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Byline: Yu. G. Mokrov An analysis of archival data of liquid radioactive waste samples and Techa River bottom sediments was made, taking into consideration the radiochemical methods for extraction and beta-emitting radionuclide activity measurements existing in the early 1950s. It was stated that the radionuclide composition of the routine and accidental liquid radioactive waste releases in 19491951 corresponded to the radionuclide composition of the fission products accumulated in the nuclear reactor fuel and in the liquid radioactive waste storage tank, with operating modes typical for that time period in reactor and radiochemical plants. It was stated that the data obtained by Ilyin (1956) for the assessment of radionuclide composition and liquid radioactive-waste release rate in the Techa River were not correct, and for retrospective assessment of the population exposure dose for near-stream residents, this could result in substantial underassessment of the data obtained.

As a result of operation of the Mayak Production Association (Mayak PA), Chelyabinsk Oblast, Russia, an enterprise for production and separation of weapon-grade plutonium in the Soviet Union, ecosystems of a number of water bodies have been radioactively contaminated. The article presents information about the current state of ecosystems of 6 special industrial storage reservoirs of liquid radioactive waste from Mayak PA: reservoirs R-3, R-4, R-9, R-10, R-11 and R-17. At present the excess of the radionuclide content in the water of the studied reservoirs and comparison reservoirs (Shershnyovskoye and Beloyarskoye reservoirs) is 9 orders of magnitude for (90)Sr and (137)Cs, and 6 orders of magnitude for alpha-emitting radionuclides. According to the level of radioactive contamination, the reservoirs of the Mayak PA could be arranged in the ascending order as follows: R-11, R-10, R-4, R-3, R-17 and R-9. In 2007-2012 research of the status of the biocenoses of these reservoirs in terms of phytoplankton, zooplankton, bacterioplankton, zoobenthos, aquatic plants, ichthyofauna, avifauna parameters was performed. The conducted studies revealed decrease in species diversity in reservoirs with the highest levels of radioactive and chemical contamination. This article is an initial descriptive report on the status of the biocenoses of radioactively contaminated reservoirs of the Mayak PA, and is the first article in a series of publications devoted to the studies of the reaction of biocenoses of the fresh-water reservoirs of the Mayak PA to a combination of natural and man-made factors, including chronic radiation exposure., (Copyright © 2015 Elsevier Ltd. All rights reserved.)