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PubMed2000

Modeled concentrations in rice and ingestion doses from chronic atmospheric releases of tritium.

The expansion of nuclear power programs in Asia has stimulated interest in the improved modeling of concentrations of tritium in rice, a staple crop grown throughout the far east. Normally, the specific activity model is used to calculate concentrations of tritium in the tissue water of edible plants to assess ingestion dose from chronic releases. However, because rice, like other grains, has much lower water content than most crops, the calculation must also account for organically bound tritium. This paper reviews ways to calculate steady-state concentrations of tritium in rice, including the methods of Canadian and United States regulatory models, and the assumptions behind them. Concentrations in rice and resulting ingestion doses are compared for the various methods, and equations for calculating concentrations are recommended. The regulatory models underestimate doses received from ingestion of rice contaminated with tritium since they do not account explicitly for organically bound tritium. The importance of including organically bound tritium is illustrated in a comparison of doses from rice, leafy vegetables and milk for an Asian diet. Dose factors from tritium for these foods are estimated to be 135, 47, and 20 nSv y(-1)/(Bq m(-3)), respectively. Assuming known air concentrations, tritium concentrations in rice, calculated with the recommended equations, are uncertain by less than a factor 2 when tritium concentrations in the rice paddy water are known, and by less than a factor of 2.3 when concentrations in paddy water are unknown.

Food Contamination, Radioactive↗
PubMed1998

Chromosome analysis of lymphocytes from radiation workers in tritium-applying industry.

OBJECTIVES: The frequency of chromosomal aberrations (CA) and micronuclei (MN) in peripheral blood lymphocytes was compared in two groups of persons occupationally exposed to tritium either through the use of luminous paints or in the weapons industry, with the aim of finding a correlation between the CA and MN assays, the extent of radiation hazard, and the duration of occupational exposure to chemical forms of tritium and the ability of the latter to induce hazards in human lymphocytes. METHODS: CA analysis and the cytochalasin B micronucleus test were performed. Urinary tritium in both groups was measured using a liquid scintillation method. For purposes of comparison, 2 control groups (40 persons) were examined; 24 exposed individuals were matched to their controls according to age, sex, and smoking habits. RESULTS: Values recorded for the frequency of CA in the group of workers handling tritium in luminous dial painting were 0.015 +/- 0.014 dicentrics/cell, 0.023 +/- 0.017 total unstable CA/cell, and 0.035 +/- 0.019 MN/binucleated cell. Urinary levels of tritium in this group of employees ranged from 1.35 to 9.43 MBq/l. As compared with their matched controls, in these workers the differences in the yield of CA as well as in MN were statistically highly significant (P < 0.005 and P < 0.003, respectively). The same parameters analyzed in workers employed in the armament industry gave values of 0.001 +/- 0.003 dicentrics/cell, 0.010 +/- 0.008 total unstable CA/cell, and 0.021 +/- 0.029 MN/binucleated cell. No detectable concentration of urinary tritium was found. As compared with their matched controls, in these workers the differences were also statistically significant (P < 0.027 and P < 0.012, respectively). The yield of CA, particularly the yield of dicentrics, was significantly higher (P < 0.005) in the group of luminous dial painters as compared with the weapons industry workers. The difference found in the yield of MN between the two groups of workers was also statistically significant (P < 0.084). Intercontrol differences in the yields of spontaneous CA as well as in MN were insignificant (P < 0.683 and P < 0.735, respectively). The results are discussed with respect to individual variations in the response to low doses of ionizing radiation, disorders in the handling of radionuclides, the duration of occupational exposure, and the chemical properties of the radionuclides used. CONCLUSION: Tritium in the chemical form of luminous paint is a more powerful clastogenic agent than tritium gas. Statistical analysis demonstrated that lymphocyte effects are due to the concentration of tritium in urine rather than to the duration of occupational exposure. Since the radiation hazard measured by the MN assay did not differ from that determined by the CA assay, the MN test can be recommended as a rapid assay for screening purposes in cases of occupational exposure to low radiation doses.

