Granite plates used in households

In the past, newspapers reported about granite in homes as a source of potential radiation exposure. Indeed, natural stone and other building materials contain the natural radionuclides uranium-238, thorium-232 and their decay products as well as potassium-40.

However, these naturally occurring radionuclides in natural stones usually contribute only an insignificant radiation exposure for inhabitants. Only in cases where large amounts of building materials with elevated activity concentrations are used, the radiation emitted from the material might be not considered as negligible. Small amounts of stone as, e. g. used for worktops in kitchens are generally unproblematic.

As an intermediate of the uranium-238 decay chain, the radioactive gas radon (radon-222, half-life 3.8 days) originates from radium-226. However, in most instances the proportion of radon from building materials and natural stone in homes is small compared to the amount of radon emitted from soil.

Granite

Granite is the name of stones that have solidified underground in greater depth from fluid magma.

Compared to other building materials granites frequently show enhanced concentrations of potassium-40 and nuclides of the uranium and thorium decay series. Although mainly consisting of quartz, feldspar and dark, ferrous or magnesian minerals, their composition may vary broadly, depending on their geology and origin, which is recognisable by different colour and structure.

However, based on considerations geared to the specific utilisations, processing and maintenance of materials, the correct term for this type of stone is not always used in trade. Thus, "granite" does not necessarily need to signify the geological meaning of granite stone and it occurs that for building materials this term is also used for gneiss, diorite, granodiorite, and others.

In trade, the term "granite" is also used for gneiss, diorite, granodiorite, and others. Source: StudioDin/Stock.adobe.com

Radon: Cause of lung cancer

Radon is part of the natural decay chain of uranium-238 and is known to cause lung cancer. The risk to contract lung cancer on account of radon in indoor air depends on the long-time indoor concentration.

However, comprehensive studies in Germany have clearly shown that enhanced indoor concentrations in the predominant number of cases are not due to radon escaping from building materials but to radon entering the house from the soil via the cellar. There are only very rare cases where enhanced indoor concentrations are being caused by the used building materials.

This has been confirmed by recent studies on the radon release from building materials and natural stone (also including granite) conducted by the BfS during the last few years.

How to assess the radionuclide content

The Radiation Protection Law requires for certain granites that the manufacturer or importer has to measure the concentrations of the natural radionuclides and must prove that the legal reference value for the exposure of the users of buildings is not exceeded through the building material. The Radiation Protection Ordinance describes how the manufacturer can prove this.

At the same time, the European Standards Institute CEN is developing standards for the measurement and evaluation of building materials within the framework of the Construction Products Regulation. Ultimately, the CE mark on a building material will also prove that the European radiation protection requirements have been met.

However, those regulations apply only, if the building materials is used as wall, floor or ceiling constructions, including their sheathing, of rooms in buildings (§ 5 Radiation Protection Act - StrlSchG). Granitic materials, which are used for decoration purposes or used as furniture, e.g., kitchen worktops, are not covered by this definition.

Recommendations

Interested in granite for the home and like to take account of radiation exposure? Please consider to ask distributor or manufacturer for information on radionuclide concentrations. Source: KristinaBlokhin/Stock.adobe.com

If you are interested in granite for your home and would like to take account of radiation exposure, please ask potential distributors or manufacturers for information on the radionuclide concentrations before the purchase. Even if there is no obligation to measure and declare radionuclide concentrations for granite used as furniture, such data may be available and help in the decision process.

Arrange for measurements of the radon concentration in your home. An increased radon concentration in homes represents a health risk to the inhabitants, independent of its origin. Laboratories for measurements, which are subjected to quality assurance in Germany, are participating in the annual comparative measurements for passive radon detectors of the BfS.

If laboratories offer radon measurements at workplaces, they must be acknowledged by the BfS as "acknowledged body in accordance with § 155 Radiation Protection Ordinance". This ensures the quality of the providers. The BfS recommends applying this quality standard to radon measurements in general, and provides an overview of recognized bodies from which measuring devices can be requested.