Cesium-137 of Chernobyl origin in lake–river systems of Eastern Fennoscandia: 30 years after the accident

Contamination of waters of lake–river systems after many-year migration of ¹³⁷Cs in water bodies was studied. In lakes with the ¹³⁷Cs fallout density lower than 8 kBq m^–2, the radionuclide concentrations in water after 24–29 years did not exceed 2–3 Bq m^–3, and at a fallout level of 37 kBq m^–2 it was in the range 11–34 Bq m^–3. The natural half-clearance time Т of lake waters from ¹³⁷Cs was 6–7 years at the exposure of up to 20 years. The ¹³⁷Cs migration in the lake–river systems that occurred during ~30 years did not lead to structural changes in the water contamination: The initially low ¹³⁷Cs level in lake waters did not become high, and vice versa. Among rivers feeding Lake Ladoga, the ¹³⁷Cs level in the Vuoksa River is ~3 times higher than in waters of the Volkhov and Svir rivers. During the period 1988–2015, 21.3 TBq of ¹³⁷Cs was supplied to Lake Ladoga with Vuoksa waters. The Vuoksa source from the Saima lake system with increased contamination with ¹³⁷Cs of Chernobyl origin leads to long-term supply of this radionuclide to Lake Ladoga.     

Sorption of 90Sr and 137Cs on Natural Sorbents in Model Environmental Systems

Sorption of ⁹⁰Sr and ¹³⁷Cs from both tap drinking water and water of Beloyarsk storage basin on samples of natural ion exchangers, glauconite concentrate and white alluvial clay, was studied under static conditions. The distribution coefficients of ⁹⁰Sr and ¹³⁷Cs between these sorbents and water were studied as influenced by the equilibration time and water type. With white alluvial clay and glauconite concentrate the sorption equilibrium is reached within 90 and 270 days, respectively. Sorption characteristics of these natural sorbents allow them to be recommended for water decontamination from ⁹⁰Sr and ¹³⁷Cs.     

Effect of Site-Specific Parameters on the Transfer of 137Cs and 90Sr into Freshwater Fishes1,2

The content of ¹³⁷Cs in fallout, fish, and water was measured with the aim to study the role of site-specific parameters on the transfer of ¹³⁷Cs into fishes. The temporal changes of 137Cs and 90Sr in various types of fishes were studied at two sites of Lake Saimaa. The ¹³⁷Cs content in fishes in the Ukonvesi area, which is the north-western part of the lake, was clearly lower than that in the southern parts of the lake, in Ala-Saimaa, although the fallout of ¹³⁷Cs to the Ukonvesi area was somewhat higher than that to Ala-Saimaa. The fallout in 1986 was about 6 kBq m^{- 2} to the Ukonvesi area and about 3 kBq m^{- 2} to the southern parts of the lake. The ¹³⁷Cs content in fishes was the highest in 1988-1989 in Ala-Saimaa, approximately 700 Bq kg^{- 1}, while that in the Ukonvesi area was only about 300 Bq kg^{- 1}, where the values were the highest in 1987. In Ukonvesi the ¹³⁷Cs content in fishes decreased rapidly, being already in 1990 almost at the same level as in 2000. In the southern parts of the lake the decrease in the ¹³⁷Cs content in fishes was much slower. Also the ⁹⁰Sr content in fishes in Ukonvesi was lower than that in Ala-Saimaa. The ¹³⁷Cs content of the water in the Ukonvesi area decreased rapidly, being about 7 Bq m^{- 3} in 1998, while that in the lower areas of the lake was still 15 Bq m^{- 3} in 2000. The ⁹⁰Sr content in water was approximately the same at the both sampling sites (7-8 Bq m^{- 3}). The water chemical parameters, such as potassium, total phosphorus, total nitrogen, chlorophyll a, and electrical conductivity were significantly higher in Ukonvesi than in Ala-Saimaa.     

