[en] After the nuclear accident at TEPCO's Fukushima Dai-ichi power station in March, hydrogen explosions and reactor building explosion resulted in releases of radionuclides in the environment. Severe radioactive cesium and iodine contaminations have been observed in fallout deposition samples and soils in the East Japan. Radioactive cesium, iodine, uranium, and transuranic radionuclides were set as the monitoring targets in food safety tests. However, so far, only radioactive cesium and iodine were daily measured and reported by the Ministry of Health, Labour, and Welfare. The tedious and time consuming conventional alpha spectrometric method hampered the emergency monitoring U contamination in foods. In this work, we propose a simple and rapid analytical method for ²³⁸U and ²³⁵U/²³⁸U isotope ratio analysis in fresh vegetables. This method was applied to the emergency monitoring of radioactive contamination after the nuclear accident at TEPCO's Fukushima Dai-ichi power station. The results showed no U contamination in fresh vegetables collected in Chiba and Ibaraki prefectures in April and May, 2011. (author)

[en] Of the major radioactive selenium isotopes, Se-79, a beta emitter with a half-life of about 1.1 million years, is of special interest because it is one of the most important radionuclides for the long-term dose assessment of radioactive waste disposal. This radionuclide can reach human beings through several transfer paths in the environment. To predict Se-79 behavior from the environment to human beings, it would be useful to obtain the following information: stable Se concentration in environmental samples; soil-soil solution distribution coefficient (K_d); and soil-to-plant transfer factor (TF). In the present study, stable Se concentrations in river water, soil and crop samples collected in Japan, K_ds and TFs were obtained. The results showed that geometric mean (GM) concentrations of river water, soil and crops were 0.057 μg/L (range: < D.L.-1.17 μg/L), 0.43 mg/kg (range: 0.068-1.56 mg/kg-dry), and 0.015 mg/kg-dry (range: < D.L.-0.24 mg/kg-dry), respectively. GMs of K_ds for paddy field soil and upland field soil samples were 116 and 67, respectively, whereas GMs of TFs for brown rice and upland field crops were 0.066 and 0.024, respectively. Probably due to longer growing period and different water management in the paddy fields for brown rice compared to those for upland field crops, the TF would be high in brown rice. (authors)

[en] Removal of radiocesium from food by processing is of great concern following the accident of TEPCO's Fukushima Daiichi Nuclear Power Plant accident. To provide more Cs removal rates, we studied the applicability of K data using edible plant samples. Values were compared for ¹³⁷Cs and ⁴⁰K of the food processing retention factors, F_r (total activity in processed food/total activity in raw food), and they were found to be close to the 1:1 line and highly correlated (R = 0.96, p < 0.001). Thus, K can be an analogue to estimate radiocesium removal rates by food processing of vegetables. Using the literature K values, we calculated the K removal rates (%), that is, (1 - F_r) x 100, for ten vegetable types to provide potential Cs removal rates. The average percent of K removal were as follows: dried pulses, 33; fresh pulses, 15; leafy vegetables, 52; fruit vegetables, 7; flower vegetables, 44: root crops, 18; tubers, 16; ferns, 93: mushrooms, 32; and others, 30. (author)

[en] Radiocarbon (¹⁴C) partitioning ratios in the soil solid, liquid, and gas phases was determined by batch sorption experiments using 63 paddy soil and 79 upland soil samples to understand the behavior of ¹⁴C in agricultural fields. The mean ¹⁴C partitioning ratios for all agricultural soil samples were 35 % for the soil solid phase, 5 % for the liquid phase, and 60 % for the gas phase. A comparison of the ¹⁴C partitioning between paddy and upland samples showed significant differences. This difference was caused by soil solution pH. Land use would affect the behavior of the ¹⁴C as the sodium acetate form. (author)

[en] For safety assessments of geological repositories of nuclear waste, understanding of uranium (U) fate in estuarine areas is important because U chemical behavior in the areas is expected to be complex. Environmental transfer parameters such as sediment-water distribution coefficients (K_d) and concentration ratios (CRs) for marine organisms are useful in mathematical models for the assessment. However, due to its low concentration in estuarine water, K_d and CF data for U are scarce. Thus we studied a rapid method for separation and concentration of U from estuarine water samples using NOBIAS-CHELATE PA1 resin columns followed by inductively coupled plasma mass spectrometry (ICP-MS) for U measurement. Chemical recovery was about 100% at pH of 5.7 ± 0.1 from the water samples and alkali and alkaline earth metals were removed. The method was used to measure U concentrations in estuarine water samples collected at eight Japanese estuarine areas; they ranged from 0.1 to 3.8 μg L^-1. We also measured U concentrations in sediment and marine organism samples by ICP-MS after acid digestion. Using these values, we observed K d (range: 39-284 L kg^-1) and CRs (0.86-52 L kg^-1 for macroalgae, 0.087-15 L kg^-1 for crustaceans, and 0.52-93 L kg^-1 for molluscs). (author)

