1 The Mining-Geology-Petroleum Engineering Bulletin Radon mapping in Croatia UDC: 910.27 and its relation to geology DOI: 10.17794/rgn.2018.3.1 Review scientiƤ c paper Ana Moste«ak1; Dario Perkovi©2; Frankica Kapor3; Želimir Veinovi©4 1 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, 10000 Zagreb, Croatia 2 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, 10000 Zagreb, Croatia 3 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, 10000 Zagreb, Croatia 4 University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, 10000 Zagreb, Croatia Abstract Radon is known as the main contributor to natural background radiation exposure and the mapping of diơ erent radon phenomenon presents an important task in both a scientiƤ c and regulatory context. Considering the aspect of radon eơ ects on health, identiƤ cation of areas with elevated radon levels is a crucial step in radon monitoring and the preven- tion of adverse eơ ects on the population and the environment. Diơ erent needs regarding the monitoring of the environ- mental radioactivity levels in Europe led to initiatives such as the development of the European Atlas of Natural Radia- tion (EANR). To present diơ erent methods of radon mapping, the European Indoor Radon Map and European Geogenic Radon Map projects are described brieƪ y. The aim of this paper is to present the mapping of diơ erent aspects of radon (indoor and geogenic) and its importance in data visualization and information dissemination. The practical experi- ences worldwide provide context for future activities of radon mapping in Croatia. Existing Croatian initiatives in the Ƥ eld of radon risk research are mostly related to the investigations of indoor radon concentrations and identiƤ cation of radon prone areas through one national study and several focused studies. A comparison of indoor radon levels in Croa- tia and several geological parameters identiƤ ed new areas appropriate for future research that could lead towards a geo- genic map of radon potential in Croatia. Keywords: radon mapping, geology, Croatia, GIS, natural radioactivity. 1. Introduction signi¿ cant amounts. The most common isotope, usually known as radon, is radon-222 (222Rn), which is a mem- One of the main concerns of environmental protec- ber of the 238U decay series with a half-life of 3.82 days. tion is the issue of protection of humans and the environ- The other two isotopes are radon-220 (220Rn), known as ment from harmful levels of exposure and mitigation of thoron, with a half-life of 55.6 s and radon-219 (219Rn), harmful effects arising from the exposure to hazards. known as actinon, with a half-life of 3.96 s. As a colour- Even though the exposure to ionizing radiation from less, tasteless, and odourless gas, radon is dif¿ cult to de- natural sources is considered as “a continuing and ines- tect even in high concentrations. Figure 1 shows the capable feature of life on earth” (UNSCEAR, 2000), complete 238U decay chain. radon is known as the main contributor to natural back- The source and the amounts of radon present in the ground radiation exposure. Besides radon’s importance environment are natural but are also inÀ uenced by an- in radiation prevention and protection, it is also the most thropogenic activities. In rocks and soils, radon is usu- studied geochemical precursor in earthquake prediction research. ally locked inside the mineral matrix but is released to the interstitial space between grains when the radium Radon is an inert, alpha-emitting gas that is generated decays (UNSCEAR, 2000). The radon emanation factor from the uranium series i.e. one of the four known natu- i.e. the fraction of all radon atoms that escape the grains ral decay series that occur naturally, also known as pri- is determined by several characteristics, like the radium mordial radionuclides. It has no stable isotopes and they atom content of the soil and its distance from the parent all differ in their half-lives. Out of 34 known isotopes of radium atom, etc. (Tracy, 2010; Sykora, 2010). Before radon, only three originate from the decay of primordial their release into the atmosphere or their decay, radon radionuclides and two are present in the environment in atoms are transported by diffusion and advection (UN- Corresponding author: Ana Mosteþak SCEAR, 2000). According to Gregoriþ et al. (2012), [email protected] hydro-meteorological conditions govern the exhalation 1-11 Moste«ak, A.; Perkovi©, D.; Kapor, F.; Veinovi©, Ž. 2 Figure 1: Uranium decay chain of radon, while transport in the earth is related to the major public, regulatory, and scienti¿ c interest for two geophysical and geochemical parameters. According to to three decades” (Dubois et al., 2010). The Euratom Etiope and Martinelli (2002) in different geological Treaty requires the European Commission to “collect, scenarios the transport