What is Radon and How are We Exposed to It?

Radon accounts for around a half of all human exposure to radiation. It is also the most important cause of lung cancer after smoking and the leading cause of lung cancer among non-smokers. According to WHO, radon is estimated to cause between 3% to 14% of all lung cancers. Depending on the average radon level indoors and smoking prevalence, long-term exposure can significantly increase the risks. The risk of lung cancer from radon is substantially greater for smokers: they are around 25 times more likely to develop lung cancer than non-smokers. 

The International Agency for Research on Cancer (IARC) classified radon as a proven human carcinogen along with tobacco smoke, asbestos and benzene.  

Radon occurs naturally in significant quantities in three different chemical variations, or isotopes, but only two of these present a risk.

Radon-222 — a product of Uranium-238 or Radium-226 decay — is the most dangerous one. It has a long decay rate, so it can accumulate indoors, and it is quite common due to high concentrations of Uranium-238 in the ground in some regions, as well as due to varying concentrations of Radium-226 in certain building materials. Sometimes together with Radon-220 — a product of Thorium-232 decay — Radon-222 acts as the main contributor to radiation exposure for the public. In terms of the protection to be provided, no differentiation is made between these two causes of exposure.

Radon-219 is not considered dangerous .

Radon concentrations indoors tend to differ among countries and even individual buildings because of differences in climate, construction techniques, types of ventilation provided, domestic habits and, most importantly, geology.

After released from bedrock material, radon passes through the soil, diluting in the air before entering buildings. Granites, migmatites, some clays and tills are particularly rich in uranium and radium, which decay into radon. Radon exhalating from the ground beneath buildings is the main source of radon in indoor air.

Radon may enter buildings through cracks in the floor, gaps in construction, windows, drains or spaces around cables and pipes. This is particularly common in temperate and cold regions due to the pressure driven flow of gas which arises because buildings are normally at a slight underpressure compared to pressure under the building.

Radon does not dilute in indoor air as quickly as outside and tends to accumulate in the enclosed spaces of buildings, serving as a significant source of public exposure to radiation.

Radon can dissolve and accumulate in groundwater sources, such as water pumps or drilled wells in uranium rich geological areas. Radon in water can be released into the air during routine water use such as showering or laundry. 

Epidemiological studies have not confirmed a connection between consumption of drinking water containing radon and an increased risk of stomach cancer, so the associated risks of lung cancer come primarily from radon released into the air and inhaled. In general, water tends to be a less significant source of radon exposure than soil beneath buildings.  

Most building materials produce an insignificant amount of radon naturally. At the same time, some specific materials can act as significant sources of radon exposure. Such materials tend to have a combination of high levels of Radium-226 (which decays into radon) and high porosity, which allows the radon gas to escape. These include lightweight concrete with alum shale, phosphogypsum and Italian tuff. Use of material from old uranium tailings (by-products of uranium mining) as filling under the buildings can also contribute to significant concentrations of radon indoors.

High levels of radon in buildings can be reduced by various corrective actions. One approach is based on preventing radon from entering the indoor environment through isolation in combination with indoor air pressure manipulation. Attention should also be paid to the thermal retrofitting of existing buildings as low ventilation rates decrease the overall quality of indoor air and can increase radon levels.

Preventing radon accumulation in newly built houses is now included in many national building codes. This approach is normally cheaper than corrective actions and is often highly cost-effective compared with other public health interventions.

Frequent ventilation is also helpful.

For more information on methods of mitigation and prevention of radon in buildings, read this publication.

Radon occurs at most indoor workplaces for the same reason as in dwellings. All types of workplaces may be affected: offices, workshops, mines, tunnels.

In underground workplaces radon levels may be elevated due to the geological conditions or limited ventilation. The workplaces particularly affected are often associated with work in mines, tunnels and basements. A large proportion of normal above ground workplaces such as factories, shops, schools, museums and offices may also have high concentrations of radon due to its presence in the ground, poor ventilation or processing of raw materials. 

Levels of radon can be high in groundwater, particularly in areas of granite rock. Radon levels may be high in workplaces in water treatment facilities or spa facilities using natural water.

If measurements indicate that radon concentrations exceed the workplace norms established by the relevant national authority, the employers should undertake remedial/corrective actions. In case remedial action is impossible or ineffective, national authorities must be notified and special regulatory requirements will apply to this workplace.

If you want to read more information on the protection of workers exposed to radon in workplaces other than mines, read this publication.

• The IAEA publishes safety standards on the protection of the public against radon exposure, including a safety guide to assist national governments, which includes guidance on how to  establish regulatory control for protection against radon and, if needed, how to prepare a national radon action plan.
• The Agency has also published technical recommendations of radon preventive and corrective measures and exposure in the uranium mining and processing industry.
• The IAEA conducts webinars specifically on radon, seeking to spread awareness of the associated risks and mitigation methods. Those are targeted at national governments, health care or building professionals and anyone else interested in the topic.
• The IAEA provides guidance on designing and conducting indoor radon surveys, as well as on measurement and calculation of radon releases from mining and milling.
• The IAEA develops training modules that teach the basics of how to initiate national radon programmes.
• The IAEA carries out technical cooperation projects on establishing enhanced approaches to  control public exposure to radon.

This article was first published on 1 June 2021.