Why researchers say lowering Canada's radon limit could prevent more cases of lung cancer and save lives

When Maureen helen hayes number one tried her capital of canada place for radon a little over a year ago, the initial reading was far below Canada's current threshold to take action.

Her device showed 114 becquerels per cubic metre (Bq/m³), well under the 200 Bq/m³ guideline for hiring a radon professional, according to Health Canada's guidance. 

But Hayes soon realized the country's recommended limit for this invisible, cancer-causing radioactive gas is actually double that of the World Health Organization (WHO). And as she kept testing, she saw her home's levels hit 180 Bq/m³ and beyond — still under Canada's threshold yet firmly above the WHO's guideline.

Hayes was concerned — and confused. "The government issues these guidelines," she said, "but they're different internationally."

The current standard is "failing to protect Canadians" who live in buildings that exceed a level that the WHO considers safe, said health policy researcher Lisa Gue, who works as the national policy manager for the David Suzuki Foundation, an environmental advocacy non-profit.

"Canada's radon guideline is due for an update," she said. "Having a higher guideline can lead to some complacency and prevent remedial action, when it would be cost effective to [lower it] and have clear health benefits."

The cancer-causing gas hiding in millions of homes

The country's radon guideline was last updated in 2007, dropping the threshold way down to 200 Bq/m³ from the prior cutoff of 800 Bq/m³. (The measurement of Bq/m³ refers to the amount of radioactive radon gas present in a volume of air.)

Given low radon testing rates in Canada, the department said its focus is raising awareness and getting every Canadian to test, "rather than redefining the action level."

But Gue, who authored a 2015 report on the country's last radon guideline update, said it was essentially outdated from the get-go and muddles the messaging on what level of radon poses a danger.

"Unfortunately what we found was that, just as the Canadian standard was being finalized, new research was coming to light that really put a finger on the extent to which higher levels of radon exposure were a significant risk to population health," she said.

There's scientific consensus that long-term exposure to indoor radon can cause lung cancer, with a growing body of global studies over the last two decades showing clear links.

The WHO launched an international radon research project in 2005, and by 2009, the health body officially recommended that countries aim for a national reference level of 100 Bq/m³, and "wherever this is not possible, the chosen level should not exceed 300 Bq/m³." (Guidelines vary among countries, with some European nations still using thresholds as high as 300-400 Bq/m³.)

That 2009 report cited pooled data from more than a dozen countries across Europe which showed the relationship between radon exposure and lung cancer risk was roughly linear, with risk rising by 16 per cent for each additional 100 Bq/m³ of radon in someone's home. 

Lung cancer is the deadliest form of cancer in Canada, with roughly 30,000 cases per year and close to 20,000 of those resulting in death. It rarely shows major symptoms early on, and is often caught far too late, when the cancer has spread beyond the lungs. Radon exposure is responsible for an estimated 3,000 of those deaths, making it the second-leading cause of lung cancer after smoking.

One Canadian study published more than a decade ago estimated that, at the current Canadian guideline, more than 900 lives could be saved each year if all homes above the threshold reduced their indoor radon level to the same safe, heavily-diluted concentration as outdoor air. 

An additional 700 lives would be saved annually if all homes above the WHO's threshold were mitigated, the authors wrote.

"It is correct that fewer people would have negative health outcomes if the regulatory level is lower," said Anne-Marie Nicol, a toxicology researcher and associate professor at Simon Fraser University.

How to check for radon gas in your home

The 2024 Cross Canada Radon Survey suggests 20 per cent of detached homes in Canada may have radon levels higher than 200 Bq/m³, while another 26 per cent have levels between 100 and 199 Bq/m³ — meaning close to half of all detached houses could have radon levels above the WHO's guideline, along with plenty of other types of dwellings.

But that's changed. Health Canada says modern mitigation work can dramatically reduce indoor radon levels by more than 80 per cent when done correctly. 

"Now that we know it is possible," Nicol said, "there is a good argument for revisiting the guideline and reducing it [to 100 Bq/m³] in Canada."

Most radon mitigation systems involve a pipe installed in the home's foundation floor, along with a fan that draws radon gas from below the home and releases it safely outside before it ever has a chance to build up indoors. 

An update to Canada's national building code, released in late December, also requires newly built homes to include a passive radon stack, which acts like a chimney to help reduce indoor radon buildup. That update still needs to be adopted by the provinces.

Health Canada also emphasizes there is "no safe level of radon exposure" and encourages Canadians to "reduce radon levels as much as possible," the department said.

Its guidelines on indoor radon levels balance health risk reduction with socio-economic considerations, "recognizing that the burden of mitigating would typically fall to individual homeowners."

Nicol said more government assistance for cash-strapped families could encourage homeowners to install mitigation systems to reduce their risk, particularly as more Canadians already take advantage of energy efficiency grant programs for air sealing, insulation, and new windows and doors — home changes which can, in turn, actually trap more radon.

"It's a bit of a disconnect because public health is here, and the people that give the grants are over here," Nicol said.

Others say to better tackle the issue of radon, Canada still needs a more fulsome understanding of how the risks are evolving inside millions of homes before overhauling the country's approach.

The threshold of 200 Bq/m³ was selected in an era of "exceptionally clean air" compared to many other countries, said Aaron Goodarzi, one of Canada's leading radon researchers, "but of course it's changing with time and climate change and the prevalence of wildfire smoke."

Goodarzi's team has been studying radon exposure in individuals, and the next phase of their research will also track indoor air quality to determine the added impact of increasingly common wildfires — since radon gas appears to hitch a ride on smoke particles, whether it's from a fire or a cigarette. 

"I always think of the particulate matter as the taxi that drives the radon into your lungs … the dirtier the air, the greater the dose from the radon," said the University of Calgary professor and scientific director of the Evict Radon National Study.

Based on the team's research to date, Goodarzi expects to see heightened risk of radon-induced health issues when non-tobacco sources of smoke are factored in. 

"But we need to understand that," he said. "And from there, perhaps that's when the conversations about shifting the guidance happen in a more informed way."

Senior Health & Medical Reporter

---

---