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Radionuclides released and deposited because of the 2011 Fukushima Dai-ichi Nuclear Power Plant accident caused an increase in air dose rates in Fukushima Prefecture forests. Although an increase in air dose rates during rainfall was previously reported, the air dose rates in the Fukushima forests decreased during rainfall. This study aimed to develop a method to estimate rainfall-related changes in air dose rates, even in the absence of soil moisture data, in Namie-Town and Kawauchi-Village, Futaba-gun, Fukushima Prefecture. Moreover, we examined the relationship between preceding rainfall (Rw) and soil moisture content. The air dose rate was estimated by calculating the Rw in Namie-Town from May to July 2020. We found that the air dose rates decreased with increasing soil moisture content. The soil moisture content was estimated from Rw by combining short-term and long-term effective rainfall using half-live values of 2 h and 7 d and considering the hysteresis of water absorption and drainage processes. Furthermore, the soil moisture content and air dose rate estimations showed a good agreement with coefficient of determination (R 2 ) scores >0.70 and >0.65, respectively. The same method was tested to estimate the air dose rates in Kawauchi-Village from May to July 2019. At the Kawauchi site, variation in estimated value is relatively large due to the presence of water repellency in dry conditions, and the amount of 137Cs inventory was low, so estimating air dose from rainfall remained a challenge. In conclusion, rainfall data were successfully used to estimate soil moisture and air dose rates in areas with high 137Cs inventories. This leads to the possibility of removing the influence of rainfall on measured air dose rate data and could contribute to the improvement of methods currently used to estimate the external air dose rates for humans, animals, and terrestrial forest plants. [Display omitted] • Soil moisture content and air dose rate were estimated using effective rainfall. • Air dose rate changes were estimated using measured soil moisture content changes. • Magnitude of soil shielding effect was elevated by preceding rainfall. • This method might reveal influences besides rainfall on air dose rate changes. [ABSTRACT FROM AUTHOR]

We developed a simple and rapid method for detecting dissolved radio-Cs in litter and/or soil seepage water using nonwoven fabrics impregnated with copper-substituted Prussian blue (Cu-NF). In laboratory and field experiments, litter and/or soil seepage water including dissolved radio-Cs were passed through traditional lysimeter systems combined with seven sheets of the Cu-NF. We then examined the recovery ratios of dissolved 137 Cs in the Cu-NF. In the laboratory experiments with faster flow rates (11–2200 mm h −1 ), over 86% of the total dissolved 137 Cs in litter seepage water was detected in the Cu-NF and over 82% of the collected 137 Cs was present in the first three sheets. In the field experiments, 99% of the total dissolved 137 Cs litter seepage water was collected in the Cu-NF and more than 96% of the collected 137 Cs was present in the first three sheets. Furthermore, the recovery ratio of dissolved 137 Cs increased with increasing installation Cu-NF length, probably because the packed soil in the Cu-NF lysimeter become more stable over time. Finally, because only the Cu-NF is measured, it is not necessary to undertake traditional measurement preparations such as filtration to remove particulate radio-Cs materials and evaporative concentration for low concentration of radio-Cs. As a result, we can save time and effort in measurement preparation by using the Cu-NF lysimeter method. [ABSTRACT FROM AUTHOR]

The spatial variation of the radiocesium inventory in forest soil was studied c.a. 44 km northwest of the Fukushima Daiichi Nuclear Power Plant, Japan. This study focuses on the effects of canopy interception and downward transfer from the forest canopy to the forest floor via stemflow and throughfall. We established a study plot (400 m 2 ) in the canopy layer of a secondary mixed deciduous forest dominated by Japanese oak ( Quercus crispula ) and Japanese fir ( Abies firma ), in August and November 2014. Soil was sampled from 0 to 5 cm depth and 137 Cs was measured under the canopy using a 2-m grid and also at the tree trunk bases. We divided the study plot into the five different types of subplot according to the canopy projection areas and the tree species for the analysis. The geometric mean and coefficient of variation of the 137 Cs inventory were 202 kBq m −2 and 0.11 (0.52 in the arithmetic coefficient of variation), respectively. Within the forest, the variation in the 137 Cs inventory under trees was larger than in crown gap areas. The large spatial variation may be attributed to canopy interception of the initial deposition and downward transfer of radiocesium via stemflow and throughfall. [ABSTRACT FROM AUTHOR]

Ingestion of edible wild mushrooms collected in areas contaminated with radiocesium released from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident may pose a risk of internal dose to their consumers. A species-specific aggregated transfer factor (T ag), which is calculated using radiocesium concentration in a wild mushroom species (Bq kg−1 wet mass [WM]) divided by the total concentration in the soil surface area (Bq m−2), would be a useful tool to estimate the dose from wild mushrooms by ingestion. In this study, we especially focused on the T ag data collected in 2016–2020 to use these values for a long-term dose assessment. We assumed that 137Cs concentrations after that year were almost the same, thus the soil-mushroom system would be in an apparent steady-state condition. In all, we could obtain T ag values of 137Cs in 62 edible wild mushroom species native to Japan. The geometric mean (GM) values were 1.5 × 10−3 m2 kg−1 WM using GMs of 13 saprobic type species and 5.0 × 10−3 m2 kg−1 WM using GMs of 21 mycorrhizal type species (N > 2). On average, the GMs of species-specific T ag values were 1.9 ± 0.9 times higher than those reported in a previous study of wild mushrooms made after the FDNPP accident, probably due to the different approaches for T ag calculation. • Aggregated transfer factor (T ag) of 137Cs from soil to wild mushroom was calculated. • Open source in-situ soil measurement data of 137Cs were used for T ag calculation. • T ag values obtained before and after the Fukushima accident did not change much. • 137Cs could be estimated for each mushroom species by using T ag values. [ABSTRACT FROM AUTHOR]