Ionizing Radiation
Full Profile
General Information
Ionizing radiation consists of particles or rays emitted by natural and artificial radioactive materials, nuclear reactions, and radiation producing machines.[2] An atom is said to be radioactive when the number of neutrons within its nucleus is too small or too large for the number of protons, resulting in an unstable nucleus. Radiation particles and rays are defined as “ionizing” when they carry sufficient energy to knock out electrons from molecules (such as water, protein, and DNA).[2] For a list of isotopes and radioactive compounds, please refer to synonyms listed in HSDB.[7]
Ionizing radiation includes:
- X and gamma [γ] rays – packets of energy (photons) having neither charge nor mass. Generally classified as external hazards since they penetrate the skin and internal organs.[2,3,4]
- Alpha [α] and beta [β] particles - small, fast moving particles which are primarily an internal hazard when deposited in the body through inhalation, ingestion or injection.[3,5] They are carried by dust, suspension solutions or gases.[5]
Radiation dose is described in 3 ways:
- Absorbed dose – Given in Grays (Gy) – the amount of energy left behind when radiation passes through matter.[6]
- Equivalent dose – Given in sieverts (Sv) – absorbed dose multiplied by a radiation weighting factor dependent on the type & amount of radiation.[6]
- Effective dose – Given in sieverts (Sv) – equivalent dose multiplied by a tissue weighting factor, dependent on the sensitivity of a given tissue or organ.[6]
DNA is the most critical molecule for radiation damage, although other important cellular components are reported to be affected by exposure to radiation.[2] Overexposure to large amounts of ionizing radiation may result in health effects such as skin burns, hair loss, birth defects, cancer, mental retardation, and death.[2] Exposure to substantial amounts of ionizing radiation to a fetus during pregnancy may cause negative pregnancy and birth outcomes, such as miscarriage, birth defects, hereditary effects, and a higher risk of childhood cancer and cancer in adult life.[8]
Ionizing radiation has been classified by IARC in three separate monographs as Group 1, carcinogenic to humans: Vol. 75: X and gamma radiation, Vol. 78: alpha, beta and neutrons, and, most recently, Vol. 100D, part of a volume reviewing all Class 1 carcinogens.[3,5,23] Epidemiological evidence has confirmed a strong association between ionizing radiation and leukemia, as well as cancers of the thyroid, breast and lung.[4] The risk of developing cancer can be influenced by factors such as dose, dose rate, age, sex, genetics, lifestyle, environmental exposures and time post exposure.[3,4]
How did CAREX choose this agent for review?
For more information on radon, a naturally occurring radioactive gas, please refer to the CAREX Carcinogen Profile for Radon-222 & its decay products.
Regulations and Guidelines
Occupational Exposure Limits (OEL)
All nuclear facilities and devices, such as nuclear plants, medical radiation devices and uranium mines, are regulated federally by the Canadian Nuclear Safety Commission (CNSC).[11] The CNSC was established under the Nuclear Safety and Control Act in 2000 to replace the former Atomic Energy Control Board (AECB).[10] Under the Nuclear Safety and Control Act, the Radiation Protection Regulations established occupational exposure limits for ionizing radiation in Canada (shown in following table).[9] In exposure situations where the CNSC does not have jurisdiction, such as where radiation is used in health care settings, the provinces/territories are responsible for setting and enforcing occupational exposure limits for ionizing radiation.
