Search

In order to eliminate atmospheric tritium gas (HT) released from tritium handling apparatus, we proposed to use the HT oxidizing ability (hydrogenase enzyme) of bacterial strains isolated from surface soils instead of a high temperature precious metal catalyst. Among the isolated strains with high HT oxidation activity, several strains were selected to develop a tritium elimination (detritiation) system. Bioreactors were made of bacterial cells grown on agar medium on a cartridge filter and stored in a refrigerator until use. The detritiation ability of these bioreactors at room temperature was investigated during the intentional HT release experiments carried out in the Cassion Assembly for Tritium Safety Study (CATS) in TPL/JAERI. When HT contaminated air from the CATS was introduced into the biological detritiation system, in which three bioreactors were connected in series, 86% of HT in air was removed as tritiated water in these bioreactors at a flow rate of 100 cm 3 /min for 2 hours.

Heavy water (D 2 O) vapor release experiments were carried out in a greenhouse using deuterium as a substitute for tritium and uptake and loss kinetics of D 2 O in leaf of a tangerine tree and formation, translocation and retention of organically bound deuterium (OBD) in tangerine exposed to D 2 O under different growth stage were investigated. Rate constants of D 2 O uptake in leaves of tangerine were 0.2 - 1.11 hr -1 in the daytime release and 0.03-0.12 hr -1 in the nighttime release. Rate constants of D 2 O loss in leaf after daytime release were almost the same as those after the nighttime release. No significant differences in the half time of D 2 O loss were observed between daytime and nighttime releases, but those in winter experiments were about 6 times higher than those in summer ones. The retention of OBD of the edible part of tangerine at harvest was very low and OBD was 0.08% or 0.07% on average of D 2 O in air moisture in daytime or nighttime releases.

The re-emission process of tritiated water (HTO) deposited on a soil surface is an important process to assess tritium doses to the general public around nuclear fusion facilities in future. A field experiment using heavy water (HDO) as a substitute for HTO was carried out in the summertime to investigate the re-emission process of HTO from soil to the atmosphere. In the experiment, the time variations of depth profiles of HDO concentrations in soil exposed to HDO vapour and soil mixed with HDO were measured during the re-emission process on the field. The HDO concentrations in soil water in top soil layers of both the exposed and mixed soil rapidly decreased with time during the re-emission. However, the decrease of exposed soil was much greater than that of mixed soil. The re-emission process was analysed using a model including the evaporation of HDO from soil, the exchange between soil HDO and air H2O, and the diffusion of HDO in soil. It was found that the model is applicable to calculating the time variations of detailed depth profiles of HDO concentration in soil water in surface soil layers, using an estimated exchange velocity.

As a substitute of tritium, deuterated water (D2O) vapor release experiments were performed in a greenhouse to estimate the different formation and subsequent retention of organically bound deuterium in rice plants between daytime and nighttime exposure. Potted rice plants were exposed to D2O vapor in the greenhouse for 8 h, under day or night conditions. Deuterium concentrations in free water and organic matter in rice leaves and ears were investigated until harvest time. The formation of organically bound deuterium in the daytime was higher than during the nighttime by the factors of 2.4 for the ear and 2.9 for the leaf. The decrease of the organically bound deuterium concentration in the ear after the nighttime exposure was faster than that after the daytime exposure. Data analysis was carried out using a compartment model in which different generating processes of organic matter were considered. The calculated organically bound deuterium retention in rice agreed with the measured value.

A novel hyper-sensitive detection system was developed to detect Hprt-deficient mutations using Hprt deficient hamster fibroblast cells which carry a normal human X-chromosome. The system has been found to be 100-fold more sensitive for detecting mutations than the conventional system which uses an internal Hprt gene. The mutation frequency induced by 1 Gy of tritium radiation at different dose rates (0.9, 0.4, 0.04, and 0.018 Gy/h) was measured. No significant differences in mutation frequencies were observed within the range of dose rates used, suggesting that if a reverse dose-rate effect exists, it may not be observable with tritium radiation at dose rates over 0.018 Gy/h. Interestingly, molecular analysis of the Hprt locus in Hprt-deficient mutants induced by tritium showed that deletion sizes observed in the hamster cell's human X-chromosome under these conditions are much smaller in cells exposed at 0.04 (and 0.018 Gy/h) than in cells exposed at 0.9 Gy/h. This phenomenon seems to be specific for tritium radiation because it was not apparent after exposure to γ-rays. The novel hyper-sensitive detection system used here is useful for analysis of the mutagenic effects of low doses of tritium radiation delivered at low dose rates.

