Contamination of terrestrial ecosystem components with <Superscript>90</Superscript>Sr, <Superscript>137</Superscript>Cs,and <Superscript>226</Superscript>Ra caused by the deterioration of the multibarrier protection of radioactive waste storages

The spatial-temporal features of the radioactive contamination of terrestrial ecosystem components caused by the deterioration of the multibarrier protection of regional radioactive waste storages of the State Research Center of the Russian Federation-Leipunskii Institute of Physics and Power Engineering at the input of radionuclides into the soil and ground water were studied. The composition of the radioactive contamination was determined, and the hydrological and geochemical processes resulting in the formation of large radioactive sources were described. The natural features of the radioactive waste storage areas favoring the entry of ⁹⁰Sr, ¹³⁷Cs, and ²²⁶Ra into the soils and their inclusion in the biological turnover were characterized. The directions of the horizontal migration of ⁹⁰Sr, ¹³⁷Cs, and ²²⁶Ra and the sites of their accumulation within the superaquatic and aquatic landscapes of a near-terrace depression were studied; the factors of the ⁹⁰Sr accumulation in plants and cockles were calculated. The results of the studies expand the theoretical concepts of the mechanisms, processes, and factors controlling the behavior of radionuclides at the deterioration of the multibarrier protection of radioactive waste storages. The presented experimental data can be used for solving practical problems related to environmental protection in the areas of industrial nuclear complexes.     

Vertical distribution of <Superscript>137</Superscript>Cs in alluvial soils of the Lokna River floodplain (Tula oblast) long after the Chernobyl accident and its simulation

Profiles of vertical ¹³⁷Cs distribution in alluvial meadow soils on the low and medium levels of the Lokna River floodplain (central part of the Plavsk radioactive spot in Tula oblast) 28 years after the Chernobyl fallout have been studied. A significant increase in the ¹³⁷Cs pool is revealed on the low floodplain areas compared to the soils of interfluves due to the accumulation of alluvium, which hampers the reduction of the total radionuclide pool in alluvial soils because of radioactive decay. The rate of alluvium accumulation in the soil on the medium floodplain level is lower by three times on average. An imitation prognostic model has been developed, which considers the flooding and climatic conditions in the region under study. Numerical experiments have quantitatively confirmed the deciding role of low-mobile forms in the migration of maximum ¹³⁷Cs content along the soil profile in the absence of manifested erosion–accumulation processes.     

Concentrations of Radionuclides (<Superscript>226</Superscript>Ra, <Superscript>232</Superscript>Th, <Superscript>40</Superscript>K,and <Superscript>137</Superscript>Cs) in Chernozems of Volgograd Oblast Sampled in Different Years

Data on the concentrations of natural (²²⁶Ra, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides and on the physicochemical properties of chernozems sampled in different years are presented. In 1952, upon the creation of the Penza-Kamensk state shelterbelt, three deep (up to 3 m) soil pits were examined within the former arable field under two-year-old plantations of ash and maple along the transect crossing the territory of the Beloprudskaya Experimental Station of the USSR Academy of Sciences in Volgograd oblast. The samples from these pits were included into the collection of dated soil samples of the Dokuchaev Central Soil Science Museum. Five pits were examined along the same transect in 2009: three pits under shelterbelts (analogues of the pits studied in 1952) and two pits on arable fields between the shelterbelts. In the past 57 years, certain changes took place in the soil structure, bulk density, and the content and composition of humus. The salt profile of soils changed significantly under the forests. The comparison of distribution patterns of natural soil radionuclides in 1952 and 2009 demonstrated their higher contents at the depth of 10–20 cm in 2009 (except for the western shelterbelt). Background concentrations of natural radionuclides in parent materials and relationships between their distributions and the salt profiles of soils have been determined; they are most clearly observed is the soils under shelterbelts. Insignificant contamination with ¹³⁷Cs (up to 34 Bq/kg) has been found in the samples of 2009 from the upper (0–20 cm) horizon. The activity of ¹³⁷Cs regularly decreases from the east to the west; the highest concentrations of this radionuclide are found in the topmost 10 cm. This allows us to suppose that ¹³⁷Cs was brought with aerial dust by eastern winds, and the shelterbelts served as barriers to the wind flow.     

