Concentrations of iodine-129 in livestock, agricultural, and fishery products around spent nuclear fuel reprocessing plant in Rokkasho, Japan, during and after its test operation.

Concentrations of iodine-129 (129I) and atomic ratios of 129I/127I in livestock (grass and milk), agricultural (cabbage, Japanese radish, and rice), and fishery (flatfish and brown alga) products collected from locations around the first Japanese commercial spent nuclear fuel reprocessing plant in Rokkasho were measured from 2006 to 2016. The actual spent nuclear fuel rods were cut and processed to test the functioning of the plant that discharged controlled amounts of 129I to the atmosphere and coastal seawater during the period from 2006 to 2008 (the "cutting period"). Statistically significant increases in 129I concentration and 129I/127I ratio were observed during the cutting period in livestock products and flatfish. On the other hand, these parameters were statistically comparable during and after the cutting period in the other products. The radiation dose through the ingestion of the maximum 129I concentrations, measured in the different products, was estimated to be in the nanoSievert per year level. This value is much smaller than 1 mSv yr-1, which is the permissible authentic radiation dose for the general public. The 129I levels in the samples, especially in milk and flatfish, are discussed in context of the 129I discharge history from the plant.

Biokinetics of 13C in the human body after oral administration of 13C-labeled glucose as an index for the biokinetics of 14C.

The retention of 13C in the human body after oral administration of 13C-labeled glucose was studied in three healthy volunteer subjects to estimate the 50 year cumulative body burden for 13C as an index of the committed dose of the radioisotope 14C. After administration of 13C-labeled glucose, the volunteers ingested controlled diets with a fixed number of calories for 112 d. Samples of breath and urine were collected up to 112 d after administration. Samples of feces were collected up to 14 d after administration. Hair samples were obtained at 119 d after administration and analyzed as a representative index of the rate of excretion of organic 13C via pathways such as skin cell exfoliation and mucus secretion. All samples were analyzed for 13C/12C atomic ratio to determine the rate of excretion via each pathway. We then constructed a metabolic model with a total of four pathways (breath, urine, feces, and other) comprising seven compartments. We determined the values of the biokinetic parameters in the model by using the obtained excretion data. From 74% to 94% of the 13C administered was excreted in breath, whereas <2% was excreted in urine and feces. In the other pathway, the excretion rate constant in the compartment with the longest residence time stretched to hundreds of days but the rate constant for each subject was not statistically significant (P value > 0.1). In addition, the dataset for one of the three subjects was markedly different from those of the other two. When we estimated the 50 year cumulative body burden for 13C by using our model and we included non-statistically significant parameters, a considerable cumulative body burden was found in the compartments excreting to the other pathway. Although our results on the cumulative body burden of 13C from orally administered carbon as glucose were inconclusive, we found that the compartments excreting to the other pathway had a markedly long residence time and therefore should be studied further to clarify the fate of carbon in the human body. In addition to excreta, data for serum and blood cell samples were also collected from the subjects to examine the metabolism of 13C in human body.

DISTRIBUTION OF RADIOCESIUM IN BLACK PINE TREE FORESTS IN ROKKASHO, AOMORI, JAPAN.

Since the Fukushima Dai-ichi Nuclear Power Plant (FDNNP) accident in 2011, 134Cs had been detected in atmospheric deposition samples collected in Rokkasho and Aomori in Japan, located ~400-km north of the FDNNP, during March 2011-May 2015. To study the distribution of radiocesium (134, 137Cs) in a Japanese black pine tree forest, we measured the activity concentration of 134, 137Cs in whole black pine trees, including roots collected during 2017-19 along with soil samples in 2015 and 2017-19. The results show that most of the deposited 134Cs was retained in the forest floor in 2015, with depth distribution different from that of the weapon testing fallout. Proportions of the weapon fallout 137Cs in trunks, branches, needles and roots were 44, 17, 13 and 26%, respectively, indicating that >50% of 137Cs in above-ground part existed in the trunks. The total inventories of 134Cs and 137Cs in the forest were estimated to be 8.9 and 2.5·103 Bq m-2, respectively, and ~4.8% of 137Cs inventory was originated from the accident. Inventory of 134Cs in the forest-including the black pine trees-was 1.6 times larger than cumulative deposition outside of the forest due to the canopy effect.

TRANSFER OF CESIUM AND IODINE FROM THE SURFACE TO THE INTERIOR OF APPLE FRUIT.

