Short-term metabolism of biologically incorporated ¹²⁵I ingested by olive flounder (Paralichthys olivaceus)

Iodine-129 with a long half-time of 1.6 × 10⁷ y was discharged into the Pacific Ocean during the final safety tests of the first commercial nuclear fuel reprocessing plant in Japan, at Rokkasho, Aomori Prefecture. Olive flounder (Paralichthys olivaceus) is an important fishery along this coast. It is necessary to determine whether ¹²⁹I accumulates in this species to assess the possible public acceptance. We developed a short-term metabolism model of ¹²⁵I in the flounder using retention data for 1-6 days after the olive flounder had ingested a freshwater fish species, medaka (Oryzias latipes), that had been labeled with ¹²⁵I by keeping them in water containing ¹²⁵I for 7 days. A single compartment model constructed from whole-body retention data for ¹²⁵I in the olive flounder, excluding the gastrointestinal tract and its contents, revealed a biological half-time of 2.9 days for ¹²⁵I. When the gill and other tissues were separated to individual compartments, the biological half-time in the gill was three times longer than that in the other tissue, though the half-time in the gill is not statistically significant. The distribution of ¹²⁵I among various tissues in the flounder 6 days after the ingestion of labeled medaka once a day for 6 days differed from that of stable I, suggesting that the biological half-time is longer in certain tissues. Further study is necessary to elucidate the metabolism of radioiodine in the flounder.