Mining And Chemical Combine Research Articles

USING RADIOISOTOPE METHODS TO DATE Cs INFLOW TO BOTTOM SEDIMENTS OF THE YENISEI RIVER

The long-term study of samples of bottom sediments (BS) of the Yenisei River revealed the presence of a unique set of artificial radionuclides (Co, Cs, Eu, Eu), which made it possible to combine different methods for calculating sedimentation rates for a retrospective assessment of river BS. Studies have been carried out to determine the sedimentation rates by various methods, using natural non-equilibrium Pb, the ratios of artificial isotopes Cs/Co and Eu/Eu, and marker Co, in several sections of the Yenisei River - downstream of the radioactive discharges of the Mining and Chemical Combine (MCC) of Rosatom near the villages of B. Balchug and Atamanovo, as well as upstream of the MCC discharges in the reference areas near the villages of Esaulovo and Shivera. Estimation of sedimentation rates using non-equilibrium Pb, Cs/Co and Eu/Eu isotope ratios, and marker Co for reference areas and the areas near villages located downstream of the MCC showed that their values lay in the range of 0.5-1.3 cm/year. A chronology of Cs influx into BS was constructed using different radioisotope methods, which demonstrated that the maximum Cs influx into BS in the reference regions of the villages of Esaulovo and Shivera and in areas of the village of B. Balchug was noted during the extreme flood of 1966. Cs maxima were also found in the BS layers whose dating coincided with the floods of 1988 and 1995-1997.

Со-60 as a time marker to date sediment layers and estimate sediment transport distances during the 2006 flood event on the Yenisei River

The study of bottom sediments collected from the Yenisei River downstream of the Mining-and-Chemical Combine (MCC) conducted from 2006 to 2016 revealed increased concentrations of 60Co, which was present in dispersed form and in the form of radioactive microparticles, in the upper core layers. The increase in 60Co activity concentration occurred when the 2006 extreme flood on the Yenisei washed away the radionuclide-containing soil from the riverbank at the MCC. The 137Cs/60Co ratio in the upper layers of bottom sediments after the 2006 flood varied between 0.2 and 1.5 and differed considerably from the 137Cs/60Co ratio in the upper sediment layers before the flood (2.5–6.0). Because of the increased concentrations of 60Co, especially in the form of microparticles, in some sediment layers, 60Co was used as a time marker (2006) enabling calculation of sedimentation rates and radionuclide sediment chronology. The 137Cs sediment chronology calculated using 60Co showed that the major 137Cs peak was dated to the most extreme flood on the Yenisei, which occurred in 1966. Those calculations confirmed the appropriateness of using 60Co as a time marker. Our findings suggest that during the 2006 flood, 60Co was washed away from the MCC area to the Yenisei and transported as a component of suspended particles as far as 245 km downstream of the MCC.

Monitoring and assessment of 137Cs and 90Sr radioactive isotopes in the 'soil - rhizosphere - sedge' system of the Yenisei River floodplain (near impact zone of Krasnoyarsk MCC, Russia).

Radiocaesium and radiostrontium contamination in the 'soil - rhizosphere - plants (aerial parts)' system was monitored in the floodplain ecosystem of the Yenisei River in the near impact zone of the Krasnoyarsk Mining and Chemical Combine (MCC). The monitored system included soil, rhizosphere, and sedge vegetation on islands and the river's east bank. The 137Cs and 90Sr specific activities displayed intricate space and time patterns controlled by the river water level, including the time and duration of floods and their correlation with the sedge vegetation season. The specific activities of both radionuclides, especially 137Cs, were above the background in all years of observation, except in a few cases. The soil-to-plant transfer factor (TF) patterns showed continuous 137Cs and 90Sr influx into the system and annual variations in the shares of their bioavailable and fixed forms, especially for 90Sr. The 90Sr distribution in the 'soil - rhizosphere - plants' system observed in 2014-2016 provides evidence for possible local fallout.

