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Middlesex-London Health Unit and Radon (from MLHU 2013)

What is radon?

“Radon is a radioactive gas found naturally in the environment. It is produced by the decay of uranium found in soil, rock or water. Radon is invisible, odourless and tasteless and emits ionizing radiation.”1

Why is radon a concern?

“As a gas, radon can move freely through the soil enabling it to escape to the atmosphere or seep into buildings. When radon escapes from the bedrock into the outdoor air, it is diluted to such low concentrations that it poses a negligible threat to health. However, if a building is built over bedrock or soil that contains uranium, radon gas can be released into the building through cracks in foundation walls and floors, or gaps around pipes and cables. When radon is confined to enclosed or poorly ventilated spaces, it can accumulate to high levels. Radon levels are generally highest in basements and crawl spaces because these areas are nearest to the source and are usually poorly ventilated. In the open air, the amount of radon gas is very small and does not pose a health risk.”1 Visit Health Canada’s web page to view a picture of how radon enters a house.

What are the health effects of radon?

“When radon gas escapes from the ground outdoors it gets diluted and does not pose a health risk. However, in some confined spaces, like homes, radon can accumulate to relatively high levels and become a health hazard.”2 The only known health effect of radon is an increased chance of developing lung cancer.3Not everyone exposed to radon will develop cancer.3

Visit Health Canada’s web page to learn more about the health effects of radon.

Visit Public Health Ontario’s webpage for more information about the radon burden of illness in Ontario.

What is the Canadian guideline for radon?

The current Canadian guideline for radon in indoor air for dwellings should not exceed 200 Becquerel’s per cubic metre (Bq/m3).4

Is radon a concern in Middlesex-London?

A two year study from 2009-2011, conducted by Health Canada's National Radon Program, found that 98.2% of homes that were tested in Middlesex-London were in the acceptable range below 200 Bq/m3.5 If you are interested in further details of the study, view the Cross-Canada Survey of Radon Concentrations in Homes - Final Report.

What should I do if I am concerned about radon in my home?

“The only way to know if you have a radon problem is to test your home. If the radon level is high, take action to reduce it. The higher the level, the sooner it needs to be fixed.”2

How do I get my home tested for radon?

Testing a home for radon is easy and inexpensive. Health Canada2 recommends the following two options:

  • Buy a do-it-yourself radon test kit, or
  • Hire a professional radon measurement service provider (See - find a radon measurement professional such as me)

Visit Health Canada’s web page for more information on how to test for radon.

What should I do if I find a radon problem?

Health Canada  recommends you take the following steps to reduce radon in your home if it is found to be a problem:

  • Increase the ventilation to allow an exchange of air.
  • Seal all cracks and openings in foundation walls and floors, and around pipes and drains.
  • Renovate existing basement floors, particularly earth floors.

Additional Information

For more information on radon, visit Health Canada’s Radon website.

View Health Canada's Indoor Air Quality Checklist (PDF 307KB) for steps you can take to protect yourself and your family from indoor air pollutants, including radon gas.

To speak to a Public Health Inspector on the Environmental Health Team about radon, please call:

  • 519-663-5317 ext. 2300


Please note: Where indicated, the source of the information on this web page is from Health Canada’s web pages on "Radon", "What is Radon?", "What are the Health Effects of Radon?", "Government of Canada Radon Guideline", or the "Cross-Canada Survey of Radon Concentrations in Homes - Final Report". The information is a copy of an official work of the Government of Canada and has not been provided in affiliation with, or with the endorsement of the Government of Canada.

Date of creation: June 7, 2013

Last modified on:  April 2024


  • ↗Health Canada - Cross-Canada Survey of Radon Concentrations in Homes
  • Health Canada - Indoor Air Quality Checklist(PDF 307KB)

Related Content

  • Health Canada - What is Radon?
  • Health Canada - What are the Health Effects of Radon?
  • Health Canada - Government of Canada Radon Guideline
  • Public Health Ontario - Radon Burden of Illness


1Health Canada. (2012, October 25). What is radon? Retrieved from

2Health Canada. (2012, October 9). Radon. Retrieved from

3Health Canada. (2009, September 25). What are the health effects of radon? Retrieved from

4Health Canada. (2009, November 24). Government of Canada radon guideline. Retrieved from

5Health Canada. (2012, March). Cross-Canada survey of radon concentrations in homes - final report. Retrieved from

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