Shun’ichi Hisamatsu

Transfer of 137Cs and stable Cs from paddy soil to polished rice in Aomori, Japan

Rice is a staple food in Japan and other Asian countries, and the soil-to-plant transfer factor of 137Cs released into the environment is an important parameter for estimating the internal radiation dose from food ingestion. Soil and rice grain samples were collected from 20 paddy fields throughout Aomori Prefecture, Japan in 1996 and 1997, and soil-to-polished rice transfer factors were determined. The concentrations of 137Cs, derived from fallout depositions, stable Cs and K in paddy soils were 2.5-21 Bq kg(-1), 1.2-5.3 and 5000-13000 mg kg(-1), respectively. The ranges of 137Cs, stable Cs and K concentration in polished rice were 2.5-85 mBq kg(-1) dry wt., 0.0005-0.0065 and 580-910 mg kg(-1) dry wt., respectively. The geometric mean of soil-to-polished rice transfer factor of 137Cs was 0.0016, and its 95% confidence interval was 0.00021-0.012. The transfer factor of 137Cs was approximately 3 times higher than that of stable Cs at 0.00056, and they were well correlated. This implied that fallout 137Cs, mostly deposited up to the 1980s, is more mobile and more easily absorbed by plants than stable Cs in the soil, although the soil-to-plant transfer of stable Cs can be used for predicting the long-term transfer of 137Cs. The transfer factors of both 137Cs and stable Cs decreased with increasing K concentration in the soil. This suggests that K in the soil was a competitive factor for the transfers of both 137Cs and stable Cs from soil-to-polished rice. However, the transfer factors of 137Cs and stable Cs were independent of the amount of organic materials in soils.

Extractability of major and trace elements from agricultural soils using chemical extraction methods: Application for phytoavailability assessment

Abstract To assess soil-to-plant transfer of various elements more precisely, the concentrations of the elements extracted from soil samples using eight chemical solutions were compared with the results of a pot cultivation experiment of komatsuna (Brassica rapa L. var. perviridis) or buckwheat (Fagopyrum esculentum M.) using the soils. From agricultural fields in Aomori, Japan, 16 soil samples were collected. Elements in the samples were extracted using acids (1 mol L−1 HNO3, 0.1 mol L−1 HNO3, 0.01 mol L−1 HNO3), chelating agents (0.05 mol L−1 EDTA), neutral salt solutions (1 mol L−1 NH4OAc, 1 mol L−1 NH4NO3, 0.01 mol L−1 CaCl2) and pure water. The 28 elements in the extracted solutions and plant samples were determined. The extractability of many metals was higher in 1 mol L−1 HNO3, 0.1 mol L−1 HNO3 and the 0.05 mol L−1 EDTA solutions than in the other extractants. Higher extractability using the NH4OAc solution than the NH4NO3 solution was observed for some elements, in particular U. Extractability by pure water was not always lowest among these methods, probably because of dispersion of colloidal substances in the extracted solution. The pot cultivation experiment showed that the concentrations in soil and in the extracted fraction using 1 mol L−1 HNO3, 0.1 mol L−1 HNO3 or the EDTA solution did not correlate with the concentration in plant samples for most elements. Plant uptake of Zn, Y and La by komatsuna correlated well with their concentrations in extracts with neutral salt solutions or 0.01 mol L−1 HNO3. Concentrations of Al, Cu and Cd in buckwheat were also correlated with the concentrations in the extracts.

Relationship between the radiocesium interception potential and the transfer of radiocesium from soil to soybean cultivated in 2011 in Fukushima Prefecture, Japan

