Assessment of soil-soil solution distribution coefficients of global fallout 237Np and 239Pu in Japanese upland soils.

Neptunium-237 and 239Pu are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure to humans. Mobilities of these radionuclides in the environment are of particular importance for their radiation dose evaluation; therefore, in this study, we have made the assessment of the soil-soil solution distribution coefficient (Kd, L/kg) using global fallout 237Np and 239Pu in Japanese upland soils. The Kd values were determined by extracting these radionuclides from 24 soil samples using a laboratory batch method. The desorption Kd values of 237Np ranged from 3.3 × 102 to 1.0 × 104 L/kg, and their geometric mean (GM) and arithmetic mean (AM) were 1.7 × 103 L/kg and 2.6 × 103 L/kg, respectively. The desorption Kd values of 239Pu were found to vary from 9.4 × 103 to 7.1 × 104 L/kg, and their GM and AM were 3.3 × 104 L/kg and 4.0 × 104 L/kg, respectively. In Japanese upland soils, the Kd value of 239Pu was one order of magnitude higher than that of 237Np.

Surgical Outcomes with and without Prism Adaptation of Cases with Acute Acquired Comitant Esotropia Related to Prolonged Digital Device Use.

Purpose: To analyze surgical results of 32 cases with acute acquired comitant esotropia (AACE) related to prolonged use of digital devices (DDs). Patients and Methods: Medical records of cases with AACE related to prolonged use of DDs that had undergone surgery were retrospectively revised. Complete medical history and full ophthalmological examinations before and surgery were obtained for all cases. All cases also underwent neurological examinations using brain and orbital imaging. Motor success was considered as alignment within 10 prism diopters (Δ) at both near and distance. Sensory success was defined as stereopsis ≤60 arcsec. Nineteen cases (Group S) underwent surgery alone and 13 cases were treated with surgery and prism adaptation (Group S+P). Motor and sensory outcomes were compared between groups. Results: Mean age at first visit was 22.0 ± 9.0 years and mean daily use of DDs use was 6.3 ± 3.4 hours. Mean angle of preoperative alignment for distance and near were 26.5 ± 13.0Δ and 24.6 ± 16.4Δ, respectively. Surgery was performed at a mean of 23.3 ±3.5 years old and mean angle of alignment at final examination for distance and near were 5.8 ± 7.7Δ and 3.5 ± 5.7Δ, respectively. Final motor and sensory success rate were 84% and 53%, respectively. No significant differences in motor or sensory outcomes were evident between groups at initial or last visit. Conclusion: Favorable motor and sensory outcomes were achieved with surgical intervention with and without prism adaptation for AACT related to prolonged use of DDs.

Enhancement of Mass Interception Coefficient Data of Radiostrontium by Leafy Crops Using Global Fallout 90Sr and Naturally Occurring 7Be.

When artificial radionuclides are released into the atmospheric environment, one of the important processes by which they affect the human radiation dose is the direct deposition of the radionuclides onto crop surfaces. Because leafy vegetables are consumed while fresh and often raw, the mass interception coefficient [= concentration in food (Bq/kg dry mass (DM) or fresh mass)/total deposition (Bq/m2)] is a key parameter for estimating radionuclide concentrations in crops after the deposition of radionuclides on plant stands. However, such data are still sparse, especially for radiostrontium (89Sr and 90Sr). To enhance the mass interception coefficient data for leafy crops, we used global fallout 90Sr data in leafy crops harvested in 1963-1965 and the deposition data for the corresponding crop growing period. Geometric mean values of the mass interception coefficient of 90Sr for leafy crops were 2.8 m2 kg-1 DM for spinach, 0.60 m2 kg-1 DM for cabbage, and 1.3 m2 kg-1 DM for Chinese cabbage. For comparison, we measured naturally occurring 7Be in giant butterbur leaves, and the results showed that the data were similar to those of 90Sr for spinach. These data were similar to the previously obtained data by single spike radiotracer experiments. Therefore, in the case of nuclear emergency situations, mass interception coefficient data obtained using global fallout 90Sr and/or naturally occurring 7Be should be valuable to estimate radioactivity contamination levels of radiostrontium directly deposited on leafy crops.

