Organically Bound Tritium Activity Research Articles

Determination of the baseline tritium concentrations (HTO, TFWT and OBT) in soil and plants in Ontario, Canada

Tritiated water (HTO), tissue free water tritium (TFWT) and organically bound tritium (OBT) activity concentrations in soil and plant leaves, collected at background areas in Ontario, were measured to quantify the current tritium baseline. Five representative background sites, based on their geological characteristics and residential populations, have been selected for this study.Undisturbed soils, plant leaves and surface water samples were collected at 5 sites (London, Kapuskasing, Thunder Bay, Elliot Lake and Cornwall areas) in 2015. Water sample HTO activity concentrations were measured using Liquid Scintillation Counting (LSC, ALOKA), and HTO activity concentrations for soil and TFWT for plant leaves were measured by LSC (Quantulus 1220) on water extracted from frozen samples using a freeze-drying vacuum system equipped with a liquid nitrogen trap. Plant leaf OBT levels were obtained by combustion of rinsed freeze-dried samples using a Parr combustion system, while soil OBT values were obtained using a tube furnace combustion system. Combustion water was distilled before being counted by LSC (Quantulus 1220).HTO activity concentrations were found to range between 1.4 and 2.0 Bq/L (MDA = 0.5 Bq/L) in surface water and soil samples. TFWT values were less than the minimum detectable activity (MDA = 3.5 Bq/L) in plant leaves. In contrast, OBT activity concentrations (MDA = 5 Bq/L) ranged from 5.7 to 17.1 Bq/L in plant leaves and 8.3–20.7 Bq/L in surface soil (0–5 cm depth). The overall OBT activity concentrations were higher in the London and the Cornwall areas. Lower levels were measured near Thunder Bay, Kapuskasing and Elliot Lake. There was no obvious relationship between soil OBT activity concentrations and soil types.The results provide the current tritium (HTO, TFWT and OBT) baseline values in Ontario. These values will be helpful for use as background locations for the evaluation of past and future environmental tritium inputs associated with nuclear facilities, and will be taken into account when evaluating the environmental impact of nuclear facilities in Ontario. Since samples in this study were primarily taken in wooded areas, some questions remain regarding the possibility that soil samples in open, non-wooded areas could show different HTO and OBT contents than those presented in this study.

Assessment of the tritium distribution in the vegetation cover in the areas of underground nuclear explosions at the Semipalatinsk test site

This paper provides results of assessment of the tritium distribution in the vegetation cover in the areas of underground nuclear explosions at the Semipalatinsk Test Site (STS). The research was conducted at the former “Degelen” test site along the streams that are one of the main channels of tritium migration from underground nuclear explosions epicenters. The dominant plant species Carex supine and Achnatherum splendens that belong to different ecological groups in relation to humidity were selected as representatives of the vegetation cover.The TFWT (tissue free water tritium) and OBT (organically bound tritium) activity concentrations in the vegetation cover were measurement. TFWT activity concentration in the samples of both plant species had high values with an average of up to 30 kBq kg−1. The OBT activity concentration was 1–2 orders of magnitude lower than the TFWT in all plant samples. The TFWT and OBT activity concentrations in vegetation samples are closely correlated (r = 0.75, p < 0.05). No statistically significant difference was found between the content of tritium in the samples of Carex supine and those of Achnatherum splendens taken at the same locations.OBT/HTO ratios for vegetation samples of both species were close to equilibrium ratio used in environmental transfer models. In some cases, OBT/HTO ratios were significantly lower than one, which indicates that simple environmental transfer models may not accurately predict the behavior of HTO and OBT in different environmental compartments.The average OBT/HTO ratio for soil samples (0.6 ± 0.1) close to the equilibrium value indicates the equilibrium condition at the research area.The obtained [OBT]plant/[OBT]soil ratios indicate that soil organic matter accumulates tritium from year to year. However, in some locations with high tritium contamination ratios [OBT]plant/[OBT]soil were more than one due to OBT activity in soils is almost the same as OBT activity in plants.It was found that the nature of the spatial distribution of tritium in the vegetation cover in the areas of underground nuclear explosions is complex, and obviously depends on the location of the tunnels in which nuclear tests were conducted, as well as on the peculiarities of the hydrological regime of underground and surface waters, which are the main channels of tritium migration in the research area. Thus, the vegetation cover reflects the spatial distribution of tritium contamination in the sites of underground nuclear explosions and can be used as an indicator of the radiation situation when monitoring radiation-hazardous areas.

