What are the sources of radon?

Radon is a chemical element belonging to group 18 of the noble gases. In its gaseous form, it is colourless, odourless, and tasteless, and in its solid form, it is reddish. It has the atomic number 86 and the symbol Rn on the periodic table. Its average mass is 222, which means that on average it has 222-86 = 136 neutrons.

Radon can originate from several sources, including:

The soil

It is the most common cause of elevated radon levels and comes from the natural decay of uranium, thorium, and radium in the soil, which is why it is present throughout the world in varying concentrations.

This gas enters buildings through cracks, pipes, ducts, or pores in the ground and tends to concentrate inside buildings such as homes, schools, and workplaces, especially in basements, cellars, or areas most in contact with the ground. It adheres to dust particles in the air and is therefore a potential health risk. In addition, as the gas dissolves in water, homes that receive their water supply from a well may have an additional risk factor.

Some materials, such as granite, slate, or phosphate gypsum, are more permeable and allow greater amounts of radon to be emitted from the ground. At the other extreme, impermeable soils, such as clay soils, make it difficult for the chemical element to reach the surface.

Construction materials

Although the concentration from building materials such as granite, brick, or marble is very low, they also contribute to radon levels.

However, there are examples such as lightweight blue concrete, also known as ‘blue concrete’, which was widely used in Swedish homes between 1950 and 1975 (and is no longer used today) that contains radium and emits radon into the indoor air. It is estimated that around 400,000 homes were built in Sweden using this material, which is a factor to be taken into account when calculating radon concentrations in these buildings.

Domestic water

It is the least known source of radon, but no less important for that.

Wells drilled in uranium-rich areas are particularly prone to containing high levels of radon. When this water is used indoors, for example, for showering or cooking, radon is released into the air.

Radon in water is not usually a problem in public water supplies, but it is a problem when the water source is an underground well.