The concentration of radiocesium ((134)Cs and (137)Cs) in agricultural fields around Fukushima Dai-ichi Nuclear Power Plant (FDNPP) was elevated after the accident in March 2011. Evaluation of soil properties that influence phytoavailability of radiocesium is important for optimal soil management to minimize radiocesium transfer to crops. In this study, soybean grain and soil samples (0-15xa0cm) were collected from 46 locations in Fukushima Prefecture in 2011, and (137)Cs concentrations were measured. (137)Cs concentration ranges were 11-329xa0Bqxa0kg(-1)-dry in soybean grain samples, and 0.29-2.49xa0kBqxa0kg(-1)-dry in soil samples. The radiocesium interception potential (RIP) values in the soil samples ranged from 0.30 to 8.61xa0molxa0kg(-1). RIP negatively correlated with total carbon content and oxalate-extractable Si and Alxa0+ 1/2 Fe in the soils, suggesting that soils rich in organic matter and poorly crystalline clays tended to have lower RIP in this region. The soil-to-plant transfer factor for (137)Cs, analyzed in relation with various soil characteristics, varied by two orders of magnitude and was significantly negatively correlated with RIP and exchangeable K concentration in soil. The results show that RIP is useful for evaluating the efficiency of radiocesium transfer from soil to plants in this region.

Determination of total contents of bromine, iodine and several trace elements in soil by polarizing energy-dispersive X-ray fluorescence spectrometry

A non-destructive analysis method for total bromine (Br) and iodine (I) contents in soil was established using polarizing energy-dispersive X-ray fluorescence (EDXRF) spectrometry. The matrix-corrected intensity of Br and I Kα X-rays from pressed pellets of soil powder samples was calibrated with their contents measured by inductively coupled plasma (ICP)-mass spectrometry after pyrohydrolysis preparation. The calibration curves for Br and I were successfully obtained in the concentration ranges 3.8–223u2009mgu2009kg−1 and 0.91–54u2009mgu2009kg−1 respectively. Repeated analyses of the same sample with polarizing EDXRF spectrometry within one day and after approximately 1.5 years showed good reproducibility of the measurement results. The lower limits of detection for Br and I were 0.14u2009mgu2009kg−1and 0.34u2009mgu2009kg−1 respectively. The established analytical method for total Br and I contents in soil is non-destructive, simple and rapid, and is suitable for routine analysis. Trace elements such as rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), cadmium (Cd), tin (Sn), antimony (Sb), caesium (Cs), barium (Ba), light rare earth elements and lead (Pb) were also measurable simultaneously under the identical operational conditions as those for Br and I measurements.

Tritium concentrations in the atmospheric environment at Rokkasho, Japan before the final testing of the spent nuclear fuel reprocessing plant.

This study aimed at obtaining background tritium concentrations in precipitation and air at Rokkasho where the first commercial spent nuclear fuel reprocessing plant in Japan has been under construction. Tritium concentration in monthly precipitation during fiscal years 2001-2005 had a seasonal variation pattern which was high in spring and low in summer. The tritium concentration was higher than that observed at Chiba City as a whole. The seasonal peak concentration at Rokkasho was generally higher than that at Chiba City, while the baseline concentrations of both were similar. The reason for the difference may be the effect of air mass from the Asian continent which is considered to have high tritium concentration. Atmospheric tritium was operationally separated into HTO, HT and hydrocarbon (CH(3)T) fractions, and the samples collected every 3xa0d-14xa0d during fiscal year 2005 were analyzed for these fractions. The HTO concentration as radioactivity in water correlated well with that in the precipitation samples. The HT concentration was the highest among the chemical forms analyzed, followed by the HTO and CH(3)T concentrations. The HT and CH(3)T concentrations did not have clear seasonal variation patterns. The HT concentration followed the decline previously reported by Mason and Östlund with an apparent half-life of 4.8xa0y. The apparent and environmental half-lives of CH(3)T were estimated as 9.2xa0y and 36.5xa0y, respectively, by combining the present data with literature data. The Intergovernmental Panel on Climate Change used the atmospheric lifetime of 12xa0y for CH(4) to estimate global warming in its 2007 report. The longer environmental half-life of CH(3)T suggested its supply from other sources than past nuclear weapon testing in the atmosphere.

Concentration of 3 H in plants around Fukushima Dai-ichi Nuclear Power Station

A large amount of radionuclides was released from the Fukushima Dai-ichi Nuclear Power Station (FDNPS) following the damage caused by the tsunami due to the Great East Japan Earthquake on 11 March 2011. Although many radionuclides in various environmental samples around the FDNPS have been measured, 3H in the terrestrial environment has not yet been reported. We present here the first survey results of 3H concentrations in plant samples collected around the FDNPS in 2011 from shortly after the accident. The free-water 3H concentrations in herbaceous plant shoots and evergreen tree leaves were considerably higher than the previous background concentration, and diminished with distance from the FDNPS. Although reconstruction of atmospheric 3H concentrations after the accident is difficult, a rough estimate of the radiation dose due to 3H inhalation about 20u2005km from the FDNPS is on the order of a few microsieverts (μSv).