Studies on foliar uptake of tritiated water on Spinach sp. during light and dark simulated conditions using environmental chamber

Studies on foliar uptake of tritiated water (HTO) on Spinach sp. during light and dark condition was simulated inside the environmental chamber, and an attempt was made to compute CTFWT HTO, Cpfw HTO, Cpcw OBT, Cpfw OBT using basic equations available in IAEA TECDOC1616. The predicted activity was compared with the observed activity. The conversion of tissue-free water tritium (TFWT) to organically bound tritium (OBT) was more in the light condition. The ratio of OBT to TFWT varied from 0.006 to 0.082. The ratio of observed OBT activity (Bq/kg fresh weight) in light to dark conditions varied from 34% to 117%.

Development of carbon-based metabolic models for estimation of doses of organically bound tritium ingested in humans

The tritium dose coefficient is an important parameter for assessment of the radiation safety of nuclear facilities such as fusion reactors. The dose coefficient for dietarily derived organically bound tritium (OBT) for members of the public is recommended by the International Commission on Radiological Protection (ICRP), which makes some assumptions regarding the human metabolism in calculating this value, because metabolic data for tritium is limited. The objective of this study is to develop biokinetic models for OBT based on metabolic data to validate the current ICRP-recommended dose coefficient for OBT. In contrast to the ICRP model, by modifying biokinetic models for 14C developed in a previous study, the models described in this study consider OBT activity in a range of nutrient molecules. The dose coefficient estimated using these OBT models ((2.4 ± 0.1) × 10−11 Sv Bq-1) was smaller than the value recommended by the ICRP (4.2 × 10−11 Sv Bq-1), suggesting that human metabolic data support its recommendations. However, the conservative estimation considering uncertainties in metabolic data was significantly larger ((9.7 ± 3.5) × 10−11 Sv Bq-1) than the ICRP recommended value; therefore, further studies to reduce the uncertainties are required.

A method for the determination of organically bound tritium in marine biota based on an improved tubular-combustion system

A method for the measurement of organically bound tritium (OBT) in marine biota has been developed using a combustion device designed with three independent temperature control zones and a two-stage intake mode to ensure full combustion of samples. The versatility of the combustion device and combustion water recoveries were tested on nine different types of marine biota, with recoveries varying from 85.15% to 92.67%, with an average of 89.4 ± 11.34%. This indicates that our developed combustion method (combustion program and apparatus) provides stable results. Finally, the OBT activity of the marine samples measured varied from 1.88 to 12.9 Bq/L, with an average of 5.61 ± 3.21 Bq/L.

Organically bound tritium (OBT) activity concentrations in surface soil at the Chalk River Laboratories, Canada

Canadian Nuclear Laboratories (CNL)'s Chalk River Laboratories (CRL) site is home to a large nuclear research complex in Canada. CRL's air tritium releases amount to about 1015 Bq/year. The objective of the study was to characterize the spatial footprint of the 60 years of tritium atmospheric releases in surface soil by measurement of organically bound tritium (OBT). Soil OBT activity concentrations were of particular interest because soil represents a long-term tritium reservoir that can act as a historical record of tritium releases into the environment. Soil samples to a 5 cm depth were collected within the CRL site from 2012 to 2014. Each sample was analyzed for tritiated water (HTO) and OBT activity concentrations. The highest HTO and OBT measurements obtained during this study were 154.0 ± 7.8 Bq/L and 180.9 ± 37.3 Bq/L, respectively. A developed OBT map indicated that retained tritium in soil was not related to the distance of sources-term but it was related to the prevailing wind direction.

