Abstract. The large-scale nuclear accident took place at the production association "Mayak" in the Southern Urals in 1957. About 74 PBq of radioactive substances were released into the atmosphere, which resulted in the contamination of a vast area -East-Ural radioactive trace (EURT).
Abstract. The complex radioecological investigations of the East-Ural Radioactive Trace were conducted. Three transects were established in EURT area: central, eastern and western. The current levels of soil contamination near the epicenter of the accident reach 30 × 10 3 kBq/m 2 for 90 Sr and 1 × 10 3 kBq/m 2 for 137 Cs. Contamination levels are reduced in accordance with a power function with increasing distance from the accident site and at a distance of more than 100 km become close to background values. In the EURT impact area vegetation is a complex of synanthropic and semi-natural plant communities in various stages of degradation and restoration successions. The current state of phytocenosises on the sites of the demolished local villages is largely determined by the degree of human impact in the pre-accident period, and remediation activities. For most species the viability of their seed progeny, formed in a gradient of radioactive contamination, are either not different from background samples or reduced half a century after the accident. Mutability of seed progeny in impact coenopopulations in all studied species was high. Radioadaptation phenomenon, i.e. increased resistance to provocative irradiation is rare and unstable.
The Techa river was contaminated in 1949-1956 from the nuclear enterprise "MAYAK". The investigations were carried out in flood plain of the Techa river in 1992-1999. In the upper and middle parts of the river the basic contaminator is I37 Cs; downstream-more active is 90 Sr. Density of contamination of soils with 90 Sr down the river changes from 600 to 200 kBq/m 2 , and that with 137 Cs-from 2,000 to 80 kBq/m 2. Radionuclides content in soils of the central part of the flood plain (30-40 m from the riverbed) also decreases further from the discharge point 1-2 orders. The Techa flood plain may be considered to be a source of secondary radioactive contamination of the water ecosystem. We evaluated the absorption stability and water migration of radionuclides in its soils under experimental conditions. The main quantity of 90 Sr was in exchangeable (41-66 %) form. !37 Cs was in firmly fixed form (80-98 %). The study of radionuclides distribution in the liquid fraction of the soil showed that the main part of 90 Sr (84%) was found in gravitation moisture. 137 Cs (97%) was in a less mobile form of moisture which was connected with soil by capillary and sorption powers.
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