Heavy water vapor release experiments were carried out in a greenhouse using deuterium as a substitute for tritium and uptake and loss kinetics of D 2 O in leaves and formation, translocation and retention of organically bound deuterium (OBD) in rice and soybean were investigated. Rate constants of D 2 O uptake in leaves of rice plant and soybean in the daytime release were 2.4 and 3.0 hr -1 , respectively, and 5-4 times higher than those in the nighttime release. Rate constants of D 2 O loss in leaves after daytime release were about twice those after the nighttime release. The half time of D 2 O loss was 0.6-0.7 hr for leaves of rice plant and soybean. After D 2 O release, OBD concentration in unhulled rice and soybean increased with time until 4 -5 days of the experiments and then decreased with time and the extent of decrease was remarkable in soybean pea.

The distribution of molecular tritium (HT) oxidation activity and HT oxidizing bacteria in 5-cm soil sections from the surface to 20 cm depth in natural and cultivated fields in Mito was determined in in vitro experiments. HT oxidation activity was the highest in the top section of the natural soil, about twice that of the top section of the cultivated soil, and decreased with depth. From the natural and cultivated soil sections, 195 and 969 isolated strains with HT oxidation activity were obtained, respectively. The distribution profile of the occurrence rate and the sum of oxidation activity of HT oxidizing bacteria in each soil section were consistent with that of HT oxidation activity in the soil section. Most of the HT oxidizing isolates, 84% for the natural soil and 94% for the cultivated soil, were actinomycetes, Gram-positive bacteria.

The conversion rate of tritiated water (HTO) in plants' leaves to organically bound tritium (OBT) in their edible parts in the open air was obtained for several vegetables (komatsuna, radish and cherry tomato) during a chronic tritiated hydrogen (HT) release experiment at Chalk River in 1994. During the experiment, HT gas was continuously released to the atmosphere at the cultivated site for 12 days, and HTO and OBT concentrations in cultivated plants were measured. For plants' leaves, the conversion rate of HTO to OBT was about 0.2 (% hr -1 ), but it varied with their growth stage. A chamber experiment was also carried out in laboratory for comparison. The chamber experiment results showed that the conversion rate under artificial lights was half that in the field experiment.

Organically bound tritium (OBT) transfers into human body via food chain. ICRP report recommends that the dose due to OBT ingestion is 2.3 times higher than that due to HTO. Thymidine is a specific precursor of DNA. There were several reports on ingestion experiments of OBT including 3 H-thymidine. However, the concentrations of tritiated compounds used in those experiments were extremely high compared with environmental tritium concentration. Therefore, in this study, we used tritiated compounds with 100 times of concentration based on the highest concentration in rain after nuclear tests during the 1960's, i.e. 700 Bq tritium/l rainwater. Mice were chronically fed with each one of tritiated organic compounds, 3 H-thymidine, 3 H-leucine, 3 H-glucose or HTO for comparison, and the excretion and distribution of tritium in mouse body and tritium uptake into DNA in each tissue were determined at 180th, 240th, and 300th day of ingestion. Almost no significant differences were found between the dose rates from DNA-bound tritium throughout long-term exposure by ingestion of tritiated organic compounds and that of HTO.

Prostaglandin (PG)D2, which has long been implicated in allergic diseases, is currently considered to elicit its biological actions through the DP receptor (DP). Involvement of DP in the formation of allergic asthma was recently demonstrated with DP-deficient mice. However, proinflammatory functions of PGD2 cannot be explained by DP alone. We show here that a seven-transmembrane receptor, CRTH2, which is preferentially expressed in T helper type 2 (Th2) cells, eosinophils, and basophils in humans, serves as the novel receptor for PGD2. In response to PGD2, CRTH2 induces intracellular Ca2+ mobilization and chemotaxis in Th2 cells in a Gαi-dependent manner. In addition, CRTH2, but not DP, mediates PGD2-dependent cell migration of blood eosinophils and basophils. Thus, PGD2 is likely involved in multiple aspects of allergic inflammation through its dual receptor systems, DP and CRTH2.

The effects of the JCO criticality accident on the tritium, deuterium and gamma-ray nuclide concentrations in plant leaves in/around the JCO campus in Tokai-mura, Ibaraki prefecture were investigated. No significant differences were detected between the tritium and deuterium concentrations in tissue-free water in the samples collected from the JCO campus and those from outside the JCO environment including Tokyo. The organically bound deuterium concentration in each plant sample was lower than the free water deuterium concentration. 140La and 140Ba were detected in one plant sample from the JCO site.

A criticality accident occurred on September 30, 1999 at the uranium conversion facility of the JCO Company Ltd. in Tokai-mura, Japan. A collaborating scientific investigation team was organized in two groups, the first to carry out research on the environmental impact (the environmental research group) and the second to assess the radiation effects on residents (the biological research group). This report concerns only the activities of the environmental research group. Four investigative teams were sent on different dates to the accident site and its vicinity to collect samples. About 400 samples were collected and subjected to analysis. An outline of the sampling campaign is presented here along with a brief chronology of the accident and the preliminary key results obtained by the independent research group are summarised in this Special Issue of the Journal of Environmental Radioactivity.

