An estimated 500,000 Canadians are living in homes that exceed pending new federal guidelines for radon gas, a naturally occurring radioactive substance described by health officials as a quiet killer and the leading cause of lung cancer after smoking, The Vancouver Sun has learned

New research into the health risks associated with radon gas -- a byproduct of the decay of uranium in soils and rocks that can accumulate at dangerous levels in homes -- is prompting Ottawa to significantly lower the threshold at which homeowners should take remedial action to reduce the risk.

"After careful study, considering all the options, we came to the conclusion that, yes, it is indeed time to lower the guideline," Bliss Tracy, head of radiological impact for Health Canada, said in an interview.

Radon hot spots include Winnipeg, Nova Scotia, and B.C.'s Interior, where an estimated 60,000 residents live in homes that pose an unacceptable risk of lung cancer.

The B.C. Centre for Disease Control confirms "there are thousands of British Columbians blissfully unaware that their homes could be slowly and quietly killing them."

Health Canada estimates radon gas kills 2,000 people annually in this country, more than fires, drownings, air crashes, and accidental poisonings combined, and one-tenth of the estimated 20,000 radon deaths in the U.S.

Canada is poised to lower the guideline for radon gas in homes to 200 becquerels per cubic metre from 800 becquerels (a measurement of radioactivity), which means that thousands of homes that would have been considered safe are now viewed as a potential source of lung cancer.

For the relatively few Canadians who are aware of radon gas and have tested their homes for it, elevated readings can have a traumatic effect. "Oh God, now what?" is how Craig Besinque, a school bus driver from New Denver in B.C.'s West Kootenay region, responded. "We were pretty frightened."

He spent about $700 on supplies and did his own remedial work on his house, including sealing openings in the basement and installing a ventilation fan, and is now retesting with fingers crossed. "It's horrible to think your house has radon," added his wife, Lane Heywood, a retired teacher. "There are a lot of bad things to think about."

The World Health Organization estimates radon causes up to 15 per cent of lung cancers worldwide. An estimated 22,700 Canadians last year were diagnosed with lung cancer, one of the deadliest forms of cancer. The five-year survival rate for lung cancer is about 14 per cent, the B.C. Cancer Agency reports.

Health Canada has maintained the 800-becquerel guideline since 1988, but says new research showing a stronger link to lung cancer has prompted the change to 200, with support of the provinces and territories.

Officials estimate that people spending 75 per cent of a lifetime (of 70 years) inside a home with a main floor radon concentration of 800 becquerels have a one-in-10 chance of developing lung cancer from radon gas.

A comprehensive scientific study, published in Epidemiology in 2005 and entitled Residential Radon and Risk of Lung Cancer, found "direct evidence of an association between residential radon exposure and lung cancer."

The study examined radon studies in regions as widespread as North America, Europe and China, and incorporated the results of lab research, including experiments on animals, and studies of underground miners.

Individuals who test for radon and remediate their homes, however, can relatively easily reduce the risk to acceptable levels.

A Canadian scientific radon working group that settled on 200 becquerels observed in a report that Canada's longstanding guideline of 800 becquerels was the highest of westernized countries after Switzerland and "diverges greatly from those applied by the majority of countries."

Countries such as Australia, Spain, and the United Kingdom already have a standard of 200 becquerels. The U.S. has the lowest of all at 150 becquerels, a guideline adopted in 1986 and described by the Environmental Protection Agency as "a balance between health protection and what is technically feasible."

All of which raises the question: Should Canada have acted sooner to lower the radon guideline?

Tracy responded from Ottawa that the federal government did not have solid enough evidence to support the lower guideline and did not want to frighten Canadians into making unnecessary improvements to their homes.

"Before you impose a heavy burden on the homeowner, make sure there really is a hazard," he said.

"Now, we've concluded, yes, indeed, it is a hazard."

Acknowledging the U.S. seems to have taken the right course years ago, Tracy said: "They were applying the precautionary principle -- when in doubt, pick a low level. They seem to have had some foresight, yes."

A National Research Council report for the Environmental Protection Agency said that while eliminating all radon is not feasible, an estimated one-third of radon-induced lung cancers could be avoided if homes met the guideline of 150 becquerels.

Some suggest not nearly enough has been done in Canada to reduce the radon risk.

"When you compare us to the worldwide scale, it's pretty shocking how long we went with such high levels," said Erik Stout of Fernie-based Rocky Mountain Inspections, a company that specializes in testing radon in homes.

He called for greater public awareness about radon gas, noting "most people don't know what it is. Half the challenge is explaining it to people. They're not very responsive to it."

Bill Lynch, owner of a building inspection company in Nelson, urged more government testing and education to help people become aware of the problem and to remove the stigma associated with a positive test.

"We need a much more thorough study," he said, urging that special attention be paid to smaller communities. "We just don't have enough information."

Health Canada estimates three per cent of homes in this country exceed the 200-becquerel guideline, an estimate based on a cross-country survey of 17 cities close to 30 years ago. That study occurred in summer, when radon levels are lowest.

The Sun generated the estimate of 500,000 Canadians at risk by using 2001 federal census figures showing 6.6 million single-detached homes in Canada and an average 2.5 persons per home.

"I wouldn't dispute that figure," said Tracy, noting it is a rough assessment showing the magnitude of the health risk facing Canadians from radon gas exposure. "It could be lower or higher."

Dave Morley, head of environmental radiation assessment for the B.C. Centre for Disease Control, said radon is a bigger issue in B.C. generally than in the rest of Canada because of the presence of uranium and the location of population centres within those uranium areas.