We investigated the transfer of stable Cs + and I- applied as droplets directly on the fruit surface of 3-y-old plumleaf crab apple trees to the fruit interior at different developmental stages. The proportions of Cs and I transferred to the fruit flesh by harvest time were 21-66% and 41-53%, respectively, with decreasing trends as the developmental stage progressed. Most of the Cs+ was gradually transferred from the surface to the skin and flesh, while I- rapidly penetrated the fruit in the days after the application, followed by slow transfer of small proportions. For both elements, prompt penetration of the flesh occurred 1-2 d after application. A compartment model for simulating each element's behavior was constructed using all the data obtained. The Cs transfer model to the flesh can simulate the measured values well. For the model of I, prompt distribution to the skin is also necessary.

In situ experimental exposure of fruit-bearing shoots of apple trees to 13CO2 and construction of a dynamic transfer model of carbon.

Evaluating the transfer and metabolism of carbon (C) in apple fruit is key to estimating the potential accumulation of atmospheric 14C in fruit near and around nuclear facilities. We developed a dynamic compartment model for apple fruit-bearing shoots, assuming that the shoots are a simple unit of source and sink for photoassimilates. Fruit-bearing shoots of Malus domestica "Fuji" at different fruit growth stages were exposed to 13CO2in situ, followed by sampling at 72 h after exposure or at harvest. The 13C/(13C+12C) mole ratio in fruits, leaves, and current branch were measured to construct a five-compartment model of 13C (fruit, each fast and slow component of leaves, and current branch). The C inventories in the compartments were presented in accordance with the measured growth curves of C in the organs. The model simulated the 13C dynamics in plant tissues well. Simulation results of photoassimilate distribution using the model indicated that the retention of photoassimilated C at the harvest depended on the growth rate of C in the organs at the exposure.

AtKUP/HAK/KT9, a K+ transporter from Arabidopsis thaliana, mediates Cs+ uptake in Escherichia coli.

Although cesium is known to be absorbed by plants, the pathway by which cesium enters has not been identified. We found that the AtKUP/HAK/KT9 gene from Arabidopsis thaliana was functionally expressed in a potassium transport-deficient Escherichia coli mutant. AtKUP/HAK/KT9 mediated potassium uptake as well as cesium transport. We found that AtKUP/HAK/KT9 might be involved in the pathway in questions.

Short-term metabolism of biologically incorporated 125I ingested by olive flounder (Paralichthys olivaceus).

Iodine-129 with a long half-time of 1.6 × 107 y was discharged into the Pacific Ocean during the final safety tests of the first commercial nuclear fuel reprocessing plant in Japan, at Rokkasho, Aomori Prefecture. Olive flounder (Paralichthys olivaceus) is an important fishery along this coast. It is necessary to determine whether 129I accumulates in this species to assess the possible public acceptance. We developed a short-term metabolism model of 125I in the flounder using retention data for 1-6 days after the olive flounder had ingested a freshwater fish species, medaka (Oryzias latipes), that had been labeled with 125I by keeping them in water containing 125I for 7 days. A single compartment model constructed from whole-body retention data for 125I in the olive flounder, excluding the gastrointestinal tract and its contents, revealed a biological half-time of 2.9 days for 125I. When the gill and other tissues were separated to individual compartments, the biological half-time in the gill was three times longer than that in the other tissue, though the half-time in the gill is not statistically significant. The distribution of 125I among various tissues in the flounder 6 days after the ingestion of labeled medaka once a day for 6 days differed from that of stable I, suggesting that the biological half-time is longer in certain tissues. Further study is necessary to elucidate the metabolism of radioiodine in the flounder.

Effects of organic amendments on the natural attenuation of radiocesium transferability in grassland soils with high potassium fertility.

Organic amendments affect the behavior of radiocesium in soil-plant systems in a complex way; they can inhibit radiocesium fixation by clay minerals by blocking selective sorption sites, whereas K supplied to the soil solution by amendments can reduce Cs uptake by plant roots. Here, we investigated the influence of inorganic and organic amendments on the transferability of radiocesium from soil to grass seedling in a humus-rich Andosol with high exchangeable K content. Soil samples were spiked with a137Cs tracer, treated with N, N-P-K, compost (cattle manure using rice straw), or no amendment (control soil), and subjected to repeated two-week wetting and air-drying treatments for one year in an artificial climate chamber. Small-scale cultivations of orchard grass were performed four times during the experimental period to assess temporal changes of availability of 137Cs in the soils. The 137Cs transfer factor (TF), defined as the 137Cs concentration in the plant divided by that in the soil, decreased with time in the control soil. The soil treated with compost showed higher TFs than the control soil in each cultivation and a slower attenuation of 137Cs transferability. By comparing the extractability of 137Cs, NH4+, and K+ with the observed TFs, we show that K released from the compost was not effective in reducing root uptake of 137Cs, but enhanced 137Cs desorption from the soil under K-rich conditions. This result suggests that organic amendment is ineffective in reducing root uptake of radiocesium under high exchangeable K concentrations, and may instead enhance the long-term availability of radiocesium in soils.