Adult↗
PubMed2005

Rodents as receptor species at a tritium disposal site.

New methods are being employed on the Department of Energy's Savannah River Site to deal with the disposal of tritium, including the irrigation of a hardwood/pine forest with tritiated water from an intercepted contaminant plume to reduce concentrations of tritium outcropping into Fourmile Branch, a tributary of the Savannah River. The use of this system has proven to be an effective means of tritium disposal. To evaluate the impact of this activity on terrestrial biota, rodent species were captured on the tritium disposal site and a control site during two trapping seasons in order to assess tritium exposure resulting from the forest irrigation. Control site mice had background levels of tritium, 0.02 Bq/mL, with disposal site mice having significantly higher tritium concentrations, mean=34.86 Bq/mL. Whole body tritium concentrations of the mice captured at the disposal site were positively correlated with tritium application and negatively correlated with precipitation at the site.

Animals↗
PubMed1996

Tritium isotope effects in adenosylcobalamin-dependent methylmalonyl-CoA mutase.

Methylmalonyl-CoA mutase from Propionibacterium shermanii is an adenosylcobalamin-dependent enzyme which catalyzes the reversible isomerization of methylmalonyl-CoA and succinyl-CoA. The rate of tritium loss from 5'-[3H]adenosylcobalamin during the enzymic reaction and the relative rates of tritium appearance in substrate and product were examined. Upon the addition of methylmalonyl-CoA to a solution of holoenzyme, tritium was completely released from the cofactor within about 500 ms. No tritium was found either bound to the enzyme or released into the water. The radioactivity was found in methylmalonyl-CoA and succinyl-CoA in a constant ratio of 1 to 3, which did not change during the first 300 ms of the reaction. Upon the addition of succinyl-CoA to a solution of holoenzyme, tritium was released at essentially the same rate, and the radioactivity was found in methylmalonyl-CoA and succinyl-CoA in the identical constant ratio of 1 to 3. The tritium isotope effect on the enzyme-catalyzed hydrogen transfer, measured using 14C-labeled methylmalonyl-CoA as substrate, was kH/kT = 4.9. This low value shows that hydrogen transfer is only partly rate limiting and that at least one subsequent slow step, such as product release, contributes substantially to the overall reaction velocity. The identical partitioning of tritium, regardless of the substrate used, shows that the rearrangement of the substrate radical into the product radical is not rate limiting. The very low tritium isotope effect and the fact that all the tritium is found bound either to the CoA esters or to the cofactor make it very unlikely that a protein radical is an intermediate in the methylmalonyl-CoA mutase-catalyzed rearrangement.

Acyl Coenzyme A↗
PubMed1993

Skin-contact exposure to tritium-gas-contaminated stainless-steel surfaces.

One of the radiation protection problems potentially encountered in tritium-handling facilities is contamination of metal surfaces. Experiments with hairless rats have demonstrated that when intact skin is brought into contact with tritium-gas-contaminated stainless-steel surfaces, tritium can be fixed as organically bound tritium (OBT) and as tritiated oxide (HTO) in the skin. The radiological hazard associated with this route of tritium uptake is determined by the retention and distribution of tritium in the skin and other organs. The experimental data suggest that the OBT in the skin serves as an input source to the rest of the body. The urinary excretion of tritium shows a biphasic excretion for OBT and a single-phase clearance for HTO from the body. The results indicate that the exposure from this mode of contamination results in long retention of tritium in the skin as well as in non-uniform distribution of tritium in organs and macromolecules. This information is useful in evaluating the possible dosimetric concerns from this mode of exposure.

Animals↗
PubMed2001

[The transference and distribution of tritium water in the soybean-soil system].

