Radon is a ubiquitous, naturally occurring radioactive gas that comes from the decay of uranium, which is distributed throughout soil and rocks in Canada in varying concentrations. Although radon receives little public attention, it is one of the most toxic sources of indoor air pollution in Canada. Recent studies have established that radon is the second most important cause of lung cancer after smoking, accounting for 9 to 15 percent of lung cancer deaths.
The report Radon: The Unfamiliar Killer was prepared as a series of recommendations for strengthening Canada's radon guideline, which was the weakest in the industrial world prior to being updated in June 2007. The new Canadian guideline for radon is 200 becquerels per cubic metre (Bq/m³).