Geolocation of premises subject to radon risk: Methodological proposal and case study in Madrid☆
Graphical abstract
Introduction
Uranium (U-238), an element present on the planet since it formed, is the head of the natural decay chain of radionuclides that includes radon (Rn-222).
Inhaled radon gas (222Rn) is a well-known carcinogen (IARC, 1998) and the leading source of ionising radiation to which the population at large is exposed (UNSCEAR, 2000). After pooling epidemiological studies for Europe (Darby et al., 2005), China (Lubin et al., 2004) and North America (Krewski et al., 2006), the World Health Organization estimates that the risk of lung cancer rises 16% for every extra 100 Bq/m3 in radon concentration (WHO, 2009).
Radon is presently acknowledged to be the second leading cause of lung cancer after smoking and the number one cause of lung cancer in non-smokers (WHO, 2009), accounting for 3%–14% of cases worldwide. Around 100 000 deaths from lung cancer are attributed to indoor radon exposure worldwide (Lim et al., 2012) and 21 000 in the United State of America (EPA Environmental Protection Agency, 2003).
Other factors such as occupation, premise use profiles, genetics, diet and especially tobacco related habits, are vital to accurately calculating data on lung cancer. (Ruano-Ravina, Figueiras, and Barros-Dios, 2003).
Aware of the implications for public health, in 2013 the European Commission adopted Directive 2013/59/Euratom (European Parliament, 2014) setting out the guidelines for legislation to be enacted by EU Member States. The Directive requires Member States to coordinate measures adopted by the authorities involved under ‘national action plans’, map high-risk areas, establish radon measurement and diagnostic protocols and lay down construction guidelines to mitigate or prevent indoor radon ingress in buildings.
In Spain, radon exposure at the workplace has been regulated since 2011 (BOE, 2012) and a maximum recommended level for housing has been set at 300 Bq/m3 (CSN Spanish Nuclear Safety Council, 2012). The national radon action plan is still in the drafting stage, however, although some progress has been made, driven by Directive 2013/59/Euratom. More specifically, a new addition to the Technical Building Code on radon protection measures (prepared and made available for public review and comment in July 2018) would require the adoption of different levels of radon protection in new builds depending on the local radon risk classification. Integrating land use and geolocated cadastral data with radon risk categories would contribute to more effective protection, prevention and risk communication policies and strategies.
Spain's Nuclear Safety Council (CSN) made an early attempt to formulate a radon map of the country under its MARNA (Spanish initials for natural gamma radiation map) project (Suarez et al., 2000). MARNA was drawn from 799 440 gamma radiation measurements made at an elevation of 1 m above ground. Using cut-off values of 7.5 and 14 μR/h (19.35 × 10−10 C/kg·h and 36.12 × 10−10 C/kg·.h), the country was divided into three radon risk regions based on empirical linear regression analysis of the relationship between γ−radiation levels and 226Ra content in soils to model indoor radon concentrations using the RESRAD code (Garcia-Talavera San Miguel et al., 2013a).
In the same timeframe, the existing indoor radon measurement database grew substantially under the 10 × 10 project, coordinated by the University of Cantabria with the Autonomous University of Barcelona (UAB) and the University of Santiago de Compostela (USC) as collaborating institutions (Sainz-Fernandez et al., 2014). By the time the project drew to an end, Spain had a database of over 12 000 radon measurements.
That number was clearly insufficient, however, to formulate a radon risk map based on radon measurements alone. The resolution of such maps logically depends on the number of measurements available. In recent decades, extensive indoor radon surveys have been conducted in a number of countries to narrow geolocation data uncertainties. In the United Kingdom, for instance, over half a million radon concentration readings have been made in dwellings (Health Protection Agency, 2009).
In Spain, a hybrid method was designed, combining indoor radon measurements with other co-related variables (García-Talavera et al., 2013b); in particular, gamma radiation and lithostratigraphic information was combined with the available indoor radon measurements to produce the country's radon potential map (https://www.csn.es/mapa-del-potencial-de-radon-en-espana). Similar hybrid approaches using geological parameters (Miles and Appleton, 2005, Drolet et al., 2014), soil gas radon (Cinelli et al., 2015) or uranium content in bedrock (Ielsch et al., 2017) have been proposed, used and compared (Chen and Ford, 2017) (Watson et al., 2017). Methods have also been put forward recently to enhance the resolution of Europe-wide radon risk maps for the European Atlas of Natural Radiation (Ciotoli et al., 2017).
The present exercise combines Spain's radon potential map with urban and building data from official records and regional radon risk classifications to formulate indicators usable for radiological protection studies and mitigation policies.
That 1:200 000 scale radon potential map (https://www.csn.es/mapa-del-potencial-de-radon-en-espana) classifies regions by indoor radon potential concentration on a five-point scale defined in terms of the 90th percentile. In an area classified in the highest risk category, ‘5_P90 > 400 Bq/m3’, for instance, 90% of the buildings would have levels lower and 10% higher than 400 Bq/m3. In the Madrid region shown in Fig. 2, risk was found to be highest (orange shading) in the mountains where the terrain is predominantly granitic (Hercynian geosyncline).
Section snippets
Objective
This proposal constitutes an innovative approach to depicting housing-related data from population census and cadastral records on building use and urban land occupancy. By cross-referencing the Information on potential radon risk by geographic location with data from other sources, the proposal aims to describe the details constituting the human and building fabric in a given area affected by radon, i.e., the number and type of premises built in the area and the number of inhabitants involved.
Method
The procedure implemented consisted in cross-referencing:
- (1)
data on potential risk by type of terrain, identified in the Spanish Nuclear Safety Council's potential radon risk map (CSN, 2017) and
- (2)
data on urban land, population and habitable premises in contact with the terrain, further to the criterion set out below on vulnerability to radon ingress.
Radon is the result of the spontaneous disintegration of radium 226, present in soil, rock and water in concentrations that vary with terrain geology (
Results
This section describes the results of filtering and cross-referencing in the two stages of the study.
Discussion
Cross-referencing census, cadastre and land occupancy data for the geographic areas of potential risk yields indicators that can be used to analyse radon risk from different perspectives.
The percentage of urban land area located on radon risk terrain 4 or 5 (>300 Bq/m3) by number of municipalities is shown if Fig. 5. This bar plot was built from data collected in Stage 1 (see sections 3. Method and 4. Results for further details).
According to Fig. 5 and 96 municipalities were sited primarily on
Conclusions
The method proposed detects urban areas in which buildings are at risk of radon ingress and classifies them into risk categories. That information can be used, for instance, to define the municipalities affected with a view to preventive measures. When applied to the region of Madrid, the method classified the municipalities by size of the population possibly affected. According to the findings, in more than 70% of the built land area in 65 of a total of 179 municipalities (Fig. 5), at least
Acknowledgements
This study, conducted at the Eduardo Torroja Institute for Construction Science, was funded by the Spanish National Research Council (CSIC) [BIA 2014-58887-R], a body under the aegis of Spain's Ministry of Economy and Competitiveness.
Nuclear Safety Council permission to reproduce the potential radon risk maps included in this paper is gratefully acknowledged.
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Cited by (0)
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This paper has been recommended for acceptance by Dr. Kimberly Hageman.