Distribution of <Superscript>137</Superscript>Cs in the particle-size fractions and in the profiles of alluvial soils on floodplains of the Iput and its tributary Buldynka Rivers (Bryansk oblast)

Pits of sandy alluvial soils were studied in different parts of the floodplains of the Iput River and its tributary the Buldynka River near the settlement of Starye Bobovichi (Bryansk oblast). The ¹³⁷Cs content in the soil horizons varied from 0.01 to 31.2 Bq/g reaching the maximum in the initially polluted layers buried at depths of 6 to 40 cm. Radiocesium was found in all the particle-size fractions with its predominate concentration in the finest fractions. The specific ¹³⁷Cs activity in the fractions of <1, 1–5, 5–10, and >10 μm comprised 44.1 ± 11.5; 33.3 ± 7.6, 20.9 ± 4.9, and 2.4 ± 0.6 Bq/g of soil. However, the contribution of the coarse (>10 μm) fractions to the total radiocesium pool in the soils (19–60%, or 34 ± 2% on the average) was comparable with that of the clay fraction (16–71%, or 38 ± 3% on the average), because of the predominance of the sand-size fractions in the soils. The highest coefficient of variation with respect to the relative contribution of particular fractions to the total soil pool of ¹³⁷Cs was characteristic of the fraction of 5–10 μm; in the other fractions, it varied from 31 to 41%. The portion of ¹³⁷Cs bound with the finest fractions increased in the deeper layers. The total ¹³⁷Cs activity in the polluted horizons of the soils was mainly determined by its concentration in the clay fraction (Spearman’s coefficient of rank correlation (r) for the moderately polluted horizons comprised 0.926 at n = 14). It was experimentally proved that clay particles, upon the destruction of organic films on their surface, could readsorb the released radiocesium for a second time.     

秦山核电站周围农业生态环境放射性本底调查

本研究调查了秦山核电站站址周围50km半径范围内土壤、水和农作物的总α、总β放射性水平,土壤中天然放射性核素含量,以及γ外照射积累剂量。结果表明:土壤中总α、总β值分别为0.54—1.48×10~(-8)Ci/kg和1.90—2.96×10~(-8) Ci/kg,低于全国一般地区平均水平,且0—100cm土层变化不大。土壤中~238U、~226Ra、~232Th、~40k、~137Cs的放射性活性分别为0.67—5.00×10~(-9)、4.49—11.4×10~(-10)、0.88—1.69×10~(-9)、0.39—2.09×10~(-8)和0.89—4.32×10~(-10)Ci/kg。河水、湖水以及核电站废水排放口处海水总β值分别为1.32—8.62、3.6和2.55×10~(-12)Ci/L。大米和油菜叶中的总β值分别为2.53和3.0×10~(-9)Ci/kg。室内外月平均γ照射量各为10.6—14.7和9.16—13.7mR。     

<Superscript>137</Superscript>Cs in natural ecosystem components within the 30-km impact zone of the Smolensk nuclear power plant

The accumulation and redistribution of ¹³⁷Cs in natural ecosystems within the 30-km impact zone of the Smolensk nuclear power plant (SNPP) are analyzed. It is shown that the radioactive pollution of this territory is mainly due to the Chernobyl-derived radioactive fallout. However, the radioactive decay of ¹³⁷Cs from the Chernobyl disaster is partly compensated for by the ¹³⁷Cs technologic emission from the SNPP. The highest rate of the vertical migration of ¹³⁷Cs is typical of the bog phytocenoses and deciduous forests. The components of biota may be ranked by their capacity for ¹³⁷Cs accumulation as follows: higher fungi > mosses > herbs and shrubs > trees. The organisms and their parts that may serve as bioindicators of the modern radioactive contamination of the territory have been identified. These are the assimilative organs and bark of the trees, various fern species among herbs, sphagnum mosses and Pleurozium schreberi (among mosses), and Typolius felleus among higher fungi.     

Dynamics of Chernobyl <Superscript>137</Superscript>Cs contamination fields at long distances

Structural changes in the ¹³⁷Cs contamination fields in natural and agroecosystems of the northern forest steppe (the remote zone of the Chernobyl accident) were studied. It was shown that the lateral and vertical distribution of ¹³⁷Cs in soils of different biogeocenoses depends on the features of functioning biogeocenoses and the spatial variation of the initial fallout. The effect of biogeocenosis on the spatial variation of the contaminant distribution increases with time. At present, the variation of primary distribution in soils of agrocenoses is changing. The soils of forest biogeocenoses have retained the features of primary distribution, particularly in the upper 0-to 5-cm sublitter layer. The ¹³⁷Cs penetration depth is greatest in the soils of layland and functioning agrocenosis and least in the soils of forest biogeocenoses.     

