Tritium uptake in crops in the area with a high level of atmospheric tritium oxide in the territory of the former Semipalatinsk test site

Abstract

During the period from 2019 to 2021, a series of experiments were carried out to study the uptake of tritium by crops in an area heavily contaminated with atmospheric tritium oxide (HTO), at the former Semipalatinsk test site in Kazakhstan. A quantitative assessment is given of the tritium uptake by typical crops (lettuce, tomatoes, peppers and beans) cultivated all over Kazakhstan in the case of a short-term tritium oxide vapor exposure. The plant samples were collected during and after exposure and analyzed for the tritium concentration in two chemical forms: tissue-free water tritium (TFWT) and organically bound tritium (OBT). During the entire series of experiments, the tritium concentration in free water from leaves and ambient air was of the same order of magnitude. The tissue water tritium concentrations of stems and edible parts was 1 to 2 orders of magnitude lower than in the surrounding air. The average value of the TFWT/HTOatm ratio in the leaves and the edible part was (0.73±0.2) and (0.04±0.002), respectively. The organically-bound tritium concentration is 1-2 orders of magnitude lower than the tissue water tritium and ambient air concentrations. Under aerial tritium oxide uptake, the distribution of tritium in non-leafy crops was as follows: leaf-stem-fruit (in decreasing order). After exposure, a non-significant amount of tritium is firmly retained in plants for a long time. The tissue water tritium concentrations correlate closely with atmospheric tritium oxid (r = 0.76), correlate weakly with temperature (r = 0.43) and relative humidity (r = -0.43), and correlate moderately with solar radiation intensity (r = 0.56). There was no reliable correlation between the concentration of tritium in organic matter and in ambient air. The concentration of tritium in the free water of leaves is closely correlated with the concentration in the free water of the stems (r = 0.95) and fruits (r = 0.78). The organically-bound tritium concentration in leaves is closely correlated with the organically-bound tritium concentration in stems (r = 0.99) and fruits (r = 98). The results of the study should be considered when evaluating the impact of tritium oxide emissions on the population living near nuclear power.

Fig 1. The location of the crop exposure place at the former technical test site "Degelen" (on the photo is lettuce exposure).

Fig 2. Scheme [37] and photo of a device for extracting tritium from plants’ tissue free water (1 –organic glass container; 2 –lid; 3 –cone-shaped refrigerator; 4 –receiving tank holder; 5 –receiving tank; 6 –sample container; 7 –sealer; 8 –plant sample; 9 –condensate containing plants’ free-water tritium).

Fig 3. Variation in HTO concentration in air moisture during each exposure (L–symbolizes lettuce exposure, T–symbolizes tomato exposure, B–symbolizes bean exposure, P–symbolizes pepper exposure; error bar shows S.D. of three replicates).

Fig 4. Time courses of TFWT activity concentration in plants during exposures.

Fig 5. Time courses of TFWT activity concentration in plants after exposure.

Fig 6. Time courses of relative OBT concentration in plant parts during exposer to atmospheric HTO.