Internal Dose from radioactive ceasium in Indoor Dust collected in Ibaraki and Chiba Prefectures, 150-200 km South from the Fukushima Daiichi Nuclear Power Plant

摘要

The radiation dose effects due to the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident are of public concern. Although indoor dust is an important exposure route for some hazardous chemicals, the radiation exposure dose from the radioactive caesium (Cs) in it has not been well investigated yet. In this study, we measured the radioactive Cs in the indoor dust of private houses in order to estimate the resulting human exposure. We collected vacuum cleaner dust twice (in April and June 2012, n = 250 and 241, respectively) in the prefectures of Chiba and Ibaraki, from houses located 150-200 km south from the'FDNPP. The activity concentrations of Cs-134 and Cs-137 in the indoor dust were measured using germanium y-ray detectors, and the exposure dose was calculated and the household-to-household variations (e.g., in terms of surrounding environment and spontaneous decontamination activities) were analysed. The median activity concentrations of Cs-134 + Cs-137 in the indoor dust collected in April and June were 1,470 and 1,340 Bq/kg, respectively. The median committed effective doses via indoor dust ingestion were estimated as 0.73, 0.66, and 0.43 × 10A-3 mSv/year, and those via inhalation were estimated as 0.003, 0.004, and 0.006 × 10A-3 mSv/year for one-and ten-year-old children and adults, respectively. The univariate analysis revealed that the radioactive Cs concentration was higher in samples collected from detached houses than from multiple dwellings. Within the detached houses, the multiple regression analysis showed that wet wiping was a significant reduction factor of the Cs concentration; however, the small determination coefficient implies the presence of factors that were not considered in this study. In conclusion, in this study area, the estimated committed effective doses via indoor dust related to the FDNPP accident were comparable to those via soil and much smaller than the long-term target dose of 1 mSv/year.