The Thunder Bay District Health Unit says it will expand radon testing in homes to two other communities in the Thunder Bay area next year.

Radon is a naturally-occurring gas, but it can be dangerous, said Lee Sieswerda, the manager of environmental health for the health unit.

"It's invisible, people don't see it," Sieswerda said. "So, they're breathing it in, and if they breathe in enough of it — if their home has a high enough concentration of radon — they're at risk for lung cancer."

Public health officials have estimated 16 per cent of homes in the city have radon levels above the threshold considered safe by Health Canada. That is "well above" both national and provincial averages, Sieswerda added.

"Radon is a radioactive gas and the only thing about radon that causes us problems in a sense in terms of public awareness is that it's colourless and odourless,"  he said.

The health unit made radon testing kits available in Thunder Bay in 2014, while Health Canada also held its own information session in the city two years ago.

At a September, 2016 board of health meeting, $10,000 was officially earmarked to carry out testing in two other communities within the health unit's coverage area, which stretches from Upsala, Ont. east to Manitouwadge. That's expected to start in 2017.

The initiative will include the distribution of testing kits, Sieswerda said.

He said he hopes to have the two communities chosen by the end of this year.

With files from Matt Prokopchuk. Edited/packaged by Casey Stranges