Radon is a colourless, odourless, radioactive gas that can cause lung cancer. It can be found all over Ontario in buildings such as homes, schools, and offices.
Lung Cancer Risk from Radon in Ontario, Canada: How many lung cancers can we prevent? quantifies the burden of illness associated with radon in Ontario. According to the calculations 13% or almost 850 lung cancer deaths each year in Ontario are attributable to radon. It was also found that these estimates vary by health unit across the province.
(From Public Health Ontario)