Tissue Free Water Tritium Concentration Research Articles

Assessing the variability of tissue-free water tritium and non-exchangeable organically bound tritium in pine needles in Fukushima using atmospheric titrated water vapor

When conducting environmental tritium monitoring at nuclear and fusion facilities, it is important to understand how tritium concentrations vary within the soil-plant-atmosphere continuum. Past measurements of organically bound tritium (OBT) concentrations have been conducted from the standpoint of ascertaining the persistence of tritium in terrestrial vegetation, and it has been reported that OBT concentrations fluctuate depending on the influence of atmospheric sources and meteorological conditions. The present study provides information on the variability of tritium concentrations in vegetation growing close to atmospheric sources of tritiated water (HTO) in Japan. We conducted measurements of tissue-free water tritium (TFWT) and non-exchangeable OBT (NE-OBT) in pine needles collected from locations near the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Plant from 2018 to 2021. The results we obtained indicate that TFWT concentrations fluctuate in response to short-term changes in atmospheric HTO vapor concentrations and that NE-OBT concentrations vary primarily in response to the time-averaged TFWT concentration during the pine needle growing season, which is in turn mainly determined by atmospheric HTO vapor concentrations. Although it is difficult to ascertain the time-averaged TFWT concentration during the growing season by measuring plant materials, our results show that the measurement of atmospheric HTO vapor concentrations provides an effective alternative method of doing this. We believe our findings can lead to better understanding of the potential impact on the terrestrial environment associated with the atmospheric discharge of HTO and can contribute to improving the strategy of environmental tritium monitoring.

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.

Tritium distribution in typical plants around tritium laboratory in south-west of China

A low-temperature desorption method was developed to remove the tissue free water tritium (TFWT) in plants, which dramatically reduces the sample-preparation time from several days to only 2–3 h. Two factors, including spatial distribution and seasonal variation, that influence the tritium distribution and the organic bound tritium (OBT)/TFWT ratios in plants were investigated based on three different kinds of subtropical-basin plants located near the decommissioned nuclear facility in south-west of China. Under the same environmental condition, higher tritium concentration was seen in pine needle (PN) compared with flat bamboo-root (FBT) and wild cotton (WC), while these three plants show similar location- and season-dependent trend of tritium distribution. The location-dependent investigation shows that OBT and TFWT concentration are significantly higher in plants growing in the downwind direction of the tritium laboratory than that in plants growing in the upwind and cross direction. In different seasons, the TFWT in plants reached peak in winter and valley in summer, while the OBT increased continuously with the season changing from spring to winter. The ratios of OBT/TFWT were investigated to evaluate the ability of plants to concentrate tritium into organic matter, which were 0.97–2.72 for PN, 0.89–1.64 for FBR, and 0.80–1.62 for WC.

Tissue free water tritium (TFWT) and organically bound tritium (OBT) in marine eco system at Tarapur on the west coast of India

The low level tritium, released to marine environment from nuclear facilities, incorporated by marine matrices as tissue free water tritium (TFWT) and organically bound tritium (OBT), was studies for 3 years at Tarapur, situated on the west coast of India. Results show that the tritium concentration in sea water was correlated with TFWT concentration in sea weeds, sediment and marine animals as, with correlation coefficients of 0.6, 0.8 and 0.96 respectively. The TFWT to OBT ratios were observed to be 5.7, 4.9 and 3.6 respectively in seaweed, sediment and marine animals.

Tritiated water (HTO) uptake and loss in maize plant after short-term exposure of atmospheric HTO vapor at daytime and nighttime

Maize plants were exposed to atmospheric tritiated water (HTO) in the field for 1 h during the day and night under different growth periods. The uptake of HTO vapor by leaves and tissue free water tritium (TFWT) loss in maize plants were investigated. Rate constants of uptake of HTO from the atmosphere by maize leaves were 0.10 ± 0.02–0.21 ± 0.01 h−1 during the daytime exposure and 0.035 ± 0.001–0.13 ± 0.01 h−1 in the nighttime exposure. The uptake rate tended to decrease as the exposure increased and harvest neared. At the end of exposure, the TFWT concentration was highest in the leaf and lowest in the ear, the TFWT concentration in different parts of maize varied by a factor of 3–28 for daytime release and 2–30 for nighttime release. After the end of every exposure, TFWT was lost rapidly from different maize tissues for one day and then at a much slower rate until to harvest. At harvest, the TFWT concentrations varied with different maize tissues by factors of 1–4. The decrease was by factors of 4–351 for daytime exposure and 6–605 for nighttime exposure. The reduction of TFWT varied with the exposure time by the factors of 1–10 depending on plant parts. The reduction factor was lowest in kernel. This result suggests that the HTO vapor uptake rates in maize leaves and TFWT loss rates in the ear may be lower than those in C3 plants.

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.

