STUDY OF AERIAL TRITIUM UPTAKE BY VEGETABLE CROPS UNDER CHAMBER AND FIELD CONDITIONS

Under laboratory (in a chamber) and full-scale conditions (at the former Semipalatinsk Test Site), pepper and eggplant were exposed several times to tritium in the form of НТО at different growth stages. In chamber experiments, tritium activity concentration in the free water (TFWT) of plants’ leaves during exposure increased, and under full-scale conditions, it was marked by an unsteady dynamic. TFWT activity concentration in leaves of both crops was 1–2 orders of magnitude higher than in stems and fruits. Values of TFWT/HTO_air. showed that TFWT activity concentration at the end of exposure reached equilibrium only in leaves. Both in full-scale and chamber experiments, tissue free water was noted to be enriched with tritium compared to the ambient air (TFWT/HTO_air >1). In the post-exposure period, FWT activity concentration in both crops quickly dropped on the first day (over 90–95%). In the next 2 weeks (336 h), a reduction in TFWT was markedly slowing down. In all experiments, activity concentration values of organically bound tritium (OBT) in pepper and eggplant leaves are 1–2 orders of magnitude lower than TFWT. OBT activity concentration in both crops on the first day after exposure was marked by both a positive and negative dynamics. After 2 weeks (336 h) following the exposure, the loss of OBT was 60–95%. A close correlation relationship was established between TFWT activity concentration in leaves and HTO in the air (r = 0.73; р<0.05), and a moderate one – between TFWT activity concentration in leaves and the air humidity (r = 0.54; р<0.05). No significant correlation relationship was revealed between OBT activity concentration in leaves and environmental factors (photosynthetically active radiation, temperature, relative humidity). Findings showed that a possible contribution by organically bound tritium to the annual average internal exposure dose on consumption of crop products exposed to a short-term aerial contamination by HTO will be negligible. Data from full-scale experiments, taking into account the impact by actual climatic factors, could be used to test regional models of tritium transport by air in the “air-to-agricultural plant” system.

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