and redistribution of trace gases validate and provide information about the levels of ra- (Rn, He) is often determined by the carrier gases (CO2, dioactivity in the environment” (De Cort et al., 2011). Several authors mention different needs regarding the CH4) which can even be considered as a controlling fac- tor in the transport of rare gases (Etiope and Martinelli, monitoring of the environmental radioactivity levels 2002). Radon is also dissolved in water and tends to re- present on the European legal, regulatory and scienti¿ c main dissolved in water and contribute to the concentra- levels that led to the initiatives such as the development tion of the levels present in the groundwater (Tracy, of the European Atlas of Natural Radiation (EANR) 2010). Radon concentrations in the soil are responsible (Dubois, 2005; Gruber et al.; 2013; Tollefsen et al., for diffusion to the atmosphere, which is dictated by soil 2014; Cinelli and Tollefsen, 2016). The EANR project properties, especially soil moisture (UNSCEAR, 2000) was started by the Radioactivity Environmental Moni- and the pressure gradient. Radon concentration close to toring (ERM) group at the European Commission’s Joint the surface, i.e. a few meters below the ground, provides Research Centre (JRC), with the main objectives of in- information in determining radon exhalation rate in the troducing the concept of natural radioactivity to the gen- atmosphere (UNSCEAR, 2000). There are three main eral public, identifying the areas where natural radioac- factors inÀ uencing indoor radon levels: uranium and ra- tivity levels are elevated and providing reference materi- dium content in the soil/rock, environmental conditions als and data to the scienti¿ c community (Gruber et al., that affect radon’s transport from the soil, and meteoro- 2013; Dubois et al., 2010). EANR should provide an logical parameters that affect the exhalation of radon overview of the different variables related to the sources from the soil to the atmosphere (Ciotolli et al., 2017). of natural radioactivity and their geographic distribution The Harvard Center for Cancer Prevention states that in different stages, e.g. the generation stage and the stage ionizing radiation is the most studied environmental car- of the actual phenomenon that causes concern (Gruber cinogen, with the exception of tobacco smoke (Wake- et al., 2013). The European Indoor Radon Map (EIRM) ford, 2004). According to the UNSCEAR report from project has made signi¿ cant progress and its outputs will 2000, radon health risks related to underground mine be presented in the upcoming section. It was based on exposure were well known, but research on the health national indoor radon measurement initiatives across the effects arising from the indoor radon exposure only Member States. The European Geogenic Radon Map started in the 1970s (UNSCEAR, 2000). For humans, (EGRM) presents a challenging task with the aim of the main exposure pathway for radon is through inhala- mapping only what Earth itself delivers, i.e. the radon tion. Since radon alone is not very active and is elimi- levels resulting from natural reasons, “irrespective of nated from the body, it’s the inhalation of radon decay anthropogenic factors and temporally constant over a products (218Po, 214Po, 214Pb, 214Bi) that poses the greatest geological timescale” (Gruber et al., 2013). In this con- health risk by disposition along the airways and irradia- text, the radon phenomenon is termed as geogenic radon tion of the bronchial tree and lungs (UNSCEAR, 2000). potential (GRP). A more detailed overview of the differ- Besides smoking, exposure to radon progeny is consid- ent aspects of geogenic radon mapping will be given in ered one of the main contributors to the occurrence of the next section. Besides the maps covering the indoor lung cancer (ICRP, 1987; ICRP, 2010; WHO, 2009). radon values and the geogenic radon potential, cosmic Considering the aspect of radon effects on health, identi- radiation, terrestrial gamma, and outdoor radon maps are ¿ cation of areas with elevated radon levels presents a also planned (De Cort et al., 2011). According to De crucial step in radon monitoring and the prevention of Cort et al., the long-term overall goal of the EANR is to adverse effects on the populations and the environment. calculate the total dose caused by the natural radioactiv- According to Dubois et al., map visualization of the ity for a population by using different data and to present occurrence of 222Rn and its decay products “has been of these values in a map (De Cort et al., 2011). The Mining-Geology-Petroleum Engineering Bulletin and the authors ©, 2018, pp. 1-11, DOI: 10.1177/rgn.2018.3.1 3 Radon mapping in Croatia and its relation to geology The Article 103 of the EC Directive 2013/59/Euratom no country used the same methodology.