Calculation of the Radiation Dose for Some Hydrobionts of the River Yenisei During the Operation of the Nuclear Fuel Cycle Enterprise - Mining and Chemical Combine, Krasnoyarsk

The given work considers the accumulation levels of technogenic radionuclides by some components of the river Yenisei near the discharge area of the water containing a big number of technogenic radionuclides, this water being discharged from the Mining and Chemical Combine (MCC). The investigation was carried out during the operation of the nuclear reactor included into the facility of the given enterprise (2006-2009). The content of gamma-emitting technogenic and natural radionuclides was measured. Using the method of gamma spectrometry, a considerable amount of technogenic radionuclides of the activation type ( 24Na – up to 1950 Bq·kg-1 , 51Cr – up to 2860 Bq·kg-1) were detected in biological objects. Making some assumptions in calculating the dose rate, for the organisms under study the following largest doses were revealed (μGy·day-1): aquatic plants – up to 39, fish: grayling - 22,3 and pike - 36,4. These values are considerably lower than the accepted radiation dose for aquatic biota which amounts to 10 mGy·day-1 .

A long-term study of radionuclide concentrations in mushrooms in the 30-km zone around the Mining-and-Chemical Combine (Russia)

ABSTRACT137Cs concentrations were measured in mushrooms in an area affected by radioactive discharges of the Mining-and-Chemical Combine (MCC) (Rosatom, Russia) in 2002–2017. The sources of radionuclides in the study sites were global fallouts and waterborne and airborne radioactive discharges of the MCC. The mushroom species Suillus granulatus and S. luteus showed the highest 137Cs concentrations (140–7100 Bq kg−1) for this area. Over the entire monitoring period, no significant change in 137Cs concentration was observed in the Suillus spp. samples collected from the sites with the aerial deposition of radionuclides. In the floodplain site with the radionuclide deposition from water and air, a significant decrease in the average 137Cs concentration was observed in the period between 2004 and 2017: a three-fold decrease in Suillus spp. and a nine-fold decrease in Lactarius deliciosus. The effective half-lives of 137Cs in fruiting bodies of the mushrooms L. deliciosus and Suillus spp. in this site were 3.6 ± 0.6 and 9.2 ± 2.7 years, respectively.

Time-dependent trends of artificial radionuclides in biota of the Yenisei River (Siberia, Russia)

We investigated time-dependent trends of artificial radionuclides in aquatic moss, zoobenthos (amphipods and caddisfly larvae), and three abundant wild fish species (Northern pike, Arctic grayling, and Siberian dace) inhabiting the Yenisei River in the vicinity of the radioactive discharge site in 2007–2015, in a period before and after the shutdown of the last nuclear reactor plant at the Mining-and-Chemical Combine (MCC), which occurred in 2010. From our research, we learned that concentrations of short-lived radionuclides, whose discharges to the Yenisei either stopped or declined after the shutdown of the reactor plant at the MCC (24Na, 46Sc,51Cr, 54Mn, 58Co, 59Fe, 60Co, 65Zn, 103Ru, 141,144Ce, 152,154Eu, 239Np), decreased in biota samples as well. The ecological half-life (EHL) of 65Zn (0.4–0.7 y) was similar to the physical half-life of this isotope, the EHLs of 60Co (1.2–2.1 y) and 152Eu (1.8 y) were shorter than the physical half-lives of these isotopes. Concentration of 137Cs did not decrease significantly in biota of the Yenisei after the shutdown of the last reactor plant because the discharges of this radionuclide to the Yenisei continued at the same level. On a longer-term scale (since 1973 and since 1991), concentration of 137Cs in fish muscle had significantly decreased, following the decrease in annual discharges of this radionuclide to the Yenisei, and the EHL of 137Cs was estimated as 6.5–12.8 y. Statistically significant correlation with annual discharges of 137Cs was revealed for the concentration of this radionuclide in grayling (whole bodies and muscle); dace (muscle), and amphipods. Despite their ability to accumulate high concentrations of 137Cs, aquatic moss and caddisfly larvae (analyzed together with their stony casings) were not sensitive to interannual fluctuations in the releases of this radionuclide to the Yenisei. Among the analyzed fish species of the Yenisei, the highest activity concentration of 137Cs was revealed in pike (body and muscle), indicating biomagnification of this radionuclide in the top level of the trophic chain.