Agroecological optimums concerning saturation with calcium of soils contaminated by <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr

A close negative correlation between the biological availability of ⁹⁰Sr and ¹³⁷Cs for agricultural crops and the content of exchangeable calcium in soils has been revealed in a field experiment performed for soddy-podzolic loamy sandy soil. The efficiency of soil saturation with exchangeable calcium regarding ⁹⁰Sr discrimination is much higher in soils with a low supply of plants with this nutrient. For the bulk of the studied crops, the minimal biological availability of ⁹⁰Sr is registered at 1200–1400 mg/kg (6.0–7.0 mg-equiv./100 g) of the exchangeable calcium content in the soil and that of ¹³⁷Cs is registered at 1000–1100 mg/kg (5.0–5.5 mg-equiv./100 g). The crop productivity varies significantly depending on the exchangeable calcium content in the soil.     

The effect of tree roots on the redistribution of <Superscript>137</Superscript>Cs in the soils of pine and birch forests of the radioactive contamination zone

Accumulation and distribution of ¹³⁷Cs by the root systems of forests in the radioactive contamination zone of Bryansk oblast have been discussed. It has been found that the phytomass and distribution of roots of pine and birch trees along the soil profile in the studied BGCs differ considerably. The specific activity of ¹³⁷Cs in the roots changes depending on their diameter: the lowest specific activity is observed in small fractions of the roots, and the highest one in large fractions. It has been shown that the contribution of roots in the total reserves of ¹³⁷Cs in the soil layer of 0–50 cm of various biogeocenoses is different: the largest contribution is characteristic for birch forests (1.66%) with variation of this parameter in separate soil layers from 1.12 to 3.53%, while the contribution for pine forests is lower (0.97%) with the variation from 0.82 to 7.5%. The contribution of roots to the overall contamination of soils in the studied plant communities increases with depth.     

The role of mineralization of the organic matter of soddy-podzolic and peat bog soils in the accumulation of <Superscript>137</Superscript>Cs by plants

The role of mineralization of soil organic matter (SOM) in the mobilization of ¹³⁷Cs was estimated on the basis of data on the biokinetic fractionation of the organic matter of soddy-podzolic sandy-loam and peat bog soils and on the coefficients of the soil-to-plant transfer of radiocesium under field conditions. The peat bog soils were richer than the soddy-podzolic soils in the total organic carbon (by 7.9–23.8 times), the potentially mineralizable carbon (by 2.4–6.5 times), and the carbon of the microbial biomass (by 2.9–4.6 times). The agricultural use of the soddy-podzolic and peat bog soils led to a decrease in the SOM mineralization capacity by 1.1–1.8 and 1.4–2.0 times, respectively. Simultaneously, the portions of the easily, moderately, and difficultly mineralizable fraction of the SOM active pool changed. The coefficients of the ¹³⁷Cs transfer from the peat bog soils to plants were 3.3–17.6 times higher than those for the soddy-podzolic soils. The content of ¹³⁷Cs in plants grown on the peat bog soils was 2–65 times higher than that in the mobile (salt-extractable) soil pool by the beginning of the growing season. Strong positive linear correlations were found between the coefficients of the soil-to-plant transfer of ¹³⁷Cs and the total content of the SOM, the content of the microbial biomass, the content of the potentially mineralizable carbon, and the intensity of its mineralization. It was concluded that the decisive factors controlling the intensity of the ¹³⁷Cs transfer from mineral and organic soils into plants are the SOM content and its mineralization potential. The mineralization of the SOM is accompanied by the release of both ¹³⁷Cs and mineral nitrogen; the latter facilitates the transfer of radiocesium into plants.     