The isotope trace techniques of simulation contamination were applied to explore the rule of transference and distribution of tritium water in a simulated soybeam-soil ecosystem. The activity ratio of two forms of tritium in plant and soil sample were measured by 50 days simulation experiment. The results showed that when tritium water was entered the soil, it not only was transferred to other compartments in the system, but also vaporized into atmosphere rapidly. Both free water tritium and bound tritium were found in the soybean and the soil. The activity ratio of free water tritium reduced after reaching the maximum (19.4 Bq.g-1 in root, 12.3 Bq.q-1 in stem and leaf) at 6th hour in the soybean. The bound tritium increased slowly. The activity ratio of total tritium in soybean root was upper than those in stem and leaf in the earlier stage, they reach equipoise each other in the later stage. The activity ratio of two tritium in the surface soil reduced continuously. The compartment model of tracer kinetic was applied to imitate the experimental data. The activity ratio of soil Cs = 88.37e-11.847t + 7.38e-0.030t and the activity ratio of soybean Cb = 10.30(e-0.030t - e-11.847t) were gained.

Soil↗
PubMed2005

[Uptake HTO from seawater by seashell and formative dynamics of bound tritium in seashell].

Uptake HTO from seawater by five kinds seashell and formative dynamics of bound tritium in organ of seashell are studied by using the isotope-tracer techniques in order to get a better understanding of the marine environmental behavior of HTO. The results show that the tritium in seashell exists in free water tritium and bound tritium form. The free water tritium is main form; its content observed was more than 97.4% of total tritium. The bound tritium content was very lower, only being 0.4% - 2.6% in total tritium. The speed of HTO untaken by seashell is very rapid, specific activity of HTO in three kinds seashell had reached their maximum only 2 h after treatment. The bound tritium in seashell increases slowly with time. The results of analysis of concentration factor (CF) values indicate that HTO would not concentrate in the seashell.

Animals↗
PubMed1978

Biokinetic aspects of tissue-bound tritium in algae.

For the estimate of the radiation exposure of man and for the calculation of the risk of artificial tritium from nuclear power plants, organic tissue-bound tritium is of decisive importance. In model experiments, a tritium incorporation of 61 to 71% was found from tritiated water (HTO) into organic matter of planctonic algae under under reproducible conditions and this was related to the theoretical value. In further experiments the tritium release from these high tritiated algae was of interest. Kept in darkness in tritium-free, non-sterile river water, so that autolytic processes and bacterial decomposition could occur, the concentration of HTO was measured over a period of three weeks. A relatively long half-life of tissue-bound tritium was found under various temperature conditions. Therefore it must be considered that a significant retention of tritium in biological matter has to be taken into account in a natural ecosystem. In streams into which the cooling water of a nuclear reactor is released all conditions are found already for a long turnover and cycling of artificial tritium in living organisms as well as the conditions for a favourable transport of tritium by food chains to man.

Ecology↗
PubMed1978

Comparative incorporation of tritium from tritiated water versus tritiated thymidine, uridine or leucine.