Distribution of organically bound tritium (OBT) activity concentrations in aquatic biota from eastern Canada

A survey of eastern Canadian biota was conducted to determine the distribution of activity concentrations of organically bound tritium (OBT). Fish samples were collected from Lake Ontario and the St. Lawrence River in areas continuously receiving inputs of tritiated water (HTO) from operating nuclear power plants, and from Lake Nipissing, a background area. Components of their aquatic environments were sampled. The data collected also provides some insight on how tritium activity concentrations in ambient water influence tissue free water tritium (TFWT) and OBT activity concentrations in biological tissues.Using an ALOKA liquid scintillation system, fish TFWT and OBT were quantified. Fish TFWT averaged 1.6 ± 0.1 Bq/L in Lake Nipissing and 3.1 ± 0.3 Bq/L in Lake Ontario. In contrast, TFWT ranged from 11.1 to 80.8 Bq/L in the St. Lawrence River near the Gentilly-2 Canada Deuterium Uranium (CANDU) site. Fish tissue OBT levels were 4.0 ± 0.4 Bq/L and 5.3 ± 0.2 Bq/L for Lake Nipissing and Lake Ontario, respectively, and between 18.1 and 134.2 Bq/L for CANDU sites.The activity concentrations of TFWT and OBT were reviewed for algae, freshwater mussel and various fish samples collected near Gentilly-2, Pickering and Darlington Nuclear Power Generating Stations. TFWT in aquatic biota was found to correlate with the tritium activity concentrations measured in waters at the time of sampling (TFWT/HTO of ambient water was 0.3–4.3). The OBT concentration factors (OBT/HTO of ambient water) were found to be higher in freshwater mussels (between 17 and 47) compared to algae and fish (0.3–10). These results point to a heterogeneous distribution of biota OBT content in these aquatic ecosystems. It was also noted that all fish and algae samples were found to be within the range of tritium activity concentrations that has been historically measured in the same waters. Values in freshwater mussels were above this range.

Effects of in vivo exposure to tritium: a multi-biomarker approach using the fathead minnow, Pimephales promelas

Tritium (3H) is a radioactive isotope of hydrogen. In the environment, the most common form of tritium is tritiated water (HTO). However, tritium can also be incorporated into organic molecules, forming organically bound tritium (OBT). The present study characterized the effects of tritium on the health of the fathead minnow, Pimephales promelas. Fish were exposed to a gradient of HTO (activity concentrations of 12,000, 25,000, and 180,000Bq/L) and OBT using food spiked with tritiated amino acids (OBT only, with an activity concentration of 27,000Bq/L). A combined exposure condition where fish were placed in 25,000Bq/L water and received OBT through feed was also studied. Fish were exposed for 60days, followed by a 60-day depuration period. A battery of health biomarkers were measured in fish tissues at seven time points throughout the 120days required to complete the exposure and depuration phases. HTO and OBT were also measured in fish tissues at the same time points. Results showed effects of increasing tritium activity concentrations in water after 60days of exposure. The internal dose rates of tritium, estimated from the tissue free-water tritium (TFWT) and OBT activity concentrations, reached a maximum of 0.65μGy/h, which is relatively low considering background levels. No effects were observed on survival, fish condition, and metabolic indices (gonado-, hepato-, and spleno-somatic indexes (GSI, HSI, SSI), RNA/DNA and proteins/DNA ratios). Multivariate analyses showed that several biomarkers (DNA damages, micronucleus frequency, brain acetylcholinesterase, lysosomal membrane integrity, phagocytosis activity, and reactive oxygen species production) were exclusively correlated with fish tritium internal dose rate, showing that tritium induced genotoxicity, as well as neural and immune responses. The results were compared with another study on the same fish species where fish were exposed to tritium and other contaminants in natural environments. Together with the field study, the present work provides useful data to identify biomarkers for tritium exposure and better understand modes of action of tritium on the fathead minnow.

