Fractionation of some natural radionuclides in Albic Retisol.

In the present work, the fractionation of heavy natural radionuclides was investigated in Albic Retisol in the Moscow region of Russia. Fractionation was performed using the Pavlotskaya method. 238U and 232Тh were measured via inductively coupled plasma mass spectrometry and 226Ra was measured using an alpha-radiometer that considered the decay of Ra isotopes and accumulation of the resulting decay-related products. Results showed that the potential mobility of radionuclides during migration to adjacent environments and biological availability to plants follows the order 226Ra > 238U > 232Тh. The depletion of 226Ra in the humus horizon A was manifested as a decrease in the 226Ra/238U activity ratio to below 1 in fraction F4.1 (associated with organic matter) and fraction F4.2 (acid-soluble compounds). The profile distribution of 226Ra and 238U in the residual fraction revealed the genetic relationship between these radionuclides. Mobile compounds of 238U and 232Th leached into the lower part of the profile where they became fixed, mainly as the components of fractions associated with organic matter and crystallized iron oxides. A similar profile distribution was found for 238U, 232Тh, and Fe in the acid-soluble fraction associated with crystallized iron oxides. The results obtained herein can form the basis for regulating the mobility and bioavailability of radionuclides to ameliorate their adverse effects on plants and soil ecosystems.

[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.

[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.

[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.