Bioaccessibility of Fukushima-Accident-Derived Cs in Soils and the Contribution of Soil Ingestion to Radiation Doses in Children

Assessment of cyto- and genotoxic effects of Cesium-133 in Vicia faba using single-cell gel electrophoresis and random amplified polymorphic DNA assays

The aim of this study was to evaluate the ecotoxic effect of high concentration cesium (Cs) exposure on plant root growth and its toxicological mechanism. The radicle of broad bean (Vicia faba) was selected as experimental material. The cytotoxic and genotoxic effects of plants exposed to different Cs levels (0.19-1.5 mM) for 48 h were evaluated using scanning electron microscopy (SEM), X-ray fluorescence (XRF) analysis, single-cell gel electrophoresis (SCGE) and random amplified polymorphic DNA (RAPD) assays. The results showed that radicle elongation decreased clearly after 48 h of exposure treatment with different concentrations of Cs solution. The root cell structure was obviously damaged in the Cs treatment groups (0.19-1.5 mM). At a Cs concentration of 1.5 mM, the percentages of viable non-apoptotic cells, viable apoptotic cells, non-viable apoptotic cells, and non-viable cells were 40.09%, 20.67%, 28.73%, and 10.52%, respectively. SCGE showed DNA damage in radicle cells 48 h after Cs exposure. Compared with the control group, the percentage of tail DNA in Cs exposed group (0.38-1.5 mM) increased by 0.56-1.12 times (P < 0.05). RAPD results showed that the genomic stability of V. faba radicles decreased by 4.44%-15.56%. This study confirmed that high concentration Cs exposure had cytotoxicity and genotoxicity effects on plants.

Estimation of the radiation dose via indoor dust in the Ibaraki and Chiba prefectures, 150-200 km south from the Fukushima Daiichi Nuclear Power Plant

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. Hence, 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 ¹³⁴Cs and ¹³⁷Cs in the indoor dust were measured using germanium γ-ray detectors, and the exposure dose was calculated and the household-to-household variations were analysed. The median activity concentrations of ¹³⁴Cs + ¹³⁷Cs in the indoor dust collected in April and June were 1470 and 1340 Bq kg^-1, respectively. The median committed effective doses via indoor dust ingestion were estimated as 0.73, 0.66, and 0.43 × 10^-3 mSv year^-1, and those via inhalation were estimated as 0.03, 0.04, and 0.06 × 10^-3 mSv year^-1 for one- and ten-year-old children and adults, respectively. Those were much smaller than the annual dose limit of 1 mSv year^-1, which was set as a goal to be achieved in the a few years or decades (clear period has not been set). Within the detached houses, multiple regression analysis showed that wet wiping of floor was a significant reduction factor of the Cs concentration in dust; however, the small determination coefficient implies the presence of factors that were not considered in this study.

A soil ingestion pilot study for teenage children in China

Soil ingestion by people is an important route of exposure to environmental contaminants. Studies on soil ingestion using tracer mass-balance method are mainly for young children and adults, scarcely for teenagers. In such case, the soil ingestion rate for teenagers recommended by regulators is generally identical to that of adults based on one activity pattern modeling study. However, teenagers are expected to have different soil ingestion exposure via ingestion pathway due to different activity patterns and exposure scenarios. We conducted a pilot study on soil ingestion in 30 teenage children aged 12.0-16.5 years from Hubei Province of China, using the best tracer method, with the results compared with previous soil ingestion studies. The estimated mean and median soil ingestion rates for teenagers in this study based on the best five tracers (Al, Ce, Sc, V, and Y) were 45.2 mg d^-1 and 44.8 mg d^-1 respectively, with the 95% confidence interval of the mean value ranging from 28.0 mg d^-1 to 50.9 mg d^-1. These soil ingestion rate estimates were slightly higher than the recommended values for adults by U.S. EPA, but lower than those for Chinese younger children observed in the other similar study. The result in this study is important to access the health risk resulting from exposure to toxic substances in soil via direct soil ingestion pathway by teenagers in China as well as other countries.

Radiocesium contamination in house dust within evacuation areas close to the Fukushima Daiichi nuclear power plant

Outdoor decontamination efforts have been ongoing since the Fukushima Daiichi nuclear power plant (FDNPP) accident; however, little is known about indoor contamination. Therefore, house dust was sampled based on particle size in 21 wooden buildings (19 residential houses and 2 community centers) within the evacuation area close to the FDNPP, Fukushima Prefecture, Japan. Activities of radiocesium (¹³⁷Cs) per gram of house dust increased with decreasing particle size (mean: 6.1 × 10³, 2.6 × 10³, 1.6 × 10³, 7.5 × 10², 5.0 × 10², and 4.6 × 10² Bq/g for <4-20, 20-63, 63-180, 180-500, 500-1000, and 1000-2000 μm, respectively). The ¹³⁷Cs concentrations in house dust were inversely related to the square of distance from the FDNPP for <4-1000 μm particles. From the results of the multiple linear regression analysis, distance from the FDNPP and direction from the FDNPP (northwest) were significantly related to the radioactivity of house dust. It was found that 19%, 33%, and 48% of ¹³⁷Cs in house dust were extracted in water, 1 M HCl, and not extracted, respectively. Considering the bioaccessibility and assuming a 20 mg/day daily intake of house dust, the daily doses would be 7.2 Bq/day (mean) and 18 Bq/day (95th percent quantile). These results provide valuable insight into indoor radioactive Cs contamination in the area around the FDNPP and possible oral exposure to indoor radioactive Cs after returning home.