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The risks of radon

17 January 2013

The Dutch National Institute for Public Health and the Environment (RIVM) announced this week that it will inspect some 3,000 Dutch houses for radioactive radon and thoron. Emeritus Professor Rob de Meijer did just that in the 1980s. With his colleagues from the KVI, the University of Groningen institute for atomic and subatomic physics, De Meijer put the risks of radon on the radar.

You don’t need a nuclear power plant to create a radiation hazard. Natural basalt or granite rocks contain quite a bit of uranium. The radioactive decay of uranium can produce radioactive radon gas, which can seep through cracks in rocks. If your house is built on such rocks, radioactive radon may accumulate in your crawl space.

‘A famous case occurred in Pennsylvania, in the 1970s,’ De Meijer recalls. ‘On the building site of a nuclear power plant, one guy kept setting off the contamination alarms, even when he arrived at work. They eventually checked his house and found a huge amount of radioactive radon in the basement. It turned out that the house was built on a fault line in the granite, which vented a lot of radon gas into this house. In the end, the house was demolished.’

Supplier of protective foil against radon in the US.
Supplier of protective foil against radon in the US.

When radon seeps into a house from rocks, ventilation in the crawl space or basement will disperse most of the radiation. However, the situation is different in the Netherlands. ‘We don’t have a rocky subsurface here, but when we started measuring, we did find radon,’ De Meijer explains.

The first measurements were actually made in his own house in the village of Roden, near Groningen. ‘It turned out that the radon was seeping out of construction materials like plasterboard, brick or concrete.’

Back then, industrial waste was often used in building materials. ‘And in such waste, you get an accumulation of toxic and radioactive components.’ Simply following international procedures and increasing ventilation in the crawl spaces wouldn’t help.

‘There was a company that installed a special foil that was supposed to stop radon seeping from the crawl space. They advertised this stuff; they still do. But our measurements showed that it didn’t make any difference at all. We concluded that the best way to reduce radiation from radon was to increase the air pressure inside the house.’


Overpressure reduces the speed at which the radon seeps from the building materials. ‘Radon has a short half-life, just a couple of days. So just keeping it inside the building materials for a short while will mean most of it will decay into non-volatile decay products.’ By adjusting the active ventilation systems installed in most modern houses, enough overpressure can be created to neutralize the radon problem.

But builders didn’t like the solution, for reasons unknown to De Meijer. ‘In the end, the government made a covenant with the building industry to maintain radon levels at the rates found in the 1980s. So now the RIVM periodically checks a number of houses.

Rob de Meijer
Rob de Meijer

De Meijer, who retired from the University of Groningen in 2005 but is still working on several projects and is a professor by special appointment at University of the Western Cape, South Africa, thinks the new radon/thoron project must be part of the covenant with the building industry. ‘In many cases, industrial waste has been replaced in building materials by cleaner alternatives. But with the current emphasis on recycling, there is a danger that more waste will be used in building materials. There is also a tendency to reduce ventilation to prevent heat loss. Both could increase the amount of radon in a house.’

De Meijer’s initial measurements didn’t include comprehensive data on thoron. ‘Thoron is also a product of uranium decay, but it has a very short half-life, just minutes. Although it was deemed less of a risk, it can still cause problems.’

And the overall risk of radon and thoron should not be underestimated: ‘We calculated that there may be 800 to 1,500 deaths from radon-induced lung cancer a year in the Netherlands. And recent risk estimates have arrived at similar figures.’

Cover of the book on radioactivity
Cover of the book on radioactivity

So, should we be worried? That’s a difficult one, according to De Meijer. ‘The risk is real. On the other hand, if you smoke your risk of lung cancer is already ten times higher, so in that case it is a waste of time to be worrying about radon. But then again, we humans suffer most from the fear of what might happen.’ And, he adds, simply creating a bit of overpressure in your house will reduce the radon and thoron risk significantly.

When De Meijer restored his 19th century farmhouse near Roden (not the house where the initial radon measurements were made) he installed a modern ventilation system capable of creating overpressure. ‘But I’ve never switched it on. There’s plenty of natural ventilation. And at my age, the small risk of radon is not particularly relevant.’

Several years ago, Rob de Meijer published a book on radioactivity, together with a colleague from the University of Groningen.

Last modified:06 October 2017 1.36 p.m.
View this page in: Nederlands

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