Radioactive particles in the Yenisei River floodplain (Russia): Characterization, leaching and potential effects in the environment

The operation of the Mining-and-Chemical Combine (MCC), the largest producer of weapons-grade plutonium in Russia, has resulted in radioactive contamination of the Yenisei River floodplain. Investigations carried out in Novosibirsk and Krasnoyarsk institutes have shown that the floodplain of the Yenisei downstream of the MCC is contaminated by radioactive particles (RP) of various types and activities. Analytical characterization of the RP showed that most of them were fuel particles, which were carried into the Yenisei after incidents at the MCC reactors. The plutonium and caesium isotope ratios (238Pu/239,240Pu; 137Cs/134Cs) vary substantially between the particles, indicating different source terms and time intervals when the RP were formed. In addition to fuel RP, there were particles that contained activation radionuclides. The experiment on dissolution of RP using the model solution (the simulated stomach fluid) showed different cumulative extractions of radionuclides from the particles: 60Co and 137Cs extractions were the lowest, the extracted fractions of europium and americium isotopes were the largest, and plutonium occupied an intermediate position. High concentrations of radionuclides in RP are sources of exposure of organisms in aquatic and terrestrial ecosystems to low radiation doses. The plant bioassays of the effects of γ-radiation from RP showed the effect of low doses of γ-radiation on growth parameters of aquatic plant Elodea canadensis growing in the Yenisei River floodplain. The presence of RP from different sources in the Yenisei River floodplain makes this region a unique site for studying environmental effects of the particles.

DETECTION OF PATHWAYS OF TRITIUM ENTRY INTO FRESHWATER ORGANISMS IN THE EXPLOITATION OF THE MINING AND CHEMICAL COMBINE

The global pollution of the environment and the functioning of the Mining and Chemical Combine (MCC), Rosatom State Corporation are potential sources of tritium in the Yenisei River ecosystem. The distribution of residual tritium in organs and tissues of the freshwater rayfinned fish Carassius gibelio (Prussian carp) as a representative of the Carassius phytophagous genus of Cyprinidae family was studied for the determination of the 3Н accumulation in the aquatic plants-fishes food chain in water bodies contaminated with radionuclides. At the first stage, the work was done on the accumulation of tritium by the biomass of hydrobiont plants. To do this, 3000 g of biomass in terms of wet weight were placed in aquaria with a volume of 100 liters with specific water activity of 100 kBq/l. The work shows mentioned aquatic plants to accumulate actively the introduced tritium, storing up to 70% of the radionuclide. At the same time, the content of organically bound tritium in biomass increased to 21% of total accumulated tritium. Then the plants (hornwort, duckweed) were dried, mixed with dry fish food (1: 1), and the mixture was compressed into pellets, each with activity up to 50 Bq. The pellets were used for forcible feeding of fish, during the experiment, each individual absorbed up to 330 kBq of tritium radionuclide for 550 days. Studies have shown about 75% of the total accumulated amount of tritium in fish specimens to present in muscle tissue. When determining the content of tritium in proteins and lipids in experimental systems, no specific features have been revealed in the use of Ceratophyllum and Lemna as a source of nutrition.

Unique diversity of radioactive particles found in the Yenisei River floodplain

The long-term operation of three reactors and the radiochemical plant of the Mining-and-Chemical Combine (MCC), Russia’s largest producer of weapons-grade plutonium, has resulted in radioactive contamination of the Yenisei River floodplain. From 1995 to 2016, we found more than 200 radioactive particles (RP) in the Yenisei floodplain, downstream of the MCC. Analytical characterization showed that most of the RP were fuel particles, which were carried into the river after incidents at the MCC reactors. Having compared the 137Cs/134Cs ratios in the particles, we determined three time intervals when the RP were formed. The plutonium isotope ratios (238Pu/239,240Pu) vary substantially between the particles and indicate several different source terms. In addition to fuel RP, we found particles that only contained activation products (60Co or europium isotopes). SEM and γ-spectrometry showed that the cobalt particles could have originated from the corrosion of the reactor coolant system and the europium particles – from the damaged compensating rods. No europium particles have been found anywhere else in the world. The presence of RP from different sources (fuel, cobalt, and europium particles) in the Yenisei River floodplain makes this region a unique site for studying environmental effects of the particles. These RP represent point sources of radioecological significance.