Pre- and post-accident environmental transfer of radionuclides in Japan: lessons learned in the IAEA MODARIA II programme.

An international review of radioecological data derived after the accident at the Fukushima Daiichi nuclear power plant was an important component of activities in working group 4 of the IAEA Models and data for radiological impact assessment, phase II (MODARIA II) programme. Japanese and international scientists reviewed radioecological data in the terrestrial and aquatic environments in Japan reported both before and after the accident. The environmental transfer processes considered included: (a) interception and retention radionuclides by plants, (b) loss of radionuclides from plant and systemic transport of radionuclides in plants (translocation), (c) behaviour of radiocaesium in soil, (d) uptake of radionuclides from soil by agricultural crops and wild plants, (e) transfer of radionuclides from feedstuffs to domestic and wild animals, (f) behaviour of radiocaesium in forest trees and forest systems, (g) behaviour of radiocaesium in freshwater systems, coastal areas and in the ocean, (h) transport of radiocaesium from catchments through rivers, streams and lakes to the ocean, (i) uptake of radiocaesium by aquatic organisms, and (j) modification of radionuclide concentrations in food products during food processing and culinary preparation. These data were compared with relevant global data within IAEA TECDOC-1927 'Environmental transfer of radionuclides in Japan following the accident at the Fukushima Daiichi Nuclear Power Plant'. This paper summarises the outcomes of the data collation and analysis within MODARIA II work group 4 and compares the Japan-specific data with existing radioecological knowledge acquired from past and contemporary radioecological studies. The key radioecological lessons learned are outlined and discussed.

Aggregated transfer factor of 137Cs in edible wild plants and its time dependence after the Fukushima Dai-ichi nuclear accident.

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.

Soil-soil solution distribution coefficients of global fallout 239Pu and 237Np in Japanese paddy soils.

239Pu and 237Np are long-lived radionuclides that emit alpha rays, and once released into the environment, they are present there for a long period of time. Therefore,239Pu and 237Np are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure to humans. Mobilities of these radionuclides in the environment are of particular interest; therefore, in this study, we have made the first-time determination of the soil-soil solution distribution coefficient (Kd, L/kg) using global fallout 239Pu and 237Np in soil. The Kd values were determined by extracting these radionuclides from 23 soil samples using a laboratory batch method. The desorption Kd values of 239Pu were found to vary from 3.2 × 103 to 1.4 × 105 L/kg, and their geometric mean (GM) and arithmetic mean (AM) were 2.3 × 104 L/kg and 3.2 × 104 L/kg, respectively. The desorption Kd values of 237Np ranged from 8.9 × 102 to 2.1 × 104 L/kg, and their GM and AM were 4.1 × 103 L/kg and 6.4 × 103 L/kg, respectively. A comparison between the obtained Kd values of 239Pu and 237Np indicated that the former were about 6-fold higher than the latter in Japanese paddy field soils. Pearson's correlation analysis suggested that the main factors contributing to the sorption and desorption of Pu isotopes in Japanese paddy soils were related to the amounts of Fe and Mn oxides, while the sorption and desorption of 237Np in them would be controlled by an ion-exchange reaction, and/or complex-formation with organic matter, especially in Fluvisols.

Aggregated transfer factor of 137Cs in wild edible mushrooms collected in 2016-2020 for long-term internal dose assessment use.

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 (Tag), 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 Tag 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 Tag 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 Tag 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 Tag calculation.

Inequality in the distribution of 137Cs contamination within freshwater fish bodies and its affecting factors.

