Changes in HTO and OBT activity concentrations in the Perch Lake aquatic ecosystem

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.

Effects of 90Sr on Tree Swallow Nestlings Near Groundwater Contaminant Plumes

Discharge of groundwater contaminant plumes has created elevated concentrations of Sr in some aquatic sediments at Chalk River Laboratories. Tree swallows (Tachycenita bicolor) feed and supply their nestlings almost exclusively with airborne insects that developed as larvae in aquatic sediments. To monitor the uptake and test for potential detriment due to Sr in a terrestrial animal, we measured the gross beta concentrations in the bone of 12-d-old tree swallow nestlings in areas having sediments with elevated levels of gross beta (Sr and Y) and in several control areas where sediment gross beta was primarily due to naturally occurring K. Nesting behavior and reproductive success of the tree swallows were similar regardless of the gross beta concentrations in sediments near their nest boxes. Radiation can damage DNA and cause micronuclei to form in cells, so we examined the frequency of micronuclei in erythrocytes of nestlings. The formation of micronuclei in the erythrocytes of the nestlings was also similar wherever nestlings were analyzed. The results revealed no significant increases even near sediments with the highest gross beta levels. At Perch Lake, where Chalk River Laboratories has a large area of Sr-contaminated sediments, the bones of 12-d-old nestlings contained gross beta concentrations as high as 29 Bq g. This would produce a skeletal dose rate of 9 μGy h, which is one-fourth of the threshold dose rate of 40 μGy h, above which detriment could occur. Failing to find any indication of detriment in the field study, we irradiated wild eggs in the lab and returned them to their nest for natural incubation, hatching, and feeding by the parents. There was an increase in formation of micronuclei following a dose of 3.2 Gy, and the other results were consistent with existing literature.

Evidence for tritium persistence as organically bound forms in river sediments since the past nuclear weapon tests

Tritium of artificial origin was initially introduced to the environment from the global atmospheric fallout after nuclear weapons tests. Its level was increased in rainwaters by a factor 1000 during peak emissions in 1963 within the whole northern hemisphere. Here we demonstrate that tritium from global atmospheric fallout stored in sedimentary reservoir for decades as organically bound forms in recalcitrant organic matter while tritium released by nuclear industries in rivers escape from such storages. Additionally, we highlight that organically bound tritium concentrations in riverine sediments culminate several years after peaking emission in the atmosphere due to the transit time of organic matter from soils to river systems. These results were acquired by measuring both free and bound forms of tritium in a 70 year old sedimentary archive cored in the Loire river basin (France). Such tritium storages, assumed to be formed at the global scale, as well as the decadal time lag of tritium contamination levels between atmosphere and river systems have never been demonstrated until now. Our results bring new lights on tritium persistence and dynamics within the environment and demonstrate that sedimentary reservoir constitute both tritium sinks and potential delayed sources of mobile and bioavailable tritium for freshwaters and living organisms decades after atmospheric contamination.

HTO activity concentrations in soil and plants in the vicinity of Qinshan Nuclear Power Plant Base

To explore the distributions of tritiated water (HTO) in soil and plants after routine release of tritium, this study focused on the Qinshan Nuclear Power Plant Base(QNPPB) using both soil samples at different depths (0-2 cm, 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, and 20-25 cm) and vegetation samples (including leaves and grasses) from eight sampling points. Then, HTO activity concentrations were measured in all samples. The results showed that the range in HTO activity concentrations in the leaves was 24-39.5 Bq/L and in the grasses was 27-85.5 Bq/L.HTO activity concentrations in the topsoil sample (0-2 cm) from the Qinshan Phase III were greatest. At a same sampling point, the HTO activity concentration was the greatest in the topsoil sample. In most case, except for the top soil layer, HTO activity concentration in different depth soil layer differed slightly. Overall, the HTO activity concentration in leaves and grasses were lower than that in the soil at the same site, and the ratios of HTO activity concentration in plant to soil were found to vary between 0.38 and 2.1, with a mean value of 0.79. This result suggests that some parameters used in the specific activity model proposed to predict tritium activities provide a conservative estimate for the QNPPB site; it should be revisited to better account for the behavior of HTO in the actual environment.

Assimilation and transport of organic bound tritium in an irrigated pine forest

The speciation of radioactive tritium (T) in a naturally-established subtropical loblolly pine forest that has been irrigated with highly-contaminated pond water for the last 20 years is reported. This irrigation project was created to limit the underground transport of a tritium-rich plume which also contains low levels of toxic organics, metals and radionuclides such as carbon-14 (14C) from a nearby low-level waste burial ground. The levels of tritiated water (HTO) in the wood cores were not influenced by recent irrigation activities. However, the tritium levels in the last 20 years of tree growth were more than 3-fold higher than that of tritium in the older growth. This was due to recent irrigation with organic-bound tritium (OBT)-rich water and subsequent accumulation of high levels tritium as OBT relative to tissue HTO. High levels of pond irrigation water OBT resulted from biogenic processes that converted HTO to OBT. Data for 14C that were acquired for some of the forest materials indicated that the processes controlling the movement and accumulation of 14C in this system are somewhat different than that of tritium. Spectroscopic characterization of tree core tissue of <20 years in age found no explanation for the unusually wide dark growth rings. It was concluded that the trees were over-irrigated based on results from other published studies with wood from severely-flooded areas. Although HTO is indeed toxic to biota, OBT represents a relatively greater hazard to biota because it can be bioaccumulated and retained for long periods of time in living tissues.

An updated review on tritium in the environment

Various studies indicated more or less recently that organically bound tritium (OBT) formed from gaseous or liquid tritium releases into the environment potentially accumulates in organisms contradicting hypotheses associated to methods used to assess the biological impact of tritium on humans (ASN, 2010). Increasing research works were then performed during the last decade in order to gain knowledge on this radionuclide expected to be increasingly released by nuclear installations in the near future within the environment. This review focusses on publications of the last decade. New unpublished observations revealing the presence of technogenic tritium in a sedimentary archive collected in the upper reaches of the Rhône river and findings from the Northwestern Mediterranean revealing in all likelihood the impact of terrigenous tritium inputs on OBT levels recorded in living organisms are also presented. Identifying and understanding the physicochemical forms of tritium and the processes leading to its persistence in environmental compartments would explain most observations regarding OBT concentrations in organisms and definitively excludes that tritium would "bio accumulate" within living organisms.