Use of Iodine-131 to Tellurium-132 Ratios for Assessing the Relationships between Human Inhaled Radioactivity and Environmental Monitoring after the Accident in Fukushima

Significant differences in findings were seen between the intake amounts of iodine-131 that were derived from direct measurements and the estimated intake from environmental monitoring data at the Fukushima accident. To clarify these discrepancies, we have investigated the iodine-131 and tellurium-132 body burdens of five human subjects, who after being exposed to a radioactive plume, underwent 21.5 h whole body counter measurements at Fukui Prefectural Hospital, so clear intake scenario and thyroid counter measurement data were available. To determine the iodine-131 and tellurium-132 body burdens, we introduced a new method of whole body counter calibration composed of a self-consistent approach with the time-dependent correction efficiency factors concept. The ratios of iodine-131 to tellurium-132, ranging from 0.96 ± 0.05 to 2.29 ± 0.38, were consistent with results of the environmental measurements. The 24 h iodine uptake values ranging from 12.1-16.0% were within euthyroid range in Japanese people. These results suggest, even if the relatively low thyroid iodine uptake in the Japanese population was taken into consideration, that there is no doubt about the consistency between direct measurements and environmental monitoring data. Adequate intake scenario is suggested to be principally important to estimate the inhaled radioactivity in areas in or around nuclear accidents.