Validating the application of the revised ICRP's biokinetic models for organic C and organically bound tritium to members of the public

C標識有機物及び有機結合トリチウムに関するICRPの体内動態モデル改訂版の一般市民への適用検証

増田 毅*; 真辺 健太郎   

Masuda, Tsuyoshi*; Manabe, Kentaro

HやCを含む有機物を体内に取り込んだ場合、一定の割合で無機物に代謝されて素早く排泄される。一方、有機物のまま残留したHやCは無機物に比べて生物学的半減期が長く、被ばく線量への寄与が大きい。そのため、有機物の代謝割合が線量評価上重要となる。しかしながら国際放射線防護委員会(ICRP)は、動物実験又は炭素の物質収支から代謝割合を設定している。そこで、重水素やCで標識した有機物をヒトに経口摂取させて代謝割合を測定した結果を参照して線量評価を行った。その結果、ICRPの線量係数は、H有機物については適切であったものの、C有機物については2倍程度保守的な評価であることが明らかになった。

If organic compound containing tritium or C-14 is taken into the body, it is metabolised into inorganic matter at a certain rate and excreted quickly. On the other hand, tritium and C-14 that remain in the organic form have a longer biological half-life than inorganic forms, and therefore contribute more to the radiation dose. For this reason, the metabolic ratio of organic matter is important for dose assessment. However, the International Commission on Radiological Protection (ICRP) sets the metabolic ratio based on animal experiments or carbon mass balance. Therefore, we conducted a dose assessment by referring to the results of measuring the metabolic ratio by orally administering organic matter labelled with deuterium or C-13 to humans. As a result, it was found that the ICRP dose coefficient was appropriate for organic matter containing tritium, but that it was about twice as conservative for organic matter containing C-14.