Contamination of freshwater fishes with 137Cs remains as a serious problem in Japan, nearly 10 years after the Fukushima nuclear power plant accident, but there is limited information on the distribution of 137Cs contamination in fish bodies. The 137Cs distribution can be used for the estimation of internal radiation exposure through the consumption of fish and for the dose estimation of fish themselves. In this study, the 137Cs distribution in the bodies of 8 freshwater fish species was investigated as percentages of total body burden for fish inhabiting Lake Inba. Fish samples were caught in stake nets placed close to the shore approximately once a month. After the measurement of body length and fresh weight, the radioactivities of 137Cs in muscle, internal organs, spawn, milt and bone were assayed using high-purity germanium detectors. Analysis of all fish samples showed that the 137Cs distribution was highest in muscle (54 ± 12%), followed by internal organs (7.8 ± 4.6%), spawn (7.4 ± 5.4%), milt (3.2 ± 2.1%) and bone (1.2 ± 0.58%). Among fish species, the highest proportion of 137Cs in muscle was detected in largemouth bass (71 ± 1 3%), followed by snakehead (69 ± 14%), channel catfish (63 ± 17%), common carp (62 ± 14%), barbel steed (58 ± 6.5%), silver carp (57 ± 7.7%), bluegill (53 ± 4.7%), and crucian carp (50 ± 10%). These results suggested that the 137Cs in muscle was likely to be high in piscivorous fishes compared to omnivorous fishes, especially crucian carp. The proportion of 137Cs in muscle of crucian carp was not explained either by body length or fresh weight. However, a positive correlation was found between the proportion of 137Cs in muscle and the condition factor which was an indicator of nutritional status calculated from a length-weight relationship. This correlation implied that more 137Cs accumulated in muscle tissue of a fish species with high nutritional status. This is the first study to show that condition factor is more important than body length and wet weight in explaining the high proportion of 137Cs in muscle tissues, at least for crucian carp.

Collation of Strontium Concentration Ratios from Water to Aquatic Biota Species in Freshwater and Marine Environments and Factors Affecting the Ratios.

The fate of strontium-90 (90Sr) from water to aquatic biota is of concern since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident because of continuous small 90Sr releases to the seawater from the FDNPP site. The Japanese diet includes many edible marine and freshwater species, and the environmental parameter, that is, the concentration ratio (CR) from water to biota, is useful to estimate the potential 90Sr intake, especially from frequently consumed seafoods. However, widely used CR data for radiation dose assessment only have provided values for biota types such as fish, crustaceans, macroalgae, and so forth, and thus, it is difficult to identify specific data for each species. In this study, therefore, we collated CR data of Sr for aquatic biota by surveying available open data sources from the 1950s to 2019, not only for edible parts but also for whole and inedible parts. In total, we obtained 3800 CR data: 3013 data for marine biota, 28 data for brackish water biota, and 759 data for freshwater biota. The results showed that species-specific CRs may decrease the uncertainties compared to those published in IAEA documents; however, different diets and living areas by species may lead to different uncertainties for different species.

Simple and sensitive determination of radium-226 in river water by single column-chromatographic separation coupled to SF-ICP-MS analysis in medium resolution mode.

This article describes a novel and simple method to measure ultra-trace 226Ra in river water samples at fg L-1 (mBq L-1) levels as a means for surveying 226Ra in an unintended contamination in river water. To simplify the procedure, a single column was used for separation and purification; 10 mL of AG 50W-X8 resin was packed into a 10 mL Eppendorf pipette tip, which was used as a separation column. A 500 mL sample solution was loaded, and interfering elements were removed with 80 mL 4 M HCl in 20% ethanol. Subsequently, Ra together with Ba was eluted by 20 mL 5 M HNO3 prior to SF-ICP-MS analysis; this allows the naturally existing Ba in water samples to be employed as a yield tracer for 226Ra analysis. Using the medium mode of SF-ICP-MS, the instrumental detection limit of 380 fg L-1 (10 mBq L-1) was obtained. An extremely low method detection limit of 0.46 fg L-1 (0.02 mBq L-1) was achieved with 500-fold pre-concentration. Finally, the developed technique was applied to analyze natural water samples collected from Japanese rivers, in which the 226Ra concentrations varied in the range of 0.7-49.6 fg L-1 (0.03-1.82 mBq L-1).

Comparisons of effective half-lives of radiocesium in Japanese tea plants after two nuclear accidents, Chernobyl and Fukushima.

