VARIATION IN RADIATION DOSE RATES FROM RADIONUCLIDES DISCHARGED BY THE SPENT NUCLEAR FUEL REPROCESSING PLANT IN ROKKASHO UNDER DIFFERENT YEARLY WEATHER CONDITIONS.

The radiation dose rate from radionuclides released by the spent nuclear fuel reprocessing plant in Rokkasho, Japan, was assessed for a year specified in the safety review during which the weather conditions were not significantly different from those of the other 10 y. However, the actual year-by-year variation in annual radiation dose rate was not examined. A model system for evaluating the dose rate from the radionuclides released into the atmosphere was constructed. In this study, the radiation dose rate in the weather conditions of 24 weather bins was estimated for a standard year by the model. The annual maximum dose rate from 1959 to 2012 was estimated using a simplified method that integrated the dose rates of each weather bin in the standard year by estimating the annual frequency of the bin in the target year. We obtained ~1.3 as the maximum/minimum ratio of the annual maximum dose rate.

RELATIONSHIP BETWEEN SOIL-SOIL-SOLUTION DISTRIBUTION COEFFICIENTS OF 125I AND 127I IN PASTURE SOIL.

We measured the depth profiles of soil-soil-solution distribution coefficients (Kd) of native 127I (127I-Kd) and exogenous 125I- (125I-Kd) in soils from a pasture near the spent nuclear fuel reprocessing plant in Rokkasho, Japan, and investigated their relationships to depth profiles of the concentration in soil of 127I and organic C and Kd of organic C (C-Kd). The depth profiles of 125I-Kd and 127I-Kd were similar. The relatively low 127I concentrations and low values of both 127I-Kd and 125I-Kd indicate that some of the I deposited on the soil surface have been transported to depths greater than 10 cm. On the other hand, high 127I-Kd/125I-Kd ratios in the uppermost 10 cm of soil indicate that some of the 127I bound to that soil could not be exchanged with exogenous 125I. Although a previous study has shown a power function relationship between 125I-Kd and C-Kd, our data show that the relationships of both 125I-Kd and 127I-Kd to C-Kd are exponential functions. The reason for these conflicting results is unknown. Nonetheless, our data clearly show Kd values for both 125I- and 127I to be dependent on C-Kd. In addition, the dependence of both 127I-Kd and 125I-Kd on C-Kd suggests that organic material in the soil has a role in the transport of I down the soil profile.

SPECIATION OF IODINE IN SOIL SOLUTION IN FOREST AND GRASSLAND SOILS IN ROKKASHO, JAPAN.

The behaviour of I in soil depends on its chemical form in soil solution. Stable I (127I) in the soil solution under actual soil conditions was investigated as a natural analogue of long-lived radioiodine (129I). Soil samples were collected at 5-cm depth intervals down to 20 cm from forests and grasslands in Rokkasho, where the Japanese first commercial nuclear fuel reprocessing plant is located, and the soil solution was extracted by centrifugation. Almost half of total I in the soil solution was iodide, and the other half was dissolved organic I (DOI), with iodate under the detection limit. The proportion of DOI in total I at 0-5 cm depth was larger than the proportions at 5-20 cm depth. The concentration of DOI was positively correlated with that of DOC in the soil solution, suggesting that the behaviour of DOI in the surface soil is affected by labile organic matter dynamics.

222Rn concentrations in greenhouses in Aomori Prefecture, Japan.

Greenhouses are possible places with high 222Rn concentrations, since soil, the source of 222Rn, is directly exposed inside them. To examine this point, 222Rn concentrations in 28 greenhouses at five locations in Aomori Prefecture were measured for approximately 1 year with passive Rn detectors. For 1 week, measurements of 222Rn concentration and working level were also carried out with active detectors to get equilibrium factors and the ratio of 222Rn concentration in working time to non-working time in selected greenhouses. The geometric mean of annual 222Rn concentrations in greenhouses was 13 Bq m-3, and the same as that in dwellings and lower than that in indoor workplaces in the prefecture. However, variation of the 222Rn concentrations was far larger than in other environments, and ranged from the lowest level in outdoor workplaces to the highest level in indoor workplaces. Significant seasonal variation was also observed in 222Rn concentrations. The mean effective dose from 222Rn and its progenies was estimated to be 0.047 mSv year-1 for a farmer working in a greenhouse.

Changes in the chemical form of exogenous iodine in forest soils and their extracts.