Role of soil-to-leaf tritium transfer in controlling leaf tritium dynamics: Comparison of experimental garden and tritium-transfer model results

Environmental transfer models assume that organically-bound tritium (OBT) is formed directly from tissue-free water tritium (TFWT) in environmental compartments. Nevertheless, studies in the literature have shown that measured OBT/HTO ratios in environmental samples are variable and generally higher than expected. The importance of soil-to-leaf HTO transfer pathway in controlling the leaf tritium dynamics is not well understood. A model inter-comparison of two tritium transfer models (CTEM-CLASS-TT and SOLVEG-II) was carried out with measured environmental samples from an experimental garden plot set up next to a tritium-processing facility. The garden plot received one of three different irrigation treatments – no external irrigation, irrigation with low tritium water and irrigation with high tritium water. The contrast between the results obtained with the different irrigation treatments provided insights into the impact of soil-to-leaf HTO transfer on the leaf tritium dynamics. Concentrations of TFWT and OBT in the garden plots that were not irrigated or irrigated with low tritium water were variable, responding to the arrival of the HTO-plume from the tritium-processing facility. In contrast, for the plants irrigated with high tritium water, the TFWT concentration remained elevated during the entire experimental period due to a continuous source of high HTO in the soil. Calculated concentrations of OBT in the leaves showed an initial increase followed by quasi-equilibration with the TFWT concentration. In this quasi-equilibrium state, concentrations of OBT remained elevated and unchanged despite the arrivals of the plume. These results from the model inter-comparison demonstrate that soil-to-leaf HTO transfer significantly affects tritium dynamics in leaves and thereby OBT/HTO ratio in the leaf regardless of the atmospheric HTO concentration, only if there is elevated HTO concentrations in the soil. The results of this work indicate that assessment models should be refined to consider the importance of soil-to-leaf HTO transfer to ensure that dose estimates are accurate and conservative.

Tritium concentration in soybean plants exposed to atmospheric HTO during nighttime and daytime

Potted soybean plants were exposed to evaporate HTO for 1 h inside an exposure box at two different growth stage (flowering and podding stage, filling stage) during nighttime and daytime. The concentration of tissue-free water tritium (TFWT) and organically bound tritium (OBT) in leaves and beans was measured at the end of the exposure. The results indicated that the quasi-equilibrium between the TFWT concentrations in the soybean leaves and the HTO concentration of the ambient air moisture required more than 1 h to be reached. The relative TFWT concentrations in the nighttime represent about 1/2 to 2/3 of the concentrations obtained in the day in the leaves compared to about 1/2 to 4/3 in the beans. The relative OBT concentrations under night conditions were about 2/5 to 1/2 of those under day conditions in the leaves, contrary to 1/2–7/10 for the beans. By developing tritium concentration assessment model with a short-term release of atmospheric HTO, we comprehensively considered the plant growth stage and the environmental conditions.

Organically bound tritium level in vegetation at ICIT tritium removal facility

In order to evaluate the impact of tritium on wild vegetation around ICIT we have monitored the tritium concentrations in precipitation, air, soil, grass and green wheat from a specific area near the tritium removal facility during vegetation periods in 2012–2013. The tissue free water tritium concentration showed the influence of tritium level in precipitation, with higher values during the summer (around 2 Bq l−1) and lower values during the autumn (around 1.3 Bq l−1). The same behavior was observed for the total organically bound tritium level.

Development and validation of a dynamical atmosphere–vegetation–soil HTO transport and OBT formation model

A numerical model simulating transport of tritiated water (HTO) in atmosphere-soil-vegetation system, and, accumulation of organically bound tritium (OBT) in vegetative leaves was developed. Characteristic of the model is, for calculating tritium transport, it incorporates a dynamical atmosphere-soil-vegetation model (SOLVEG-II) that calculates transport of heat and water, and, exchange of CO 2. The processes included for calculating tissue free water tritium (TFWT) in leaves are HTO exchange between canopy air and leaf cellular water, root uptake of aqueous HTO in soil, photosynthetic assimilation of TFWT into OBT, and, TFWT formation from OBT through respiration. Tritium fluxes at the last two processes are input to a carbohydrate compartment model in leaves that calculates OBT translocation from leaves and allocation in them, by using photosynthesis and respiration rate in leaves. The developed model was then validated through a simulation of an existing experiment of acute exposure of grape plants to atmospheric HTO. Calculated TFWT concentration in leaves increased soon after the start of HTO exposure, reaching to equilibrium with the atmospheric HTO within a few hours, and then rapidly decreased after the end of the exposure. Calculated non-exchangeable OBT amount in leaves linearly increased during the exposure, and after the exposure, rapidly decreased in daytime, and, moderately nighttime. These variations in the calculated TFWT concentrations and OBT amounts, each mainly controlled by HTO exchange between canopy air and leaf cellular water and by carbohydrates translocation from leaves, fairly agreed with the observations within average errors of a factor of two.

