Dosimetry of radon progeny deposited on skin in air and thermal water

Exposure to radon gas in groundwater in southwest Angola (Lubango-Huíla): Implications of geology and climate change

In southern African countries most of the population uses groundwater collected in dug wells for domestic consumption instead of water from public distribution systems. To investigate the impact of natural and human factors on urban groundwater quality, 276 samples were collected in the Lubango region (Angola) in water distribution systems and dug wells ranging from a few meters to almost one hundred meters in depth. Radon concentrations (RC) were determined by liquid scintillation counting according to ISO 13164-4:2015. Geology is the main source of the variability of RC, with median values higher than 100 Bq/L in granitoid units and lower values in mafic and sedimentary units (ranging from 5 to 38 Bq/L). On average, RC was higher in dug wells compared to public water distribution systems. The annual effective dose due to ingestion of radon in water is, on average, ten times lower in the later compared to dug wells. Therefore, from a public exposure perspective, water distribution systems are preferred as means for water distribution. A severe multi-year meteorological drought over the past decade affecting 76-94 % of the population in southern Angola has been linked with climate change. Consequently, a regional lowering of the water table was observed, as well as a reduction in the productivity of shallower wells, leading to a search for water at greater depths. This work demonstrates an increase in median RC from 66 Bq/L in wells shallower than 30 m to values over 100 Bq/L with increasing depth of water extraction and for the same geological unit. The highest RC observed were also observed at the deepest wells. The dose ingested is proportional to RC, being also higher at deeper water extraction depths. The increase in public radiation exposure from radon ingestion due to water extraction at greater depths is attributed to the underlying issue of climate change. Monitoring water quality in terms of radionuclide concentration is advised to ensure the exposure to ionizing radiation remains at acceptable levels in the future.

Radon Solubility and Diffusion in the Skin Surface Layer

In specific situations such as bathing in a radon spa, where the radon activity concentration in thermal water is far higher than that in air, it has been revealed that radon uptake via skin can occur and should be considered for more precise dose evaluation. The primary aim of the present study was to numerically demonstrate the distribution as well as the degree of diffusion of radon in the skin, with a focus on its surface layer (i.e., stratum corneum). We developed a biokinetic model that included diffusion theory at the stratum corneum, and measured radon solubility in that tissue layer as a crucial parameter. The implementation of the model suggested that the diffusion coefficient in the stratum corneum was as low as general radon-proof sheets. After a 20-min immersion in water, the simulated depth profile of radon in the skin showed that the radon activity concentration at the top surface skin layer was approximately 103 times higher than that at the viable skin layer. The information on the position of radon as a radiation source would contribute to special dose evaluation where specific target cell layers are assumed for the skin.

Dosimetric Comparison of Exposure Pathways to Human Organs and Tissues in Radon Therapy

Three therapeutic applications are presently prescribed in the radon spas in Gastein, Austria: exposure to radon in a thermal bath, exposure to radon vapor in an exposure chamber (vapor bath), and exposure to radon in the thermal gallery, a former mine. The radiological exposure pathways to human organs and tissues in these therapeutic radon applications are inhalation of radon and radon progeny via the lungs, radon transfer from water or air through the skin, and radon-progeny deposition on the skin in water or air. The objectives of the present study were to calculate radon and radon-progeny doses for selected organs and tissues for the different exposure pathways and therapeutic applications. Doses incurred in red bone marrow, liver, kidneys, and Langerhans cells in the skin may be correlated with potential therapeutic benefits, while doses to the lungs and the basal cells of the skin indicate potential carcinogenic effects. The highest organ doses among the three therapeutic applications were produced in the thermal gallery by radon progeny via inhalation, with lung doses of 5.0 mSv, and attachment to the skin, with skin doses of 4.4 mSv, while the radon contribution was less significant. For comparison, the primary exposure pathways in the thermal bath are the radon uptake through the skin, with lung doses of 334 μSv, and the radon-progeny attachment to the skin, with skin doses of 216 μSv, while the inhalation route can safely be neglected.