Information about the chemical form of exogenous iodine in soil is important for predicting the mobility and behaviour of radioiodine in the terrestrial environment. In this study, soil samples collected at various depths in a pine forest in Rokkasho, Japan, were spiked with stable iodine (as iodide or iodate); after incubation of the spiked soils for 1 or 14 d, the chemical forms of iodine were investigated in both the soils and their water extracts. In surface soil and its extracts, inorganic iodine was found to have been transformed to organically bound forms after incubation for 14 d, resulting in a decrease in the amount of water-extractable iodine in the soil. In contrast, in subsurface soil, which had low organic matter content, the predominant chemical form of iodine after incubation did not differ from that in the spiked soil, and the amount of water-extractable iodine did not decrease noticeably.

Estimation of 85Kr dispersion from the spent nuclear fuel reprocessing plant in Rokkasho, Japan, using an atmospheric dispersion model.

The spent nuclear fuel reprocessing plant of Japan Nuclear Fuel Limited (JNFL) located in Rokkasho, Japan, discharged small amounts of (85)Kr into the atmosphere during final tests of the plant with actual spent fuel from 31 March 2006 to October 2008. During this period, the gamma-ray dose rates due to discharged (85)Kr were higher than the background rates measured at the Institute for Environmental Sciences and at seven monitoring stations of the Aomori prefectural government and JNFL. The dispersion of (85)Kr was simulated by means of the fifth-generation Penn State/NCAR Mesoscale Model and the CG-MATHEW/ADPIC models (ver. 5.0) with a vertical terrain-following height coordinate. Although the simulated gamma-ray dose rates due to discharged (85)Kr agreed fairly well with measured rates, the agreement between the estimated monthly mean (85)Kr concentrations and the observed concentrations was poor. Improvement of the vertical flow of air may lead to better estimation of (85)Kr dispersion.

Placental transfer and distribution of 241Am in the rat.

The placental transfer and distribution of 241Am in the feto-placental system were studied in pregnant rats. Rats were injected intravenously with 241Am citrate at 15 or 18 days of gestation. Groups injected at 15 days of gestation were sacrificed 2, 24, 48, or 120 hr after injection, and the group injected at 18 days was sacrificed 24 hr after. The radioactivities of 241Am in fetus, fetal membrane, and placenta were determined, and its distribution in the feto-placental system was investigated by high-speed autoradiography using a silver-activated zinc sulfide-coated membrane as an intensifying screen. The deposition of 241Am in feto-placental units increased with the number of days of gestation. Results of autoradiography revealed that major deposition sites of 241Am in the fetus are the skeleton and liver. Heavy deposition of 241Am in the yolk sac splanchnopleure and its existence in the exocoelom strongly suggest that the yolk sac placenta plays an important role in the placental transfer of this nuclide.

Effect of gavaged chemical form of 241Am on its retention in mice.

The retention of 241Am in mice 48 h after administration by gavage is reported here. The 241Am was given to mice in the form of either 241Am nitrate or 241Am citrate. The 241Am was also injected into rats in the same form. The homogenized livers of those rats were subsequently administered by gavage to another group of mice. The retention of 241Am citrate was 1.5 X 10(-2)% of the original dose and was the highest among the compounds examined. The retention of biologically incorporated 241Am into the liver as 241Am nitrate and as 241Am citrate was 2.4 X 10(-3) and 2.6 X 10(-3)%, respectively, and was similar to the retention of 241Am nitrate, which was 2.8 X 10(-3)%. The ratio of the retention in the carcass to that in the liver for the 241Am citrate was lower than that of the 241Am nitrate and the biologically incorporated 241Am. This difference indicates that the distribution of 241Am in the animal body depends on the chemical form administered. The retention of liver-incorporated 241Am as citrate after autolysis of the liver is similar to that of fresh liver-incorporated 241Am citrate.

Concentration of fallout plutonium in tissues of Japanese who died during 1980-1984.

The concentrations of fallout 239 + 240Pu in various body tissues of subjects who were born before 1941 and who died in Akita and Niigata Prefectures in Japan during 1980-1984 are reported. The median concentrations in vertebrae, sternum, liver, lung, spleen, and kidney were 0.21, 0.08, 0.62, 0.11, 0.08, 0.03 pCi/kg wet weight, respectively. The concentration levels in vertebrae were approximately three times higher than in the sternum. No significant correlation between the concentration in the various tissues and age at the time of death was observed. No differences in the concentration levels in liver and lung were observed between the sexes. Correlation between the concentration in liver and that in lung was not significant. The concentration in liver was similar to that estimated from the ICRP 30 model. However, the concentration in lung was considerably higher than the estimated value. This difference may be caused by the pulmonary lymph nodes contained in the present lung samples. To obtain the average concentration of plutonium in the entire skeleton, further information regarding the macrodistribution of plutonium is required.

