[Spatial Distribution of ¹³7Cs in Soil of Spruce Forest in the Distant Zone of Chernobyl Fallout].

The vertical distribution of ¹³7Cs in Albeluvisols of the spruce forest in the Roslavl district of Smolensk region was investigated. The statistical characteristics of spatial variability and distribution laws for the activity con- centrations and activity depositions of ¹³7Cs in upper soil layers (forest litter, 0-5, 5-10, 10-19 cm) were de- termined. Positive correlations between the height, crown length of spruce trees and the content of ¹³7Cs in the soil under them were revealed. The regularities of spatial configuration of ¹³7Cs contamination in soil were related to the parcel structure of spruce forest. The lateral trends for distribution of 137Cs along the tessers un- der spruce and during the transfer to the open positions between the trees were recorded.

[On the problem of biodiagnostics under conditions of radioactive contamination].

The possibilities of biodiagnostics methods (bioindication and bioassay) have been analyzed for conditions of radioactive contamination of natural ecosystems components. The prospects of using biodiagnostics data to address some practical radioecology problems are discussed. The data on dynamics of long-term indicators in the ecosystems contaminated after the Chernobyl accident are shown. The authors have formulated a number of provisions relating to the accumulative bioindication for structural components of forest ecosystems (arboreal and herbaceous vegetation, mosses, lichens, higher fungi).

[Spatial variability of quasidiffusion coefficients for 137Cs in grey forest soils in the distant zone of contamination from the Chernobyl NPP].

The calculated values of quasidiffusion coefficients for 137Cs for the 15-year period after the Chernobyl fallout in the top mineral thickness of grey forest soils of the Tula region vary within 0.18-0.35 cm2/year, accruing among biogeocenoses: pine forest < oak forest < birch forest < pasture. Correlations are revealed and the equations of linear regression for quasidiffusion coefficients for 137Cs depending on soil properties are constructed. Estimates of the periods of effective residence half-time of 137Cs in grey forest soils are made: for a layer of 0-5 cm - 11-14 years 0-15 cm - 22-25 years, 0-30 cm - 27-28 years. The periods necessary for the decrease in the contents of 137Cs in a 0-5 cm layer of soils to the level of 37 kBq/m2 are considered, taking into account a spatial variation of fallout and heterogeneity of quasidiffusion. Forecasts of the vertical migration of 137Cs on the basis of the diffusive model with spatially distributed soil parameters are submitted.

[Distribution of 137Cs, 90Sr and their chemical analogues in the components of an above-ground part of a pine in a quasi-equilibrium condition].

The additional study of the distribution of radioactive isotopes of caesium and strontium and their chemical analogues in the above-ground components of pine in the remote from the accident period was carried out. The results of the research confirmed the existence of analogy in the distribution of these elements on the components of this type of wood vegetation in the quasi-equilibrium (relatively radionuclides) condition. Also shown is the selective possibility of using the data on the ash content of the components of forest stands of pine and oak as an information analogue.

[The role of vegetation cover in regulation of fluxes of the technogenic radionuclides at the different stages after radioactive fallout].

In remote period after the radioactive fallout the biological cycle of 137Cs in pine forests of northern forest-steppe zone and Bryanskoe Polissye become different. In pine forests (northern forest-steppe zone) with dark grey forest soil 137Cs flux to the soil with litterfall exceeds its influx to the vegetation by a factor of 5. Thus biological cycle of 137Cs differs from the cycle of stable K and till now its main characteristic feature is domination of 137Cs flux to the soil with litterfall. In pine forests (Bryanskoe Polissye zone) with podzolic illuvialiron sandy soil annual 137Cs influx to above-ground vegetation via root uptake exceeds its return to the soil with litterfall. Under these conditions biological cycle of 137Cs approaches it to the biological cycle of stable K.

[The comparative analysis of 137Cs, 40K, K, 90Sr and Ca allocation in builders of an ground part of wood plants in a quasi-equilibrium condition].

The examinations of allocation of radioactive isotopes of caesium and of strontium and of their chemical analogs in a stand of forest ecosystems are carried out. By results of examinations and analysis of literary data the presence of analogy in allocation of these elements on builders in quasi-balanced (concerning radionuclides) state was confirmed. The question about the opportunity of use of data about behaviour of K and of Ca is considered at an explanation of the mechanisms of redistribution of 137Cs and of 90Sr in wood plants and for buildup of mathematical models of behaviour of datas of radionuclides in ground ecosystems.

