Gastrointestinal absorption rate in rats for radioeesium in soil collected near fukushima power plant or doped artificially with 134CsCl

Abstract

The whole-body retention of radiocesium derived from soil was investigated in Wistar strain rats using three types of environmentally contaminated soil containing 134Cs and 137Cs collected in Fukushima Prefecture, garden soil doped with 134CsCl solution, and ionic solutions of 134CsCl. Approximately 44-67% of the administered activity of the 134Cs and 137Cs in the three types of soil was cleared exponentially in 12 h, with a half-life of 2.9-7.9 h, and the remaining activity decreased below the detection limit by 30 h after initial administration. In the rats administered with the artificially contaminated soil, a biphasic retention curve (fast and slow) was observed, because the radioactivity administered was high enough to trace over the long-term. Approximately 84% and 16% of the administered activity was cleared with half-lives of 4.5 and 173 h, respectively. In contrast, approximately 23% and 77% was cleared with half-lives of 17 and 166 h, respectively, in the rats administered with the 134Cs in ionic solution. By analyzing the retention curve, we estimated that only 21% of orally administered radioeesium in artificially doped soil was absorbed into the gastrointestinal tract. This suggests that if the dose coefficient indicated by systemic models for Cs of the International Commission on Radiological Protection, in which gastro-intestinal absorption rate is assumed to be 1.0 for public, is used for the radiocesium in soil, the effective dose may be significantly larger than the actual dose.