Tritium content of some components of the middle Yenisei ecosystem

The potential sources of tritium in the Yenisei River ecosystem are global pollution of the environment and the functioning of the Mining and Chemical Combine (MCC), Rosatom State Corporation. The background tritium content of zoobenthos, bottom sediments, some commercial fish species, and the most widely occurring aquatic plant species was determined for the first time. The MCC functioning affected the tritium content in the nearest impact zone, and significant excess of the tritium content of aquatic plants over the background level was revealed.

A Study of Sediments and Radioactive Particles of the Yenisei River Using a Variety of Analytical Methods

The Yenisei River, one of the largest rivers in the world, is contaminated with artificial radionuclides released by a Russian nuclear facility producing weapon-grade plutonium, which has been in operation for many years. Examination of Yenisei River sediment samples revealed the presence of artificial radionuclides typical of radioactive discharge from the Mining-and-Chemical- Combine (MCC) nuclear facility: isotopes of europium (152Eu, 154Eu, and 155Eu), cesium (137Cs and 134Cs), 60Co, 90Sr, and transuranium elements. The MCC is also a source of radioactive particles in the Yenisei. New data on radionuclide concentrations in sediments and radioactive particles in the Yenisei River were obtained using a wide range of analytical methods. Sequential extraction performed on samples of sediment cores showed different degrees of potential environmental availability of artificial radionuclides and uranium. In a few samples, 241Am was present in the unextractable form, which may be accounted for by the presence of microparticles of the reactor fuel. These microparticles were investigated using scanning electron microscopy, and their reactor origin was confirmed.

Behavior of 137Cs in the soil-rhizosphere-plant system (by the example of the Yenisei River floodplain)

137Cs speciation and distribution in the components of the biogeocenosis of the Yenisei River floodplain such as soils, rhizosphere, and plants were studied. The study was carried out near zones of influence by the Krasnoyarsk Mining and Chemical Combine (MCC). Variation in the specific activity of radionuclides with increasing distance from the pollution source and its ratio in the soil and rhizosphere and distribution in the plant body were studied. A variety of occurrence forms of 137Cs, including mobile ones, was revealed. The amount of 137Cs leached from plants during flooding was calculated from the results of laboratory experiments.

The relationship of mineral and geochemical composition to artificial radionuclide partitioning in Yenisei river sediments downstream from Krasnoyarsk

Discharges from the Mining-and-Chemical Combine (MCC) of Rosatom, downstream from Krasnoyarsk, resulted in radioactive contamination of sediments of the River Yenisei. The concentration of artificial gamma-emitting radionuclides ((137)Cs, (60)Co, (152)Eu, and (241)Am) was determined with the objective to analyze the migration processes leading to the transport of these radionuclides. The content of artificial radionuclides in the surface layers of the study area varied in wide ranges: (137)Cs-318-1,800 Bq/kg, (60)Co-87-720 Bq/kg, (152)Eu-12-287 Bq/kg and (241)Am-6-76 Bq/kg. There was a sequence of migration of radionuclides investigated in the surface layer of sediments that were collected in the near zone of influence of the MCC: (241)Am ≈ (152)Eu > (60)Co > (137)Cs. Radionuclide species have been found to be directly related to sediment structure and composition.

First data on the uranium content in water of the Yenisei River basin in the area affected by the operation of Rosatom plants

