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Sources of Radon Exposure
  • Radioactive decay of uranium through radium produces radon, which can move from soil into the air. It decays into a series of progeny, some of which are short-lived and emit alpha and beta particles and gamma rays.
Radon gas is derived from the radioactive decay of radium, a ubiquitous element found in rock and soil. The decay series begins with uranium-238 and goes through four intermediates to form radium-226, which has a half-life of 1,600 years. Radium-226 then decays to form radon-222 gas. Radon's half-life, 3.8 days, provides sufficient time for it to diffuse through soil and into homes, where further disintegration produces the more radiologically active radon progeny ("radon daughters"). These radon progeny, which include four isotopes with half-lives of less than 30 minutes, are the major source of human exposure to alpha radiation (high-energy, high-mass particles, each consisting of two protons and two neutrons). This alpha radiation produces damage that, if not repaired, results in cellular transformation in the respiratory tract, which can lead to radon-induced lung diseases or cancer.
  • Radon, a colorless, odorless gas, is both chemically inert and imperceptible to the senses.
  • Its infiltration into buildings is the main source of indoor radon; however, building materials and the water supply can also be sources.
Radon itself is imperceptible by odor, taste, and color, and causes no symptoms of irritation or discomfort. There are no early signs of exposure. Only by measuring actual radon or progeny levels can people know whether they are being exposed to excessive levels of radon. Radon seeps from the soil into buildings primarily through sump holes, dirt floors, floor drains, and cinder block walls, and through cracks in foundations and concrete floors (Figure 1). When trapped indoors, especially during a temperature inversion that reduces its escape from the building, radon can become concentrated to unacceptable levels. When radon escapes from the soil to the outdoor air, it is diluted to levels that offer relatively little health risk.
Most houses draw less than one percent of their indoor air from the soil; the remainder comes from outdoor air, which is generally quite low in radon.  Houses with low indoor air pressures, poorly sealed foundations, and several entry points for soil air, however, may draw as much as 20 percent of their indoor air from the soil. Even if the soil air has only moderate levels of radon, levels inside the house may be very high.


Figure 1. Sources of Radon and Common Entry Points

Radon gas can enter a building by diffusion, but pressure-driven flow is a more important mechanism. Negative pressure in the home relative to the soil is caused by exhaust fans (kitchen and bathroom), and by rising warm air created by fireplaces, clothes dryers, and furnaces. In addition to pressure differences, the type of building foundation can affect radon entry. Basements allow more opportunity for soil gas entry, but slab-on-grade foundations (no basement) allow for less. In most cases, the increase of indoor radon due to home "tightening" for energy conservation is slight compared to the amount of radon coming from the soil.
Typical building materials, such as concrete block, brick, granite, and sheet rock, contain some radium and are sources of indoor radium. Normally, these construction materials do not contribute significantly to elevated indoor radon levels. In rare cases, however, building materials themselves have been the main source of radioactive gas
Radon might enter into homes via the water supply. With municipal water or surface reservoirs, most of the radon volatilizes to air or decays before the water reaches homes, leaving only a small amount from decay of uranium and radium. However, water from private wells might be another matter. Groundwater that comes from deep subterranean sources and passes over rock rich in uranium and radium, might dissolve some of the radon gas produced from radium decay. As the water splashes during showering, toilet flushing, dishwashing, and laundering, radon is released into the air and can result in inhalation exposure. Radon can also be present in natural gas supplies.

Radon is estimated to be the second leading cause of lung cancer in Canada. However, with proper equipment, radon is easy to detect, and even dangerously high levels can be removed from homes.

Health/cancer risks
Radon produces no immediate physical symptoms. Typically, people must be exposed to it for years before problems surface.
The primary hazard from radon is caused when you breathe in the gas and the highly radioactive, heavy metallic particles that are produced when it decays. These particles collect on dust in the air. After you inhale radon, the dust and smoke particles become deeply lodged or trapped in your lungs, where they penetrate the cells of the mucous membranes and other tissues.
Lung cancer from inhaling radon decay products is the only known health problem associated with radon. Scientists estimate that in Canada, 1700 to 2400people die of lung cancer every year because of radon.
Tobacco users are more likely than nonusers to develop lung cancer when exposed to radon, according to a 1989 study by researchers from the National Institute for Occupational Safety and Health, the Centers for Disease Control and the Harvard School of Public Health


Radon Abatement

  • The cost of remediation to reduce radon levels in the average home is about $1,800.
  • Available procedures to lower indoor radon levels are dollar for dollar, very effective in saving lives.
If excessive levels of indoor radon are found in a structure, low-cost, quick-fix methods should be implemented first. These methods include limiting the amount of time spent in contaminated areas and increasing ventilation in the areas.

Subslab depressurization is one of the most effective methods of lowering radon levels in many homes. In addition to increasing ventilation, radon control measures include sealing the foundation, subslab depressurization (creating negative pressure in the soil), pressurizing the home, and using air-cleaning devices. Methods of increasing ventilation include opening windows, ventilating basements and crawl spaces, ventilating sump-holes and floor drains to the outside of the house, and increasing air movement with ceiling fans. Ventilation must be modified properly, however, because increased ventilation can depressurize the house in some cases, causing an increase of soil gas entry to the home. Heat exchangers provide a way of bringing fresh air indoors without major heat loss, but these must be properly balanced or they can worsen the problem.

Preventing soil gas entry is more important than increasing whole-house ventilation. Prevention of soil gas entry involves sealing the foundation and depressurizing the soil. Potentially useful methods for prevention of soil gas entry include using vapor barriers around the foundation, sealing cracks and holes with epoxies and caulks, and sealing the crawl space from the rest of the house. Subslab depressurization can reduce radon levels by as much as 99%. Suction puts the soil at a lower pressure than the inside of the home, preventing inward migration of soil gas. Subslab depressurization involves sinking ventilation pipes below the foundation and continuously pumping air out.

Figure 2. Subslab Depressurization.

The cost to install subslab depressurization in an existing home is approximately $1,000 to $2,500; annual utility costs are about $100. If the equipment is installed during construction of the home, however, the cost of subslab depressurization is considerably less; it is much easier to install pipes during construction than to retrofit later. Physicians and other health professionals can perform a public service by becoming acquainted with local building codes and urging local jurisdictions to include the installation of capped pipes terminating in a space under the foundation to allow for later subslab depressurization if needed.


Pipes, attached to a suction fan, are inserted into the ground below the basement floor, creating a low-pressure region under the house.

The amount of radon that accumulates inside a home is caused by factors relating to the home’s structure and geographic location. Because the radon concentration varies greatly even among homes in the same neighborhood, each home must be tested to determine its radon level. Such testing is highly recommended by Health Canada, the Canadian Lung Association, and now many Provincial Health organizations. One in three homes in the Regina, SK, tested above the national standard in a recent government study.