The time-dependence of 137Cs in new shoots of tea (Camellia sinensis (L.) Kuntze) following a137Cs-deposition was analyzed and quantified in terms of effective half-lives. The underlying monitoring studies were performed after the accidents in the Chernobyl and the Fukushima Daiichi nuclear power plants for tea plants growing in Japan. The major transfer route for atmospherically deposited radiocaesium to the first new shoots sampled after the accidents were different: for the Fukushima accident, it was mainly translocation of radiocaesium deposited onto old leaves and twigs to the new growth, while direct deposition on the new leaves was the major source after the Chernobyl accident. The effective half-lives in new tea leaves representing the fast and slow components of the decline did not significantly differ between these accidents. Geometric means (ranges) of fast and slow effective half-lives of 137Cs after the Chernobyl accident were 66 d (25-125 d) and 902 d (342-15900 d), respectively, and those after the Fukushima accident were 50 d (26-105 d) and 416 d (222-1540 d), respectively. From these results, 137Cs declines in new tea leaves were similar although contamination conditions were different for these two accidents.

The transfer of fallout plutonium from paddy soil to rice: A field study in Japan.

Reported transfer factor (TF) values of Pu from paddy soil to rice are rather scarce, despite the radiotoxicity of Pu and the irreplaceable role of rice in Asian peoples' diets. Here, we conducted a field study to investigate the transfer of global fallout Pu from paddy soil to rice grain (hulled rice) in Japan. The 240Pu/239Pu atomic ratios in two rice grain samples out of 16 samples were determined and the ratios corresponded well with the global fallout value. The soil-to-rice TFPu in 12 Japanese prefectures ranged from 4.5 × 10-6 to 1.2 × 10-4 with a geometric mean of 3.3 × 10-5. The TFs of rice obtained in this study were compatible to the TFs for the broad heading "cereals" compiled in the IAEA Technical Report Series No. 472. Weak correlations were found between the TF and the investigated soil characteristics such as soil pH and loss on ignition. Regarding the TFs for cerium (Ce) and thorium (Th) which are commonly considered as Pu analogues, we observed no significant correlations between the log(TFPu) and log(TFCe) or log(TFPu) and log(TFTh). On the other hand, interestingly, a significantly positive correlation (r = 0.795, p < 0.001) was observed between log(TFPu) and log(TFU). In view of the observed similarity of TF values for U and Pu from soil to rice, we thought that using the easy-to-measure TFU to estimate TFPu from soil to rice might be suggested although the mechanism was unclear.

Radiocaesium transfer and radiation exposure of frogs in Fukushima Prefecture.

The International Commission on Radiological Protection has proposed an environmental assessment framework. This includes ionising radiation exposure assessment for different frog life-stages, but radiocaesium transfer parameters are unavailable. We collate data from the Fukushima Prefecture (contaminated by the Fukushima accident) and estimate radiocaesium concentration ratio (CRwo-water) values for tadpoles and adult frogs, presenting the largest available amphibian CRwo-water dataset. In total, 513 adult frogs and 2540 tadpoles were analysed in 62 and 59 composite samples respectively. Results suggest that equilibrium was reached between water and amphibian radiocaesium activity concentrations circa one-year after the accident. Radiocaesium transfer to tadpoles was higher than to adult frogs. Dose rates were estimated for different life-stages and species in both the aquatic and terrestrial environment. Estimated dose rates to adults and tadpoles were typically similar because external exposure dominated for both organisms; frogspawn dose rates were estimated to be orders of magnitude lower than other life-stages. For the two sites assessed, which were outside of the most contaminated areas of the Fukushima Prefecture, estimated dose rates were below those anticipated to present a risk to wildlife populations; it is likely that dose rates in more contaminated areas were in excess of some effects benchmark values.

Changes in the Soil to Brown Rice Concentration Ratio of Radiocaesium before and after the Fukushima Daiichi Nuclear Power Plant Accident in 2011.

Radiocaesium (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 (aging effect). Consequently, the RCs activity concentration in plants grown in soil was 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 for periods before and after the accident. For this purpose, soil and rice data were collected after the accident specifically from paddy fields that did not have additional potassium fertilizer added (for remediation purposes). The geometric mean rice/soil CR of RCs for all types of soil was 1.2 × 10-2 in 2011 ( n = 62) and by 2013 the value had declined to 3.5 × 10-3 ( 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.

Effects of litter feeders on the transfer of 137Cs to plants.