This study is devoted to investigating the content of uranium isotopes in water of the Yenisei River and its tributaries within the territories affected by the operation of Rosatom plants (mining chemical combine, and electrochemical plant). Long-term monitoring of the 238U content by mass spectrometry carried out in two institutes of the Siberian Branch of the Russian Academy of Sciences first revealed the multiple excess of 238U over the background content in different areas of the Yenisei River basin, such as the region of the Yenisei River near the effluents of the mining and chemical combine (MCC), and the territories of the Bol’shaya Tel’ and Kan rivers. In these regions, the 238U content in water reaches 2.1–4.0 μg/l, which exceeds its content upstream from the MCC (0.3–0.6 μg/l) by almost an order of magnitude. The studies of the isotopic composition of uranium in water samples, which were carried out at the Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, showed the presence of a technogenic isotope of uranium 236U in the samples from the Bolshaya Tel’ River and revealed the deviation of the isotope ratio 238U/235U (167 ± 3 and 177 ± 3) from the equilibrium natural ratio (238U/235U = 138). These facts attest to the technogenic origin of part of the uranium in water of the Bol’shaya Tel’ River connected with the activity of MCC. The excess uranium content in the Kan River requires additional studies to ascertain the fraction of uranium of technogenic origin connected with the activity of the electrochemical plant (ECP) (Fig. 1, Table 4).

Artificial radionuclides in sediment of the Yenisei River

Releases from the nuclear facility Mining-and-Chemical Combine (MCC) located at Zheleznogorsk have contributed to the radionuclide contamination of the Yenisei River since operations commenced in 1958. The aim of this study was to assess the activity concentrations of artificial radionuclides and the strength of their binding in Yenisei River sediments. Investigation of Yenisei River sediment samples revealed the presence of artificial radionuclides typical of the MCC radioactive discharge: namely, isotopes of europium, caesium, 60Co and transuranium elements. The concentrations of artificial radionuclides in the sediment layers remain relatively high as far as 200 km downstream of the MCC. In sediment cores collected upstream of the MCC, γ-spectrometric measurements registered only one artificial radionuclide, 137Cs, with a maximal activity of 8 Bq·kg−1. Sequential extraction performed on samples of the upper layers of the sediment core showed different degrees of potential environmental availability for artificial radionuclides: the highest was recorded for 241Am and 152Eu (up to 85% of initial activity), followed by 60Co (up to 32%), and finally, 137Cs (up to 15%). In a few samples, 241Am was present in the unextractable form, which may be accounted for by the presence of reactor fuel microparticles.

The effect of radionuclide and heavy metal contamination of the Yenisei River on cytogenetics of aquatic plantElodea canadensis

The study was done to determine concentrations of radionuclides and heavy metals and to evaluate the frequency of chromosomal aberrations in samples of Elodea canadensis , a submerged plant, collected in different parts of the Yenisei River. Samples were collected in the area subjected to radioactive impact of the Mining-and-Chemical Combine (MCC) at Zheleznogorsk and in the control areas, upstream of the MCC. The investigations showed that Elodea biomass in the area affected by MCC operation contained a long inventory of artificial radionuclides typical of the MCC discharges. Upstream of the MCC, in the control sampling areas, the sediments and the Elodea biomass contained only one artificial radionuclide – 137 Cs. Thus, the exposure doses to Elodea shoots and roots upstream of the MCC are small (not more than 8 μGy/d) and the main contribution to them is made by natural radionuclides. At the MCC discharge site (the village of Atamanovo) and downstream of it, the total dose rate increases almost an order of magnitude, reaching its maximal values – 72 μGy/d for Elodea shoots and 58 μGy/d for roots. Cytogenetic investigations of Elodea roots showed that at the MCC discharge site (the village of Atamanovo) and downstream of it the occurrence of chromosomal aberrations in ana-telophase and metaphase cells of Elodea was considerably higher than in the control area. It is highly probable that this simultaneous dramatic increase in the total exposure rate and the occurrence of chromosomal aberrations in Elodea is associated with the radiation factor. It is suggested that Elodea is affected not only by the radiation factor but also by the chemical factor – toxicity of heavy metals.

