Radon

Full Profile

General Information

Radon is a naturally occurring radioactive gas found in several isotopic forms.^[2] It is produced from the natural breakdown of uranium in soils and rocks and is colorless, tasteless, and odourless.^[2] When radon decays it produces ionizing radiation as well as other species, which are referred to as radon daughters or progeny.^[3] Two radon isotopes are found at significant concentrations in the human environment, 222Rn and 220Rn (thoron).^[2] 222Rn is the most important isotope of radon because 220Rn has a very short half-life.^[2]

Radon and its decay products are found ubiquitously in air, water, and soil. Radon may also be referred to as alphatron or nitron.^[4]

Radon has been classified by IARC as Group 1, carcinogenic to humans, with a well established link to lung cancer.^[4] A recent IARC review of Class 1 carcinogens reaffirmed this classification.^[21] Although the decay products of radon cannot penetrate the skin, they can be inhaled, where they can damage bronchial and lung tissue leading to respiratory cancers in the lung, trachea and bronchi.^[3]

Several epidemiological studies have shown a causal relationship between occupational exposure to radon gas at high doses and an increased incidence of lung cancer.^[2] Concurrent exposure to radon and cigarette smoke has been shown to have a synergistic effect on the development of lung cancer.^[5,6]

In Canada, radon is estimated to account for ~10% of lung cancer deaths every year.^[7] In 1997, it was estimated that 1,589 Canadian deaths from lung cancer were attributable to radon.^[8] In 2006, the National Cancer Institute of Canada estimated 10,700 men and 8,600 women died from lung cancer, 10% of which may have been caused by radon exposure (>2,000).^[9]

Radon has been ranked by CAREX Canada for both the occupational and environmental settings as Group A (immediate high priority). Prioritization was based on the carcinogenicity and other toxic properties of the substance, the prevalence of exposure in Canada, and the feasibility of assessing exposure.

Regulations and Guidelines

Occupational Exposure Limits (OEL)

Canadian Jurisdictions	OEL
Canada Labour Code	Not listed
BC, AB, SK, ON, QC	Not listed
NT, NU	4 WLM/year*
YT	ALARA
Other Jurisdiction	OEL
ACGIH 2011 TLV	Not listed

Canadian Environmental Guidelines

Jurisdiction	Limit	Year
Government of Canada Radon Guideline	200 Bq/m3	2009[10]

Main Uses

Radon has no significant industrial purpose, but it is produced in small quantities for research purposes where it is used to initiate and influence chemical reactions.^[2]

Radon was used historically for the treatment of ulcers, allergies, arthritis, and tumours.^[2] It continues to be used today for therapeutic purposes in some European countries, providing pain relief from rheumatoid arthritis.^[11,12]

Occupational Exposures

Inhalation is the most important route of occupational exposure.^[3]

Radon in groundwater, soil, or building materials may enter the working environment and then decay, emitting ionizing radiation.^[4] Levels of radon in confined spaces or underground (e.g. basements) are often elevated above outdoor air levels.^[3] The highest exposed workers are those involved in underground mining, especially for uranium.^[2] Other workers who spend time underground (i.e. subway and utility tunnel workers) are also at increased risk in areas where radon is present. Indoor workers of any type may also be exposed, especially if they work in areas and rooms with higher concentrations of radon (e.g. basements).

Other occupations with the potential for exposure to radon include remediation workers (especially of mine sites), phosphate fertilizer producers, researchers who use radon, and construction excavators.

There is little information available on radon occurrence in Ontario workplaces. Although there are no active uranium mines in Ontario, radon exposure may occur in underground gold mines found in the province.^[13] In 1998, high levels of radon were associated with propane production in British Columbia, with concentrations reaching as high as 4,958 Bq/m³.^[14]

Occupational radon exposure is measured by the Radiation Protection Bureau of Health Canada. This data is held in the National Dose Registry (NDR) and contains exposure data for radiation exposed workers over time from across Canada.^[15]

Environmental Exposures

The most important route of exposure to radon for the general population is inhalation. Exposure via ingestion of drinking water is possible, but inhalation is expected to be much more important.^[3]

Radon accounts for approximately half of the annual worldwide average background effective dose of radiation, at 2.4 mSv.^[4]

Environmental radon concentrations vary with geology and soil characteristics.^[3] The highest concentrations are found in areas with uranium and thorium ore deposits and granite formations.^[3]

In Canada, radon can be found in public buildings, hospitals and new and older homes.^[8] It is more common in older buildings, where foundation cracks or other pathways for radon entry are more likely. Most Canadian homes contain some level of radon gas. Indoor levels are significantly higher than outdoor but can vary depending on building structure, sealing and ventilation.^[8]

The average level of radon in outdoor air in Canada is 10 Bq/m³. However, levels can fluctuate and reach much higher concentrations in short periods of time.^[9] The average indoor concentration of radon is approximately 50 Bq/m³, and usually ranges between 30 and 100 Bq/m³.^[9,16]

