Preliminary results from a Health Canada survey suggest that seven per cent of Canadian homes contain elevated concentrations of radioactive radon gas, which can cause cancer.
Health Minister Leona Aglukkaq said people should have the air in their homes tested for radon.
"You can't see it, smell it or taste it," she said Tuesday. "The only way to know if you have a radon problem is to test your home."
The findings from the first year of a two-year project found that New Brunswick, Manitoba, Saskatchewan and Yukon had the highest percentages of homes with radon levels above the national guideline.
The national limit is 200 becquerels per cubic metre of air.
In New Brunswick, 11.7 per cent of homes had levels between 200 and 600 becquerels and 5.3 per cent had levels above 600 becquerels.
In Saskatchewan 14.2 per cent were in the first elevated level, with 1.6 per cent above 600.
In Manitoba, the survey found 22.1 per cent of homes with levels between 200 and 600 and 1.4 per cent over 600.
Yukon had 10.6 per cent between 200 and 600 and 5.3 per cent over 600.
In contrast, Ontario had only 4.9 per cent of homes with any elevated level and Quebec had nine per cent. There were no homes found with elevated radon levels in Nunavut.
The survey looked at 9,000 homes in the first year, with 9,000 more to be tested in the second year.
Colourless, odourless gas
Radon is a colourless, odourless gas produced by the natural decay of uranium in rocks and soil. If it is released into the atmosphere, it quickly gets diluted and is harmless.
But if it seeps into homes, it can concentrate, especially in winter, when houses tend to be sealed up against the cold.
Radon is suspected as the culprit in hundreds of lung cancer deaths, said Heather Borquez, president and CEO of the Canadian Lung Association.
"Last year, lung cancer claimed the lives of 20,500 Canadians," she said. "It's estimated that about 10 per cent of lung cancer deaths are related to long-term exposure to residential radon."
She urged home testing as well.
Health Canada suggests that homeowners check radon levels with test kits available at some hardware stores or through the Internet.
The test devices are deployed for a minimum of three months during cold weather. If levels are high in a home, there are remedies, Health Canada said.
Some problems can be solved simply with better ventilation. Sealing cracks in foundation walls and floors and around pipes and drains can also help.
There are also systems that use a fan and piping to draw the radon from under the home and expel it outside.