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We assessed the repeatability and reproducibility of methods for determining low dissolved radiocesium concentrations in freshwater in Fukushima. Twenty-one laboratories pre-concentrated three of 10 L samples by five different pre-concentration methods (Prussian-blue-impregnated filter cartridges, coprecipitation with ammonium phosphomolybdate, evaporation, solid-phase extraction disks, and ion-exchange resin columns), and activity of radiocesium was measured. The z-scores for all of the 137Cs results were within ± 2, indicating that the methods were a good degree of precision. The relative standard deviations (RSDs) indicating the reproducibility among different laboratories were larger than the RSDs indicating the repeatability in each separate laboratory.

Fallout radiocaesium (137Cs) has been used to trace soil migration (i.e., by erosion and redistribution) and soil-to-crop transfer levels of radiocaesium in agricultural fields. For soil erosion studies, reference site settings (initial 137Cs inventory, Bq m-2) are critical. Typically, non-disturbed and flat grasslands have been selected as reference sites. However, it will be difficult to justify the 137Cs concentrations for these reference sites in the future because already almost 50 years have passed since the heaviest annual global fallout was reported and 137Cs has been redistributed in some of the selected reference sites. It would be helpful if empirically derived initial 137Cs inventory data were available for the sites for comparison. In this study, we focused on areas in Asia and northern Australia where the major source of 137Cs is global fallout. We carried out a literature survey, and a total of 83 inventory datasets of global fallout 137Cs were collated for those areas in the region extending from 72.85° E to 141.35° E and from 12.43° S to 49.19° N. These data included global fallout deposition data in Japan obtained before the Fukushima Daiichi Nuclear Power Plant accident. We found a good correlation between the logarithm of global fallout 137Cs concentrations at reference sites and latitudes (R=0.805, p

This section provides a synthesis of data on the transfer of radiocaesium to agricultural crops in Japan after the FDNPP accident. The main processes for radiocaesium transfer to crops are discussed and the available data for Japan are presented and compared with data from before the FDNPP accident where possible. The processes considered include interception, weathering, translocation, uptake from soil to crops, and transfers from crops to farm animals. Some general concepts and methodologies that are relevant for the transfer of all radionuclides to food crops are described in Section 4.1 (mass interception and weathering) and 4.2 (soil). For three important crops in Japan, rice, fruit and tea, separate sections are provided that present and discuss transfer parameter data collected after the FDNPP accident. Data for other crops are compiled in an additional section. Effective half-lives for the different types of crops are also included in each section. Key processes that affect the extent of transfer of radiocaesium are also described.

Review of environmental transfer parameters after the Fukushima Daiichi Nuclear Power Plant accident were carried out especially on "Concentration ratio changes with time for rice". Transfer data of radiocaesium from paddy soil-to-brown rice were collected and compared before and after the nuclear accident. These data sets were updated for the MODARIA II WG4, MODARIA II, WG4, Fukushima Parameter Subgroup Interim Meeting 2018

Caesium-137 (137Cs), with its high release rate and long half life, is the most important longterm contributor to environmental contamination of all the radionuclides released by the accident at the Fukushima Dai-ichi nuclear power plant in March 2011. There have been many surveys of the fate of 137Cs in terrestrial environments, especially after the atmospheric nuclear tests of the 1950s and 60s and the Chernobyl accident in 1986. Previous surveys revealed that most of the 137Cs deposited on land remains in the surface soil for decades and that 137Cs rarely exchanges with other cations (atoms that have lost an electron to become positively charged). The immobilization of 137Cs in soil is mostly ascribed to selective adsorption on clay minerals, particularly on illitic minerals. 137Cs is irreversibly retained at the fringe of the layered structure of illitic minerals, called the frayed-edge site, with much higher selectivity than other cations. Comparison of the radiocaesium interception potential (RIP) between soils and clay minerals indicates that the difference in the frayed-edge site capacity is largely dependent on the degree of weathering and the degree of hydroxy-Al interlayering in illitic minerals. Here we investigate the difference in the RIP values between mineral soils to predict the level of contamination of crops grown in 137Cs contaminated fields.