Potted plants were exposed to D2O vapor in a greenhouse and uptake of D2O by leaf and deposition of D2O to pot soil were examined. Atmospheric D2O concentration in the greenhouse increased rapidly after starting the release and reached constant level in a few hours. Although the variation of D2O concentration in leaf followed that in air with showing a time delay, D2O concentration in leaf did not become the same level as that in air and vein showed lower concentration that lamina. D2O concentration in the pot soil increased slowly with diffusing in deeper layer.

Radioprotective effects of sodium tungstate (ST) on 60Co gamma-ray induced decrease in hematocrit value and in survival rate in Wistar strain male rats were examined. A long-term administration of ST (less than 150 mg/kg body weight/day) for 60-300 days had no significant effects on body and organs weights and survival days. The LD50/60 in 20 weeks old rats was 220 mg/kg body weight/day. Daily administration of 38, 75 or 150 mg from 7 days before and after irradiation to 60 days significantly mitigated the decrease in hematocrit values, especially at 23 days after irradiation (P < 0.05). The highest mitigation rate of the decrease in hematocrit value was observed in rats administered at a dose of 38 mg ST/day. Simultaneously, a dose of 38 mg ST/day inhibited lethal effect of 60Co gamma-rays significantly. The dose-reduction factor for survival of 38 mg ST administered rats was 1.14.

Field experiments using heavy water as a tracer instead of tritiated water (HTO) were carried out in November 1995 and August 1996 in Japan. The objective of these experiments was to estimate the behavior of HTO in the environment when HTO was released to the atmosphere. We measured the evolution of depth profiles of heavy water concentrations in soil water and compared the reemission rates with the evaporation velocities to study the deposition and reemission of heavy water to/from soil. The depth profiles of heavy water concentrations in soil were expressed by exponential functions of which the gradient depended on the deposition period. The initial reemission rates of heavy water from the soil were the highest, regardless of the meteorological conditions. The reemission occurred not only during the day but also at night, suggesting that the exchange of heavy water in the soil surface layer with H2O in air played a dominant role during night-time.

Deuterium, a stable isotope of tritium, was released into a vinyl house in autumn 1995 and summer 1996 to study the transfer of tritium from air to plant and soil. Temporal variation of D2O concentrations in plant and soil water, and plant physiological parameters such as transpiration rate and leaf temperature, were measured during these experiments. D2O concentrations of plants were fitted to a first order kinetic model: Cp = Cmax (1 – e–kt), where Cp is the D2O concentrations in plants at time t, Cmax is the steady-state concentration in plants and k is the rate constant. The rate constant was also calculated using measured plant physiological parameters for comparison. The D2O uptake by paddy rice was most rapid and the value of k was 3.63 ± 0.31 h–1 followed by radish, cherry tomato, Komatsuna and orange. The day/night concentration ratio for cherry tomato and orange was higher than that for radish and Komatsuna.

Environmental factors (nutrients and pH) influence the retention of Sr, Cs, and Ba as analogue of long-lived radionuclides by the microorganism. The effect of pH and concentration of organic nutrients are proved to be significant factors for retention of cations (Sr, Cs and Ba) by the microorganisms inoculated from surface soil. Microorganisms can affect the speciation of Sr, Cs, and Ba in the environment. Concentration of organic nutrients and pH are indicated to be the important environmental factors in the consideration of the migration of the radionuclides through microbial processes in the terrestrial environment.

Indomethacin is a widely used nonsteroidal anti-inflammatory drug and is generally known to exhibit its multiple biological functions by inhibiting cyclooxygenases or activating peroxisome proliferator-activated receptors. In this study, we present evidence demonstrating that the novel PGD2 receptor chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) is another functional target for indomethacin. Indomethacin induced Ca2+ mobilization in CRTH2-transfected K562 cells at submicromolar concentrations (approximate EC50, 50 nM) in a Gαi-dependent manner as PGD2 did. Other nonsteroidal anti-inflammatory drugs (aspirin, sulindac, diclofenac, and acemetacin) had no such effect even at micromolar concentrations. In chemotaxis assay, three CRTH2-expressing cell types, Th2 cells, eosinophils, and basophils, were all significantly attracted by indomethacin (EC50, 50–500 nM) as well as by PGD2 (EC50, 2–20 nM), and the effects of indomethacin were blocked by anti-CRTH2 mAb. These results suggest the involvement of CRTH2 in mediating some of therapeutic and/or unwanted side effects of indomethacin, independently of cyclooxygenases and peroxisome proliferator-activated receptors.

