Radon solubility and diffusion in the skin surface layer

皮膚表面層におけるラドンの溶解と拡散

迫田 晃弘   ; 石田 毅*; 神崎 訓枝   ; 田中 裕史 ; 片岡 隆浩*; 光延 文裕*; 山岡 聖典*

Sakoda, Akihiro; Ishida, Tsuyoshi*; Kanzaki, Norie; Tanaka, Hiroshi; Kataoka, Takahiro*; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*

ラドン温泉の入浴のような温泉水中のラドン濃度が空気中よりも著しく高い状況においては、皮膚を通じたラドンの摂取が起こるため、より正確な線量評価には本経路を考慮すべきであると考えられている。本研究の目的は、皮膚表面層(角質層)に着目して、皮膚中のラドン分布と拡散の程度を明らかにすることである。角層での拡散理論を含む体内動態モデルを作成し、その重要なパラメータである角層へのラドン溶解度を測定した。モデル計算により、角質層におけるラドンの拡散係数は、一般的なラドン難透過シートと同程度に低いことが示された。入浴20分間後の皮膚中ラドンの深さ分布について、皮膚最表面のラドン濃度は表皮・真皮層の1000倍ほど高いことがわかった。ラドンの位置情報は、皮膚に特定の標的細胞を想定するような線量評価に貢献すると考えられる。

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 layers (i.e., stratum corneum). We made a biokinetic model that included diffusion theory at the stratum corneum, and measured radon solubility in the stratum corneum to get 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. The depth profile of radon in the skin was found to be that after a 20-minute immersion in water, the radon activity concentration at the top surface skin layer was approximately 1000 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.