EVALUATION OF 137Cs AND 90Sr TRANSFER FROM SOIL TO SCOTS PINE (PINUS SYLVESTRIS L.) BY THEIR DISCRIMINATION COEFFICIENTS

Radionuclides migrate in the soil in both vertical and horizontal directions. Radionuclide migration is predetermined by physical and chemical properties, climatic conditions, environmental relief, soil type, hydrological regime in the territory, the type of flora, agrochemical specificities of agriculture and other factors. While making an analysis of Cs-137 behaviour in the forest ecosystem, two processes are distinguished, as a result of which Cs-137 enters a tree: due to fallout on the top and trunk of a tree and because of cesium assimilation through roots from the soil. It should be mentioned that internal change of cesium in a tree also occurs; however, it is not as distinct as cesium uptake from the atmosphere and soil. Sr-90, having deposited from the atmosphere on the soil, under the effect of natural factors, participates in the migration process of substances. With account taken of the physiological specific features of the plant of each species, plants assimilate certain ions from the soil through the root system. Of monovalent ions, K-40 is the most important for the plants. In the case of potassium shortage, plants assimilate other monovalent ions, like cesium. This phenomenon is called the potassium discrimination effect on cesium transfer. The discrimination coefficient is estimated according to Cs-137 and K-40 activities in the soil and the plant. It is assumed that potassium ions may predetermine cesium assimilation. This expression of discrimination coefficient may be also applied for Sr-90, but in this case instead of K-40 specific activities Ca is evaluated, and instead of Cs-137 - Sr-90. The discrimination effect of Sr-90 on assimilation depends greatly on the plant species. The accumulated amount of Sr-90 in the plant depends also on the presence of the proper forms of calcium in the soil solution, close to the root area.