The effects of the Japanese horned beetle larvae on the transfer of 137Cs from a contaminated leaf litter to the leaf vegetable, komatsuna (Brassica rapa var. perviridis) was studied. Feces of the larvae which were fed 137Cs-contaminated leaf litter were added to a potting mix in which komatsuna plants were cultivated. The presence of feces increased the harvest yield of komatsuna, suggesting that feces provided nutrients for the plant growth. In addition, the amount of exchangeable 137Cs in leaf litter was experimentally confirmed to be enhanced by the presence of feces which were excreted by larvae feeding. However, there was no difference in the soil-to-plant transfer factor of 137Cs for the presence and absence of feces. Interactions between clay minerals and exchangeable 137Cs in the soil beneath the litter layer may diminish the root uptake of 137Cs. From these results, it was concluded that the effect of exchangeable 137Cs released from feces was limited for the transfer of 137Cs to plants if plant roots were not present in litter layers.

Establishing rapid analysis of Pu isotopes in seawater to study the impact of Fukushima nuclear accident in the Northwest Pacific.

In order to assess the impact of the Fukushima derived Pu isotopes on seawater, a new analytical method to rapidly determine Pu isotopes in seawater by SF-ICP-MS including Fe(OH)2 primary co-precipitation, CaF2/LaF3 secondary co-precipitation and TEVA+UTEVA+DGA extraction chromatographic separation was established. High concentration efficiency (~100%) and high U decontamination factor (~107) were achieved. The plutonium chemical recoveries were 74-88% with the mean of 83 ± 5%. The precisions for both 240Pu/239Pu atom ratios and 239+240Pu activity concentrations were less than 5% when 15 L of seawater samples with the typical 239+240Pu activity of the Northwest Pacific were measured. It just needs 12 hours to determine plutonium using this new method. The limit of detection (LOD) for 239Pu and 240Pu were both 0.08 fg/mL, corresponding to 0.01 mBq/m3 for 239Pu and 0.05 mBq/m3 for 240Pu when a 15 L volume of seawater was measured. This method was applied to determine the seawater samples collected 446-1316 km off the FDNPP accident site in the Northwest Pacific in July of 2013. The obtained 239+240Pu activity concentrations of 1.21-2.19 mBq/m3 and the 240Pu/239Pu atom ratios of 0.198-0.322 suggested that there was no significant Pu contamination from the accident to the Northwest Pacific.

Rapid determination of ultra-trace plutonium isotopes (239Pu, 240Pu and 241Pu) in small-volume human urine bioassay using sector-field inductively coupled plasma mass spectrometry.

A rapid method with enhanced 238U decontamination was developed for ultra-trace Pu analysis in small-volume urine bioassays. This method consists of acid digestion, co-precipitation, extraction chromatography and sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS) measurement. Parameters that may influence the analytical performance were studied systematically. This method achieved a high 238U decontamination factor (3.8 × 106) and the 242Pu recovery was stable for 20 mL and 100 mL urine bioassays with an average value of 72.7 ±â€¯5.5%. The limits of detection for 239Pu, 240Pu and 241Pu by the method were 0.016 fg mL-1, 0.016 fg mL-1 and 0.019 fg mL-1 for 20 mL urine samples and 0.003 fg mL-1, 0.002 fg mL-1 and 0.003 fg mL-1 for 100 mL urine samples, respectively. Considering the small volume of urine employed in this study, the absolute detection limits of the method were comparable or even better than those measured with thermal ionization mass spectrometry and accelerator mass spectrometry. All procedures for 20 mL and 100 mL urine bioassays were completed in 9.5 h and 11 h, respectively, and analysis of 10 samples could be finished within one day. With the considerably low detection limits of Pu isotopes and high sample throughput, this method would be a promising tool for the quick response to radiological emergencies and for rapid screening of unexpected occupational exposures of workers involved in the future FDNPP reactor decommissioning operations.

Comparison of radiocesium concentration changes in leguminous and non-leguminous herbaceous plants observed after the Fukushima Dai-ichi Nuclear Power Plant accident.