Estimation of dietary 14C dose coefficient using 13C-labelled compound administration analysis.

Carbon-14 released from nuclear facilities has been assessed to contribute significantly to the radiation dose that people are exposed to through the food chain. However, the current dose coefficient for members of public, which is the ratio of the 50-year committed effective dose to ingested 1 Bq 14C, recommended by the International Commission on Radiological Protection (ICRP) is not based on experimental human metabolic data for 14C in nutrients and diet. Therefore, to validate the coefficient, we administered 13C-labelled nutrients consisting of four amino acids, three fatty acids, and one monosaccharide to volunteers as substitutes for 14C labelled nutrients and measured the 13C concentration in various excreta samples. Although metabolic models were constructed from the excretion data, a significant fraction of administered 13C was not recovered from some nutrients. The dose coefficients of 14C in uniformly labelled Japanese diet, which were estimated under several assumptions about the unrecoverable fraction, varied from (6.2 ± 0.9) × 10-11 to (8.9 ± 4.4) × 10-10 Sv Bq-1 and were approximately comparable to the current value of 5.8 × 10-10 Sv Bq-1 recommended by the ICRP. Further studies are necessary to elucidate the metabolism of 14C in various nutrients in the unrecoverable fraction.

Effect of the counter anion of cesium on foliar uptake and translocation.

Direct deposition of radioactive material onto crops is one important pathway for safety assessment of radionuclides released from nuclear facilities. Foliar uptake of Cs by radish (Raphanus sativus L. cv. Redchim) was studied by applying droplets of Cs solution (CsCl or CsNO3) on an upper leaf surface. The uptake of Cs was strongly affected by counter anions of Cs in the applied solution. Approximately 80% of Cs was absorbed for CsCl solution, while only 20% was absorbed for CsNO3. The partition of absorbed Cs between leaf and root tuber was quite similar for both Cs compounds, which indicated that behavior of the absorbed Cs in radish was the same for both.

A SIMULATION STUDY OF DEPOSITION PARAMETERS FOR 129I DISCHARGED FROM THE ROKKASHO REPROCESSING PLANT.

The first commercial spent nuclear fuel reprocessing plant at Rokkasho in Japan discharged 129I from actual spent nuclear fuel into the atmosphere during its test operation from 2006 to 2008. Previously, we measured monthly atmospheric concentrations of gaseous and particulate 129I and atmospheric deposition rates of 129I from the campus of our institute, which is 2.6 km east of the main stack of the plant. In this study, we simulated the atmospheric concentrations and deposition rates of 129I using a combination of the Fifth-Generation Penn State/NCAR Mesoscale Model and the improved CG-MATHEW/ADPIC models, Version 5.0. Here, we report on the optimised deposition parameters of 129I used to simulate the measured values using 129I atmospheric discharge rates from the main stack.

Life-Shortening Effect of Chronic Low-Dose-Rate Irradiation in Calorie-Restricted Mice.

Calorie restriction is known to influence several physiological processes and to alleviate the late effects of radiation exposure such as neoplasm induction and life shortening. However, earlier related studies were limited to acute radiation exposure. Therefore, in this study we examined the influence of chronic low-dose-rate irradiation on lifespan. Young male B6C3F1/Jcl mice were divided randomly into two groups, which were fed either a low-calorie (65 kcal/ week) or high-calorie (95 kcal/week) diet. The latter is comparable to ad libitum feeding. The animals in the irradiated group were continuously exposed to gamma rays for 400 days at 20 mGy/day, resulting in a total dose of 8 Gy. Exposure and calorie restriction were initiated at 8 weeks of age and the diets were maintained for life. The life-shortening effects from chronic whole-body irradiation were compared between the groups. Body weights were reduced in calorie-restricted mice irrespective of radiation treatment. Radiation induced a shortened median lifespan in both groups, but to a greater extent in the calorie-restricted mice. These results suggest that calorie restriction may sensitize mice to chronic low-dose-rate radiation exposure to produce a life-shortening effect rather than alleviating the effects of radiation.

