BIOACCUMULATION OF TRITIUM IN NATURAL AND TECHNOLOGICAL SYSTEMS

Abstract

The distribution of tritium in the soil-vegetation complex was studied on a series of combined samples taken in the area of the radioactive waste storage facility (RWSF). It is shown that bioaccumulation of tritium by vegetation is determined mainly by the position of each specific object (testing point) in relation to the predominant direction of atmospheric transport of the nuclide. In locally selected samples of herbaceous and arboreal vegetation, the content of the nuclide changes according with a high degree of correlation, and its distribution in fractions of freely migrating (transpirational) tritiated water (TW) and in the form of organically bound tritium (OBT) also changes according with a high degree of correlation. In the zones of intense and persistent atmospheric migration tritium forms radiogeochemical anomalies in the soil and vegetation. Under the conditions of stationary atmospheric migration flows, pseudoequilibrium ratios of nuclide concentration in the components of the soil-vegetation system are established, while under the conditions of the functioning of short-term soil flows, the concentration equilibrium of the nuclide in the components of the soil-vegetation system is not observed. Higher concentrations of tritium are observed in more tightly bound forms in both soil and vegetation, which obviously reflects a large dynamic dependence of the mobile form on weather and climate conditions. The ratios of activity concentration of tritium in different forms of presence determined for different types of vegetation as concentration ratio (CR) indicate that tritium accumulates more effectively in arboreal plants - bushes, trees than in herbaceous ones (grass), it is equal to 1.10 and 1.20, respectively. Freely migrating (transpirational) tritiated water possibly due to greater mobility and greater dependence on changes in the activity concentration of tritium in the atmospheric plume and moisture saturation of the air, has a lower activity concentration of tritium than the organically fixed form (OBT), respectively 1.14 and 1.29, which does not have such temporal dependence. During the emission of tritium from RWSF there was a significant accumulation of the heavy isotope of hydrogen in an organically bound form, that is more than half of the tritium absorbed by vegetation is retained during the existence of organic matter and is temporally excluded from the biological cycle in the case of arboreal vegetation. In conditions of the forest landscape of the sanitary protection zone (SPZ) of the RWSF, root absorption of tritium by grass from the humus layer is from 20 to 31% of its total amount accumulated in the soil. The degree of absorption of tritium from the soil is almost the same in herbaceous and arboreal vegetation. This indicates that during the long-term existence of the atmospheric-radio-geochemical anomaly caused by the constant emission of tritium from the storage of RW in organic matter, an equilibrium balance of the content of transpirational HTO and OBT has been formed. In turn, the establishment of such a balance in plant matter can be used as an indicator of a prolonged regime of tritium emission from RWSF. Herbaceous and arboreal vegetation make it possible to determine the spatial position of atmogeomigratory paths of tritium distribution. Plant indicators indirectly reflect the impact of this migration flow on the direct absorption of tritium by organic matter from the air, or its absorption from the root layer of the soil, where the heavy isotope of hydrogen enters with atmospheric precipitation.