Transfer of radiocesium from soil to crops is an important pathway for human intake. In the period from one to two years after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, food monitoring results showed that radiocesium concentrations in soybean (a legume) were higher than those in other annual agricultural crops; in these crops, root uptake is the major pathway of radiocesium from soil to plant. However, it was not clear whether or not leguminous and non-leguminous herbaceous plants have different Cs uptake abilities from the same soil because crop sample collection fields were different. In this study, therefore, we compared the concentrations of 137Cs in seven herbaceous plant species including two leguminous plants (Trifolium pratense L. and Vicia sativa L.) collected in 2012-2016 from the same sampling field in Chiba, Japan that had been affected by the FDNPP accident fallout. Among these species, Petasites japonicus (Siebold & Zucc.) Maxim. showed the highest 137Cs concentration in 2012-2016. The correlation factor between all concentration data for 137Cs and those for 40K in these seven plants was R = 0.54 (p < 0.001) by t-test, thus potassium uptake ability by species would affect radiocesium uptake; however, for each species, no correlation between 137Cs and 40K was found. Interestingly, 40K concentrations in T. pratense, V. sativa and Poaceae family plants did not differ significantly, but 137Cs data in the Poaceae family plants were significantly lower than those in T. pratense (p < 0.001) and V. sativa (p = 0.017). The results indicated that leguminous species would have higher 137Cs uptake ability than Poaceae family plants.

Time trends in radiocaesium in the Japanese diet following nuclear weapons testing and Chernobyl: Implications for long term contamination post-Fukushima.

Estimation of time changes in radiocaesium in foodstuffs is key to predicting the long term impact of the Fukushima accident on the Japanese diet. We have modelled >4000 measurements, spanning 50 years, of 137Cs in foodstuffs and whole diet in Japan after nuclear weapons testing (NWT) and the Chernobyl accident. Broadly consistent long term trends in 137Cs activity concentrations are seen between different agricultural foodstuffs; whole diet follows this general trend with remarkably little variation between averages for different regions of Japan. Model blind tests against post-NWT data for the Fukushima Prefecture showed good predictions for radiocaesium in whole diet, spinach and Japanese radish (for which good long term test data were available). For the post-Fukushima period to 2015, radiocaesium in the average diet followed a declining time trend consistent with that seen after NWT and Chernobyl. Data for different regions post-Fukushima show a high degree of mixing of dietary foodstuffs between regions: significant over-estimates of average dietary 137Cs were made when it was assumed that only regionally-produced food was consumed. Predictions of mean committed effective internal doses from dietary 137Cs (2011 to 2061) in non-evacuated parts of the Fukushima Prefecture show that average internal dose is relatively low. This study focused on average regional ingestion dose rates and does not attempt to make site specific predictions. However, temporal trends identified could form a basis for site specific predictions of long term activity concentrations in agricultural products and diet both outside and (to assess potential re-use) inside currently evacuated areas.

High-Performance Method for Determination of Pu Isotopes in Soil and Sediment Samples by Sector Field-Inductively Coupled Plasma Mass Spectrometry.

Plutonium is extensively studied in radioecology (e.g., soil to plant transfer and radiological assessment) and geochemistry (e.g., sediment dating). Here, we reported a new chemical separation method for rapid determination of Pu in soil and sediment samples, based on the following investigations: extraction behaviors of interfering elements (IEs, for inductively coupled plasma mass spectrometry (ICPMS) measurement) on TEVA resin; decontamination of U using TEVA, UTEVA, and DGA resins; and the impact of coprecipitation on Pu determination. The developed method consists of four steps: HNO3 leaching for Pu release; CaF2/LaF3 coprecipitation for the removal of major metals and U; the proposed TEVA + UTEVA + DGA procedure for the removal of U, Pb, Bi, Tl, Hg, Hf, Pt, and Dy; and ICPMS measurement. The accuracy of this method in determining 239+240Pu activity and 240Pu/239Pu and 241Pu/239Pu isotopic ratios was validated by analyzing five standard reference materials (soil, fresh water sediment, and ocean sediment). This method is characterized by its stable and high Pu recovery (90-97% for soil; 92-98% for sediment) and high decontamination factor of U (1.6 × 107), which is the highest reported for soil and sediment samples. In addition, the short analytical time of 12 h and the method detection limits, which are the lowest yet reported in literature, of 0.56 µBq g-1 (0.24 fg g-1) for 239Pu, 1.2 µBq g-1 (0.14 fg g-1) for 240Pu, and 0.34 mBq g-1 (0.09 fg g-1) for 241Pu (calculated on the basis of a 1 g soil sample) allow the rapid determination of ultratrace level Pu in soil and sediment samples.