Alpha track analysis and fission track analysis for localizing actinide-bearing micro-particles in the Yenisey River bottom sediments

Distribution of actinides in bottom sediment and flood land soil cores collected from the Yenisey River near the Krasnoyarsk Mining and Chemical Combine (MCC) were analyzed. Actinide-bearing micro-particles were localized using alpha track analysis (ATA) and fission track analysis (FTA). Different types of radioactive micro-particles were found by analysis of the ratios of fission tracks to α -tracks from single particles. The different origin of these particles was confirmed by scanning electron microscopy with energy dispersed microanalysis (SEM-EDX), secondary ion mass-spectrometry (SIMS) and single-particle α -spectrometry. It is established that for most of the radioactive micro-particles ATA and FTA are the only possible techniques to obtain information concerning their origin. For the studied samples of bottom sediments and flood land soils, it was established that 80–90% of alpha radioactivity is attributed to hot-particles with 238Pu and 239,240Pu as the major radionuclides. According to the sequential extraction data most of 238Pu and 239,240Pu is found in the residual low-soluble fraction.

Dynamics of radiostrontium leaching from radioactively contaminated floodplain soils of the Yenisei River

Gleyzation-mediated leaching of radiostrontium from floodplain soils of the Krasnoyarsk Mining and Chemical Combine (MCC) activity zone [Atamanovskii Island (front part), Oseredysh Island (front part), and Berezovyi Island (rear part)] is studied with model systems. Leaching of radiostrontium from waterlogged soils is analyzed in terms of the model of anaerobic biosolubilization of gel films. The leaching of radiostrontium is found to correlate with that of iron, confirming the cosolubilization model. Addition of glucose (0.5%) as a stimulant for growth of iron-reducing microorganisms increases the dynamic coefficient of radiostrontium leaching, particularly in soils with lower organic matter content. The model experiments showed that the radiostrontium leaching rate from floodplain soil is higher by 2–3 orders of magnitude than that of radio-cesium, suggesting the possibility of escape of radiostrontium from the floodplain of the Yenisei River with the intrasoil runoff. This conclusion is supported by the experimental data on the 90Sr/137Cs ratio in the floodplain of the Yenisei River downstream of MCC (0.01–0.1).

Actinides and other radionuclides in sediments and submerged plants of the Yenisei River

The source of radioactive contamination of the Yenisei River floodplain, including contamination with actinides, is the Mining-and-Chemical combine (MCC), which has for many years been producing weapons-grade plutonium. Actinides have been detected not only in the soil and sediment of the river but also in the biomass of aquatic plants. The aim of our investigation was to assess the levels of actinides and other radionuclides in sediments and aquatic plants both near the MCC and at a considerable distance from it, down the Yenisei River. Investigations of the Yenisei River sediment samples revealed high activity concentrations of actinides (Pu isotopes and 241Am), which were 100 times higher than their global fallout levels. Sequential extraction of radionuclides from samples of sediments collected near the MCC showed that the amounts of extracted 241Am were the largest (up to 98% of initial activity). It was found that aquatic plants of the Yenisei River collected both near the MCC discharge site and at a distance up to 200 km downstream contained several actinide isotopes. The aquatic moss, Fontinalis antipyretica, was found to contain higher levels of radionuclides than Potamogeton lucens. Leaves of P. lucens contained higher levels of radionuclides, including 239Np, than stems. Sequential extraction of radionuclides from samples of aquatic plants showed that 239Np levels in exchangeable and adsorption fractions of P. lucens biomass were higher than in the respective fractions of F. antipyretica biomass.

Total and cancer mortality of the residents living in a zone of weak technogenic radioactive contamination

Radioactive contamination of the floodplain of the Yenisei River with the wastes dumped by the Krasnoyarsk Mining and Chemical Combine (MCC) might cause external and internal irradiation of a large part of the rural population inhabiting the banks of the Yenisei. Contrary to official data, a few independent studies of the doses received by the exposed population showed that they were quite significant though within the range of low doses. Due to the lack of comprehensive data on the dose status and doses received by the population, the health parameters of the population were studied by comparing the recorded incidences of diseases and mortality in areas located at different distances from the MCC, in the periods before and after the MCC was put into operation, and in different age groups (younger and older than 30, children, working-age persons, and retirement-age persons). Time and space gradients of the cancer morbidity and mortality rate in the RAC area have been found. In the riverside settlements of the RAC area, the mortality from malignant neoplasms (MN) of blood, blood-forming organs, and lymphatic system is higher than in settlements located farther from the Yenisei. As the distance from the MCC down the Yenisei gets greater, the mortality of children due to leukaemia decreases.