To quantify the rate of oxidation of tritium gas (referred to as HT) to tritiated water in the environment, various woody and herbaceous plant leaves and roots, mosses and lichens taken from a forest and fields in Ibaraki prefecture, and a forest in Toki, Gifu prefecture, were investigated as to their ability to oxidize atmospheric HT in in vitro experiments. The HT oxidation activity in vegetation was compared with that in the surrounding surface soil (0-5 cm in depth). The rate of oxidation of HT in woody plant leaves including pine needles was extremely low, only about 1/10000-1/1000 that in the surface soil, as well as in herbaceous plant leaves with some exceptions (Phalaris arundinacea and Vaccinium smallii), whereas the rate in mosses and lichens was 50-500 times that in pine needles. The HT oxidation activity in roots of several plants including Phalaris arundinacea, Pieris japonica and Lespedeza homoloba was quite high and comparable to that in the surrounding surface soil. These results suggest that mosses, lichens and the leaves or roots of particular plants with high HT oxidation activity can be used to monitor the accidental release of HT into the environment.

The oxidation of atmospheric molecular tritium (HT) in vegetation was determined by in vitro experiments for pine needles, pine bark, lichens attached to pine trees, taken from a coastal pine forest in Ibaraki prefecture and comparison of such measurements was made with those in soil. The oxidation of HT in pine needles was extremely low, being only about 1/40000 that in the surface soil of a pine forest, whereas its oxidation in pine bark with a lichen was almost 1000-7000 times higher than that in pine needles. HT oxidation in pine bark, a lichen and a moss was determined in each case under light and dark conditions and was found to be essentially the same. All mosses and lichens examined in the present study were found to have unusually high levels of HT oxidation whether their habitat was tree or ground surface.

In vivo laboratory experiments on tritium gas (HT) fixation in pine trees were conducted using one-way circuit inhalation apparatus and dwarf pine trees. After 2 hours of exposure to HT, tritium distribution in pine needles, branches, trunk, roots and soil was measured. The specific activity of tritium in pine needles was almost the same as that in the branches and about one fiftieth that in the small roots or soil. To eliminate the contribution of HT oxidation in the soil from the plants, a dwarf pine tree, washed and with its root system sealed, was exposed to HT. Oxidation activity of HT was also determined in in vitro experiments for each part from a dwarf pine tree. Oxidation activity of plant parts above the ground was quite low. In vivo and in vitro experiments were also conducted on dwarf zelkova trees and similar results were obtained.

The conversion of atmospheric molecular tritium (HT) to tritiated water in soils was examined. The oxidation rate of HT varied with soil depth, temperature and soil water content. Among three sandy loam soils, rate constant was highest in the top section (0-5 cm) of grassy forest soil, 0.196/min, and in lower sections with soil depths of 5 to 10 cm and 10 to 15 cm, the rate constants were one fourth and one eighth, respectively, of that of the top section. The rate constants of the top sections of paddy and upland fields were 0.038/min and 0.058/min. Oxidation occurred over a broad temperature range from 0 to 75°C. Optimal water content for HT oxidation ranged from 10 to 25% of soil dry weight. The addition of KCN or NaN3 to the soil partially decreased HT oxidation and pretreatment with chloroform or acetone (20%) reduced the oxidation rate by a half. HT oxidation activity in the surface soil (0-5 cm) under anaerobic conditions was somewhat less than that under aerobic conditions, but below this depth, the activity was essentially the same under either condition.

Phospholipase B bound tightly to the membrane fraction of baker's yeast (Saccharomyces cerevisiae) was purified approximately 226-fold by extraction with sodium deoxycholate (DOC), acetone precipitation, ammonium sulfate fractionation, and column chromatographies on Phenyl-Sepharose CL-4B, DEAE-Sepharose CL-6B, and Sepharose 4B. Only one major activity peak with an apparent molecular weight of 330,000 was detected by gel filtration on Sepharose 4B. However, two glycoprotein bands, one major and one minor, were evident on SDS-polyacrylamide gel electrophoresis in the absence of 2-mercaptoethanol. Isoelectric focusing also revealed two activities, pI 3.4 (major) and pI 3.0 (minor). The purified enzyme had phospholipase B activity (in the presence of DOC) and lysophospholipase activity in a ratio of 1:4.8. Both activities had an optimum pH of 3.5-4.0. Phospholipase B activity was appreciably stimulated only by DOC among bile acids, but lysophospholipase activity was markedly inhibited by them. Both activities were not stimulated by Ca2+ and inhibited by SDS, Triton X-100, Fe3+ and Al3+. The purified enzyme hydrolyzed the acyl ester bonds of phosphatidylcholine sequentially, first the 2-acyl and then the 1-acyl groups. It preferentially hydrolyzed 1-acyl-sn-glycero-3-phosphocholine and, to a lesser degree, 2-acyl-sn-glycero-3-phosphocholine.