Let’s go deeper on radon!

Radon is one of the major sources of radiation exposure to the public. It is a radioactive gas which is colorless, odorless and inert: special equipment is required to detect it. Radon (Rn) is a heavy radioactive noble gas of Group 18 of the periodic table, it is generated by the radioactive decay of radium.
Rn is the heaviest of all gasses naturally present in air (about eight times heavier than air and more than 100 times heavier than hydrogen), this means that it accumulates near the ground. When the traces of radium present in rocks, soil and water decay, Rn gas is produced; from underground it moves towards the surface to be released into the atmosphere or it can be dissolved into water. It enters buildings through basements and through water supplies derived from wells. The gas can accumulate in the air of poorly ventilated houses.

Rn has several isotopes, but it is rare in nature because its source radium-226, the daughter of uranium-238, is scarce, and all of its isotopes are unstable and therefore short-lived. The most stable isotope is Rn-222 with a half-life of 3.823 days.
Other isotopes that occur in trace quantities are ²¹⁸Rn, ²¹⁹Rn and ²²⁰Rn. ²¹⁸Rn and ²²²Rn, these are intermediate decay products in the decay chain of ²³⁸U, ²¹⁹Rn of ²³⁵U and ²²⁰Rn of ²³²Th.

The decay chain of Rn-222 is represented in Figure 1. At each step of the decay process, radiation is produced. The decay of Rn produces solid radioactive daughters (polonium, bismuth, and lead isotopes) that can be ingested from well water or can be absorbed in dust particles and then inhaled into the lungs.

Figure 1 - Decay chain of Rn-222

Radon gas had been recognized as a potentially serious health hazard by the late 1980s ⁽¹⁾.  The IARC, International Agency for Research on Cancer, classified 222Rn and its decay products in Group 1 ⁽²⁾, as a human carcinogen, based on sufficient evidence in humans. In fact, exposure to high concentrations of Rn and its daughters over the course of many years can greatly increase the risk of developing lung cancer as the amount of energy released during the decay can damage lung tissue. Indeed, Rn is now thought to be the greatest cause of lung cancer among nonsmokers. Rn levels are highest in homes built over geological formations that contain uranium mineral deposits.

The main sources of Rn found in the indoor air of homes are mainly the soil and, in minor amounts the water supply. The air pressure inside homes is

usually lower than pressure in the soil that is around the home. This allows Rn to be drawn in through foundation cracks and other openings. Rn is present in the water supply more likely when its source is groundwater, (e.g., a private well or a public water supply system that uses ground water). It is released when water is used, for example when showering. It poses an inhalation risk and an ingestion risk but the risk of cancer is much higher in lungs than the stomach.

The level of Rn can be tested and there are several proven methods to reduce Rn in your home. When Rn is present in indoor air, the primary solution is a vent pipe system and fan, which pulls Rn from beneath the house and vents it to the outside. This reliable technique used for Rn reduction is called active soil depressurization (ASD) that removes Rn from beneath the building before it can enter the home.
The removal of Rn from water can be done in two ways, depending on whether it is applied at the start or the end point of the water supply. Point-of-entry treatment is the most effective, it removes Rn from water before it enters your home. National and International Agencies and Institutions (EC European Commission, WHO World Health Organization, IAEA International Atomic Energy Agency, EPA US Environmental Protection Agency, FDA Food and Drug Administration, ERA European Radon Association, NSC National Security Council etc.) deal with the protection of the public from radiation and promote awareness about Radon and the possible solutions ⁽³⁾. Different documents and guidelines are available for indoor residential and school environments.