Radioactive Fallout and Accumulated Level of Soil Surface Contamination with 90Sr and 137Cs around St. Petersburg in 1954-1999

Systematic data on radioactive atmospheric fallout in 1954-1999 and accumulated levels of contamination of the soil-vegetable cover with ⁹⁰Sr and ¹³⁷Cs around St. Petersburg, estimated on 1998, are presented. Comparative analysis is made of these data and directly obtained data on the vertical distribution of these radionuclides in the surface horizon (0-25 cm) of soddy-podzolic sandy loam soil: the levels of surface contamination with ^90Sr and ¹³⁷Cs were found to be 580±90 and 6500±600 Bq m^-2 on 1998. Before April 28, 1986 the ⁹⁰Sr and ¹³⁷Cs radioactivity in the investigated region corresponded to the global level. After Chernobyl accident the contamination levels with ⁹⁰Sr and ¹³⁷Cs increased, respectively, from 1200 to 1280 (by 6.3%) and from 2400 to 7050 Bq m^-2 (by a factor of 2.9). The ⁹⁰Sr and ¹³⁷Cs vertical distributions throughout the soil profile are considerably different: ¹³⁷Cs is practically totally fixed in the surface horizon, its activity being exponentially declining; whereas the stock of ⁹⁰Sr in horizons 0-10 and 0-25 cm represents only 22 and 59% of the integral accumulated inventory of ⁹⁰Sr in the soil (990 Bq m^{- 2}). The activity ratio of ¹³⁷Cs to ⁹⁰Sr in the atmospheric fallout in 1963-1985 was 1.85±0.42, and in river water in the same period, ca. 0.18, suggesting higher mobility in the soil of ⁹⁰Sr as compared to ¹³⁷Cs, and, therefore, higher rate of self-cleaning of the surface soil horizon with respect to ⁹⁰Sr.     

From global <Superscript>137</Superscript>Cs to determinations of the sedimentation rate in deep lakes and sea estuaries

Sedimentation rate in deep lakes and estiaries of the Baltic, Pechora, and Laptev Seas was determined using global ¹³⁷Cs as a sedimentogenesis marker. The sedimentation rate in Lake Ladoga and Levinson- Lessing Lake was 0.3–3 mm year^?1, and that in estuaries of the Baltic, Pechora, and Laptev Seas was 0.74–1.76, 1.0, and 3.3–5.0 mm year^?1, respectively. At a sedimentation rate of >1–2 mm year–1, the concentration peaks of global and “Chernobyl” ¹³⁷Cs in the bulk of the bottom sediments do not overlap, and the sedimentation rate is estimated for each kind of nuclides separately. At a sedimentation rate of <1 mm year^?1, “Chernobyl” ¹³⁷Cs + ¹³⁷Cs from dumping into sea mask in the bottom sediments the subsurface maximum of the global ¹³⁷Cs concentration and prevent the sedimentation rate determination. The use of ¹³⁷Cs for sedimentation rate determinations is appropriate for the poorly studied shelf zone of Russian Arctic seas.     

Distinctive Features of the Formation and Migration of Radioactive Contamination in the Iput River after the Accident at the Chernobyl Nuclear Power Plant

With the example of the Iput river, studies are performed and based on them an analysis is made of the formation of contamination of elements of a river system by radionuclides ¹³⁷Cs and ⁹⁰Sr after the accident at the Chernobyl Nuclear Power Plant. It has been revealed that before the years 1990–1994 the contamination of the river system was mainly formed by the primary fallout of radionuclides on the water surface of the river but after the year 2000 it will be determined only by the ingress of radioactive contaminants with surface flow from a water catchment. The studies have shown that the contamination of the Iput river in the territory of Belarus is substantially influenced by the transfrontier transfer of radionuclides from the territory of Russia. According to our estimates, at the end of 1986, this contribution amounted to 30% for ¹³⁷Cs and 96% for ⁹⁰Sr; as of now, it is 86% and 65% for ¹³⁷Cs and ⁹⁰Sr, respectively.     