[The concentration and distribution of 137Cs in soils of forest and agricultural ecosystems of Tula Region].

The paper deals with a comparative study of 137Cs contamination in forest, old arable and cultivated soils of Tula Region. Initial interception of Chernobyl derived 137Cs is higher in forest ecosystems: oak-forest > birch-forest > pine-forest > agricultural ecosystems. Vertical migration of 137Cs in deeper layers of soils was intensive in agricultural ecosystems: cultivated soils > old arable soils > birch-forest soils > oak-forest soils > pine-forest soils. In study have been evaluated spatial variability of 137Cs in soil and asymmetrical distribution, that is a skew to the right. Spatial heterogeneity of 137Cs in agricultural soils is much lower than in forest soils. For cultivated soil are determined the rate of resuspension, which equal to 6.1 x 10(-4) day(-1). For forest soils are described the 137Cs concentration in litter of different ecosystems. The role of main accumulation and barrier of 137Cs retain higher layers of soils (horizon A1(A1E) in forest, horizon Ap in agricultural ecosystems) in long-term forecast after Chernobyl accident.

[Radioecological problems in coastal landscapes of the Sea of Azov].

The features of the spatial distribution, of the migration, and of the accumulation of natural (232Th) and manmade (137Cs) radioactive nuclides in the coastal landscapes of the Sea of Azov are studied. It was shown, that the specific activity of 232Th in the accumulation of the so-called "black sands" was shown as high as 6000 Bq/kg, that increases the natural geochemical background in 200 times. The impact of aerial transfer of the "black sands" on 232Th migration and accumulation in the soil-plant system was clarified. The 232Th distribution down the soil profile suggests that the "black sands" are likely the product of the erosion of the coastal parent materials enriched by natural radionuclides. In general, the specific activity of 137Cs in the beach sand is not high and it is close to the background (global fallout) value. It was determined that 137Cs content in the coastal ecosystems is connected only by aerial pathway as a part of global and Chernobyl-born fallout.

[137Cs distribution and accumulation in the tissues of cultivated fungi (Pleurotus ostreatus)].

The authors examined 137Cs accumulation and distribution in different structures and tissues of Pleurotus ostreatus cultivated under laboratory conditions. The fungi were shown to concentrate 137Cs. A higher concentrations of the radionuclides in the fungi compared to their substrate is manifested at the first stages of the fruit body formation, the maximum content of 137Cs is accumulated by fungi in the middle of bearing stage. The fungus tissues are different by their accumulative capacity as follows (ascending range): central, more dense part of the stipe < stipe < mycelium < cap < generative tissues. 137Cs accumulation in the fruit bodies depends also on the fungus size and age.

[Basic features of seasonal and multi-year dynamics of Cs-137 and Sr-90 in wood]. / Osnovnye zakonomernosti sezonnoi i mnogoletnei dinamik nakopleniia 137Cs i 90Sr v drevesine.

Basic features of seasonal and multiyear dynamics of accumulation of Chernobyl-derived 137Cs and 90Sr in wood are considered. Seasonal variation in the radionuclide concentration are shown to be more regular and predictable than the multiyear variation. Seasonal dynamics of 137Cs is opposite by trend to that of 90Sr. The multiyear dynamics of both 137Cs and 90Sr in the wood is variable and depends on chemical nature of individual radionuclide, type of landscape, kinetics of the radionuclide plant-available forms, and irreversible fixation of the radionuclides in the root-abundant soil layer.

Association of Chernobyl-derived 239+240Pu, 241Am, 90Sr and 137Cs with different molecular size fractions of organic matter in the soil solution of two grassland soils.

