Radioactive Contamination of Alluvial Soils in the Taiga Landscapes of Yakutia with <Superscript>137</Superscript>Cs, <Superscript>226</Superscript>Ra,and <Superscript>238</Superscript>U

The concentrations and distribution of ¹³⁷Cs in alluvial soils (Fluvisols) of the upper and middle reaches of the Markha River in the northwest of Yakutia and ²²⁶Ra and ²³⁸U in alluvial soils within the El’kon uranium ore deposit in the south of Yakutia have been studied. It is shown that the migration of radiocesium in the permafrost-affected soils of Yakutia owing to alluviation processes extends to more than 600 km from the source of the radioactive contamination. The migration of ¹³⁷Cs with water flows is accompanied by its deposition in the buried horizons of alluvial soils during extremely high floods caused by ice jams. In the technogenic landscapes of southern Yakutia, active water migration of ²³⁸U and ²²⁶Ra from radioactive dump rocks. The leaching of ²³⁸U with surface waters from the rocks is more intense than the leaching of ²²⁶Ra. The vertical distribution patterns of ²³⁸U and ²²⁶Ra in the profiles of alluvial soils are complex. Uranium tends to accumulate in the surface humus horizon and in the buried soil horizons, whereas radium does not display any definite regularities of its distribution in the soil profiles. At present, the migration of ²³⁸U and ²²⁶Ra with river water and their accumulation in the alluvial soils extend to about 30 km from the source.     

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.     

<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.     

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.     

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.     

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.     

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.     

Adaptive Capability of the VERT_MIG Algorithm to Simulate Vertical Migration of Radionuclides in Soils

The possibility of using the VERT_MIG algorithm in simulation models of the vertical migration of radionuclides in soil is discussed. The algorithm was successfully used to develop models of ¹³⁷Cs and ⁹⁰Sr migration for radioactive contamination of different soils as a result of the accidents at the Chernobyl and Fukushima-1 nuclear power plants. The modeling results are given. Prospects for further use of this algorithm and some aspects of using imitation modeling in this area are discussed.     

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.     

Potential Remediation of 137Cs and90 Sr Contaminated Soil by Accumulation in Alamo Switchgrass

Cesium-137 (¹³⁷Cs) and Strontium-90 (⁹⁰Sr) are radionuclides characteristic of nuclear fallout from nuclear weapons testing and nuclear reactor accidents. Alamo switchgrass (Panicum virginatum L.) is a perennial C⁴ species native to central North America that produces exceptionally high biomass yields in short periods of time. In three separate experiments, Alamo switchgrass plants were tested for their ability to accumulate ¹³⁷ Cs and⁹⁰ Sr from a contaminated growth medium. Plants in experiment 1 were grown in 33 × 20 × 7 cm plastic pans containing 2.5 kg sand. Plants in experiments 2 and 3 were grown in 30 × 3 cm diameter test tubes containing 0.3 kg growth medium. After 3 months of plant growth, either 102 Bq ¹³⁷Cs or 73 Bq⁹⁰ Sr g^?1 soil were added to the growth medium. Plants in all three experiments were grown within a greenhouse that was maintained at 22 ± 2 °C with a photosynthetic active radiation of 400–700 µmol m^?2 s^?1 and a 14–16 h photoperiod. Above-ground plant biomass did not differ between plants that were not exposed to these radionuclides (controls) and those that were exposed to growth medium containing ¹³⁷Cs or⁹⁰ Sr over the course of the experiment. Plants accumulated 44 and 36% of the total amount of ⁹⁰Sr and¹³⁷ Cs added to growth medium after the first 5 harvests. After the first two harvests, the concentration of ¹³⁷Cs and⁹⁰ Sr in plant tissue and the amount of ¹³⁷Cs or⁹⁰ Sr removed from growth medium declined with each successive harvest. Duration of exposure correlated curvilinearly with accumulation of both ⁹⁰Sr and ¹³⁷Cs by plants (r² = 0.95 and 0.78, respectively). As concentration of both ¹³⁷Cs and ⁹⁰Sr in growth medium increased, plant accumulation of both radionuclides increased and correlated curvilinearly in seedlings (r² = 0.83 and 0.89 respectively).     

Sources and behavior of anthropogenic radionuclides in the Ottawa river waters

Multiphase radionuclide measurements on Ottawa River waters are reported for the period October 1984 to March 1986. Numerous radionuclides are present in detectable amounts in raw, drinking and centrifuged waters as well as in suspended sediment and water filtration plant floc samples. The sediment/water partitioning behavior of these radionuclides is also reported. The prevailing low particle flux allows rapid migration of radionuclides through the system. Most of the ⁹⁰Sr in the river derives from its fallout inventory in the watershed rather than from the Chalk River Nuclear Laboratories (CRNL). On the other hand, fallout and CRNL-derived ¹³⁷Cs appear to contribute equally to the prevailing levels of this radionuclide in the river. The data also suggest that the prevailing levels of the naturally-occurring ²²⁶Ra impart more dose than ⁹⁰Sr insofar as the radiological quality of the drinking water is concerned. Many of the radionuclides are removed by the floc during filtration of the receiving waters. Though their removal efficiencies cannot be precisely defined from the currently available measurements, the results show that processes other than simple association with suspended sediments may also play significant role in the retention of some radionuclides by the floc.     