[en] Plant uptake of radiocesium (¹³⁷Cs) was investigated in consideration of the relationships with naturally existing ¹³³Cs and potassium (K). We first determined plant-unavailable fraction of ¹³⁷Cs in soil by batch sorption and sequential extraction methods with a radiotracer. Then, using the data obtained from the batch sorption and extraction methods, we clarified the relationships of plant-available and plant-unavailable fractions between ¹³⁷Cs, ¹³³Cs, and K in soil. Additionally, ¹³⁷Cs concentrations in crop were estimated using ¹³⁷Cs in soil and several factors, i.e. fixation ratio of ¹³⁷Cs in soil, cation exchange capacity, and K concentration in crop. The results implied that the fixation ratio of ¹³⁷Cs in soil was a very important key to understanding ¹³⁷Cs plant uptake. (author)

[en] Uranium (U) concentrations in crop samples are usually low, making it difficult to obtain soil-to-plant transfer factors (TFs) under agricultural field conditions. In this study, U concentrations in rice and associated soil samples have been determined by inductively coupled plasma mass spectrometry (ICP-MS) after chemical separation with TRU resin (Eichrom). After U extraction on the resin by sample solution loading, tetramethyl ammonium hydroxide was studied for U elution behavior from the resin cartridges. Chemical recovery with this method was about 85%. Then U concentrations in three kinds of rice grain samples, brown rice (hulled rice), white rice (polished rice) and bran (63 samples each), were measured by ICP-MS after the TRU resin extraction method. U concentrations in all samples were measured and the geometric means in white rice, brown rice and bran samples were 7.3 x 10^-5, 9.7 x 10^-5 and 3.7 x 10^-4 mg/kg-dry, respectively. TFs for white rice ranged from 6.2 x 10^-6 to 7.9 x 10^-5 with a geometric means of 2.7 x 10^-5, whereas those for brown rice ranged from 5.5 x 10^-6 to 4.6 x 10^-4 with a geometric means of 3.6 x 10^-5. These values were 2 orders of magnitude lower than the TF for cereals of 1.3 x 10^-3 proposed by IAEA. (authors)

[en] In this study, we experimentally obtained partitioning ratios of radioiodide (¹²⁵I^-) in the three phases at two different temperatures, 4 and 23 deg C, in order to observe the effect of biological activity for upland soil samples. Even at 4 deg C, ¹²⁵I emission was found; its partitioning ratio in the gas phase ranged from 0 to 27 %. As expected, the ratio at 23 deg C was higher than that at 4 deg C. Additionally, in comparison of the data for upland soil samples obtained in this study and our previous data for paddy soil samples, for the latter, I^- was not only sorbed in the soil but also more of it was released into the air than for upland soil samples. The land-use difference for I^- partitioning in soil might be attributed to the differences of exchangeable K and stable I concentrations in soil from the statistical analysis. On the other hand, there were good correlations of partitioning ratios in solid, liquid, and gas phases between the two temperatures. The results implied that the biological activity can enhance partitioning in not only the gas phase, but also the solid phase. Indeed, the soil-soil solution distribution coefficient at 23 deg C was about three times as high as that at 4 deg C. (author)

[en] To accurately determine "2"4"1Am by mass spectrometry, interfering elements (IEs) including Bi, Hf, Hg, Pb, Pt, Pu and Tl need to be decontaminated. In this study, the extraction behaviors of IEs in HNO_3 and HCl mediums were systematically studied for the employed extraction resins (TRU, DGA-N and DGA-B). Based on the results, chemical separation procedures were proposed. After cooperation with proper co-precipitation methods, the proposed procedures can be used to determine "2"4"1Am in environmental samples. The results of evaluation showed that IEs in soil samples were completely removed and "2"4"1Am was accurately determined for all proposed procedures. (author)

[en] The characterization of Pu isotopes in a sediment core collected in the western North Pacific off Fukushima in January 2013 was determined. We compared the results with that of the marine sediments collected from July 2011 to July 2012. Both the ^239+240Pu activities and the ²⁴⁰Pu/²³⁹Pu atom ratios showed no variation in the marine sediments in the last 2 years since the FDNPP accident. Pu contamination in the marine sediments in the investigated areas still originated from global fallout and the Pacific Proving Ground close-in fallout. (author)