A geogenic approach for the Radon monitoring and the exposure assessment at a regional scale: The results of the Rad_Campania project

Adv. Geosci., 52, 87–96, 2020 https://doi.org/10.5194/adgeo-52-87-2020 © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. A geogenic approach for the Radon monitoring and the exposure assessment at a regional scale: The results of the Rad_Campania project Simona Mancini1,2 , Michele Guida1,2 , Albina Cuomo3 , and Domenico Guida3,4 1 Department of Computer Engineering, Electrical Engineering and Applied Mathematics (DIEM), University of Salerno, Fisciano, 84084, Italy 2 Laboratory of Environmental Radioactivity “Ambients and Radiations” (Amb.Ra.), University of Salerno, Fisciano, 84084, Italy 3 Department of Civil Engineering (DICIV), University of Salerno, Fisciano, 84084, Italy 4 interUniversity Centre for the Prediction and Prevention of Major Hazards (CUGRI), University of Salerno, Fisciano, 84084, Italy Correspondence: Simona Mancini () Received: 31 May 2020 – Revised: 14 September 2020 – Accepted: 17 September 2020 – Published: 5 November 2020 Abstract. The aim of this paper is to analyse and discuss the results of the regional program Rad Campania for the monitoring and the assessment of the radon risk. An innovative methodology, based on a geogenic approach, was developed, supported by a comprehensive campaign of radon measurement performed in soil gas, natural waters, drinking natural water samples and indoor air. Data refer to field measurements carried out in three provinces of the Campania Region (Italy): Salerno, Avellino and Benevento. The programme was completed with the main purpose to investigate the peculiarities of the radon issue at a provincial scale and to redact a map of the radon potential from soil as a tool for authorities to recognise critical areas (“Radon prone areas”) to monitor. Since the experience demonstrates that the high radon potential from soil is not indicative of high indoor radon concentrations, in this paper the authors have tried to identify a possible general correlation between geological features of the soil and structural characteristics of the buildings, elaborating more in depth all data collected. The main purpose is to categorize and analyse the performance of different kind of construction, typical of the local area, in order to develop, in a future work, an indicator of the building performances as a useful tool, for authorities, to recognise constructions potentially more exposed to high indoor radon activity concentrations. Results and perspectives have been discussed. 1 Introduction Since its very first moments on the Earth, Mankind has been continuously exposed to ionizing radiations from environmental radioactivity, consisting in three kinds of contribution: cosmogenic, primordial and anthropogenic. Among them, the one produced by naturally occurring primordial sources provides the largest percentage to the human exposure. The most important primordial source is constituted by radionuclides, such as 40 K and the uranium and thorium decay families (238 U, 232 Th and 235 U series). Many of the intermediate radioisotopes in these chains are metals and chemically reactive. For this reason, once formed by the predecessor’s decay, they remain confined in the rocks, where they were generated, unless dispersed into the environment due to the erosion mechanisms made by weathering processes. The only exception is represented by radon, the heaviest chemical noble element, which occurs in the gaseous state at Standard Temperature and Pressure (STP) conditions and naturally does not create chemical bonds. It tends, therefore, to migrate within the rock materials in the soil, where it has been formed (emanation process), and transported in the near-surface soils by fluid carriers (water, air, CO2 , CH4 ), through advective and diffusive displacements, favoured by the soil mechanical characteristics, (porosity, structure and particle size) and the environmental conditions reaching the atmosphere (exhalation process) or spatial locations distant Published by Copernicus Publications on behalf of the European Geosciences Union. 88 from the source (Hosoda at el., 2012; Stavitskaya et al., 2019). The most abundant naturally occurring radon isotope is 222 Rn (half-life of 3.82 days) and, also from the human health protection point of view the most relevant together with its short-lived alpha emitting progeny. In fact, regarding its relevance as hazard for humans, this radionuclides easily bind to the aerosol present in the indoor air, and, once inhaled, deposit on the bronchial tree, where emitting alpha ionizing radiation turns to be harmful for basal cells of the bronchial epithelium, critical targets for any cancerous changes (Ismail and Jaafar, 2011). Inhalation of radon and its decay products contributes to about the 50 % of the individual annual dose due to natural radioactivity and is considered the most important cause of lung cancer, after smoking (WHO, 2009). Because at the moment there is no known threshold value below which radon exposure carries “zero Risk” of lung cancer to humans, there is a general interest and concern to minimize the exposure of the population to levels as low as possible. Besides its relevance as a harmful hazard for people health, radon has such peculiar physical features that make it extremely useful in environmental and earth science (Baskaran, 2016). Radon assessment has been used like one additional tool (seismic precursor) to register the possible occurrence of seismic events by means of its possibly occurring activity concentration anomalies (Buttafuoco et al., 2007; Iovine et al., 2018), associated to land movements due to volcanic eruptions and occurring in geothermal areas; in fact, gases can be released can be generated and pressurized by hot regions such as volcanos and stress can be generated by the build-up of strains that precede earthquakes and volcanic eruptions (De Lauro et al., 2009; Falanga et al., 2019). The main exposure to high radon activity concentrations generally occurs in basement or/and poor ventilated environments, where, once exhalated in the air from a source (soil is the most relevant one), radon can accumulate reaching levels harmful for the occupants. Building materials play a secondary role and in some cases water and gas supplies represent a further non-negligible source. Outdoor radon level is in the range of 5–15 Bq/m3 range, due to the effectiveness of mixing processes in the atmosphere (Nero, 1989; Nero and Nazaroff, 1984, 1988, UNSCEAR, 2000). But, even in presence of a relevant source of radon production, the total indoor activity concentration mainly depends on the ability of the gas to penetrate inside a closed environment. Radon migration depends on two independent processes: the advection mechanism driven by a pressure gradient and the molecular diffusion, due to gas concentration gradient. The parameters affecting the transport process are essentially the diffusion coefficient and the permeability o (...truncated)