Abstract
A study of the bioavailability of a tightly bound tritium in the soil in situ under the conditions of the Semipalatinsk test site (STS) and in a laboratory vegetation experiment was conducted. Significant concentrations of organically bound tritium (OBT) were recorded in Stipa capillata plants growing on the territory of the STS. At the same time, tritium in the free water of plant tissues (TFWT) was not detected. In a model experiment using Cucumis sativus culture, the specific activity of tightly bound tritium in the composition of the solid phase of the soil and tritiated water (HTO) in the composition of the soil solution at the beginning and at the end of the experiment differed significantly. At the same time, TFWT activity in Cucumis sativus was 2 orders of magnitude less compared to the activity of tightly bound tritium in the soil and slightly differed from the activity of tritiated water in the soil solution, which is accessible to the root system of plants. The results of vegetation studies have shown that the direct source of tritium for experimental plants was a soil solution. However, changes in the tritium activity in the soil liquid and solid phases in vegetation vessels indicate that the source of tritiated water in the soil solution was a tightly bound form of radionuclide as a result of leaching processes. It is assumed that the possible causes of leaching of tightly bound radionuclide from the solid phase into the soil solution are the moisture regime, as well as the influence of the rhizosphere of plants.