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.     

Influence of Organic Amendments on the Accumulation of 137Cs and 90Sr from Contaminated Soil by Three Grass Species

Bahia grass (Paspalum notatum), johnson grass (Sorghum halpense) and switchgrass (Panicum virginatum) werecompared for their ability to accumulate ¹³⁷Csand ⁹⁰Sr from three different contaminated soilsin the presence and absence of either sphagnum peator poultry litter amendments. Above-ground plantbiomass did not differ between plants that were notexposed to these radionuclides and those that wereexposed to soil containing ¹³⁷Cs or ⁹⁰Sr.After three harvests, bahia, johnson and switchgrassplants accumulated from 17.2 to 67.3% of the¹³⁷Cs and from 25.1 to 61.7% of the ⁹⁰Sradded to the soil. Poultry litter and peat mossamendments increased aboveground plant biomass,activity of ¹³⁷Cs or ⁹⁰Sr in plant tissue, %accumulation of ¹³⁷Cs or ⁹⁰Sr from soil andthe plant bioconcentration ratio at each harvestcompared to the control (no amendment) treatment. Thegreatest increases in plant biomass, and radionuclideaccumulation were observed with poultry litter foreach of the three grass species. Johnson grass hadgreater aboveground plant biomass, activity of¹³⁷Cs and ⁹⁰Sr in plant tissue, %accumulation of ¹³⁷Cs or ⁹⁰Sr from soil andbioconcentration ratio in each soil amendment, at eachharvest compared to bahia and switchgrass. Thegreatest accumulation of ¹³⁷Cs and ⁹⁰Sr wasmeasured in johnson grass grown in soil that wasamended with poultry litter. These results suggestthat plant species selection and agronomic practicesmay need to be considered to maximize phytoremediationof radionuclide contaminated soils.     

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.     

Influence of rehabilitation measures on <Superscript>137</Superscript>Cs uptake by crops from soils contaminated during the Chernobyl NPP accident

The dynamics of ¹³⁷Cs uptake by crops and the influence of rehabilitation measures on the accumulation of this radionuclide in agricultural products have been estimated by the example of southwestern regions of Bryansk oblast. In 20 yr after the Chernobyl NPP accident, three stages of a decrease in the concentration of ¹³⁷Cs in the crops can be distinguished. At present (in 15–20 yr after the accident), the rate of the decrease in the concentration of ¹³⁷Cs in some crops corresponds to the half-decay period of this radionuclide.     

Assessment of Radionuclides, Trace Metals and Radionuclide Transfer from Soil to Food of Jhangar Valley (Pakistan) Using Gamma-Ray Spectrometry

The gamma spectrometric analysis of soil and essential foodstuffs, e.g., wheat, millet, potato, lentils and cauliflower, which form the main component of the daily diet of the local public, was carried out using high purity germanium (HpGe) detector coupled with a computer based high-resolution multi-channel analyzer. The activity concentration in soil samples for ²²⁶Ra, ²³²Th and ⁴⁰K ranged from 30.0 Bq kg^?1 to 81.2 Bq kg^?1, 31.4 Bq kg^?1 to 78.25 Bq kg^?1 and 308.8 Bq kg^?1 to 2177.6 Bq kg^?1, with mean values of 56.2, 58.5 and 851.9 Bq kg^?1, respectively. The average activity measured for ²²⁶Ra, ²³²Th and ⁴⁰K in soil samples was found higher than the world average. The major radionuclide found in the food items studied was ⁴⁰K, while ²²⁶Ra, ²³²Th and ¹³⁷Cs were detected in very nominal amounts. The results clearly indicate that these radionuclides have no health hazard to human beings, as they are well below the annual limit of intake (ALI) for these radionuclides. The transfer factors of these radionuclides from soil to food were also studied. The mean transfer factors of ⁴⁰K, ²²⁶Ra, ²³²Th and ¹³⁷Cs from soil to food were estimated to be about 0.17, 0.07, 0.16 and 0.23, respectively. An artificial radionuclide, ¹³⁷Cs, was also present in detectable amount in all samples. The internal and external hazard indices were measured and had mean values of 0.70 and 0.55, respectively. Absorbed dose rates and effective dose have been determined in the present study. Concentration of trace metals, such as Cr, Pb, Ni and Zn, was also determined in the soil samples. The concentrations of radionuclides and trace metals found in these samples during the present study were nominal and do not pose any potential health hazard to the general public.     

The modern radioecological situation at the Globus-1 site

This article is dedicated to analysis of the modern radioecological situation at the site of the Globus-1 peaceful nuclear explosion in the Ivanovo region. The variability of the ionizing radiation background, specific activity of ¹³⁷Cs and ⁹⁰Sr in the 0–20 cm soil layer, and dominant species of meadow vegetation near the site of the explosion are presented. Higher levels of ⁹⁰Sr contamination of plants in this territory and water from a research well were determined. The indices of contamination of the meadow biogeocoenosis components according to ¹³⁷Cs did not exceed the established norms.