In vitro activity of the hairpin ribozyme derived from the negative strand of arabis mosaic virus satellite RNA.

The negative strand of the satellite RNA of tobacco ringspot virus [(-)sTRSV] is a self-cleaving RNA, of which self-cleaving domain is called the hairpin ribozyme. The negative strand of the satellite RNA of arabis mosaic virus [(-)sArMV] has been suggested to have a hairpin ribozyme-like secondary structure, and we have previously shown that this hairpin domain of (-)sArMV has ribozyme activity. Here we report characterization of the cleavage reaction of the (-)sArMV hairpin ribozyme. Mutagenesis analyses in a trans-acting system revealed, surprisingly, that the wild-type ribozyme was less active than almost all the other mutant ribozymes tested. In a cis-acting system (self-cleaving reaction), however, the reaction of the RNA containing the wild-type sequence proceeds highly efficiently. This result suggests that the inefficient cleavage of the wild-type substrate in trans-acting system may be due to low efficiency at the substrate-binding step but not at the chemical cleavage step in the reaction. We also constructed a chimeric ribozyme between the catalytic hairpin domain from (-)sArMV and the substrate-binding site from (-)sTRSV. This chimeric ribozyme had the highest activity among the trans-acting hairpin ribozymes tested.

Geographical distribution of cerebrovascular disease mortality and food intakes in Japan.

The present study focuses on an analysis of the relationship between cerebrovascular disease mortality and food intake. For this purpose, standardized mortality ratios(SMRs) from cerebrovascular disease were calculated for 3341 basic administrative units (wards, cities, towns and villages) between 1969 and 1978 in Japan. The major nutrient intakes and 30 selected food items were obtained from the 1974-1974 Ministry of Health and Welfare, National Nutrition Surveys in 1040 randomly sampled census tracts in 600 areas (18% of the nation). Our analysis demonstrates that the geographical pattern of cerebrovascular disease SMRs in Japan vary from higher in East Japan to lower in the West, and higher in the less urbanized areas, and lower in the more urban ones. Foods positively associated with cerebrovascular disease were rice and other starchy foods, pork, algae (seaweed), and salty foods such as miso (soybean paste), pickled vegetables, soy sauce and salted fish. All of these foods, with the exception of pork, are part of the traditional Japanese diet. On the contrary, mortality was negatively associated with intakes of wheat, butter and margarine, beef and eggs, items considered to be representative of a European diet. Using a stepwise multiple regression analysis, miso and salted fish were selected as positive, and beef and eggs as negative correlates of cerebrovascular disease mortality. According to these results, it is suggested that these four foods are useful as negative and positive indicators of improvement in dietary intakes as related to the reduction in the occurrence of cerebrovascular disease.

Tritium concentration in unpolished rice.

Inoue and Iwakura recently reported that the specific activity ratio of organically-bound 3H to free water 3H in polished rice samples collected in Japan and China was lower than unity. Their paper was the first to report the systematic apparent elimination of 3H for incorporation to organically-bound form in samples collected from the general environment. To confirm their result, seven unpolished rice samples obtained just after harvesting were analyzed for 3H. The mean specific activity ratio of organically-bound 3H to free water 3H was found to be 0.57, somewhat lower than the data by Inoue and Iwakura. This small difference may be caused by the different sampling years and/or the possible replacement of free water by atmospheric water vapor after harvesting.

Organically-bound tritium concentration in unhulled rice samples harvested between 1979 to 1991.

Organically-bound 3H (OBT) concentrations in unhulled rice samples harvested between 1979 to 1991 are reported. The sample reaped in 1979 had the highest OBT concentration. OBT concentrations in the samples yielded recently have been at approximately 1 Bq (L-combustion water)-1 or less.

Tritium concentrations in pine needle, litter and soil samples.

Samples of pine needle, litter and soil samples collected in/around Akita City and Rokkasho Village in 1989 were analyzed for both free water 3H (FWT) and organically-bound 3H (OBT). The FWT concentrations decrease in the order, litter or soil > pine needle. FWT concentrations in soil depend on the moisture content, and tend to increase with decreasing soil moisture content. This relationship is consistent with the observation that FWT in the soil increases with oxidation of atmospheric tritiated hydrogen gas (HT) and decreases with rainwater dilution. The OBT concentrations increase in the order pine needle < litter < soil at most of the sampling locations. This suggests that historically high soil 3H concentrations may be reflected as high OBT concentrations in soils of the present.

Rice uptake and distributions of radioactive 137Cs, stable 133Cs and K from soil.