Role of Suspended Matter and Dissolved Organic Substances in Behavior and Migration of Anthropogenic Radionuclides in River-Sea Aquatic Systems

Distribution of Cs, Sr, and Pu nuclides between suspended matter and the aqueous phase and the features of interaction of these radionuclides with dissolved organic matter are studied, to gain a better insight into the radionuclide behavior in the Ob and Yenisei estuaries and adjacent Kara Sea. For radionuclide speciation, the experimental study included determination of the radionuclide activities in aqueous solutions after filtration and ultrafiltration of large-volume water samples and membrane fractionation of small-volume water samples by passing the solution through a cartridge with filters of regularly decreasing pore size followed by mass-spectrometric determination of elements. In the water-soluble fraction, the ¹³⁷Cs activity increases with increasing salinity, whereas that of ⁹⁰Sr decreases, which can be attributed to the differences in the physicochemical behavior of the radionuclides in solutions and also to the effect of contamination sources. In seawater, suspended material can retain 1-10% of ¹³⁷Cs and ⁹⁰Sr. In the estuarine zones, these values can be 20-40%. More than 50% of ⁹⁰Sr and ^239,240Pu are associated with dissolved organic matter. In saline water this effect is less pronounced.     

Aluminosilicophosphate geoceramics as matrices for the immobilization of partitioned 90Sr and 137Cs wastes

Immobilization of ⁹⁰Sr and ¹³⁷Cs in geoceramic matrices synthesized on the basis of phosphatized calcinate of simulated radioactive wastes and apatite ore dressing tailings is studied. The samples were sintered at 950–1150°C for 1 h. Leaching tests were carried out at 90°C with double-distilled water in the quasiflow and accumulative modes. The leaching was monitored by the conductivity of the liquid phase. To estimate the leaching rates R, the Na, Cs, and Sr concentrations were measured by flame photometry. The best samples of geoceramics are characterized by R of (5–15) × 10^?6 and <0.3 × 10^?6 g cm^?2 day^?1 with respect to Cs and Sr, respectively. Aluminosilicophosphate geoceramics show promise as materials for immobilization of partitioned ⁹⁰Sr and ¹³⁷Cs radioactive wastes.     

Sorption of 137Cs and 90Sr by potassium production wastes, clay-salt slimes

Sorption of ¹³⁷Cs and ⁹⁰Sr by clay-salt slimes from model aqueous salt solutions (4.0–40.0 g l^?1 NaCl + KCl) was studied under static conditions. The influence of the sorption parameters (time, specific consumption, salt content) on the efficiency of the ¹³⁷Cs and ⁹⁰Sr recovery with finely dispersed sorbents was studied. The activity of the aqueous salt solution decreases by two orders of magnitude owing to the recovery of ¹³⁷Cs.     

Effect of basic chemical characteristics of soils on mobility of radionuclides in them

Interplay between the basic chemical characteristics of soils of the Belarussian Polessie and the tightness of fixation of Chernobyl-derived ¹³⁷Cs and ⁹⁰Sr in them is studied. The mobility of radionuclides in the soil proved to be controlled essentially by the soil type and organic matter content. In the investigated soils, nonexchange sorption of ¹³⁷Cs and exchange sorption of ⁹⁰Sr dominate.     

Retrospective estimation of the contamination of Lake Onega with global <Superscript>90</Superscript>Sr and of natural decontamination of its water

The dynamics of the concentration of global ⁹⁰Sr in Lake Onega water for a 40-year period was reconstructed. The natural decontamination of Lake Onega water was characterized by a decrease in the ⁹⁰Sr content with the half-clearance time T = 16.5 years. By the end of formation of the major part of cumulative ⁹⁰Sr inventory in the lake ecosystem (1965), the ⁹⁰Sr inventories in water and bottom media were in 1: 1.2 ratio. By that time, only 55% of the ⁹⁰Sr ingress passed from the lake water to bottom sediments. The water exchange in the lake occurred two times faster than the ⁹⁰Sr clearance. Decelerated natural decontamination of the lake water from ⁹⁰Sr was attributed to buffer properties of the system catchment area-deep lake-river drainage. The annual removal of ⁹⁰Sr from the lake with water of the Svir River was partially compensated by the ⁹⁰Sr supply to the lake from the catchment areas of rivers flowing into the lake. The cumulative inventory of global ⁹⁰Sr in the volume of Lake Onega water during the period from 1964 to 2005 decreased by a factor of ∼5, from 10 to 1.9 TBq.     