240Pu/239Pu and 242Pu/239Pu atom ratios of Japanese monthly atmospheric deposition samples during 1963-1966.

Global fallout plutonium isotopic ratios from the 1960s are important for the use of Pu as environmental tracers. We measured the 240Pu/239Pu and 242Pu/239Pu atomic ratios of monthly atmospheric deposition samples collected in Tokyo and Akita, Japan during March 1963 to May 1966. To our knowledge, our results represent the first data measured for actual atmospheric deposition samples collected continuously during the 1960s. Both atomic ratios increased rapidly from March 1963 to June 1963, followed by a gradual increase until September 1963. Then, both ratios declined with a half-life of approximately 5.6 months. The observed temporal changes of the ratios were likely caused by the upper-stratospheric input of nuclear debris from high-yield atmospheric nuclear weapon testing during 1961-62, followed by its downward transport to the troposphere.

Concentration and specific activity of fallout 137Cs in extracted and particle-size fractions of cultivated soils.

Fallout (137)Cs and stable Cs in soils were separated with two extractants (1M CH(3)COONH(4) solution and 0.8M CH(3)COONH(4) in 5% HNO(3) solution after H(2)O(2) oxidization). The residue remaining after removal of the oxidizable organic-bound fraction was separated into the particle-size fractions including clay, silt, fine sand and coarse sand with a sieving and sedimentation method. Then, the concentrations of (137)Cs and stable Cs in the extracted fractions and the particle-size fractions were determined. The (137)Cs contents in the exchangeable and organic-bound fractions in the soil were approximately 10 and 20%, respectively. The (137)Cs content in the strongly bound fraction was about 70%, and the concentration of (137)Cs in the clay was the richest among the particle-size fractions. The specific activity of (137)Cs (concentration ratio of fallout (137)Cs/stable Cs) decreased in the order exchangeable, organic-bound and strongly bound fractions. The data suggest that equilibrium between (137)Cs and stable Cs was not reached among those fractions, even though most of the (137)Cs that had been deposited on the soil was derived from fallout weapons tests that occurred several decades ago. The concentration of (137)Cs among the particle-size fractions in each soil was different, whereas the specific activity of (137)Cs in the particle-size fractions had a relatively similar value.

Plant induced changes in concentrations of caesium, strontium and uranium in soil solution with reference to major ions and dissolved organic matter.

For a better understanding of the soil-to-plant transfer of radionuclides, their behavior in the soil solution should be elucidated, especially at the interface between plant roots and soil particles, where conditions differ greatly from the bulk soil because of plant activity. This study determined the concentration of stable Cs and Sr, and U in the soil solution, under plant growing conditions. The leafy vegetable komatsuna (Brassica rapa L.) was cultivated for 26 days in pots, where the rhizosphere soil was separated from the non-rhizosphere soil by a nylon net screen. The concentrations of Cs and Sr in the rhizosphere soil solution decreased with time, and were controlled by K+NH(4)(+) and Ca, respectively. On the other hand, the concentration of U in the rhizosphere soil solution increased with time, and was related to the changes of DOC; however, this relationship was different between the rhizosphere and non-rhizosphere soil.

Deposition of 137Cs in Rokkasho, Japan and its relation to Asian dust.

Biweekly atmospheric depositions of (137)Cs were measured in Rokkasho, Aomori, Japan from March 2000 to March 2006 to study recent (137)Cs deposition. Although the deposition level was generally lower than the detectable limit, deposition samples collected in spring occasionally had measurable levels of (137)Cs. The annual (137)Cs deposition from 2001 to 2005 was 0.04-0.69 Bq m(-2) with a mean value of 0.27 Bq m(-2). Depositions of insoluble Al, Fe and Ti were strongly correlated with the (137)Cs deposition, suggesting that suspension of soil particles was the main source of the recent (137)Cs deposition. Asian dust events were coincident with some of the significant (137)Cs depositions in spring. It was found that the ratios of (137)Cs/Al and Fe/Al could be used as indices for discriminating Asian dust from suspension of the local surface soil. Backward trajectory analysis suggested southern Mongolian and northeastern China regions as sources of the significant (137)Cs depositions.