Canadian Dose Limits for Exposure to Licensed Sources of Radiation[9]
| Population | Dose Limit (mSv) | Time Period and Type of Exposure |
|---|---|---|
| Nuclear energy worker | 50 | Annual effective dose |
| 100 | 5-year cumulative effective dose | |
| 4 | Effective dose during pregnancy | |
| 150 | Annual equivalent dose, to the lens of the eye | |
| 500 | Annual equivalent dose, to the skin, hands and feet | Non-nuclear energy worker | 1 | Annual effective dose |
| 15 | Annual equivalent dose, to the lens of the eye | |
| 50 | Annual equivalent dose, to the skin, hands and feet |
The American Conference of Industrial Hygienists (ACGIH) have also developed guidelines for exposure to ionizing radiation:
| Dose Limit (mSv) | Time Period and Type of Exposure |
|---|---|
| 50 | Annual effective dose |
| 100 | 5-year cumulative effective dose |
| 10 × age in years | Lifetime cumulative effective dose |
| 150 | Annual equivalent dose to the lens of the eye |
| 500 | Annual equivalent dose to the skin, hands and feet |
| 0.5 | monthly equivalent dose for embryo/fetus |
Canadian Drinking Water Guidelines[12]
| Naturally Occurring Radionuclides | MAC |
|---|---|
| Total uranium | 0.02 mg/L |
| Lead-210 | 0.2 Bq/L |
| Radium-226 | 0.5 Bq/L |
| Artificial Radionuclides | MAC |
| Tritium | 7000 Bq/L |
| Strontium-90 | 5 Bq/L |
| Iodine-131 | 6 Bq/L |
| Cesium-137 | 10 Bq/L |
Main Uses
Since the discovery of X-rays in 1895, ionizing radiation has been used medically for diagnostic examination and treatment of benign or malignant disease; it was used in 80-90% of all imaging procedures in 1996.[7] Diagnostic procedures using x-rays include positron emission tomography,[4] radiographic imaging (most widespread use), fluoroscopic imaging, and computed tomography.[4,7]
Ionizing radiation is used to examine welded joints in structures; it is also used in the oil industry to determine geological structures in bore holes.[4] Ionizing radiation may also be used to sterilize and preserve food products.[7]
Countries using nuclear power include Canada (17%), Germany (29%), Sweden (47%), and the former Soviet Union (42%).[2] In the military, materials and processes that emit x-radiation and gamma radiation are used for nuclear weapon production, testing and application.[4]
Sources of ionizing radiation may be found in various consumer products, such as smoke detectors, televisions and radioluminescent clocks and watches.[4]
Production and Industry
Canada opened its first Canada deuterium uranium (CANDU) reactor in 1971.[13] In Canada today, there are 18 operational commercial nuclear power reactors located in Ontario (16 reactors in 3 locations), Quebec (1 reactor), and New Brunswick (1 reactor).[13] Approximately 12 additional nuclear reactors are proposed for Ontario, Alberta and New Brunswick (operation projected to begin between 2014 and 2018).[13]
Canada is an international supplier of isotopes, including cobalt-60, heavy water, and tritium.[15] Canada is also currently the world's largest producer of uranium, accounting for 20.5% of world production in 2008 (9,000 tonnes); the majority of uranium production occurs at two Northern Saskatchewan mines.[16]
As of 2011, uranium production will increase with the opening of several new mines.[16]
Occupational Exposures
Inhalation, ingestion, wound contamination and dermal absorption are all potential routes of ionizing radiation intake.[7]
Occupations exposed to natural sources of radiation above typical background levels include uranium, coal and other underground miners, airline crews, and astronauts.[2,4] Occupational exposure to ionizing radiation may also occur in the nuclear industry, military, research laboratories, medical services (x-ray personnel and dental personnel), in other industries using radiography or radioactive materials, and as a result of industrial accidents.[2,4,17]
Canadians working in occupations with exposure to radiation have been monitored by the National Dose Registry (NDR), maintained by Radiation Protection Bureau of Health Canada, since the 1940s.[18]
