Abstract
Thoron (220Rn), an isotope of radon with a strong α-decay energy, and its short-lived metallic progeny can pose an elevated lung cancer hazard in room air when unfired-soil derived building materials are used in earthen dwellings. Changes in moisture content and density influencing the thoron exhalation rate from earthen materials into room air were studied in the laboratory with terra rossa from a village on the Ðồng Văn Karst Plateau Geopark, Việt Nam, where ethnic minorities construct traditional dwellings with unfired terra rossa walls and floors. Our results show that the thoron exhalation rate from mud surfaces depends on (i) the content of radioactive parental nuclides in mineral components; (ii) the moisture content of mud where ∼5–10 weight % water maximizes the 220Rn exhalation rate; and (iii) the density of dry mud as primarily controlled by internal macroscopic voids, fractures, and porosity. Additional time-series of 220Rn exhalation data from an interior mud wall of a terra rossa-built house under different seasonal and weather conditions show that the temperature is influencing thoron exhalation via the water vapor pressure deficit (VPD) in air and the associated amount of atmospheric moisture adsorbed onto indoor mud surfaces. Our data suggest that occupants of “mud house” earthen dwellings in northern Việt Nam are exposed to an increased thoron geohazard during cooler weather, low VPD, and high relative humidity in air. Detailed studies are needed to evaluate the thoron geohazard for inhabitants of mud-built dwellings in other climates and geological terrains.
Highlights
Most radioactivity in room air of buildings is typically caused by radon isotopes and their radioactive metallic progeny after exhalation of radon isotopes from building materials, soil, sediment, and rock containing parental radionuclides
This study addresses the thoron geohazard from terra rossa that is typically utilized by economically disadvantaged ethnic minorities for the construction of traditional earthen dwellings in mountainous regions of northern Viê.t Nam
The measured concentrations for 226Ra and 232Th in terra rossa samples are above their corresponding worldwide average concentrations in natural soils (i.e., 35 Bq kg−1 for 226Ra and 30 Bq kg−1 for 232Th), whereas the concentrations of 40K in terra rossa samples fall below the worldwide average concentration of 400 Bq kg−1 for 40K in soils
Summary
Most radioactivity in room air of buildings is typically caused by radon isotopes and their radioactive metallic progeny after exhalation of radon isotopes from building materials, soil, sediment, and rock containing parental radionuclides. The name of the element radon is often used uncritically and synonymously for the isotope 222Rn (Faheem and Matiullah, 2008; Chen et al, 2010; Sakoda et al, 2010; Hassan et al, 2011; Bavarnegin et al, 2013; Yang et al, 2019), whereas few studies are concerned with the exhalation of the radon isotope 220Rn called thoron with a half-life of only 55.6 s (Tuccimei et al, 2006; Hosoda et al, 2007; Ujicet al., 2008, 2010; Kanse et al, 2013). The relatively short half-life of 220Rn and its limited transport distance via diffusion and convection from solid sources into room air often results in the common misconception that thoron exhalation and its radiation geohazard from building materials are negligible. In light of the World Health Organization (WHO) (2009) efforts to reduce radiation from radon, proper recognition of the thoron radiation geohazard is important, especially for inhabitants of unfired soil-derived dwellings with significant concentrations of thoron in room air (Meisenberg and Tschiersch, 2011; Meisenberg et al, 2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