Radiocesium is normally bound only rather weakly and unspecifically by humic substances, in contrast to the actinides Pu and Am. Recently, however, it was observed that fallout 137Cs in the soil solution from an Of-horizon of a podzol forest soil (slightly decomposed plant material) was associated essentially only with one single size fraction of the humic substances. In deeper soil layers with well humified material (AOh-horizon), radiocesium was associated with all size fractions of the dissolved organic matter (DOM). To examine whether this unexpected behaviour is also observable for DOM isolated from other soils, we determined the association of fallout 137Cs, 90Sr, 238Pu, 239+240Pu and 241Am with various size fractions of DOM from in situ soil solutions isolated from two layers (0-2 cm and 2-5 cm) of two grassland soils (a soddy podzolic soil and a peat soil) within the 10 km zone of the nuclear reactor at Chernobyl (Ukraine). The four size fractions of DOM as obtained by gel filtration of the soil solution were (mean nominal molecular weight in daltons): fraction I: > or = 2000, fraction II: 1300; fraction III: 560, fraction IV: inorganic compounds. The results for the well humified DOM (humus accumulation horizon of podzol, deeper layer of peat soil) showed that Pu and Am are essentially associated with the high molecular weight fractions, while Sr is present only in the 'inorganic' fraction. Radiocesium is found in all the size fractions separated. A quite similar pattern was also found for Pu, Am, and Sr in the soil solution from only slightly decomposed plant material (0-2 cm of peat soil), but not for radiocesium. This radionuclide was again essentially only observable in one single low molecular weight fraction of DOM. The above results thus support our recent observations in the different horizons of a forest podzol mentioned above, even though no reason for the different binding of radiocesium by well humified soil organic matter and by only slightly decomposed plant material can be given at present. The data demonstrate, however, that information on only the total amount of a radionuclide in the soil solution will not be sufficient to interpret or predict its fate adequately in the soil.

[Consequences of radioactive pollution of forests in the zone affected by the accident at the Chernobyl power plant]. / Posledstviia radioaktivnogo zagriazneniia lesov v zone vliianiia avarii na ChAES.

The effect of forests on the radionuclide primary distribution in different components of the contaminated ecosystems is considered by the example of Chernobyl accident. A basic mathematical model is developed describing 137Cs biogeochemical cycling under conditions of quasi-steady state radionuclide redistribution in the ecosystem. The radionuclide fluxes between different ecosystem components are estimated. Forest ecosystems are proved to diminish radionuclide migration in the environment, and forest should be regarded as an important sanitary factor. The contribution of contaminated forests and forest products to the total irradiation dose to local population is estimated. Special countermeasures are elaborated in order to diminish unfavorable consequences of forest radioactive contamination. A long-term dynamics of radioactive situation in the forest ecosystems is forecasted and further studies on the subject are drafted.

Dynamics of 137Cs in the forests of the 30-km zone around the Chernobyl nuclear power plant.

Dynamics of the 137Cs content in the components of the forests in the 30-km zone around the Chernobyl nuclear power plant (NPP) in 1986-1994 are associated mainly with such factors as the size of radioactive particles in the fallout, ecosystem humidification and soil type, tree age. The influence of particle size was especially noticeable between 1986-1987 and was displayed by low biological availability of radionuclides in the near part of the zone (within the 10-km radius circle around the NPP) in comparison with more distant regions (within the 30-km radius circle). Later, the expression of this influence decreased and transfer factor (the ratio of 137Cs content in overground phytomass to the soil contamination density) became approximately the same for all plots with similar ecological and fallout characteristics. Humidity of landscape and soil type determined the velocity of radionuclide vertical migration in the soil and 137Cs biological availability. These parameters were maximum for the hydromorphic soils of wet landscapes enriched in organic substance and poor clayey minerals. Differences of 137Cs accumulation in overground phytomass of trees caused by tree age are displayed in the higher 137Cs concentration in structural parts of young trees as compared with old ones.

[The biogeochemistry of the radionuclides of the Chernobyl release in the forest ecosystems of the European portion of the CIS]. / Biogeokhimiia radionuklidov Chernobyl'skogo vybrosa v lesnykh ékosistemakh Evropeiskoi chasti SNG.

The 9-years dynamic of Chernobyl-derived radionuclides in the vegetation and soil covers of the forest ecosystems of the European part of the CIS is considered. The quantitative estimation has been done for main fluxes of Cs-137 in the forests of automorphic landscapes: influx to the vegetation, return with the litterfall, stem flow and throughfall, vertical migration in the soil profile (including intrasoil flow), and redistribution within the system of geochemically connected landscapes.

Chemical forms of gamma-emitting radionuclides in soils adjacent to the Chernobyl NPP.

