FRACTIONATION, MOBILITY AND BIOLOGICAL ACCESSIBILITY OF RADIONUCLIDES IN THE ENVIRONMENT
Yu. A. IZRAEL
Institute of Global Climate and Ecology under the Russian Academy of Sciences and Roshydromet, Moscow, Russian Federation
Fractionation of radionuclides is stipulated by varied distribution of certain isotopes on aerosol particles from nuclear explosions and accidents. The character of isotope distribution on the aerosol particles governs peculiarities of radionuclide distribution in the environments - the air, soil, surface and ground water and sea environment. Mobility of radionuclides after their fallout on the Earth’s surface is determined by possibility of their contact with the aquatic environment and chemical properties of elements (or their compounds) in the form of which the radionuclides do exist.
Biological accessibility is determined by mobility of radionuclides and their penetration into living organisms. The presentation discusses the degree of transition of radioactive isotopes of certain elements from the particles to the water and muriatic acid (and gastric juice); the dependence is highlighted between biological accessibility of radionuclides, the distance from an epicentre of an explosion or accident and characteristic features of particles - carriers of radioactivity.
The processes of wash-off of radionuclides from soil to the water, vertical migration into the soil and their redistribution by surface and ground water are described. The use of wash-off coefficients, obtained by observation after nuclear explosions, provided a possibility to forecast already in May 1986 water contamination in rivers and storages in summer, 1986 and spring flood of 1987 in the zone of the Chernobyl accident.
The paper demonstrates that the reliable data on fractionation and biological accessibility are needed to solve effectively the problems of rehabilitation of the zones contaminated after nuclear explosions and accidents. The most important characteristics stipulating the behaviour and transformation of radionuclides in the natural environment are their fractionation, mobility, susceptibility to dissolving, and further biological accessibility responsible for their penetration into living organisms including the human body.
A knowledge of the listed characteristics together with physical properties of radionuclides (the decay rate, type of emitted radiation, etc.) provides the possibility to estimate contamination hazard and take the most effective measures to prevent or reduce the hazard and rehabilitate contaminated natural objects to a degree suitable for life and economic activities.