He added B.C. has also done more to investigate the issue than other areas of Canada that have radon.

In B.C., provincial health officials and the University of B.C. searched for high radon levels around the province 10 to 15 years ago. Those studies identified the Clearwater, Barriere, and Castlegar areas as hot spots, with elevated readings also found in Prince George, the Okanagan, and elsewhere in the Kootenays.

Radon levels are below both new and old federal guidelines in major cities such as Toronto and Vancouver (along with other areas of the B.C. coast, including Victoria). The province's northeast, including Fort St. John, is also low.

Schools found to have high levels in the Interior in the 1990s were remediated. The Interior Health Authority is now doing follow-up testing in homes between Barriere and Blue River, including Clearwater.

Kamloops, immediately to the south, is not affected because its clay soils act as a buffer to passage of radon gas.

"If your septic field works well, they have a potential for radon problems," said Morley.

Canadians living in known radon hot spots, especially those with porous soils, are urged to test for radon gas and take remedial action on their homes as necessary to reduce the risk.

Radon test kits are available on the Internet for less than $50 and are completed over three to six months during winter, when doors and windows are closed and radon levels are highest.

Remediation options, costing from a few hundred to a few thousand dollars, include sealing cracks in concrete floor slabs, fitting airtight covers on sumps, installing special traps in basement drains, covering over exposed soils, and installing a ventilation system to move the radon outdoors.

Officials are concerned there might not be enough tradespeople available and with the necessary knowledge to conduct remedial work on homes for residents unable to complete the work themselves.

Radon gas is odourless, colourless and tasteless; like smoking, it can take many years of radon inhalation to damage lung tissue at the DNA level and result in cancer.

"Radon is not a drop-dead-tomorrow situation," said Brian Phillips, director of radiation protection services for the B.C. Centre for Disease Control. "It's a lifetime health risk."

Residents of radon hot spots should take the issue seriously, he said. "People need to be paying attention to this one. They must make an informed judgment."

Some people may not want to test for radon for fear that their property values could suffer. But homes located in hot spots do not necessarily have excessive radon levels.

Sometimes two homes situated side by side can have dramatically different readings, based on soils and house construction. Unless people conduct a test, they have no way of knowing whether they are affected or not.

"It can be difficult to persuade someone to do the testing, even if you supply the monitor," Morley said. "A lot of people don't want to know. They're not interested in dealing with the problem."

Federal Health Minister Tony Clement is expected to approve the new federal guideline soon. In the meantime, an intergovernmental committee is working on an implementation plan.

The guideline is not a formal regulation, meaning it's up to each province and territory to decide how to apply it.

B.C.'s representative on the committee, Phillips, said the new guideline could have implications for building codes and real estate transactions.

Ultimately, it is up to individual homeowners to assess their relative level of risk, he added.

Seniors might not think it's worth spending the money given their advanced years and the time it takes to potentially develop lung cancer. Younger families who plan to stay long-term in their home would be more inclined to pay for remediation than a family that planned to stay only a few years and move on.

"At the end of the day, homeowners are responsible," Phillips said. "It's a personal risk."

Uranium mining, which occurs in Canada only in northern Saskatchewan, is not generally to blame for radon gas seeping into homes. An exception is Oka, Que., where radioactive tailings from an old niobium mine has been blamed on elevated readings in homes, said Tracy.

Dave Lefebure, chief geologist with the Ministry of Energy, Mines, and Petroleum Resources in Victoria, said low levels of uranium are found in granitic rocks throughout B.C. Only in certain areas are these background levels sufficient to cause radon gas problems in homes.

He said B.C. has never had a uranium mine, and not a lot of exploration activity.

International Ranger Corp., involved in uranium exploration activity above the rural community of Birch Island, north of Clearwater on the North Thompson River, was hit with a cease-trade order last summer by the B.C. Securities Commission for its reporting and promotion of claims in news releases.

RADON 101:

What is radon gas?

A naturally occurring radioactive substance produced by the decay of uranium in soil and rocks.

What does it do?

Radon gas can seep into homes through basement cracks. Inhaled at high levels over many years, the gas can damage lungs at the DNA level, potentially leading to cancer.

How serious is the threat?

Radon is the leading source of lung cancer after smoking and is estimated to kill 2,000 Canadians every year.

How do I know if my home is at risk?

Radon test kits are available over the Internet for less than $50. The tests take three to six months to complete.

What if I get an unacceptably high reading?

Remediation options range from sealing cracks and drains in basements to installation of ventilation systems.

Is the remediation work costly?

That depends on how handy you are around the house. Costs typically range from a few hundred to a few thousand dollars.

Will radon lower my property values?

That depends on individual buyers. Some might be scared off, whereas others might feel more comfortable knowing the owner has looked for radon and, where applicable, done the remediation.

WHERE TO GO FOR FURTHER INFORMATION:

- B.C. Centre for Disease Control, http://www.bccdc.org/content.php?item=69

- Health Canada, http://www.hc-sc.gc.ca/iyh-vsv/environ/radon_e.html

- Canada Mortgage and Housing Corp., http://www.cmhc-schl.gc.ca/en/ and search for radon

- U.S. Environmental Protection Agency, http://www.epa.gov/radon/index.html

- Natural Resources Canada, http://gsc.nrcan.gc.ca/gamma/radon_e.php

- The Canadian Centre for Occupational Health and Safety, http://www.ccohs.ca/oshanswers/phys_agents/radon.html

- Radon Information Centre, http://www.radon.com/, 1-800-AIR-CHEK