Tritium in fish from remote lakes in northwestern Ontario, Canada

Tritium is most commonly generated as a by-product of nuclear reactors. As such, environmental concentrations are typically only reported near regions of interest, and background concentrations in areas unaffected by anthropogenic disturbance are not well characterized. To provide information on background levels of tritium in the natural environment, tissue-free water tritium (TFWT) and organically-bound tritium (OBT) were measured in the flesh of 106 fish collected within three lakes located at the IISD-Experimental Lakes Area (ELA) in Ontario, Canada in 2014. For the three ELA lakes studied, water tritium (HTO) activity concentration was determined to be below reliably detectable levels (0.6 Bq/L). Fish TFWT was found to be below 0.7 Bq/L, similar to the surrounding water tritium activity concentration. Fish OBT activity concentrations, at below 5 Bq/L, were also very low. Fish size was significantly related to OBT activity in Lake Whitefish and White Sucker from Lake 302, but not in other lakes. Though we observed significant differences in potential tritium exposure to humans among lakes, the levels of tritium reported here are below the Canadian natural background radiation of 1.8 mSv/y. These results provide information on background levels of tritium in freshwater fishes in Canada.

Investigation of the potential impact of storage place on tissue free water tritium and organically bound tritium activity determination

When focusing on environmental tritium measurement, water is the most common matrix, and monitoring is mainly concerned by tissue free water tritium (TFWT) and organically bound tritium (OBT) analysis. Moreover, in order to improve knowledge on tritium behaviour and migration, TFWT and OBT determinations are performed at low activity level. TFWT and OBT determinations could also be performed after incidental releases to determine potential impact to the environment and to man. As hydrogen isotopes are prone to isotopic exchange with atmospheric moisture, the key point when analysing TFWT and OBT is to ensure appropriate preservation of the sample from its sampling to its analysis.Aiming to answer to the following question: does the storage condition could change activity level within the sample? An interlaboratory exercise was organized within the framework of a French tritium working group to follow both TFWT and OBT activity scrutinizing for any variation on a one-year period. For this study about 50 kg of grass were sampled, homogenized, packaged and frozen prior dispatching to the participants. Six aliquots were sent to each participating lab to determine both TFWT and OBT activity concentrations, starting when all the labs received the sample, continuing two weeks, one month, three months, six months and one year after to check for any variation in the measured activity concentration.The results were treated for each analysis date, for each participating lab and considering the overall population by calculating the mean and associated standard deviation. As all values are consistent, the main conclusion of this work is that TFWT and OBT activity concentrations remain constant when appropriate storage conditions are used. This point is of importance as sample conservation is always a critical parameter for tritium determination in environmental samples and also when considering the fabrication of certified reference materials.

Effects of in situ exposure to tritiated natural environments: A multi-biomarker approach using the fathead minnow, Pimephales promelas

Aquatic ecosystems are chronically exposed to radionuclides as well as other pollutants. Increased concentrations of pollutants in aquatic environments can present a risk to exposed organisms, including fish. The goal of this study was to characterize the effects of tritium, in the context of natural environments, on the health of fathead minnow, Pimephales promelas. Fish were exposed to tritium (activity concentrations ranging from 2 to 23,000Bq/L) and also to various concentrations of several metals to replicate multiple-stressor environments. Fish were exposed for 60days, then transferred to the tritium background site where they stayed for another 60days. Tritium, in the forms of tritiated water (HTO) and organically bound tritium (OBT), and a series of fish health indicators were measured in fish tissues at seven time points throughout the 120days required to complete the exposure and the depuration phases. Results showed effects of environmental exposure following the increase of tritium activity and metals concentrations in water. The internal dose rates of tritium, estimated from tissue HTO and OBT activity concentrations, were consistently low (maximum of 0.2μGy/h) compared to levels at which population effects may be expected (>100μGy/h) and no effects were observed on survival, fish condition, gonado-somatic, hepato-somatic, spleno-somatic and metabolic indices (RNA/DNA, proteins/DNA and protein carbonylation (in gonads and kidneys)). Using multivariate analyses, we showed that several biomarkers (DNA damages, MN frequency, gamma-H2AX, SFA/MUFA ratios, lysosomal membrane integrity, AChE, SOD, phagocytosis and esterase activities) were exclusively correlated with fish tritium internal dose rate, showing that tritium induced genotoxicity, DNA repair activity, changes in fatty acid composition, and immune, neural and antioxidant responses. Some biomarkers were responding to the presence of metals, but overall, more biomarkers were linked to internalized tritium. The results are discussed in the context of multiple stressors involving metals and tritium.