Radon concentration in indoor occupational environments in Aomori Prefecture, Japan

The (222)Rn concentrations in indoor workplaces were measured in Aomori Prefecture, Japan, and the results are reported here. This survey was part of a program to measure background natural radiation dose rate in the prefecture where the first Japanese nuclear fuel cycling facilities are now under construction. The survey of the (222)Rn concentrations in indoor workplaces was carried out at 107 locations from 1996 to 1998. The (222)Rn concentrations were measured for approximately one year at each site with passive Rn detectors, which used a polycarbonate film for counting alpha-rays and could separate concentrations of (222)Rn from (220)Rn. Weeklong measurements of (222)Rn concentration and working level were carried out with active detectors to get the ratio of (222)Rn concentration during working hours to non-working hours as well as equilibrium factors in selected locations. Diurnal variation of (222)Rn concentration depended on building structure, air-conditioning, time of day and day of the week (week days or weekend). The (222)Rn concentration during working hours was generally lower than that in non-working hours. Although the annual average (222)Rn concentration in indoor occupational environments was higher than that in dwellings, radiation dose for Aomori Prefecture residents from Rn in the former was 14% of the total indoor dose by Rn because of the lower concentration in working hours and lower occupancy factor.

Low-Level Measurement with a Noble Gas Mass Spectrometer for Organically Bound Tritium in Environmental Samples

Abstract We developed an analytical method for organically bound 3H (OBT) in biological environmental samples by using noble gas mass spectrometry of 3He produced from 3H. Three environmental samples with background level OBT concentrations were analyzed, and the results agreed well with those by the conventional liquid scintillation counting of electrolyzed combustion water of the samples. This showed that the method is practical and effective. We also developed an analytical method for non-exchangeable OBT as a combination of pre-treatment of dried samples with free water 3H and our newly developed analytical method for OBT. The repeated analysis of a grass sample with moderate 3H concentration had smaller variance of results for non-exchangeable OBT than for OBT. The sum of non-exchangeable and exchangeable OBT agreed well with OBT measured in the samples. The developed method was successfully applied to terrestrial and marine environmental samples with background 3H levels.

Tritium Concentration in River Water and Groundwater Collected in Rokkasho, Aomori, Japan

Abstract In order to study the effect of 3H released from the commercial spent nuclear fuel reprocessing plant on 3H concentration in the local fresh water environment, river water and well water samples were collected at seventeen and nine points, respectively, around the plant. Concentrations of 3H were measured in the samples collected during the period of the final testing using actual spent fuel in the plant. The stable isotope ratios of hydrogen and oxygen in water samples were also measured for a hydrological study around the plant area. Concentrations of 3H in the river water samples were in the background level, and their variation among sampling locations was small. Although well water samples also did not have significantly high 3H concentrations originating from the 3H released from the plant, the variation in 3H concentration among sampling locations was larger than that in the river water samples. Comparison of ΔD and Δ18O data with a local meteoric water line suggested that groundwater around the plant area is mainly recharged by precipitation in winter.

Validation of a Radionuclide Transfer Model in Brackish Lake

Abstract In order to simulate the behavior of radionuclides in a brackish lake, Lake Obuchi, adjacent to the first commercial spent nuclear fuel reprocessing plant in Japan, we constructed a transfer model for radionuclides using a three-dimensional hydrodynamic model coupled with an ecosystem model. To validate the hydrodynamic model using actual field data, the concentration of tritium (3H) was measured in water samples collected in and around the lake from 2005 to 2008. The samples collected from 2006 to 2008 occasionally showed higher concentrations than background when high concentration seawater flowed into the lake with the tide. 3H concentrations in the lake water estimated by the model were generally within 10% of the observations, although the observed values were overpredicted by a factor of 2 in a few cases.