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When using rocks and soils for building purposes, radionuclides contained therein or released from them may lead to a radiation exposure of the population. Of special importance are the radionuclides of the radioactive decay chains of uranium-238, thorium-232 and potassium-40.
- Examination and evaluation
- Radon of special importance
- Higher radon concentrations in some building materials
- Industrial residues as secondary raw material
- Natural radionuclides in natural stones
- Specific activities of the examined natural stones
- EU Recommendation "Radiation Protection 112"
Causes for the radiation exposure of occupants of indoor spaces caused by natural radionuclides in building materials are the gamma radiation emitted by the building materials affecting the body from outside and the inhalation of the gas radon and its decay products released from the building materials in the interior of houses.
Examination and evaluation
For over 30 years, examinations and evaluations of the radioactive substances contained in building materials and building products have been carried out in Germany. The Federal Office for Radiation Protection (BfS) has data of the specific activities of the relevant radionuclides from over 1,500 samples of natural stones, building materials and mineral residues. For a large number of samples, the radon release was additionally determined.
|Material||Radium-226 in becquerel per kilogram|
Mean value (range)
|Thorium-232 in becquerel per kilogram|
Mean value (range)
|Potassium-40 in becquerel per kilogram|
Mean value (range)
|Granite||100 (30 - 500)||120 (17 - 311)||1000 (600 - 4000)|
|Gneiss||75 (50 - 157)||43 (22 - 50)||900 (830 - 1500)|
|Diabase||16 (10 - 25)||8 (4 - 12)||170 (100 - 210)|
|Basalt||26 (6 - 36)||29 (9 - 37)||270 (190 - 380)|
|Granite||10 (4 - 16)||6 (2 - 11)||360 (9 - 730)|
|Gravel, sand, gravel sand||15 (1 - 39)||16 (1 - 64)||380 (3 - 1200)|
|Natural gypsum, anhydrite||10 (2 - 70) < 5||(2 - 100)||60 (7 - 200)|
|Tuff, pumice stone||100 (< 20 - 200)||100 (30 - 300)||1000 (500 - 2000)|
|Clay||< 40 (< 20 - 90)||60 (18 - 200)||1000 (300 - 2000)|
|Brick, clinker brick||50 (10 - 200)||52 (12 - 200)||700 (100 - 2000)|
|Concrete||30 (7 - 92)||23 (4 - 71)||450 (50 - 1300)|
|Sand-lime brick, porous concrete||15 (6 - 80)||10 (1 - 60)||200 (40 - 800)|
|Slag from Mansfelder copper-slate||1500 (860 - 2100)||48 (18 - 78)||520 (300 - 730)|
|Gypsum from flue gas desulfurisation||20 (< 20 - 70)||< 20||< 20|
|Brown coal filter ash||82 (4 - 200)||51 (6 - 150)||147 (12 - 610)|
The mean value of the gamma local dose rate (ODL) in buildings caused by the natural radionuclides in building materials is about 80 nanosievert per hour. ODL values above 200 nanosievert per hour are rare.
The gaseous radon-222 produced from radium-226 due to radioactive decay is of special interest from the radiation protection point of view. According to the latest findings, a significant portion of the lung cancer cases among the German population is caused by exposure to radon and its decay products in buildings.
Radon of special importance
The radon release from building products is determined by the specific activity of radium-226 and other material characteristics determining the radon transport (such as porosity). Examinations have shown that the traditional use of building materials such as concrete, brick, porous concrete and sand-lime brick are generally not the cause for the annual mean value of the indoor radon concentration recommended by the Federal Office for Radiation Protection being exceeded. This is not to exceed 100 becquerel per cubic metre. The contribution of radon-222 from building products to the indoor radon concentration is maximum 70 becquerel per cubic metre. In building products currently commercially available, values clearly below 20 becquerel per cubic metres were measured.
Higher radon concentrations in some building materials
Radon release rates that may result in higher indoor concentrations were occasionally measured in residues from the incineration of coals with enhanced uranium/radium concentrations (formerly used locally to fill ceilings and referred to as “coal slag”). There were also rare cases where they were measured on natural stones with enhanced specific activities of radium-226. Despite of the comparatively high specific activity of radium-226 in Mansfelder copper-slag, no enhanced radon concentrations were measured in buildings made from this material. In some countries higher radon concentrations were detected in buildings where the so-called chemical gypsums (residues of phosphorite processing) had been used as well as in lightweight concretes made by using alum shale. There are some very few occurrences of above-average radon concentrations in the traditional mining regions, where debris or residues from ore processing with enhanced radium concentration were used as building material, as concrete or mortar additive or as foundation in house building.
