Radon isotopes (222Rn and 220Rn) generated within the upper layers of the Earth's crust by the radioactive decay of the 238U and 232Th can migrate during its brief lifetime to the atmosphere, and can enter and accumulate in indoor environments. However, background radon concentrations in the soil pores are specific of the different lithology depending on its parent nuclide 226Ra. Both background and deep radon components, defined as Geogenic Radon Potential (GRP), may lead to a human health concern: a portion of the inhaled air will contain radon, and solid short-lived radon decay products that, bound to fine aerosol particles, are inhaled, and irradiate lung and bronchial tissues. This suggests that the identification of risk areas cannot be disconnected from the underground geological environment (i.e., GRP). A survey conducted by ISPRA Ambiente (formerly ANPA, National Agency for Environmental Protection) and ARPA (the Regional Agency for Environmental Prevention and Protection) in the Veneto region of northeastern Italy, showed that indoor radon measured in the Euganean Hills district exceeds the reference values (300 Bq/m3) recommended by the European Community (Council Directive 2013/59/Euratom 5/12/2013), thus suggesting the need to investigate the possible link between the observed radon concentrations and the geological and geophysical framework of this densely populated area. Radon and thoron concentrations in soil gas were measured in situ by using the Durridge radon equipment (RAD7, Durridge UK Ltd.) in order to provide a representative coverage of the Euganean Hills. Geo-statistically treated data provide a reliable risk map connecting soil gas radon concentrations with different bedrock types and soil features, 238U decay progeny and geology. Moreover, sets of measurement points along profiles crossing structural discontinuities, such as faults and lithological contact zones, clarify their effects and influences on soil radon emission at surface, yielding a better understanding of the migration mechanisms at the base of deep radon remobilization by channelling and enrichment in the soil. Preliminary results confirm that the most important geological characteristics affecting radon concentrations in soil gas are both lithology and structural features. The highest radon concentrations occur in areas characterised by silicic volcanic and sub-volcanic rocks, such as rhyolites, trachytes, basalts and latites, and in zones close to the main structural lineaments. The estimation of the deep radon and its exhalation rate at surface is a key factor in predicting indoor concentrations, and hence two main quantities: the doses to dwellers and the risk level. Moreover, the identification of radon priority areas, as requested in the new Euratom directive, can serve as a useful guide in land use planning and in construction siting.
Geological and geochemical control on Radon occurrence in Euganean Hills district (North-Eastern Italy)
Coletti Chiara;Mazzoli Claudio;Sassi Raffaele
2017-01-01
Abstract
Radon isotopes (222Rn and 220Rn) generated within the upper layers of the Earth's crust by the radioactive decay of the 238U and 232Th can migrate during its brief lifetime to the atmosphere, and can enter and accumulate in indoor environments. However, background radon concentrations in the soil pores are specific of the different lithology depending on its parent nuclide 226Ra. Both background and deep radon components, defined as Geogenic Radon Potential (GRP), may lead to a human health concern: a portion of the inhaled air will contain radon, and solid short-lived radon decay products that, bound to fine aerosol particles, are inhaled, and irradiate lung and bronchial tissues. This suggests that the identification of risk areas cannot be disconnected from the underground geological environment (i.e., GRP). A survey conducted by ISPRA Ambiente (formerly ANPA, National Agency for Environmental Protection) and ARPA (the Regional Agency for Environmental Prevention and Protection) in the Veneto region of northeastern Italy, showed that indoor radon measured in the Euganean Hills district exceeds the reference values (300 Bq/m3) recommended by the European Community (Council Directive 2013/59/Euratom 5/12/2013), thus suggesting the need to investigate the possible link between the observed radon concentrations and the geological and geophysical framework of this densely populated area. Radon and thoron concentrations in soil gas were measured in situ by using the Durridge radon equipment (RAD7, Durridge UK Ltd.) in order to provide a representative coverage of the Euganean Hills. Geo-statistically treated data provide a reliable risk map connecting soil gas radon concentrations with different bedrock types and soil features, 238U decay progeny and geology. Moreover, sets of measurement points along profiles crossing structural discontinuities, such as faults and lithological contact zones, clarify their effects and influences on soil radon emission at surface, yielding a better understanding of the migration mechanisms at the base of deep radon remobilization by channelling and enrichment in the soil. Preliminary results confirm that the most important geological characteristics affecting radon concentrations in soil gas are both lithology and structural features. The highest radon concentrations occur in areas characterised by silicic volcanic and sub-volcanic rocks, such as rhyolites, trachytes, basalts and latites, and in zones close to the main structural lineaments. The estimation of the deep radon and its exhalation rate at surface is a key factor in predicting indoor concentrations, and hence two main quantities: the doses to dwellers and the risk level. Moreover, the identification of radon priority areas, as requested in the new Euratom directive, can serve as a useful guide in land use planning and in construction siting.
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