In 2005, nearly 150,000 workers were monitored, with 35,513 showing annual recorded doses greater than 0 mSv.[19] Medicine was the largest industrial group monitored by the NDR (74,102 workers), followed by nuclear power (21,693) and industry and research (19,200) in 2005.[19] The occupational groups with the greatest number of workers with annual doses exceeding 0 mSv include: Medical radiation technologists (3297), industrial radiographers (1650), nurses (1624), and nuclear medicine technologists (1466).[19] Two workers monitored by the NDR exceeded the maximum permissible dose of 50 mSv.[19]
Although exposure levels vary across occupations, the average annual radiation exposure of a monitored Canadian worker is approximately 0.3 mSv.[8]
Environmental Exposures
Over 80% of the general population’s annual dose is estimated to occur from exposure to natural background radiation, including cosmic radiation (from the sun and stars), radioactive elements in the earth’s crust (i.e. radon), and naturally occurring radionuclides such as potassium-40.[2,20]
Man-made ionizing radiation from sources such as medical applications (x-rays, gamma rays in cancer treatments, CT Scanners, MRIs) and dental x-rays comprise approximately 15% of the general population’s annual dose.[2,20] Consumer goods, operation of nuclear power plants, and fall out from nuclear weapons testing or accidents make up the remaining fraction of exposure.[2,20]
An individual’s background radiation dose (from cosmic rays and naturally occurring radioactive material) may vary depending on geographic location and altitude.[2] The average annual radiation dose in Canada is approximately 2.7 mSv.[20]
Consumer products, such as televisions and radioluminescent clocks and watches, may emit ionizing radiation, although there are restrictions on the maximum allowable radioactivity in the products.[4]
Ionizing radiation is not reportable to the National Pollutant Inventory (NPRI) in Canada,[21] and no household products are listed for ‘ionizing radiation’ in the US Household Products Database.[22]
Sources
- Wikimedia Commons Photo for Ionizing Radiation Hazard Symbol
- ATSDR Toxicological Profile for Ionizing Radiation (1999) (PDF)
- IARC monograph summary, Volume Vol. 75, (2000) Part 1: X and Gamma Radiation and Neutrons (PDF)
- NTP 12th Report on Carcinogens for Ionizing Radiation (2011) (PDF)
- IARC Monograph Summary, Vol 78, ionizing Radiation Part 2, Some Internally Deposited Radionuclides (2001)
- Health Canada Fact Sheet, Radiation Doses (2009)
- Hazardous Substances Data Bank entry for Ionizing Radiation (Search term: 'ionizing radiation')
- Health Canada: It's Your Health: Occupational Exposure to Radiation (2003) (PDF)
- Department of Justice Canada, Radiation Protection Regulations (SOR/2000-203)
- Department of Justice Canada, Nuclear Safety and Control Act (1997, c.9)
- Canadian Nuclear Safety Commission: Regulated Facilities and Activities (2009)
- Health Canada (2009) Guidelines for Canadian Drinking Water Quality: Guideline Techincal Document – Radiological Parameters
- World Nuclear Association Webpage, Nuclear Power in Canada (2009)
- Foreign Affairs and International Trade Canada, The Nuclear Non-Proliferation Treaty (1970)
- Ontario Power Generations: Nuclear Isotopes
- World Nuclear Association Webpage, Uranium Production in Canada (2009)
- Health Canada, Facts - Radiation in Dental Medicine (2007) (PDF)
- Health Canada: Environmental and Workplace Health: National Dose Registry
- Health Canada 2006 Report on Occupational Radiation Exposures in Canada (PDF)
- Health Canada Fact Sheet, Ionizing Radiation (2005)
- The National Pollutant Release Inventory
- Household Products Database (US Department of Health & Human Services)
- IARC Monograph Volume 100: A review of human carcinogens—Part D: radiation (2009)
Other Resources
- Health Canada, Technical Reports and Publications for Radiation (2008)
- IARC Radiation Group Webpage, Current Research Topics, Ionizing Radiation (2008)
- Health Canada Radiological Characteristics, Drinking Water Guidelines (1995) (PDF)
- The National Academies Report in Brief on Biological Effects of Ionizing Radiation (BEIR) VII: Health Risks from Exposure to Low Levels of Ionizing Radiation (PDF)