The distributions of radionuclides in plant components as to radionuclide transfer to animals are important for understanding the dynamics of radionuclides in an agricultural field. Most of the non-edible parts in these components are returned to the soil as organic fertilizer where they may again be utilized in the soil-plant pathway and/or are mixed with feed for livestock. Rice plants were grown in an experimental field and separated at harvest into different components, including polished rice, rice bran, hull, leaves, stem and root, and then the distributions of radioactive 137Cs, stable 133Cs and K in these components were determined. The distribution of 137Cs in polished rice and rice bran was similar to that of 133Cs, while that of K was different. The concentration ratios of 133Cs/K in leaf blade positions increased with aging, which means that the translocation rate of 133Cs in rice plants was slower than that of K. At harvest the distribution of dry weight in polished rice to entire rice plants was 34%, and the distributions of 133Cs in the polished rice and the non-edible parts were 7 and 93%, respectively, whereas those of K in the polished rice and the non-edible parts were 2 and 98%, respectively. Findings suggest that the transfer and distribution of 133Cs, not of K, provide better information on the long-term fate of 137Cs in an agricultural environment.

Tritium concentrations of blood samples collected throughout Japan.

Tritium concentrations were measured for blood samples collected from 20 cities throughout Japan during 1989-1990. The mean 3H concentration was found to be 1.4 +/- 0.4 Bq L-1 and 1.0 +/- 0.4 Bq L-1 (combustion water) for free water 3H and organically-bound 3H, respectively, excluding the abnormally high data of one city. The organically-bound 3H contents clearly depended on the latitudes of sampling locations, although the free water 3H concentrations showed no correlation with the latitudes. Organically-bound 3H is considered to be more suitable than free water 3H as an indicator of long time 3H exposure to human.

Fallout Pu in the Japanese diet.

The ingestion of fallout Pu from seven or six separate food groups collected in Japan during 1962 and 1983-84 are reported. The contribution of ingested Pu from algae was the highest among the food groups studied: approximately 60% of the total ingested Pu during 1962, and 74% in 1983-84. The contribution from whole marine products, i.e. algae and fish/shellfish, was approximately 70% of the total Pu ingested in 1962, and more than 90% in 1983-84. The higher Japanese ingestion rate than that of the United States is attributable to the higher consumption rate of marine food products in Japan. Also reported in this paper are the ingestion rate for 137Cs from fallout through the same food groups, and the concentration of Pu and other radioactive nuclides in specific individual foodstuffs and algae samples.

Ingestion intake of fallout Pu in Japan.

Ingestion intakes of fallout Pu throughout Japan in the 1959-1962 and 1978-1980 periods were measured by analyzing composite samples of each foodstuff or duplicate composite food samples consumed by five persons for a period of 1 d. Cumulative ingestion intake in Tokyo for the period from 1954-1980 was estimated by regression analysis. The cumulative ingestion intake, calculated by simple regression analysis between the natural log of the intake and that of annual fallout deposition of Pu, was estimated to be 450 pCi. Calculated by a multiple regression analysis, including the natural log of annual fallout deposition rates for a previous year as an additional independent variable, it was estimated to be 600 pCi. Considering in combination an ingestion intake, the value of which is calculated by the multiple regression analysis; an absorption ratio from the gastrointestinal tract of 0.001 (a recently reported value for low-level soluble Pu independent of chemical form); and the metabolic model in ICRP Publication 30, it is possible to estimate that the contribution of ingestion intake to liver and bone burden would be approximately 30%.

Tritium concentration in Akita City diet.

The 3H concentration in the diet of residents in Akita City, northern Japan, during autumn of 1987 and winter of 1988 was analyzed. Results were similar to those for spring and summer samples previously reported. No significant seasonal change of 3H concentration was observed. A simple model was constructed for estimating the mean residence time for organically-bound 3H in diet. However, more data about diet in the 1960s or 1970s are necessary for the estimation.

Fallout 3H ingestion in Akita, Japan.

To study fallout 3H ingestion in Japan, 16 separate food group samples were collected from Akita during 1985. The 3H concentration in free water and that in a tissue-bound form were determined separately. The average 3H concentration in the tissue-bound form was 2.2 Bq L-1, 1.7 times higher than in the free water of the food. The ingestions of 3H in the tissue-bound form and as free water in the diet were 0.60 Bq d-1 and 1.0 Bq d-1, respectively. Cereals represented the food group that contributed the most to the ingestion of tissue-bound 3H. Total 3H ingestion was estimated to be 4.1 Bq d-1. The contribution of the tissue-bound form to the total ingestion was 15%, considerably lower than reported for Italian diets. The ratio of 3H ingestion in the tissue-bound form to the free water form in the diet was similar to the ratio reported for New York City.