More than 1,000 people are dying every year from a poison gas which seeps out of the ground because current building guidelines are not stringent enough, researchers warn.
The gas is called radon and it leaks naturally out of the rock on which most of Great Britain and Europe stands. It is a chemically-inert pollutant produced by the radioactive decay of uranium-238, which is present throughout the Earth's crust.
Radon, when inhaled, is a cause of lung cancer and scientists believe too little is being done to tackle it. Although concentrations outdoors are low, the gas can build up indoors, significantly increasing the risks of cancer to the occupants.
In the UK, radon levels are highest in houses on Dartmoor in Devon and in Cornwall, which are built on granite, and in parts of Wales and Scotland. The gas seeps into buildings through cracks and holes in the foundations.
The current UK policy is to identify areas where radon levels are high (above 52 becquerels per cubic metre) and seal the foundations of new homes with gas-resistant membranes. In existing buildings, the owners are advised that a "radon sump" can be created by digging below the foundations and using a fan and pipe to blow the gas to the outside.
In the new study, researchers from the University of Oxford say the existing policy is misguided because more than 95 per cent of deaths from radon occur at levels of exposure below the current action level.
Many homeowners refuse to have their homes tested or to spend money to reduce their radon levels, further reducing the impact. As a result the existing policies are "costly and have a minimal impact on radon-related deaths," they say in the online version of the British Medical Journal (BMJ).
A better alternative would be a nationwide policy to install sealed membranes in all new homes, regardless of where they are built, the researchers say today. The membranes cost around £100 per house and the measure would save around 1,000 lives over the first 20 years.
The researchers calculated the risk based on data from 7,000 patients with lung cancer and 21,000 controls (people without lung cancer) across Europe. They estimate that radon accounts for 3.3 per cent of all deaths from lung cancer in the UK. Six out of seven people who die from radon-related lung cancer are smokers or former smokers.
Smoking is by far the chief cause of lung cancer and the best way of preventing it is to stop. But current and former smokers can cut their risk further by reducing exposure to radon.
Existing homeowners, who are far more numerous, can reduce radon levels where they are high, at a cost. The researchers say the current policy of offering free individual measurements to those in high radon areas (above 64 becquerels) is not cost effective, even though the homeowners pay for any remedial work themselves (only 20 per cent do so). They say the potential for reducing deaths from radon in these homes is "limited" and the case for a new policy "less clear".
A commentary on the findings in the BMJ says the study is the "most extensive and detailed evaluation to date" of policies to counter radon-induced lung cancer deaths. In Europe, which has higher average radon levels than the UK, an estimated 18,000 deaths a year are attributed to the effects of the gas.
How much it would cost to build a radon-protective membrane into each new home – a measure that would save 1,000 lives in 20 years.