradation, that can have a carcinogenic effect.
Worse than asbestos?
Based on current research, the UK government estimates that 1,100 lung cancer deaths per annum are a direct result of exposure to high concentrations of Radon. This is considerably higher that the reported number of deaths of people with lung cancer associated with asbestos.
Concentration levels of Radon are measured in Becquerels per cubic metre (Bq/m3). In the UK, the action level is 200 Bq/m3. This represents the recommended limit for the activity concentration of Radon in UK homes.
At that level, the lifetime risk of a non-smoker developing lung cancer is less than 1 in 200, but increases to 1 in 7 for a current smoker. Similarly, the lifetime risk increases significantly to 1 in 100 and 1 in 3 respectively, when indoor levels increase to 800 Bq/m3.
Concentration levels of Radon within buildings vary substantially and are influenced by a number of factors. Location is significant. There are areas in the UK where concentration levels are much higher due to the nature of the underlying bedrock, for example; some of the highest recordings to date have been made in buildings situated in Devon and Cornwall.
Buildings that have higher levels of natural or mechanical ventilation tend to have proportionally lower concentrations of Radon, for example where ground floors have a ventilated void below them. Those constructed after 1991 that incorporate Radon attenuation measures are also likely to have significantly lower levels of Radon concentrations within them.
The Radon Atlas
The Indicative Atlas of Radon in England and Wales (Health Protection Agency, 2007) sets out a series of maps of England and Wales that are colour coded to show Radon Affected Areas, indicating the number of dwellings that have been measured and found to have Radon concentrations at, or above the action level. Most other countries' health and radiation protection agencies publish similar data.
The 2002 edition of this publication contains detailed recorded data relating to the measurements of Radon in 400,000 homes, something the 2007 edition does not.
In the UK council district of Kerrier in Cornwall, for example, the 2002 data showed that Radon concentration levels were measured in 12,800 homes. The arithmetical average Radon concentration was 248 Bq/m3 and the highest recorded concentration was 10,000 Bq/m3, 50 times the action level. Overall, 5,200 homes had concentrations at or above the action level.
Conversely, in the UK county of Essex the arithmetical average Radon concentration in all homes measured was 23 Bq/m-3 and no dwellings returned a measurement at or above the action level.
The UK is not alone in facing the challenges of the Radon problem. The health protection agency of Canada Health Canada confirms that Radon related lung cancer is responsible for 3,000 deaths per year among its citizens. The United States Environment Protection Agency, meanwhile, reveals high levels of Radon across the country with some states, for example North Dakota, where 100% of households are likely to have indoor levels equivalent to 148 Bq/m3. Conversely, the Australian Government's Radiation Protection and Nuclear Safety Agency maintains that Australia has some of the lowest levels of Radon in the world, with practically the entire country recording indoor levels below 20Bq/m-3.
So what can you do?
If you're worried about Radon, the first thing to do is find out whether your home might be affected. But if it is, there's no need to panic – there are a wide range of remedial measures, from various forms of ventilation to active Radon sumps, which effectively suck the gas out of your home.
The most worrying problem at present is that too few of us understand the risks posed by this invisible gas. Knowledge really is the best protection.