Canadian inter-laboratory organically bound tritium (OBT) analysis exercise

Tritium emissions are one of the main concerns with regard to CANDU reactors and Canadian nuclear facilities. After the Fukushima accident, the Canadian Nuclear Regulatory Commission suggested that models used in risk assessment of Canadian nuclear facilities be firmly based on measured data. Procedures for measurement of tritium as HTO (tritiated water) are well established, but there are no standard methods and certified reference materials for measurement of organically bound tritium (OBT) in environmental samples. This paper describes and discusses an inter-laboratory comparison study in which OBT in three different dried environmental samples (fish, Swiss chard and potato) was measured to evaluate OBT analysis methods currently used by CANDU Owners Group (COG) members.The variations in the measured OBT activity concentrations between all laboratories were less than approximately 20%, with a total uncertainty between 11 and 17%. Based on the results using the dried samples, the current OBT analysis methods for combustion, distillation and counting are generally acceptable. However, a complete consensus OBT analysis methodology with respect to freeze-drying, rinsing, combustion, distillation and counting is required. Also, an exercise using low-level tritium samples (less than 100 Bq/L or 20 Bq/kg-fresh) would be useful in the near future to more fully evaluate the current OBT analysis methods.

Tritium uptake in rainbow trout (Oncorhynchus mykiss): HTO and OBT-spiked feed exposures simultaneously

There is currently considerable interest in organically bound tritium (OBT) formation in edible fish. The major questions revolve around whether or not tritium can accumulate in fish after being released into aquatic environments. Since OBT formation rates in large, edible fish are poorly understood, rainbow trout (Oncorhynchus mykiss) studies, where fish were simultaneously exposed to tritiated water (HTO) and OBT-spiked feed over 130 days, were conducted to evaluate tritium uptake.The measured HTO activity concentrations in fish tissue confirmed that HTO in fish tissue equilibrates quickly with HTO in tank water. The data obtained also confirmed that OBT uptake is faster when fish are ingesting OBT-spiked feed compared to when fish are living in tritiated water (and consuming non-OBT-spiked feed). The difference between the two exposure types is such that the groups exposed to tritiated water and OBT-spiked feed simultaneously were showing the same uptake rates as OBT-spiked feed only exposures. Contrary to what was expected, the rate of OBT uptake (from OBT-spiked feed) seemed to be higher in slow growing fish compared to fast growing fish. Another observation from these studies was that OBT activity concentrations in all organs (viscera) had a tendency to be higher than OBT activity concentrations measured in fish flesh.

Levels of tritium in soils and vegetation near Canadian nuclear facilities releasing tritium to the atmosphere: implications for environmental models

Concentrations of organically bound tritium (OBT) and tritiated water (HTO) were measured over two growing seasons in vegetation and soil samples obtained in the vicinity of four nuclear facilities and two background locations in Canada. At the background locations, with few exceptions, OBT concentrations were higher than HTO concentrations: OBT/HTO ratios in vegetation varied between 0.3 and 20 and values in soil varied between 2.7 and 15. In the vicinity of the four nuclear facilities OBT/HTO ratios in vegetation and soils deviated from the expected mean value of 0.7, which is used as a default value in environmental transfer models. Ratios of the OBT activity concentration in plants ([OBT]plant) to the OBT activity concentration in soils ([OBT]soil) appear to be a good indicator of the long-term behaviour of tritium in soil and vegetation. In general, OBT activity concentrations in soils were nearly equal to OBT activity concentrations in plants in the vicinity of the two nuclear power plants. [OBT]plant/[OBT]soil ratios considerably below unity observed at one nuclear processing facility represents historically higher levels of tritium in the environment. The results of our study reflect the dynamic nature of HTO retention and OBT formation in vegetation and soil during the growing season. Our data support the mounting evidence suggesting that some parameters used in environmental transfer models approved for regulatory assessments should be revisited to better account for the behavior of HTO and OBT in the environment and to ensure that modelled estimates (e.g., plant OBT) are appropriately conservative.

