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

Toward an efficient determination of tissue-free water tritium in food

Introduction

Tritium in the environment constitutes a radiological concern because it can become part of the hydrogen pool in environmental and biological reservoirs and thereby expose people to radiation.

Methods

Tissue-free water tritium (TFWT) analysis in food is an important subject of environmental radiation monitoring which plays an important role in the estimation of health risks from environmental tritium exposure. At present, tritium content in food is generally determined by liquid scintillation counter (LSC). To improve the analytical efficiency in tritium determination, we developed a novel method to treat TFWT in food using microporous membranes.

Results

The microporous membrane treatment method developed in this study has the following characteristics: It has a wide range of application and can process TFWT samples with conductivity below 5 μS/cm. Sample loss for the microporous membrane treatment is approximately 5%. The average treatment time is only 5 min, significantly shortened compared with the currently used atmospheric distillation treatment method (1.5 h). The results of the comparison and spike experiment show that the samples prepared by microporous membrane treatment provides equally satisfactory tritium measurement results as classic distillation method.

Discussion

The developed microporous membrane method is simple to operate, efficient, and environmentally friendly, and effectively improves the analysis efficiency of TFWT in food.

Improved Gaussian plume model for atmospheric dispersion considering buoyancy and gravitational deposition: The case of multi-form tritium

Various types of radionuclides have different atmospheric dispersion characteristics, such as buoyancy and gravitational deposition phenomenon of light gas and heavy particles, respectively. Gaussian plume model was widely used to describe atmospheric dispersion behaviors of radioactive effluents, particularly for the purpose of engineering environmental impact assessment or nuclear emergency support. Nonetheless, buoyancy and gravitational deposition were rarely reported in previous work for tritium in particular, which might cause a deviation in evaluating near-surface concentration distribution and radiation dose to the public. Based on the multi-form tritium case, we made a quantitative description for the buoyancy and gravitational deposition phenomenon and discussed the feasibility of developing an improved Gaussian plume model to predict near-surface concentration distribution. Firstly, tritium concentration distribution near to the surface was predicted by using computational fluid dynamics method (CFD) and standard Gaussian plume model to reach consistency without consideration of buoyancy and gravitational deposition effects. Secondly, effects of buoyancy and gravitational deposition were identified by species transport model for gaseous tritium and discrete phase model for droplet tritium with integrating the buoyancy force caused by density variation of gaseous tritium and gravitational force of droplet tritium with enough size. Thirdly, buoyancy and gravitational deposition correction factors were obtained to modify the standard Gaussian plume model. Lastly, predictive results by improved Gaussian plume model were compared with CFD method. It was proved the improved correction method enables higher accuracy in predicting the atmospheric concentration distribution of gaseous pollutants with density variation or particles with gravitational deposition properties.

Assessing the ecological risk of tritium and Carbon-14 discharge on cyanobacteria through metabolic profiling

The ecological risk posed by tritium (T) and carbon-14 (C-14) discharge from nuclear accidents has gained attention. This study evaluated the toxic impact of T and C-14 (at a concentration of 37 kBq/L for 15 days) on the cyanobacteria (Synechococcus elongatus). The results showed that the assimilation efficiency of cyanobacteria was significantly higher for C-14 than T, and the intracellular C-14 activity reached 30.62-40.58 kBq/kg. T and C-14 exposure had no significant effect on cell proliferation but impacted photosynthesis and respiration. T exposure increased the content of Ca, Mg, Na, P, K, and Mn, while C-14 exposure primarily affected trace element absorption in cyanobacteria. 31, 27, and 58 different metabolites (DEMs) were identified under T, C-14, and combined exposure conditions. These DEMs were enriched in the amino acid biosynthesis pathway, and nitrogen assimilation was one of the crucial pathways affected by T and C-14 exposure. The absorption of mineral elements by cyanobacteria was influenced by the variation in metabolites in the ABC transporter pathway caused by T and C-14 exposure. Our findings provide insights into the metabolic response of cyanobacteria to T and C-14 exposure and will help to guide the ecological risk evaluation of nuclear accidents.

Annual variation of different forms of tritium in the soil around Qinshan Nuclear Power Plant

Tritium deposited in soil forms HTO and OBT. To further understand the changes of HTO and OBT in different years, HTO and OBT in the soil around Qinshan Nuclear Power Base in different sampling years were measured. According to the annual distribution of HTO and OBT in the surface soil, it could be inferred whether there was a long-term release of tritium in the observed year. From the depth distribution of different years, OBT tends to migrate to the deep. From 2015 to 2020, the correlation analysis between OBT and HTO/soil organic matter showed that HTO contributed more to OBT in surface soil at 250-2000 μm and 53-250 μm particle sizes, but this conclusion did not apply to deep soil. However, there was no significant relationship between OBT activity and soil organic matter content.

Tritium: Doses and Responses of Aquatic Living Organisms (Model Experiments)

Tritium is a byproduct of many radiochemical reactions in the nuclear industry, and its effects on aquatic organisms, particularly low-dose effects, deserve special attention. The low-dose effects of tritium on aquatic microbiota have been intensively studied using luminous marine bacteria as model microorganisms. Low-dose physiological activation has been demonstrated and explained by the signaling role of reactive oxygen species through the “bystander effect” in bacterial suspensions. The activation of microbial functions in natural reservoirs by low tritium concentrations can cause unpredictable changes in food chains and imbalances in the natural equilibrium. The incorporation of tritium from the free form into organically bound compounds mainly occurs in the dark and at a temperature of 25 °C. When tritium is ingested by marine animals, up to 56% of tritium is accumulated in the muscle tissue and up to 36% in the liver. About 50% of tritium in the liver is bound in non-exchangeable forms. Human ingestion of water and food products contaminated with background levels of tritium does not significantly contribute to the total dose load on the human body.