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<p>Radon is a radioactive gas which emanates from rock, soil and water. Radon concentrations in the<br>atmosphere are generally very low (typically <5 Bq m-3), however it can occur at much higher levels<br>in soil (typically 10’s-100’s kBq m-3), or enclosed spaces such as buildings and caves (typically 10’s-<br>100’s Bq m-3). Exposure to radon and its daughter products is associated with an elevated risk of<br>developing lung cancer. Ireland has a population weighted indoor radon concentration of 98 Bq m-3<br>resulting in an estimated 300 annual lung cancer cases per year, representing approximately 12% of<br>the annual lung cancer cases. A national-scale legislative radon-risk map has a 10 x 10 km spatial<br>resolution and is based exclusively on indoor radon measurements (i.e. it does not contain any<br>geological information). The legislative map satisfies the European Council Directive<br>2013/59/EURATOM Basic Safety Standard, in that it defines “high radon” areas as those where >10%<br>of homes are estimated to exceed the national reference level of 200 Bq m-3. New buildings in such<br>areas are legally required to have a barrier, with low radon permeability installed.</p><p>This research focuses on a karstic region of SE Ireland, which features some exceptionally high<br>indoor radon concentrations (65,000 Bq m-3), even though it is not classified as a “high radon” area<br>on the national legislative map. Here we demonstrate the use of measuring sub-soil radon<br>concentrations and sub-soil permeability, in order to construct a radon potential (RP) map of the<br>area. Extremely high sub-soil radon concentrations (>1443 kBqm-3) and radon potential values<br>(>200) are spatially associated with Namurian shales, interbedded with limestone. Overall, we<br>classify the study area as high radon potential (RP >35) using this technique. We suggest all areas<br>underlain by Namurian shales in Ireland should undergo similar radon potential mapping, and if<br>necessary, should be re-designated as “high radon” areas. If deemed appropriate (i.e. where RP<br>>35), such a designation will help to protect the general public from the harmful effects of indoor<br>radon exposure, and will help to lower the incidence of radon-related lung cancer in these areas.</p>

Exposure to radon over time has significant detrimental effects on human health. Approximately 226,000 annual radon-related deaths have been reported from 66 countries (1). Many countries have a radon action plan, in order to reduce the harmful effects of radon exposure on the general public. Maps are routinely used to assist with mitigation strategies and delineate areas of priority regulation. Standard regulations in the European Union include the requirement for workplaces to test and the requirement to have reduction methods in newly built homes. Such laws are assigned systematically to areas that are understood to have high values of indoor radon. This article demonstrates that the boundaries of radon priority areas may vary, depending on the data set and methods used. We propose a table and a decision matrix to assist in choosing the most appropriate visual aid according to the purpose for which the map is to be used. We conclude that no single radon map is suitable to fit all objectives, and some maps are more suitable than others depending on the purpose.