Whereas the radiotoxicity of tritium has been extensively studied, comparatively little information exists on its long-term effects as a potential environmental pollutant, particularly at small dosage. This investigation was primarily aimed at assessing comparatively a possible carcinogenic potency of tritiated water versus radioactive precursors of DNA, RNA and proteins, namely tritiated thymidine, uridine and leucine in C57 Black mice. Tritium is largely released in the environment in the form of tritiated water. There are many uncertainties, however, as to how tritium is incorporated from tritiated water into cell constituents quantitively and qualitatively. In 1965, we reported on the carcinogenic effect of tritium in the form of tritiated thymidine on newborn C57 BL mice in the dose range of 0.3--1.5 muCi/g [Mewissen. 1965]. Hence the selection of tritiated water, and of tritiated precursors, in an attempt to evaluate their respective role in the tritium transfer process and to correlate their possible late effects with their specific patterns or sites of incorporation. This study deals with tritium incorporation from tritiated water and various precursors at the 1 or 10 muCi level. RSA values, i.e., the ratio of organically bound tritium per hydrogen content of dry tissue over aqueous tritium per hydrogen content of water, were estimated for newborn, juvenile and adult mice, at various time intervals (1, 8, 15, 22 and 29 days) following single administration of tritiated water, tritiated thymidine, uridine or leucine. The data available at this time show that administration of tritiated water (or precursors) result in a complex time dependent and age dependent residual activity dynamics both in the organic component and in the aqueous fraction of tissue. A few preliminary conclusions can be made. Following a single acute or brief exposure to tritiated water, values of activity become exceedingly small after a relatively short time period. In a steady state equilibrium, resulting from chronic exposure to tritiated drinking water, RSA values tend to stabilize. However, wide variations between various organs are to be expected, as suggested by their respective RSA values following a single exposure. In view of these observations, it would seem that a realistic estimate of the internal dose to the radiosensitive nucleus must take into consideration the age dependent incorporation of tritium from tritiated water, as well as the variation between organs. The carcinogenic risk has often been estimated from a uniform dose dependency model. The influence of time and space microdistribution of dose within tissues and more particularly at specific sites (such as DNA, RNA or protein) has received, as yet, little attention, as well as the relative contributions of the time sequence of dose absorption during the usually long latency period. Such factors, among others, may be critical in carcinogenesis from internal irradiation...

Age Factors↗
PubMed1992

The consequences of the isotope effect on proline dehydrogenation rates estimated by the tritium loss method.

Loss of tritium from a substrate is often used to estimate the rate of dehydrogenation. However, loss of 3H may be much slower than loss of H because of the tritium isotope effect. In order to assess the impact of the tritium isotope effect, loss of 3H from the C-5 position of proline during dehydrogenation by rat liver mitochondria and bacteroids from soybean (Glycine max [L.] Merrill) nodules was compared with appearance of 14C in products of [14C]proline dehydrogenation. Incubations were carried out in the presence of o-aminobenzaldehyde (added to trap the initial product, delta 1-pyroline-5-carboxylate). The fraction of total 14C products trapped by o-aminobenzaldehyde varied from 0.07 to 0.75 depending upon experimental conditions. With rat liver mitochondria, dehydrogenation of [14C]proline was between 3.27 and 9.25 times faster than dehydrogenation of 3H proline, depending upon assay conditions. Soybean nodule bacteriods dehydrogenated [14C]proline about 5 times faster than [3H]proline. We conclude the following: (i) the rate of proline dehydrogenation may be greatly underestimated by the tritium assay because of the tritium isotope effect, and (ii) the 14C assay may underestimate the rate of proline dehydrogenation if it is assumed that o-aminobenzaldehyde quantitatively traps delta 1-pyrroline-5-carboxylate under all conditions. The simplicity of the tritium assay makes it attractive for routine use. However, its use requires determination of the tritium isotope effect, under the specific conditions of the assay, in order to correct the results. The considerations discussed here have broad applicability to any dehydrogenase assay employing tritium loss.

Animals↗
PubMed2003

Tritium in surface waters of the Yenisei River basin.

This paper reports an investigation of the tritium content in the surface waters of the Yenisei River basin near the Mining and Chemical Combine (MCC). In 2001 the maximum tritium concentration in the Yenisei River did not exceed 4 +/- 1 Bq l(-1), which is consistent with the data of 1998-99. However, it has been found that there are surface waters containing enhanced tritium as compared with the background values for the Yenisei River. For instance, in the Ploskii Stream and the Shumikha River the maximum tritium concentrations amount to 168 and 81 Bq l(-1), respectively. The source of tritium in these surface waters is the last operating reactor at the MCC, which still uses the Yenisei water as coolant. In water and sediment samples of the Bolshaya Tel River (a tributary of the Yenisei River) the tritium content turned out to be at least 10 times higher than the background values for the Yenisei River. The measurements conducted at the RPA RADON (Moscow) revealed not only tritium but also the artificial radionuclide (14)C in the Bolshaya Tel samples. The data obtained suggest that the Bolshaya Tel River receives the major part of tritium from sediments rather than from the water catchment area. This allows the conclusion that there is water exchange between the surface waters and the radioactively contaminated underground horizons of the "Severny" testing site.