Radon gas enters the home when air pressure inside the home is lower than in the soil.^[17] This pressure differential draws air through cracks, drains, and utility penetrations from the soil and into the home.^[8] The most effective method for decreasing this pressure differential is active soil depressurization, which involves installing a fan and vent pipe in the basement floor which acts to reverse the air pressure flow.^[8]

Radon levels in homes vary across seasons. The highest levels usually occur in winter because windows are kept closed in cold weather, decreasing ventilation. Radon levels can change significantly in 24 hours (by a factor or 2 or 3).^[8]

In 1992 in a survey of BC schools, 48 schools were founds to have radiation levels >150Bq/m³, and 5 schools were found to have levels >750Bq/m³.^[18] Since 1992, most schools that required corrective action have now done so, with the BC Center for Disease Control (CDC) attempting mitigation for all schools with radon concentrations above 200 Bq/m³.^[18]

Radon can also be found in groundwater. In Canada, there are a few communities that use private or small community wells. If radon is present in the area, when this water is agitated through showering, clothes washing, and cooking radon could be released into the home.^[9]

In 2008, a radon map was created based on 6,016 measurements from locations all across Canada.^[19] The resulting map suggests the highest levels of radon in Canada are in Central and Atlantic Canada.^[19] 5 of 52 health regions had more than 20% of dwellings with radon levels above the Canadian guideline.^[9] 8 of 52 health regions had 10-20% of dwelling requiring remedial measures to control radon entry into the home.^[9] These results are incomplete as radon data is missing from more than half of the health regions included.^[19]

On average, Canadians receive a typical yearly dose of about 1.0mSv from inhalation of radon progeny. This dose varies greatly across the country according to the geological composition of the area.^[16] In Vancouver the average dose is 0.2 mSv/year, but in Winnipeg it is 2.2 mSv/year.

Strategies to increase awareness of radon remediation measures among homeowners have been developed and include education, cost-sharing incentives and real-estate disclosure procedures.^[20]

Sources

1. Wikimedia Commons Photo: Radon
2. NTP 12th Report on Carcinogens for Ionizing Radiation (2011) (PDF)
3. ATSDR Toxicological Profile for Radon (2008) (PDF)
4. IARC monograph summary, Volume 78 (2001)
5. EPA: Radon Health Risks
6. Canadian Cancer Society. Radon Exposure and Lung Cancer (2008)
7. Copes, R., and Scott, J. (2007), ‘Radon Exposure, Can we make a difference?’ Canadian Medical Association Journal, Vol. 177, No. 10, pp. 1229-1231
8. Report of the Radon Working Group on a New Radon Guidelines for Canada (2006) (PDF)
9. Health Canada & the Canadian Mortgage and Housing Corporation: Radon: A Guideline for Canadian Homeowners (2007) (PDF)
10. Health Canada: Government of Canada Radon Guideline (2009)
11. Falkenbach, A., et al (2005). ‘Radon therapy for the treatment of rheumatic diseases—review and meta-analysis of controlled clinical trials.’ Rheumatology International, Vol. 25, No. 3, pp. 205-210
12. Franke, A. et al (2000) ‘Long-term efficacy of radon spa therapy in rheumatoid arthritis—a randomized, sham-controlled study and follow-up,’ Rheumatology, Vol. 39, pp. 894-902
13. McGregor, R.G., et al. 1980, ‘Background Concentrations of Radon and Radon Daughters in Canadian Homes,’ Health Physics, Vol. 32, No. 2, pp. 285-289
14. Van Netten, C. et al, 1998, ‘Radon-222 and gamma ray levels associated with the collection, processing, transmission, and utilization of natural gas’ American Industrial Hygiene Association, Vol. 59, No. 9, pp. 622-628
15. Health Canada: ‘What is the National Dose Registry?’
16. Canadian Guidelines for the Management of Naturally Occurring Radioactive Materials (NORM), October 2000 (PDF)
17. Health Canada: It’s Your Health (Radon) (2007)
18. WorkSafeBC: Radon in British ColumbiaWork Places (2009)(PDF)
19. Chen, J. et al (2008), ‘A Preliminary Radon Map for Canada According to Health Region,’ Radiation Protection Dosimetry, Vol. 130, No. 1, pp. 92–94
20. National Collaboration Centre for Environmental Health, Radon Testing and Remediation Programs: What Works? (2008) (PDF)
21. IARC Monograph Volume 100: A review of human carcinogens—Part D: radiation (2009)
22. Atomic Energy Control Regulations (1992) (PDF)

Other Resources

1. Health Canada: Radon Frequently Asked Questions
2. National Research Council Canada: Radon
3. Health Canada: 2007 Report on Occupational Radiation Exposures in Canada
4. Natural Resources Canada: Geological Survey of Canada: Radiation Geophysics
5. Radiation Safety Institute of Canada
6. WHO Fact Sheet No. 291: Radon and Cancer (2005)
7. Brand, K.P., et al (2005). ‘Residential Radon in Canada: An Uncertainty Analysis of Population and Individual Lung Cancer Risk,’ Risk Analysis, Vol. 25, No. 2, pp. 253-269 (17)
8. Environmental Protection Agency: Radon
9. Canadian Cancer Society: Indoor Radon Exposure