Organically bound tritium (OBT) formation in rainbow trout (Oncorhynchus mykiss): HTO and OBT-spiked food exposure experiments

In order to determine the rate of organically bound tritium (OBT) formation, rainbow trout (Oncorhynchus mykiss) were exposed to tritiated water (HTO) or OBT-spiked food. The HTO (in water) exposure study was conducted using a tritium activity concentration of approximately 7000Bq/L and the OBT (in food) exposure study was conducted using a tritium activity concentration of approximately 30,000Bq/L. Fish in both studies were expected to be exposed to similar tritium levels assuming 25% incorporation of the tritiated amino acids found in the food. Four different sampling campaigns of HTO exposure (Day 10, 30, 70, 140) and five different sampling campaigns of OBT-spiked food exposure (Day 9, 30, 70, 100, 140) were conducted to measure HTO and OBT activity concentrations in fish tissues. OBT depuration was also evaluated over a period of 30 days following the 140d exposure studies. The results suggested that the OBT formation rate was slower when the fish were exposed to HTO compared to when the fish were ingesting OBT. In addition, the results indicated that OBT can bioaccumulate in fish tissues following OBT-spiked food exposure.

Modeling the Build-Up of Organically Bound Tritium in Crops after Acute Tritium Exposure in Greenhouse’s Environment

The processes of tritium uptake, losses, transformation and organically bound tritium (OBT) build-up in crops such as potatoes, tomatoes, lettuce and wheat were studied in a set of experiments on crop’ short-term exposure to tritiated water (HTO) in a greenhouse. The crops were exposed at the stage of linear growth between blossoming and ripening. The results of experiments were used to develop a model of OBT build-up in crop’s storage organs.The model allows estimate tritium uptake, losses in crop’s leaves as well as its transformation in OBT and transport to storage organs of plants. The model parameters were obtained from the measured data for each crop’s type by using regression analysis. The model was validated against experiments. The model can be used to assess OBT activity in storage organs of crops upon short-term exposure in the atmosphere contaminated by HTO.

Lichens as indicators of tritium and radiocarbon contamination

Lichens were collected in France in the surroundings of a military nuclear facility in Burgundy, near the la Hague reprocessing plant and in an area away from any direct source of contamination. Organically bound tritium (OBT) has been analysed on 18 samples and radiocarbon on 11. It appeared that on the most contaminated spots, the OBT activity in lichens was higher than the background by a factor of 1000 and was still a factor 10–100 at a distance of 20 km from the source. Radiocarbon from la Hague could be traced by lichens. The slow metabolism of lichens makes them suitable for the follow-up of 3H and 14C, which have been incorporated by photosynthesis.

Épidémiologie du saturnisme infantile en France

Aquatic ecosystems are chronically exposed to radionuclides as well as other pollutants. Increased concentrations of pollutants in aquatic environments can present a risk to exposed organisms, including fish. The goal of this study was to characterize the effects of tritium, in the context of natural environments, on the health of fathead minnow, Pimephales promelas. Fish were exposed to tritium (activity concentrations ranging from 2 to 23,000 Bq/L) and also to various concentrations of several metals to replicate multiple-stressor environments. Fish were exposed for 60 days, then transferred to the tritium background site where they stayed for another 60 days. Tritium, in the forms of tritiated water (HTO) and organically bound tritium (OBT), and a series of fish health indicators were measured in fish tissues at seven time points throughout the 120 days required to complete the exposure and the depuration phases. Results showed effects of environmental exposure following the increase of tritium activity and metals concentrations in water. The internal dose rates of tritium, estimated from tissue HTO and OBT activity concentrations, were consistently low (maximum of 0.2 μGy/h) compared to levels at which population effects may be expected (> 100 μGy/h) and no effects were observed on survival, fish condition, gonado-somatic, hepato-somatic, spleno-somatic and metabolic indices (RNA/DNA, proteins/DNA and protein carbonylation (in gonads and kidneys)). Using multivariate analyses, we showed that several biomarkers (DNA damages, MN frequency, gamma-H2AX, SFA/MUFA ratios, lysosomal membrane integrity, AChE, SOD, phagocytosis and esterase activities) were exclusively correlated with fish tritium internal dose rate, showing that tritium induced genotoxicity, DNA repair activity, changes in fatty acid composition, and immune, neural and antioxidant responses. Some biomarkers were responding to the presence of metals, but overall, more biomarkers were linked to internalized tritium. The results are discussed in the context of multiple stressors involving metals and tritium.