According to present knowledge, no materials were used in Germany for building purposes which, as a result of enhanced thorium concentrations, could lead to radiation-protection relevant exposures to the gas radon-220 (thoron) and its decay products. The possibility of unbaked clay as building material leading to individual cases of enhanced thoron values in room air, cannot be entirely excluded, however. You will find more information on the topic clay and thoron in the article "Clay as building material (Strahlenbelastung bei ungebranntem Lehm als Baumaterial)".
Industrial residues as secondary raw material
In some residues from industrial processes the natural radioactive materials accumulate. When using these residues, for example as secondary raw material in building, enhanced radiation exposures of the population cannot be excluded. To prevent this, Part A of Annex XII of the Radiation Protection Ordinance (StrlSchV)  lists the residues for which radiation protection aspects need to be observed when they are used or deposited. By compliance with the monitoring limits and quantity restrictions for the use of these materials, which are also regulated in Annex XII of the StrlSchV, it is ensured that the standard value of the effective dose of 1 millisievert per year for single persons of the population is not exceeded.
According to the Building Product Directive (BauPVO, Directive EU No. 305/2011) , a building product may only be placed on the market in the EU Member States if it fulfils the key requirements for hygiene, health and environment protection, among others with respect to the release of hazardous radiation. This EU Directive is directly binding in German law and has been effective for the manufacturers since 1 May 2013.
Natural radionuclides in natural stones
Today, natural stones are used more frequently in all areas of building, inside and outside the house. Therefore, the Federal Office for Radiation Protection, with the support of Deutscher Naturwerkstein-Verband e.V., examined in 2006 a number of marketable tiles and other sheet materials of various origin with respect to their content of natural radioactivity and from the radiation protection point of view.
The main focus was on gamma spectrometric measurements of the specific activities of radium-226, potassium-40 and thorium-232. The results have been shown in the chart. The presented median values (central values) mean that half of the samples examined are above and half are below this value.
The material is classified here according to stone type. It should be pointed out that, for considerations that are oriented towards special applications, processing and maintenance of the materials, the trade does not always use correct names for the stones. For example, when it says “granite”, it is not necessarily granite stone; this term is also used for gneiss, diorites, granodiorites and other stones.
Specific activities of the examined natural stones
The specific activities of the examined natural stones is for potassium-40 in the range between 10 and 1,600 becquerel per kilogram, for radium-226 between under 10 and 355 becquerel per kilogram and for thorium-232 between under 10 and 330 becquerel per kilogram.
For comparison and complementation cf. the above Table and the values published by Pavlidou et al. . Apart from the radionuclide concentration and the radon release, the possible radiation exposure due to the individual building materials depends on the conditions of use.
EU Recommendation "Radiation Protection 112"
There is no binding legal basis as yet for the radiological evaluation of building materials. However, the European Union’s Recommendation “Radiation Protection 112”  states an easy-to-handle method that enables an initial evaluation based on the determined specific activities of the aforementioned radionuclides and special model assumptions. This screening method was also incorporated in the European Basic Safety Standards Directive  passed on 5 December 2013. In this Directive, binding regulations for building products are demanded for the first time which have to be implemented in national law by 6 February 2018. Taking the mentioned value for the effective dose of 1 millisievert per year as a basis for persons of the population due to radionuclides of natural origin (except for radon), it can be seen that the examined currently available building products and also the examined natural stones can be used in buildings without any restriction, even if they are used on large surfaces.
 REGULATION (EU) No 305/2011 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 9 March 2011 laying down harmonised conditions for the marketing of construction products and repealing, Council Directive 89/106/EEC1
 Pavlidou, S.;Koroneos, A.; Papastefanou, C.; Christofides, G.; Stoulos, S.; Vavelides, M.: Natural Radioactivity of Granites Used as Building Materials in Greece. Bulletin of the Geological Society of Greece, Volume XXXVI, 2004
 European Commission: Radiation Protection 112 „Radiological protection principles concerning the natural radioactivity of building materials“, Luxembourg: Publications Office of the European Union, 2000, ISBN 92-828-8376-0
 COUNCIL DIRECTIVE 2013/59/EURATOM of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom
State of 2017.02.14