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Intake of radon through skin from thermal water

The biokinetics of radon in the body has previously been studied with the assumption that its absorption through the skin is negligibly. In general indoor conditions, the uptake via the lungs is much higher than via the skin. However, there are specific situations, such as bathing in a radon hot spring where the radon concentration in thermal water is far higher than that in air. The present study focused on such a situation in order to better understand the biokinetics of radon. To mathematically express the entry of radon through the skin into the body, we first modified the latest sophisticated biokinetic model for noble gases (Fig.1). Values of an important parameter for the model—the skin permeability coefficient K (m s−1)—were derived using data from previous human studies. The analysis of such empirical data, which corresponded to radon concentrations in the air exhaled by subjects during and following bathing in radon-rich thermal water, revealed that the estimated K values had a log-normal distribution. The impact of the intake of radon or its progeny via inhalation or skin absorption on radiation dose was assessed for possible exposure scenarios in a radon hot spring. It was concluded that, depending on the radon concentration in thermal water, there might be situations in which the dose contribution resulting from skin absorption of radon is comparable to that resulting from inhalation of radon and its progeny (Fig.2). This conclusion can also apply to other therapeutic situations (e.g. staying in a pool for a longer treatment period).

  • Fig. 1. Schematic diagram of the biokinetic model for inhaled, ingested or skin absorbed radon. RT-air, respiratory air; Breast-g, glandular tissue of breast; Breast-a, adipose tissue of breast; HATM, Human alimentary tract model.
  • Fig. 2. Comparisons between the model calculations and human studies of radon concentrations in exhaled air during and after bathing in thermal water. Experimental data: Furuno, 1982. The solid curve was obtained by the use of the best estimated K which was determined by fitting the experimental data. Taking into account the contribution of each exposure route, the curve ‘Total’ was then separated into inhalation and skin uptake.


Sakoda, A.; Ishimori, Y.; Tschiersch, J.: Evaluation of the intake of radon through skin from thermal water. J. Radiat. Res. 57, 336-342 (2016)

Bedeutung für die Mission des Helmholtz Zentrums München:
For treatment of chronic complex diseases (e.g. spondylitis ankylosans) frequently radon baths are applied. So far it was unclear whether skin uptake causes a significant dose contribution.

HMGU mission: The Helmholtz Zentrum München develops the fundamental principles for medicine of the future and a personalized medicine, focused on the causes of the chronic complex diseases diabetes and lung diseases. We are also making important contributions to the mechanisms of neuropsychiatric diseases, cancer, cardiovascular diseases, allergies and infectious diseases. Additionally, we investigate ecological systems with essential significance for human health.

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