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.

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.

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.

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.

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.

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.

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.

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.

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.

Temporal variation of post-accident atmospheric 137Cs in an evacuated area of Fukushima Prefecture: Size-dependent behaviors of 137Cs-bearing particles.

The concentrations of 137Cs in the air, which were divided into coarse (>1.1 µm ϕ) and fine (<1.1 µm ϕ) fractions of particulate matter (PM), were measured from October 2012 to December 2014 in an area evacuated after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Total atmospheric 137Cs concentrations showed a clear seasonal variation, with high concentrations during summer and autumn related to the dominant easterly wind blowing from the highly radioactivity contaminated area. This seasonal peak was dominated by 137Cs in the coarse PM fraction. The 137Cs specific activity (massic 137Cs concentration) in the coarse PM was also found to increase significantly in summer, whereas that in the fine PM showed no variability during the year. These results show that coarse and fine 137Cs-bearing PM have different origins and behaviors in the resuspension process. The seasonal variation in atmospheric 137Cs concentration was well correlated with the mean 137Cs surface contamination (deposition density) around the observation site weighted by the frequency of wind direction, indicating that the atmospheric 137Cs concentration in the observation site was explained by the distribution of the 137Cs surface contamination and the frequency of different wind directions. We introduced a resuspension factor corrected for wind direction, consisting of the ratio of the atmospheric 137Cs concentration to the weighted mean 137Cs surface contamination, which evaluated the intensity of resuspension better than the conventional resuspension factor. This ratio ranged from 5.7 × 10-11 to 8.6 × 10-10 m-1 and gradually decreased during the study period.

Determination of Iodide, Iodate and Total Iodine in Natural Water Samples by HPLC with Amperometric and Spectrophotometric Detection, and Off-line UV Irradiation.

We developed a rapid, simple method for the iodine speciation analysis of water and applied it to natural water samples. Simultaneous determinations of I(-) and IO3(-) were achieved with an HPLC system with amperometric detection for I(-) and spectrophotometric detection after a postcolumn reaction for IO3(-). We determined the I(-) and IO3(-) concentrations in 20-µL water samples within 10 min. Total I concentrations in water samples were determined after the decomposition of organics by off-line UV irradiation for 30 min, followed by reduction to I(-). The analytical conditions were optimized by using test solutions rich in organic matter extracted from soils. We tested the new method with samples of groundwater, spring water, precipitation, soil percolate, stream water, and seawater as well as solutions extracted from soil. The method worked well, although the concentrations of some I species were below detection. This method is suitable for routine speciation analysis, which is important for studies of I behavior in the environment.

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.

Vertical distribution of radiation dose rates in the water of a brackish lake in Aomori Prefecture, Japan.

Seasonal radiation dose rates were measured with glass dosemeters housed in watertight cases at various depths in the water of Lake Obuchi, a brackish lake in Aomori Prefecture, Japan, during fiscal years 2011-2013 to assess the background external radiation dose to aquatic biota in the lake. The mean radiation dose in the surface water of the lake was found to be 27 nGy h(-1), which is almost the same as the absorption dose rate due to cosmic ray reported in the literature. Radiation dose rates decreased exponentially with water depth down to a depth of 1 m above the bottom sediment. In the water near the sediment, the dose rate increased with depth owing to the emission of γ-rays from natural radionuclides in the sediment.

Tritium activity concentrations and residence times of groundwater collected in Rokkasho, Japan.

Tritium ((3)H) concentrations were measured in groundwater samples from four surface wells (4-10 m deep), four shallow wells (24-26.5 m deep) and a 150-m-deep well in the Futamata River catchment area, which is adjacent to the large-scale commercial spent nuclear fuel reprocessing plant in Rokkasho, Japan. The (3)H concentrations in most of the surface- and shallow-well samples (<0.03-0.57 Bq l(-1)) were similar to those in precipitation (annual mean: 0.31-0.79 Bq l(-1)), suggesting that the residence time of the water in those wells was 0-15 y. The (3)H concentrations in the samples from a 26-m-deep well and the 150-m-deep well were lower than those in the other wells, indicating that groundwater with a long residence time exists in deep aquifers and the estuary area of the catchment. It is not clear whether (3)H released during test operation of the plant with actual spent nuclear fuel affected the (3)H concentrations observed in this study.