Radiocesium (RCs) mobility in soil is initially relatively high when the nuclide first comes into contact with soil, after which the mobile fraction decreases with time due to RCs fixation to soil particles, commonly called an aging effect. Consequently, the RCs activity concentration in plants grown in soil were expected to decrease with time after the Fukushima Daiichi nuclear power plant accident in 2011. In this study, we collated data on concentration ratios (CR) of RCs between brown rice grain and paddy soil and compared CR values reported before and after the accident. For this purpose, soil and rice data collected after the accident from paddy fields which did not have additional potassium fertilizer added (for remediation purposes) were selected. The geometric mean rice/soil CR of RCs for all types of soil was 1.2×10^-2 in 2011 (n=62) and the value declined to 3.5×10^-3 in 2013 (n=32) which was similar to that for 1995-2007 of 3.4×10^-3 (n=120). The comparison suggests that the mean soil-to-rice grain concentration ratio had returned to that prevailing before the accident after less than three years. It was also confirmed that CR values for rice sampled from paddy fields were lower than those obtained from pot experiments.

Due to the Fukushima nuclear accident in March 2011, great amounts of radionuclides were released into the environment. Among the released various radionuclides, radiocesium and Pu isotopes are important for radiological assessment due to their relatively long half-lives and radioactive and chemical toxicity. Because of their expected persistent presence in the environment, it is essential to have a better understanding of their behavior in a series of environmental processes. For this purpose, powerful geochemical tracers which are capable of differentiating Fukushima accident-derived radiocesium and Pu from the global fallout source are highly required. Fukushima accident-released radiocesium has been characterized by a 135Cs/137Cs isotopic ratio of 0.34-0.39, which is different from those of global fallout (ca. 2.7) and the Chernobyl accident (0.5). Similarly, Fukushima accident-released Pu has its unique isotopic composition. Thus, 135Cs/137Cs and 240Pu/239Pu isotopic ratios have been considered as useful tracers for long-term estimation of environmental behaviors of the released radionuclides. Considering the fact that these radionuclides could be transported from forest to the ocean via inland river runoff, it is extremely necessary to quantify the Fukushima accident derived radioceium and Pu in river suspended particles, which is important for understanding the migration mechanism and fate of the released radionuclides. However, collection of large amount river suspended particles is a very difficult task, the sample size available for analysis is normally limited. In this study, we report a new analytical method for simultaneous determination of radiocesium (135Cs and 137Cs) and Pu isotopes (239Pu and 240Pu) in small sample size of 1-2 g river suspended particles. River suspended particles were collected from Kokuni, Minami Soma, Okuma and Nagadoro, in Fukushima prefecture from June 2013 to August 2014, using a solids-retaining centrifuge. After nitric acid digestion of the river suspended particles, radiocesium and Pu were sequentially pre-concentrated by using ammonium molybdophosphate and ferric hydroxide co-precipitation, respectively. After two-stage ion-exchange chromatography separation, radiocesium and Pu were measured by ICP-MS/MS and SF-ICP-MS, respectively. The developed analytical method was validated by the analysis of soil reference materials (IAEA 375, IAEA soil-6 and JSAC-0471). The results showed that 135Cs/137Cs isotopes in the investigated river suspended particles ranged from 0.339 to 0.39, with an average of 0.36 ± 0.06, indicating that the radiocesium primarily derived from the accident. Additionally, the detected 240Pu/239Pu isotopic ratios ranged from 0.182-0.208, suggesting that global fallout was the main source of Pu contamination in suspended particles. Acknowledgements: This work was partially supported by the Agency for Natural Resources and Energy, the Ministry of Economy, trade and Industry (METI), Japan., 第１７回「環境放射能」研究会 開催のご案内