Calculations of gamma ray incineration of 90Sr and 137Cs

The feasibility of the γ-ray incineration method, using the (γ, n) reaction, was examined for the long-lived radioactive waste ⁹⁰Sr and ¹³⁷Cs. The incineration of ⁹⁰Sr and ¹³⁷Cs as well as the buildup of long-lived radioactive by-products were calculated by changing the γ-ray flux as a parameter. The effect of alternative irradiation modes was also studied.     

Reconstruction of Global 137Cs Concentration in Lake Onega

The dynamics of global ¹³⁷Cs content in Lake Onega in the past 25 years was reconstructed. Based on a sorption-diffusion model of ¹³⁷Cs behavior in the lake water-bottom sediment system, the decontamination of the lake water from ¹³⁷Cs as influenced by natural factors was analyzed.     

Sorption of 137Cs and 90Sr Ionic Species on Soil of Various Types

Sorption of ¹³⁷Cs and ⁹⁰Sr ionic species on soils with different agrochemical features was studied. The dependence of ¹³⁷Cs sorption on peaty-bog soil on the ratio of the solid and liquid phases shows that sorption occurs by the ion-exchange mechanism. The correlation between the potassium content in soils and     

Sorption of Cs,Sr, and Y radionuclides on mixed layered double hydroxides of Mg,Al, and Nd from the aqueous phase

Sorption of ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y radionuclides from aqueous solutions on the solid phase of layered double hydroxides (LDHs) of Mg, Al, and Nd was studied. Sorption of ¹³⁷Cs from 10⁻⁵ M aqueous CsNO₃ solutions on the LDH-Mg-Al-Nd solid phase is extremely weak. At the same time, ⁹⁰Sr and ⁹⁰Y are efficiently sorbed on the LDH-Mg-Al-Nd solid phase from 10⁻⁵ M aqueous Sr(NO₃)₂ solutions. After 5-min contact of the solid and liquid phases, K _d of ⁹⁰Sr and ⁹⁰Y exceeds 10³ ml g⁻¹. With an increase in the Nd content in LDHs of mixed composition, their sorption properties toward ⁹⁰Sr and ⁹⁰Y are enhanced.     

Association of 90xSr, 137Cs, 239,240Pu, 241Am,and 244Cm with Soil Absorbing Complex in Soils Typical of the Vicinity of the Chernobyl NPP

Association of the main long-lived radionuclides ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm with various components of the soil absorbing complexes from soil samples collected along the western, northwestern, and northern tracks of radioactive fallout in the vicinity of the Chernobyl NPP was studied by the sequential leaching. In the samples of the sandy soil collected in the floodplain of the Pripyat river along the northwestern radioactive track, more than 85% of ⁹⁰Sr, 55% of ^239,240Pu, and 75% of ²⁴¹Am and ²⁴⁴Cm are associated with various components of the soil absorbing complex and are potentially mobile species. In the soil samples collected along the narrow western track, 80-85% of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm are incorporated in hot particles. The degree of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm association with different components of the soil absorbing complex is a function of the radionuclide type and physicochemical features of soil.     