Concentration of 129I in aquatic biota collected from a lake adjacent to the spent nuclear fuel reprocessing plant in Rokkasho, Japan.

The spent nuclear fuel reprocessing plant in Rokkasho, Japan, has been undergoing final testing since March 2006. During April 2006-October 2008, that spent fuel was cut and chemically processed, the plant discharged (129)I into the atmosphere and coastal waters. To study (129)I behaviour in brackish Lake Obuchi, which is adjacent to the plant, (129)I concentrations in aquatic biota were measured by accelerator mass spectrometry. Owing to (129)I discharge from the plant, the (129)I concentration in the biota started to rise from the background concentration in 2006 and was high during 2007-08. The (129)I concentration has been rapidly decreasing after the fuel cutting and chemically processing were finished. The (129)I concentration factors in the biota were higher than those reported by IAEA for marine organisms and similar to those reported for freshwater biota. The estimated annual committed effective dose due to ingestion of foods with the maximum (129)I concentration in the biota samples was 2.8 nSv y(-1).

Nuclear accident-derived (3)H in river water of Fukushima Prefecture during 2011-2014.

During 2011-2014, we measured (3)H concentrations in river water samples collected during base flow conditions and during several flood events from two small rivers in a mountainous area in Fukushima Prefecture, which received deposition of (137)Cs from the Fukushima Dai-ichi Nuclear Power Plant accident. (3)H concentrations above background levels were found in water samples collected during both base flow conditions and flood events in 2011. The (3)H concentrations during flood events were generally higher than those during base flow conditions. The (3)H concentrations in both rivers during base flow conditions and flood events decreased with time after the accident and reached almost background levels in 2013. We also measured (3)H concentrations in freshwater samples from 16 other rivers and one dam in eastern Fukushima Prefecture from 2012 to 2014 during base flow conditions. The measured (3)H concentrations were higher than the background level in 2012 and decreased with time. The (137)Cs inventory in the catchment area at each sampling point was estimated from air-borne monitoring results in the literature and compared with the (3)H concentrations. We found surprisingly good correlations between (137)Cs inventories in the catchment areas and (3)H concentrations in the water samples. Further studies will be necessary to clarify the reason for the good correlation.

Effects of radiocesium inventory on (137)Cs concentrations in river waters of Fukushima, Japan, under base-flow conditions.

To investigate the behavior of nuclear accident-derived (137)Cs in river water under base-flow conditions, concentrations of dissolved and particulate (137)Cs were measured at 16 sampling points in seven rivers of Fukushima Prefecture, Japan, in 2012 and 2013. The concentration of dissolved (137)Cs was significantly correlated with the mean (137)Cs inventory in the catchment area above each sampling point in both sampling years. These results suggest that the concentration of dissolved (137)Cs under base-flow conditions is primarily determined by the (137)Cs inventory of the catchment area above the sampling point. However, the concentration of particulate (137)Cs did not show a clear relationship with either the mean (137)Cs inventory or the dissolved (137)Cs concentration, thus indicating that particulate and dissolved forms do not effectively interact in rivers. To evaluate the contribution of the (137)Cs inventory within catchment areas, we analyzed relations between the (137)Cs concentration and the mean (137)Cs inventory over the area within certain flow path lengths that were traced along the river and slope above the sampling point. Coefficients of determination for dissolved (137)Cs concentrations were highest for the longest flow path, i.e., the whole catchment area, and lower for shorter flow paths. Coefficients of determination for particulate (137)Cs concentrations were only moderately high for the shortest flow path in 2012, whereas the values were quite low for all flow paths in 2013. These results suggest that dissolved (137)Cs can originate from a larger area of the catchment even under base-flow conditions; however, particulate (137)Cs did not show such behavior. The results also show that under base-flow conditions, dissolved and particulate (137)Cs behave independently during their transport from river catchments to the ocean.