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The Süddeutsche Zeitung reported on radioactivity of granite countertops in homes in the issue of the 3 December 2008 [1] referring to a similar report in the New York Times dated 24 July of the same year [2]. Both these reports addressed potential exposure of individuals living in private homes with built-in granite countertops, due to gamma radiation of naturally radioactive materials from the uranium and thorium decay chains and Potassium-40 on the one hand, and due to emanating radon on the other.
Natural radioactivity
Man has always been exposed to radiation from naturally occurring radioactive materials. These include, among others, the nuclides of the uranium and thorium decay chain as well as Potassium-40, occurring in all soils and rocks. As a result of rocks and soils used to produce building materials or natural stones directly mounted in homes, inhabitants are exposed to radiation by these radionuclides, and their geology and origin play a major role for the level of radionuclide concentration. Studies and evaluations of radioactive substances in building materials have been conducted in Germany over a period of more than 20 years. Data of specific activity concentrations of the relevant radionuclides are available at the Federal Office for Radiation Protection (BfS) obtained from studies of more than 1500 samples of natural stones, building materials and mineral residues. These studies were able to confirm that about one fifth of the mean annual radiation exposure in Germany is due to building materials [3].
Radon
Radon is part of the natural decay chains of uranium and thorium. In contrast to the other nuclides of this decay chain, radon is an inert gas which may escape from stones and building materials and enter the indoor air. The radon decay products, in turn, are radioactive and may stay in the lungs when inhaled. Radon and its decay products are known to cause lung cancer. About 10 percent of lung cancers in Germany are related to radon, corresponding to about 2000 cases per year. 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 [4]. There are only very rare cases where enhanced indoor concentrations are being caused by the building materials used. This has been confirmed by recent studies on the radon release from building materials and natural stone conducted by the BfS during the last few years.
Granite
Granite is the name of stones that have solidified underground in greater depth from fluid magma. Granites frequently show enhanced concentrations of the nuclides from the uranium and thorium series and of Potassium-40, compared to other building materials. 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 recognizable by different colour and structure. However, the correct name of stone is not always used in trade, based on considerations geared to the specific utilizations, processing and maintenance of materials. Thus, "granite" need not necessarily signify granite stone but this term is also used for gneiss, diorite, granodiorite, and other stones.
No binding legal foundation is available at present to evaluate the radionuclide concentration of building materials. However, the EU-recommendation "Radiation Protection 112" [5] recommends a simple-to-use method permitting a rough evaluation based on measured specific activity concentrations of the relevant radionuclides and on special modelling assumptions. According to that, the granites examined by the BfS are suitable for use within buildings even on a large scale without any restriction. Concerning uses of granite with exceptionally high radionuclide concentrations, no scientific findings are available to the BfS.
Recommendations
- If you are interested in granite for your home and would like to take account of radiation exposure, please ask the distributor or manufacturer for information on the radionuclide concentrations. These are mostly known to the manufacturers, either in consequence of licensing procedures and import directives of third countries, or because they want to stand out from competitors.
- 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 [6].
More information
(Note: information under [3], [4], [6] is related to further publications of this web presence)
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