Forty years after Canadian and Swedish homes were found to have comparable levels of radon gas, a new University of Calgary study suggests radon levels in recent builds in Canada now far exceed their Swedish counterparts — by 467 per cent.
Inhalation of the radioactive gas is the leading cause of lung cancer in non-smokers, and about 3,200 Canadians die from exposure each year, according to Health Canada.
And without intervention, say the team of cancer researchers and Canadian architects behind the U of C study, the average radon level of a new Canadian home will increase another 25 per cent over current levels by 2050.
Those levels are already the third-highest in the world.
"In most regions, [Canadian radon] has gone up, while Swedish radon has systematically gone down," said Aaron Goodarzi, an associate professor at the University of Calgary's Cumming School of Medicine.
And now, the researchers are trying to find out why.
"It is probably a complicated mergence of just the way we as Canadians build our houses, the way we heat our houses — which is actually quite different from the way the Swedes do it — as well as the uniqueness about Canadian behaviour," Goodarzi said.
Odourless, tasteless, naturally occurring
Goodarzi is also the scientific director of the Evict Radon National Study, a Canada-wide initiative that seeks, in part, to educate Canadians about the harmful effects of radon.
Odourless, tasteless and naturally occurring, radon gas is created from the decay of uranium in minerals found in rock, soil and water, according to Lung Cancer Canada.
It's also present in all indoor environments — but by how much is a key factor when evaluating its safety.
"One in five Canadian houses exceed 200 bq/m3," Goodarzi said. "Now, that's what Health Canada sets as the maximum tolerated radon exposure limit — you start to see a cancer risk at 100."
For their study, the U of C researchers said they chose to compare radon levels in Canada with those in Sweden because the Nordic country has similar climates, as well as data on the subject that goes back decades.
In the 1950s, Swedish properties actually exceeded Canada's houses in radon levels, Goodarzi said. This levelled off around in the 1980s, when the two countries were about the same.
For the more recent study, teams from across Canada analyzed long-term radon tests and buildings from more than 25,000 Canadian and 38,000 Swedish residential properties constructed since the Second World War.
Now, the radon picture is much different — higher across all provinces and territories in Canada — and Goodarzi said there are factors that could be exacerbating the problem.
"You have to have a [radon] source in the ground, while both Sweden and Canada have the source — the geology that hasn't changed," he said.
"You [also] need the type of property that captures, contains and concentrates it."
Radon no longer a winter problem
While Goodarzi said the researchers are not yet 100 per cent sure why Canada has seen such an increase in radon over Sweden, one difference between the two countries is the way homes are heated.
"Throughout most of Canada … 50 to 90 per cent of houses are heated with forced ventilation based on a natural gas furnace. Well, in Sweden, it's less than 10 per cent [that] use that same technology," he said.
Another factor that promotes radon exposure is human behaviour, Goodarzi said — and some examples are as simple as whether or not someone opens their windows.
"If you don't have air conditioning or you don't use yours, [and] instead you prefer to open the windows and doors, you're going to have lower radon in summer than you might if you turn the air conditioning on and had everything closed," Goodarzi said.
"[And] due to the way Canadian houses mix their air, there's really very little difference [in radon] between the basement and the upper floors."
Climate change could also be making a measurable difference, he said, and rendering radon a summer problem instead of just a winter one.
"Forest fire smoke prevalence, which is increasingly a problem for Canadian cities, means that our houses in the summer are operating very much like they do in the winter," Goodarzi said.
"The air outside is too toxic for us to have the windows and doors open."
'We can't afford to wait'
Joshua Taron, the associate dean of research and innovation with the School of Architecture, Planning and Landscape at the University of Calgary, was involved with the study.
He says that prevalent and unsafe radon levels are "rooted in the design of our built environment."
The research is urgent, he says, so that people can become more aware of the impact of their own homes on their health.
As a whole, the team is calling for proactive radon mitigation systems to be included in all new residential properties that are constructed using the 2025 building code.
"Today in Canada, you can ask a professional to come to your house and they'll retrofit your house with the mitigation. It's relatively fast, one to two days' work, relatively inexpensive and very effective," Goodarzi said.
"The idea, though, is we don't retrofit houses. We build them immune to radon in the future."
And they feel there isn't a lot of time to waste.
The researchers behind the study say that lung cancer rates in Canada are 163 per cent higher than in Sweden, despite smoking rates being essentially the same.
"We can't afford to wait," Goodarzi said.
"The lives of tens of thousands of Canadians are on the line here, not to mention tremendous amounts of health-care dollars that we will never need to spend if we work towards prevention today."