Sorption of cesium and strontium radionuclides onto crystalline alkali metal titanosilicates

Sorption of tracer amounts of ¹³⁷Cs and ⁹⁰Sr radionuclides from model solutions of various compositions onto synthetic titanosilicates, framework ivanyukite and layered SL3, both synthesized at the Center for Nanomaterials Science, Kola Scientific Center, Russian Academy of Sciences, was studied. Synthetic ivanyukite and titanosilicate SL3 well compete with Termoxid-25 ferrocyanide sorbent in the ability to take up cesium from neutral NaNO₃ solutions and from a simulated solution of bottom residue from a nuclear power plant with RBMK reactors. The maximal sorption of ¹³⁷Cs onto ivanyukite is observed at pH 6–7. The dependence of the ¹³⁷Cs distribution coefficient (K _d) on ivanyukite on the concentration of sodium and potassium ions in the solution was studied. Potassium ions affect the cesium sorption more strongly than sodium ions do. In the ability to take up ⁹⁰Sr, synthetic ivanyukite well competes with synthetic zeolite of type A and with the sorbent based on modified manganese dioxide. The dependences of K _d of ⁹⁰Sr on the concentrations of the Na⁺ and Ca²⁺ ions in the solution were determined. Calcium ions affect the strontium sorption more strongly than sodium ions do. Ivanyukite and SL3 show promise as sorbents for removing cesium and strontium radionuclides from multicomponent salt solutions.     

Coprecipitation of <Superscript>137</Superscript>Cs, <Superscript>90</Superscript>Sr,and <Superscript>90</Superscript>Y from aqueous and organic solutions with triethylenediamine complexes of <Emphasis Type="Italic">d</Emphasis>-element nitrates

Coprecipitation of ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y with low-soluble complexes of nitrates of d elements (Cu²⁺, Ni²⁺, Zn²⁺) with triethylenediamine [(CH₂-CH₂)₃N₂] from aqueous and aqueous-organic solutions was studied. ¹³⁷Cs and ⁹⁰Sr do not noticeably coprecipitate with precipitates of complexes of Cu²⁺, Ni²⁺, and Zn²⁺ with (CH₂-CH₂)₃N₂ in water; in the process, the radionuclide recovery into the precipitate phase does not exceed 10%. At the same time, the degree of recovery of ⁹⁰Y reaches 65% depending on the experimental conditions. In C₂H₅OH and CH₃CN containing 9 and 5% H₂O, respectively, ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y coprecipitate with the complexes to a greater extent, with the degree of recovery varying from 30 to 97% at the molar ratio M²⁺: (CH₂-CH₂)₃N₂ = 1 : 1.     

Prediction of Migration of Radionuclides in the Iput River Basin

Based on the multichamber model, prediction evaluations of the transfer of ¹³⁷Cs and ⁹⁰Sr in the Iput river for 100 years after the Chernobyl accident have been performed. In the course of investigation, the indicated time range was subdivided into three periods: the first period covered April–December of 1986 (retrospective evaluation), the second period embraced the years 1987–2000, and the third period covered the years 2000–2080 (long-term prediction). The prediction evaluations of migration of radioactive contaminants in the Iput river have shown that over the course of a century the concentrations of ¹³⁷Cs in the Iput river network will decrease nearly 3000 times and the concentrations of ⁹⁰Sr will decrease 10,000 times. However the levels of contamination of the river systems by these radionuclides will remain rather high.     

Sorption Recovery of 137Cs and 90Sr with Carbonate-Containing Natural Mineral Tripolite

The sorption characteristics of a carbonate-containing mineral (tripolite) were studied on model aqueous solutions and real wastewaters in a wide range of pH in the presence of isotopic and nonisotopic carriers and organic impurities. The sorption of ¹³⁷Cs and ⁹⁰Sr is adequately described by a power function. Analysis of ¹³⁷Cs sorption isotherms suggests that radiocesium is adsorbed by the ion-exchange mechanism, during which Cs⁺ ions from the solution exchange mainly with bivalent ions of the sorbent, whereas in ⁹⁰Sr sorption trivalent ions of the sorbent also participate in the process. The saturation capacities of tripolite with respect to cesium and strontium were evaluated to be 0.3 and 1.0 mg-equiv g^{- 1}, respectively.