Some geochemical and environmental aspects of the Chernobyl nuclear accident

The Chernobyl nuclear accident took place on 1986-04-26, and resulted in radionuclide pollution of vast regions of Byelorussia. This has raised several geochemical problems: (1) investigation of the distribution and behaviour of radionuclides in the natural and technogenic landscapes (which were examined as a result of a 5-a study); (2) modes of occurence of radioactive elements in the environment; and (3) preliminary estimation of radionuclide migration in the future. As background information, geochemical studies carried out within Byelorussia, as well as landscape investigations in the period 1953–1987 made under the guidance of K.I. Lukashev were very important for solving the above questions. According to the results of these investigations, the lithogeochemical and hydrogeochemical zoning of Byelorussia is understood and the radioactive background of the republic was studied in the 1960s, as well as the distribution and peculiarities of clay minerals, carbonates, FeMn oxides, organic matter, pH-Eh, and the contents of many elements in the surficial deposits of Byelorussia. All these factors are of great importance for understanding the behaviour of radionuclides.Radionuclide fallout on Byelorussia in the first days after the accident was mainly dependent on the mass movement of air and rain. In cities, fallout was confined to regions with intensive industrial dust emissions, as well as to river valleys, where degassing of deep-seated zones through faults occurred side by side with evaporation. Radionuclide washout from upland territories can be related to secondary processes.After 5 a, the radioactive emission near the surface of the Earth decreased due to the decay of short-lived isotopes and penetration of radionuclides deeper into the soil, although the major part still occurs at a depth of 1–5 cm. Bogs, peat-bog soils, aquifers with fluctuating groundwater levels, variable pH-Eh conditions and a igh biological activity are all factors contributing to radionuclide migration in the Byelorussian landscape. A part of the radionuclides is gradually removed from eluvial landscape and accumulated in subareal landscape (e.g. lakes, oxbow-lakes, water-storage basins).The Chernobyl debris are represented by the following substances: “hot” particles, pseudocolloids, aerosols and gaseous compounds. Study of the modes of occurrence of radionuclides by different methods (e.g. extracts, sorbents) made it possible to estimate the migration capacity of some radionuclides (Cs, Sr, Ce, Ru), and to distinguish two zones around the reactor—the nearest and remote ones—differing in the ratio of “hot” particles and condensate fallout, which causes a different migration capcity of radionuclides.A very important part is assigned to biological processes and organic matter, which cause the destruction of “hot” paricles, the formation of organomethallic complexes, and water migration of nuclides.In the future (within 300 and more years), the redistribution of radionuclides in the landscape involves processes of weathering, erosion and sedimentation which will strongly depend on climatic conditions, Side by side with a gradual decay of Cs and Sr, an appreciable accumulation of²⁴¹Am, which is very mobile in landscape, should be expected due to decaying²⁴¹Pu.A considerable development of scientific and applied exploration should also be expected in the future and this will help in solving problems of radioactive pollution of landscapes.