Environmental Monitoring↗
PubMed2006

Biological half-life and oxidative stress effects in mice with low-level, oral exposure to tritium.

Tritium ((3)H) may enter the environment from human activities, particularly at production, processing, or waste storage sites such as the Department of Energy's Savannah River Site, a former nuclear production facility in South Carolina. Understanding the dynamics and potential adverse effects of tritium in exposed organisms is critical to evaluating risks of tritium releases at such sites. Previous studies estimated the biological half-life of tritium in mice to be approximately 1.13 d; however, these laboratory studies were not conducted under environmentally realistic conditions. In this study, designed to be more representative of environmental exposure, mice were allowed to drink water containing tritium (activity about 300 Bq/ml) for a period of 2 wk. The induction of oxidative stress from tritium exposure was evaluated by comparing the activities of antioxidant enzymes (catalase, glutathione peroxidase, and superoxide dismutase) in exposed and control mice. From this experiment, the biological half-life of tritium was determined to be 2.26 +/- 0.04 d, almost double previous estimates. While positive controls (x-ray irradiated mice) showed responses in antioxidant enzyme activity, there was no indication of oxidative stress induction in mice exposed to tritium at this concentration.

Administration, Oral↗
PubMed2006

Radiation quality of tritium.

Tritium occurs from both natural and manufactured processes. In the environment, tritium can exist in the form of tritiated water (HTO) and in an organic form known as organically-bound tritium (OBT). Although, the concentrations of environmental OBT are relatively low, there is concern that current risk factors may underestimate the risk from OBT. Because tritium poses an internal hazard at cellular levels, microdosimetric techniques provide suitable tools for the study of radiation quality of tritium. In this study, microdosimetric simulations are performed for tritium uniformly distributed in a medium, and for tritium bound to biologically critical sites of dimensions from 10 nm to 2 microm. Results of local energy density are different for these two cases in microscopic regions. Based on the spatial distribution of energy deposition, dose mean lineal energies are calculated for tritium in forms of HTO and OBT. The dose mean lineal energies of OBT are about a factor of 1.7 higher than those of HTO in a wide range of target dimensions of biological interest. The results are consistent with radiobiological findings that OBT is about twice as effective as that of HTO.

Half-Life↗
PubMed1983

The metabolism of tritium and water in the lactating dairy cow.

Two lactating Friesian cows received tritiated water (19 nCi of tritium per ml) to drink for 25 days. Urine and milk samples were collected and analyzed for tritium content. Plateau levels in milk water, and in milk fat, lactose and casein were reached in about 18 days. Tritium concentration in milk water and urine water was about 82% that in drinking water, indicating dilution with water from food and metabolic processes, and as a result of exchange through lungs and skin. At steady state, tritium activity in milk fat, lactose and casein was about 30, 28 and 15% of that in drinking water on a weight basis; at this time, about 1.5% of the daily ingested tritium appeared in one litre of milk in both animals. Comparison of the specific activity of the various milk constituents with the specific activity of the body water showed that the highest tritium incorporation occurred in lactose (0.58), followed by milk fat (0.36) and casein (0.27). Tritium incorporation in milk dry matter (0.45) is considerably higher than in most tissue components of several mammalian species after continuous ingestion of THO as reported in the literature. Tritium levels fell rapidly in milk and urine after the administration of THO was stopped, with half-times of around 4 days for the rapid components in all milk constituents. A slow component of 44 days, 225 days and 24 days half-time was found in milk water, milk fat and casein respectively.

Animals↗
PubMed1992

Tritium dynamics in mice exposed to tritiated water and diet.