Some indices of biological cycle of <Superscript>137</Superscript>Cs and <Superscript>39</Superscript>K in forest ecosystems of Bryansk woodland in the remote period after chernobyl fallouts

The features of the biological cycle of ¹³⁷Cs and ³⁹K in the remote period after Chernobyl fallouts are considered on the example of forest ecosystems of Bryansk woodland. It is demonstrated that the maximum amount of ¹³⁷Cs in the total phytomass is concentrated in wood, the minimum amount of ¹³⁷Cs, in the external bark layers; for the annual production, in assimilating organs and the external bark layers, respectively. The distribution of ³⁹K in the total phytomass and the annual production is almost identical to that of ¹³⁷Cs. The arrival of ¹³⁷Cs to the soil with litter in pine and birch forests has recently been equal approximately to 50% of the capacity of the biological cycle. It mostly arrives with the assimilating organs (needles and leaves). In pine forests the return of ³⁹K into the soil with litter is closest to that observed for ¹³⁷Cs.     

Studying the kinetics of <Superscript>137</Superscript>Cs selective sorption by the dynamic method with the measurement of radioactivity in the sorbent solid phase

The dynamic method was proposed for studying the kinetics of ¹³⁷Cs selective sorption by the measurement of the ¹³⁷Cs activity directly in the sorbent solid phase. A thin layer of the sorbent in a disposable syringe membrane filter (MF) was eluted with a ¹³⁷Cs solution containing K⁺ and Ca²⁺ ions with a gradual decrease in the solution flow rate from 6 to 0.2 cm³/min. The activity of the sorbed ¹³⁷Cs was determined periodically by placing the same MF in the detector well of a Wizard 1480 gamma counter. It was shown that the masses of the sorbent and water in the MF had no effect on the efficiency of the ¹³⁷Cs measurement. A linear relationship between the RIP(K) value and the square root of the time for the period between 4 and 30 days was revealed using this method. The relative increase in the RIP(K) with time changed by 6 times (from 0.034 to 0.208 days^−0.5) for the soils and by 20 times (from 0.008 to 0.153 days^−0.5) for the mineral sorbents. The RIP(K) values measured for the interaction of soddy-podzolic soils with ¹³⁷Cs during 24 hours using the standard limited volume method were lower than the values determined by the proposed dynamic method for the interaction period of 30 days by 50–100%.     

Radioactivity of Selected Agricultural Soils in Croatia: Effects of Soil Properties,Soil Management,and Geological Parameters

We present a study on the radioactivity of selected Croatian agricultural soils that vary considerably with respect to geological background; physical, chemical, and biological characteristics; soil type; land use; and soil management. Our investigation is focused on the main naturally occurring radionuclides (⁴⁰K, ²³⁸U, ²²⁶Ra, ²³²Th, ²³⁵U) and ¹³⁷Cs as the most threatening long-lived anthropogenic radionuclide. We find that the radioactivity level is not influenced by the application of different soil amendments, at least in moderate quantities, and that no effect of soil management can be detected as well. In contrast, geological and location-specific properties influence radionuclide content in soil, especially regarding the naturally occurring ones. Moreover, physical and chemical soil properties such as texture and soil adsorption complex, respectively, seem to be the main factors regarding fixation of ¹³⁷Cs in soil. Calculated dose rates for external exposure to the gamma radiation originating from soil have been found to be generally low, except for two locations where they are higher but not at a level that would lead to health problems for workers on the field.     

The exchangeable fraction of selectively sorbed <Superscript>137</Superscript>Cs in soils and natural sorbents as a function of the K<Superscript>+</Superscript> and NH<Stack><Subscript>4</Subscript><Superscript>+</Superscript></Stack> concentrations

The exchangeable portion of the selectively sorbed ¹³⁷Cs extractable by a 1 M ammonium acetate solution (α _Ex ) for soils, illite, bentonite, and tripolite was found to increase with the increasing concentration of the competitive cation M⁺ (K⁺ or NH₄⁺) and can be approximated by a logarithmic relationship. For clinoptilolite, the values of α _Ex did not depend on the concentration of M⁺. The expression 1 − α _Ex (C _M=n )/α _Ex (C _M = 16) as a function of the M⁺ concentration (where α _Ex (C _M=n ) is the α _Ex value at the competitive cation concentration equal to 16 mmol/dm³) was proposed to compare the dependence of α _Ex on the concentration of K⁺ or NH₄⁺in different sorbents. For soils and illite, these dependences almost coincided, which indicated that the selective sorption of ¹³⁷Cs in soils is determined by the presence of illite-group minerals.     