Regional and global contributions of anthropogenic iodine-129 in monthly deposition samples collected in North East Japan between 2006 and 2015.

We measured the monthly atmospheric deposition flux of 129I at Rokkasho, Aomori, Japan-the location of a commercial spent nuclear fuel reprocessing plant-from 2006 to 2015 to assess the impact of the plant on environmental 129I levels. The plant is now under final safety assessment by a national authority after test operation using actual spent nuclear fuel. During cutting and chemical processing in test operations from April 2006 to October 2008, 129I was discharged to the atmosphere and detected in our deposition samples. 129I deposition fluxes largely followed the discharge pattern of 129I from the plant to the atmosphere, and most of the deposited 129I originated from the plant. In and after 2009, 129I deposition fluxes decreased dramatically to reach the background level; the 129I deposition fluxes at Rokkasho were almost the same as those at Hirosaki, where an additional sampling point was set up as a background site 85 km from the plant in 2011. The background 129I deposition fluxes showed seasonal variation-high in winter and low in the other seasons-at both Rokkasho and Hirosaki. The results of a backward trajectory analysis of the air mass at Rokkasho suggested that reprocessing plants in Europe were the origins of the high 129I flux in winter. The contribution of 129I released from the Fukushima Dai-ichi Nuclear Power Plant accident to the 129I deposition flux at Rokkasho in 2011 was small on the basis of the 129I/131I activity ratio.

Soil-soil solution distribution coefficient of soil organic matter is a key factor for that of radioiodide in surface and subsurface soils.

We investigated the vertical distribution of the soil-soil-solution distribution coefficients (Kd) of 125I, 137Cs, and 85Sr in organic-rich surface soil and organic-poor subsurface soil of a pasture and an urban forest near a spent-nuclear-fuel reprocessing plant in Rokkasho, Japan. Kd of 137Cs was highly correlated with water-extractable K+. Kd of 85Sr was highly correlated with water-extractable Ca2+ and SOC. Kd of 125I- was low in organic-rich surface soil, high slightly below the surface, and lowest in the deepest soil. This kinked distribution pattern differed from the gradual decrease of the other radionuclides. The thickness of the high-125I-Kd middle layer (i.e., with high radioiodide retention ability) differed between sites. Kd of 125I- was significantly correlated with Kd of soil organic carbon. Our results also showed that the layer thickness is controlled by the ratio of Kd-OC between surface and subsurface soils. This finding suggests that the addition of SOC might prevent further radioiodide migration down the soil profile. As far as we know, this is the first report to show a strong correlation of a soil characteristic with Kd of 125I-. Further study is needed to clarify how radioiodide is retained and migrates in soil.

Accumulation of uranium derived from long-term fertilizer applications in a cultivated Andisol.

The U concentrations in the soils of experimental fields with continuous fertilizer applications and in neighboring non-agricultural soils were determined. The surface soils in the three experimental fields with fertilizer applications contained higher amounts of U compared with the non-agricultural surface soils. The amount of U elevated in the soil was estimated by the vertical profile of U concentration, and an increase of about 200 mg m-2 of U was found in the soils at 0-35 cm depth during a 61-year cultivation period. The estimated value was almost the same as the amount of U added through the fertilizers as calculated from U concentrations in the applied fertilizers. Therefore, almost all the U from the fertilizers would still remain in the upper part of the soils. Chemical extraction results suggested that organic substances and noncrystalline clay minerals in the surface soil should play an important role for accumulation of U derived from the fertilizers.

Rapid method for the analysis of plutonium isotopes in a soil sample within 60 min.

A rapid method for the determination of Pu isotopes in a soil sample within 60 min of starting sample pretreatment was developed. The large reduction in the analysis time was attained by the rapid and perfect digestion of the sample using an alkaline fusion method with an induction heating machine. Pu concentrations were then determined by flow injection/ICP-MS using a solid extraction resin after preconcentration by batch extraction with a chelate resin. The limits of detection for 239Pu and 240Pu were 9.2 fg and 4.3 fg, corresponding to 0.03 and 0.05 Bq kg(-1), respectively, under our analytical conditions, which satisfy the lower detection limits (0.5 Bq kg(-1) of 239Pu, and 2 Bq kg(-1) of 240Pu) required for rapid analysis techniques by the Ministry of Education, Culture, Sports, Science and Technology, Japan. This method provides a powerful and practical technique for emergency monitoring in and around nuclear facilities that handle large amounts of plutonium.