The contributions of tritiated water (3HHO) and dietary tritiated amino acids to the steady-state specific activities of tissue water tritium and organically bound tritium in mice were essentially independent and additive. Following exposure (56 d), organically bound tritium clearance was resolved into two distinct compartments. The first, with a half-life of 1-2 d, likely represented exchangeable organically bound tritium, and the second, with a half-life of 20-30 d, likely represented nonexchangeable organically bound tritium. Since organically bound tritium was cleared much more slowly than tissue water tritium, organically bound tritium was the principal determinant in estimated radiation doses to mice following exposure.

Amino Acids↗
PubMed1996

A gas scintillation monitor for tritium gas in argon or in nitrogen.

For civilian purposes tritium is presently used in quantities of tens of PBq (MCi) in laboratories for the studies of tritium technology, at the Joint European Torus plant (Abingdon, Oxon, OX143A, UK) as fuel for the process of nuclear fusion, and in the manufacture of radio-luminescent items. Given the extreme mobility of tritium in most materials, it is necessary to use systems for double containment, such as glove boxes or spaces between primary and secondary containers, in which inert gas like argon or nitrogen flows. With these systems it is possible to recover tritium that escapes from the primary containment. Presently the gas flow is monitored continuously by means of ionization chambers which may present problems in particular applications ("memory effect" with high activity, strong dependence of the response on the presence of impurity, etc.). The aim of the work here presented is to determine the prospects for the realization of a new type of monitor mainly dedicated to the measurement of gas activity in isolation space of the containing systems of the high activity tritium plants. This monitor should have sufficient sensitivity, quick response, and should be easily decontaminated. As a detection technique we chose the scintillation produced in the inert gas by radioactive decay. With the first prototype, designed in cylindrical form, it was possible to observe gaseous scintillation events in mixture of tritium and argon or nitrogen. Following that, a spherical prototype was designed, of which we studied the performances and the dependence of the response varying the pressure, the concentration of tritium, the percentage of the impurity, and the gas flow rate. The results are satisfactory and suggest that the monitor could be used in glove boxes and double containment systems. The future research program will include tests involving large quantities of tritium and a study of the ideal dimensions and geometry of the detection chamber in order to optimize the detector response.

Argon↗
PubMed2005

Locating tritium sources in a research reactor building.

Despite renovation of the D2O facility, tritium concentrations in the condensates of reactor room air showed tens of Bq mL before venting resumption on July 1997. This suggested the presence of tritium sources in the research reactor-containment building. An investigation was therefore initiated to locate the source and determine the distribution of tritium in the containment building. Air monitoring in the working area using a dish of water placed in the building suggested that the source of tritium was near the reactor core. Monitoring exhaust air from the two facilities (a cold neutron source and a D(2)O tank) showed high specific activity on the order of 10 Bq mL(-1), suggesting the presence of tritium in condensates near the reactor core. The major concern was whether the leakage of liquid deuterium (4 L) and heavy water (2 x 10(3) L) used as a moderator had occurred. The concentration of tritium in condensates has not increased over the past few years in either the exhaust line or working area, and the deuterium itself has not been found in the surrounding environment. The concentration of tritium measured using an ionization chamber after Ar decay was dependent on the thermal output of the research reactor, indicating that the tritium was produced by the irradiation process within shielding/moderator materials or cover gas with neutrons.

Air Pollutants, Occupational↗
PubMed1980

Application of a continuous channel electron multiplier for measuring gaseous tritium at low pressures.

Some fundamental studies on the application of a continuous channel electron multiplier (channeltron) for monitoring gaseous tritium present in an evacuated vessel at low pressures below 10(-4) Torr were carried out. The results showed that at the tritium pressures lower than 10(-6) Torr the tritium counting rate measured by the channeltron increased linearly, in practice, with increasing tritium pressure, as was expected by assuming that the interactions between beta-particle emitted from tritium and the vessel wall and gaseous molecules during the migration of beta-particle to the channeltron can be ignored. However, in the range of pressures over 10(-5) Torr the measured tritium counting rate was found to be getting smaller than the expected with increase in tritium pressure. This is presumably due to the absorption and scattering of beta-particles by gaseous tritium.

Gases↗