The distribution of tritium in the terrestrial and aquatic environments of the Creys-Malville nuclear power plant (2002–2005)

The Creys-Malville nuclear plant, located on the left bank of the Rhône, was shut down in 1998. The facilities are currently in their initial stage of dismantling. In order to establish a baseline for tritium in the vicinity of the site prior to the main dismantling phase, we carried out a monitoring program between 2002 and 2005 in the main terrestrial and aquatic compartments of the local environment. Tritium levels in the groundwaters and in the Rhône waters correspond to the regional tritium concentration in precipitation. The data obtained for the terrestrial environment are also in good agreement with the regional background and do not show any specific signature linked to the nuclear plant. The various aquatic compartments of the Rhône (fish, plant, sediment) are significantly enriched in tritium both upstream and downstream of the power plant: although Tissue-Free Water Tritium concentrations are in equilibrium with the river water, the non-exchangeable fraction of organic bound tritium in plants and fishes shows values which outpace the river water background by one to two orders of magnitude, and up to four to five orders of magnitude in the sediments. This tritium anomaly is not related to the nuclear plant, as it is already present at the Swiss border 100 km upstream of the site. Although fine particles of tritiated polystyrene entering the composition of the luminous paints used by the clock industry have been suspected on several occasions, the exact nature and the origin of this tritium source remain unknown and require further investigations.

PREDICTION OF TRITIUM LEVEL IN AGRICULTURAL PLANTS AFTER SHORT TERM EXPOSURE TO HTO VAPOR AND ITS COMPARISON WITH EXPERIMENTAL RESULTS

This paper describes a dynamic compartment model for evaluating the tritium level in agricultural plants after a short-term exposure to HTO vapor and its comparison with experimental results to test the predictive accuracy of the model. The model uses a time-dependent growth equation of a plant so that it can predict the contamination level of tritium depending on the stage of the growth of the plant, which is a major difference from some other compartment models using a constant crop yield. The model is able to calculate the time variable concentrations of the compartments representing the atmosphere, soil, and plants of four categories including leafy vegetables, root vegetables, grains, and tuber plants. Experimental results include the tissue free water tritium (TFWT) and the organically bound tritium (OBT) concentration of rice, soybean, cabbage, and radish exposed to HTO vapor for 1 h in the daytime at different growth stages. The model predictions showed that the model could simulate well not only the time-dependent tritium concentration of the plants but also the effect of the growth stage of the plant at the exposure time. Comparison of the model predictions with the experimental results suggested that the model could predict reasonably well the observed TFWT and OBT concentrations of the plants considered.

Tritium levels in Chinese cabbage and radish plants acutely exposed to HTO vapor at different growth stages

To simulate an acute exposure of Chinese cabbage and radish plants to airborne HTO, the potted plants were exposed to HTO vapor under semi-outdoor conditions for 1 h at different times from the early to late growth stages. The plants were grown outdoors and the plant tritium was measured at the end of an exposure ( h 0) and at harvest. The leaf tissue free water tritium (TFWT) concentrations at h 0 were considerably lower than estimated equilibrium concentrations. In the leaves of Chinese cabbage, the exposure at the earlier growth stage generally ended with a higher TFWT concentration. Such a tendency was not apparent either in the leaves or roots of radish. On the other hand, the earlier stage exposure gave rise to lower TFWT concentrations at the harvest of both crops. For the OBT (organically bound tritium), however, the same occurred only in the Chinese cabbage leaves. During the period between the exposure and harvest, the TFWT concentrations reduced by factors of up to 1.1 × 10 6 for the Chinese cabbage leaves and 1.3 × 10 4 for the radish roots. Based on the activity ratios of OBT to TFWT at harvest, it is estimated that OBT mostly contributes much more to the ingestion dose than TFWT does.

Natural tritium levels in tender and ripe coconut fruit ( Cocos nucifera L.): a preliminary examination

Tissue Free Water Tritium concentrations (TFWT) were determined in tender coconut ( Cocos nucifera L.) water, ripe coconut water, and kernel milk water, and compared with the same in groundwater collected from the vicinity of the trees. Samples with a very low tritium content were enriched by the alkaline electrolysis method. All of the samples were analyzed for tritium content in an ultra-low level liquid scintillation spectrometer. The TFWT in kernel milk water was found to be approximately 20–40 times higher than that in the groundwater. The tritium concentration in descending order in these samples is: kernel milk water, ripe coconut water, tender coconut water, and groundwater. The concentration of tritium increases as the fruit grows and the significantly high concentration in the kernel milk water suggests enrichment during the growth of the fruit.

Tritium concentration in Japanese rice.

Polished rice samples harvested in 1985 were collected from 25 prefectures throughout Japan. Concentrations of both tissue free water tritium (TFWT) and organically bound tritium (OBT) were determined. Nearly uniform distribution of the TFWT and OBT concentrations was observed in Japan, taking into account a relatively large counting error. The average values for all Japanese polished rice were 2.69 +/- 0.74 Bq/L for the TFWT concentration, 2.01 +/- 0.78 Bq/L for the OBT concentration and 0.83 +/- 0.32 for the specific activity ratio. The TFWT concentration was within the range of tritium concentration of the land water reported by other researchers. The specific activity ratio below unity also confirmed by analyses of the 4 Chinese polished rice samples suggests that OBT in the rice is not equilibrated with TFWT or HTO in the environment because of isotope discrimination.