Search

Collection and cooking of wild vegetables have provided seasonal enjoyments for Japanese local people as provisioning and cultural ecosystem services. However, the Fukushima Daiichi Nuclear Power Plant accident in March 2011 caused extensive radiocesium contamination of wild vegetables. Restrictions on commercial shipments of wild vegetables have been in place for the last 10 years. Some species, including buds of Aralia elata, are currently showing radiocesium concentrations both above and below the Japanese reference level for food (100 Bq/kg), implying that there are factors decreasing and increasing the 137Cs concentration. Here, we evaluated easy-to-measure environmental variables (dose rate at the soil surface, organic soil layer thickness, slope steepness, and presence/absence of decontamination practices) and the 137Cs concentrations of 40 A. elata buds at 38 locations in Fukushima Prefecture to provide helpful information on avoiding collecting highly contaminated buds. The 137Cs concentrations in A. elata buds ranged from 1 to 6,280 Bq/kg fresh weight and increased significantly with increases in the dose rate at the soil surface (0.10–6.50 μSv/h). Meanwhile, the 137Cs concentration in A. elata buds were not reduced by decontamination practices. These findings suggest that measuring the latest dose rate at the soil surface at the base of A. elata plants is a helpful way to avoid collecting buds with higher 137Cs concentrations and aid in the management of species in polluted regions. [ABSTRACT FROM AUTHOR]

We obtained the aggregated transfer factor (Tag) for 10 common edible wild plant species (four perennial spermatophytes, bamboo shoot, two tree species, and three perennial pteridophytes) in northeastern Japan. Measurement of Tag was carried out in 2012–2019 and we also used publicly available data for 2012–2019: food monitoring data and total deposition data from an airborne survey. The Tag obtained from actual measurements agreed well with Tag values calculated from the publicly available data. The sampling locations were only identified at the municipal level and uncertainty of the deposition for the publicly available data, and thus Tag values showed substantial variation. The Tag of the perennial spermatophytes, including bamboo shoot, and perennial pteridophytes showed single exponential decline with effective half-lives of approximately 2 years, whereas those of tree species did not show distinct temporal change. These results imply that data since 2014 are applicable for Tag estimation for long-term potential ingestion dose in the future to the public because of the slow decline. The calculated Tag values of all species for 2014–2019 ranged from 6.1 × 10−5 to 5.2 × 10−3 m2/kg-fresh mass. The maximum Tag value was observed for the tree koshiabura (Chengiopanax sciadophylloides) and the minimum value was observed for the perennial spermatophyte giant butterbur (Petasites japonica). Tree species showed higher Tag than spermatophyte and pteridophyte perennials. [ABSTRACT FROM AUTHOR]

The Fukushima Dai-ichi Nuclear Power Plant accidents following the March 11, 2011 Tohoku earthquake, and subsequent tsunami released radioactive materials into the atmosphere and caused significant public health concerns, particularly thyroid cancers in children. However, the lack of measurement data for atmospheric concentrations of 131I has caused persistent and widespread uncertainty. This study estimated the maximum potential thyroid doses of inhaled 131I in the early post-accident phase between March 12 and 23, 2011 by using the hourly measured data of the 137Cs concentrations at 101 suspended particulate matter (SPM) monitoring sites, a new multi-model ensemble (MME) method of simulating 137Cs concentrations using two Atmospheric Transport and Deposition Models (ATDMs), the 131I/137Cs ratio obtained from measurement data analysis, and the internal exposure model. Based on the measurements, the maximum potential thyroid doses were estimated at 3.1–160 mSv at 5 sites in the Fukushima-Hamadori area for 1-year-old children assumed to remain outdoors, whereas they were less than 4.3 mSv at the other sites in the base case of the 131I/137Cs ratio. The spatial distribution of the maximum potential of early inhalation doses was estimated by using the MME and measurements. The inhalation thyroid doses in the evacuation scenarios were compared to the estimates reported by previous studies. The results of the present study were almost congruent with the outcomes of previous investigations except for thyroid doses contributed by highly contaminated plumes on March 12 and 15. The sensitivity analysis for the 131I/137Cs ratio indicated that these plumes carried the potential to significantly increase the thyroid doses of residents. • Early thyroid doses from inhaled 131I after the FDNPP accident were estimated. • Multi-ensemble ATDM and hourly measured 137Cs data could improve the estimation. • Plumes on March 12 and 15, 2011 had potential to change the previous estimations. [ABSTRACT FROM AUTHOR]

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. • Radioactive Cs in indoor dust (vacuum cleaner dust) from houses located 150–200 km south from the FDNPP was measured. • The median committed effective dose via indoor dust ingestion and indoor air inhalation was less than 1 × 10-3 mSv year-1. • Wet wiping of indoor floor was a significant reduction factor of the radioactive Cs concentration in indoor dust. [ABSTRACT FROM AUTHOR]