Distribution and mobility of radiocesium in relation to the clay fraction mineralogy and soil properties in the Iput River floodplain

The role of the mineralogy of the clay fraction and the physicochemical properties of alluvial soils in the floodplain of the Iput River and its tributary the Buldynka River (in the region of the settlement of Starye Bobovichi in Bryansk oblast) in the distribution and immobilization of radioactive isotope ¹³⁷Cs from the atmospheric fallout after the Chernobyl accident was studied. The soils had a sandy texture; a significant variation in the content of amorphous iron oxides (0.1–0.77%) and labile manganese (11.2–193 mg/kg), the cation exchange capacity (6.1–54.2 meq/100 g soil), and the base saturation (29–100%) was common; an appreciable content of X-ray amorphous mineral substances in the clay fraction (<1 μm) enriched with organic carbon (7.7–13.1%); the predominance of trioctahedral hydromicas (Me=50%) in the clay fraction; and the presence of fine-disperse quartz and lepidocrocite. The specific activity of the ¹³⁷Cs in the clay fraction of the moderately and strongly contaminated layers increased with the increasing portion of smectite formations and (or) hydromicas. On the whole, the presence of the clay fraction favored a decrease in the ¹³⁷Cs mobility (the correlation between its content and that of exchangeable cesium was r=?0.608, n=17). However, the portion of exchangeable radiocesium (extracted with 1 M CH₃COONH₄, 1:10) had a tendency toward an increase with increasing content of hydromicas in the clay fraction. Thus, the minerals of this group were a potential source of exchangeable ¹³⁷Cs in the soils. The significant role of amorphous and mobile iron forms in the immobilization and migration of radiocesium in the secondary contaminated horizons of the alluvial soils was revealed.     

Role of plants in the spatial differentiation of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr statuses on the aggregate level

The increased concentration of an element in plant biomass compared to the soil mass is an essential condition for the differentiated spatial distribution and status of the element on the aggregate level. Two forms of this differentiation have been revealed for ¹³⁷Cs and ⁹⁰Sr. Transfer of ¹³⁷Cs from plant roots and concentration on the surface of soil aggregates have been established experimentally. Indirect data also point to the potential localization of ¹³⁷Cs on the surface of intraaggregate pores. The effect of radionuclide concentrating on the outer and inner surfaces of aggregates is due to the rapid and strong fixation of cesium microamounts by mineral soil components. ¹³⁷Cs from the surface of aggregates is more available for the repeated uptake by plant roots than from the intraped mass. The distortion of this spatial differentiation mainly occurs during the reaggregation of soil mass, which in turn decreases the availability of the radionuclide to plants. For ⁹⁰Sr, its elevated concentration in the form of organic residues has been revealed in the inter- and intraaggregate pore space. However, due to the high diffusion rate, ⁹⁰Sr is relatively rapidly (during several months under pot experimental conditions) redistributed throughout the entire volume of soil aggregates and its major part gradually passes into the phase of humic compounds, to which the radionuclide is bound by exchange sorption. The high level of the next root uptake (higher than for ¹³⁷Cs by one to two orders of magnitude) favors the permanent renewal of loci with increased ⁹⁰Sr concentrations in the inter- and intraaggregate pore space in the form of plant residues.     

Artificial and natural radionuclides in soils of the southern and middle taiga zones of Komi Republic

Specific activities of artificial (¹³⁷Cs, ⁹⁰Sr) and natural (⁴⁰К, ²³²Th, ²²⁶Ra) radionuclides in background soils of southern and middle taiga of Komi Republic have been estimated with consideration for the landscape-geochemical features of the territory. It has been shown that their accumulation and migration in soils are determined by the following factors: position in relief, texture, and organic matter content. No anomalous zones with increased contents of radionuclides in soils have been revealed.     

Radioactive contamination of permafrost-affected soils with 137Cs and 90Sr, the products of an accidental underground nuclear explosion

The specificity of contamination of permafrost-affected soils with radionuclides derived from an accidental underground nuclear explosion at the Kraton-3 polygon located in the northern taiga subzone has been studied in northwestern Yakutia. It is shown that the high density of the radioactive contamination is preserved in the soils 23 years after the nuclear accident. The concentrations of ¹³⁷Cs and ⁹⁰Sr vary from 34 to 1025 and from 57 to 781 kBq/m², respectively, which is 30–1000 times higher than the global fallout of these radionuclides.