Samples of sandy forest soils, meadow sandy-peat soil and meadow sandy-loam soil were taken at different sites within a 30-km zone around the Chernobyl NPP (ChNPP). The samples were extracted with water and a 0.1-N solution of ammonium acetate. The extracts were measured for gamma-radionuclides and stable cation content. The content of all mobile forms of the radionuclides present in the 0-10-cm soil layer accounts for 0.5-5% of the total radionuclide content in this layer, depending on the type of radionuclide and soil. Water soluble forms of the radionuclides were found in the 0-5-cm layer only. Exchangeable radionuclide forms were represented, as a rule, by radiocaesium in both the 0-5- and 5-10-cm layers. Content of Cs-137 exchangeable forms in the organic-mineral horizon were roughly inversely proportional to the sum of stable exchangeable cations and organic matter content. Forest vegetation takes up a significant share of the mobile forms of radiocaesium from the soils.

Vertical radionuclide transfer by infiltration water in forest soils in the 30-km Chernobyl accident zone.

Vertical intrasoil flow within the 30-km zone of the Chernobyl nuclear power plant (ChNPP) was investigated by a lysimetric method in 1989-1990. The regularity of radionuclide migration within the flow has been found to be dependent on the contamination density, the type of radionuclide, and the type of ecosystem and depth.

Main investigation results on the forest radioecology in the Kyshtym and Chernobyl accident zones.

As a result of the long-term studies of radionuclide migration in forest ecosystems in zones of radioactive contamination after the Kyshtym and Chernobyl accidents, the following trends were revealed: (1) High retention capacity of stand canopy with respect to radioactive fallout. This leads to high doses absorbed by apical and leaf meristems, beta-radiation giving the main part of the dose; (2) Fast self-decontamination of crowns during the growth period and relatively slow decontamination in the phase of physiological rest, regardless of amount of atmospheric precipitation. The rate of crown decontamination determines the value and duration of radiation stress on woody plants; (3) Accumulation not less than 95% of the total radionuclide amount in the forest litter 1-2 years after the cessation of radioactive fallout; (4) Relatively slow migration of strontium and cesium radionuclides along the forest soil profile; (5) High capacity of the forest when serving as a biogeochemical barrier to the routes of horizontal and vertical radionuclide migration and export out of the zone of initial contamination, including migration into the river water; (6) Considerable difference between strontium and cesium when migrating in forest soils and in the soil-plant system; (7) Broad variations in transfer factors for uptake of cesium-137 from soil into forest plants depending on the plant species and soil type. The primary radiobiological effects connected with irradiation of organisms are considered and secondary disturbances due to changes of ecological bonds between the components of irradiated forest ecosystem are discussed.

Cs-137 content in the mushrooms of radioactive contaminated zones of the European part of the CIS.

Samples of different species of mushrooms were collected in the forests contaminated by Chernobyl (ChNPP) accident fallout debris. Sampling sites were located at a distance of 5-200 km from Chernobyl NPP. Transfer factors (TF) for Cs-137 from soil to mushrooms varied from 12 to 5060 nCi kg-1/Ci km-2; TF variability depended on the distance from ChNPP, mushroom species and growth conditions. The highest concentrations of Cs-137 were observed in Paxillus involutus and Xerocomus badius. These species are suggested as bioindicators of radioactive contamination.

Forests and forestry: radiation protection measures with special reference to the Chernobyl accident zone.

A large proportion of the area contaminated by the Chernobyl accident in the former USSR is forested and has presented unique problems when considering appropriate post-contamination management and clean-up techniques. These problems are related to the forest's role as both a source and sink for radioactive contamination. Although it has been suggested that resuspension from forested areas may provide a secondary source of contamination to adjacent land, data collected after the Kyshtym and Chernobyl accidents suggest that forest ecosystems may also be effective in limiting the further spread of contamination away from the point of initial deposition and that this effect will increase over time. Such evidence serves to highlight the importance of these ecosystems in influencing the behaviour of radionuclides immediately after their release to the environment. Management practices for forested areas adopted since 1986 are described and a critical appraisal is presented of engineering-based countermeasures implemented over the initial post-accident period. These were intended to remove large quantities of contaminated materials from the forest environment. However, it is suggested that the natural processes of self-decontamination of trees and forest floor litter layers are sufficiently rapid and efficient to necessitate radical alterations to the technology based approaches adopted in the first 2 years after the Chernobyl accident.