A.I. Shcheglov

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.

Association of Chernobyl-derived 239 + 240Pu, 241Am, 90Sr and 137Cs with organic matter in the soil solution

To investigate the extent of association of fallout radionuclides with soil organic matter, gel filtration was applied to the soil solution obtained from the three top horizons AOf, AOh and AOh + A1A2 of a forest soil within the 10 km zone of the nuclear reactor at Chernobyl/Ukraine. In the five fractions isolated (fraction 1: nominal molecular weight Mw ⩽ 2000, fraction 2: Mw = 1300-1000, fraction 3: Mw = 800, fraction 4: Mw = 400 daltons, fraction 5: inorganic compounds), 239 + 240Pu, 238Pu, 241Am, 90Sr and 137Cs were determined. For that purpose, an efficient method for the simultaneous determination of the actinides and 90Sr was developed. The data show that plutonium and americium are associated mainly with the high molecular fraction 1 and to a much smaller percentage also with the fraction 2. While the differences between plutonium and americium were rather small in the top two horizons, americium in the third soil layer is present to some extent also in the fractions 3, 4, and 5. Strontium-90 from the AOf horizon is associated almost exclusively with fraction 4. In the other two soil layers, however, this radionuclide is present essentially only in fraction 5 (inorganic compounds). Caesium-137 from the soil solution of the AOf horizon is associated essentially only with the fraction 3, but in the deeper layers progressively also with all other fractions. Thus, in the third layer, 137Cs is distributed almost uniformly between all five fractions. Because the mobility and biological availability of these radionuclides will depend on their association with soil organic matter, the present data suggest that the determination of only the total concentration of a radionuclide in the soil solution might not be sufficient to interpret or predict adequately the fate of radionuclides in the soil.

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 forests 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.

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.

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.

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.

Lysimetrical study of radionuclides in the forests around the Chernobyl nuclear power plant

Vertical intrasoil water within the 30 km zone of ChNPP was studied by lysimetrical method during 1989–1991. Explorations were carried out in different ecosystems where the sum of total accumulation deposition of the radionuclides (Ce-144; Cs-134, 137; Ru-106; Sr-90) ranged from 90 M Bq/m2 to 0·5 M Bq/m2. It was shown that 0·01–0·6% of the total amount of radionuclides was lost from the 20–30 cm layer of soil every year depending on the type of radionuclide, type of ecosystem and the location of study plot. Main absorption of the radionuclides from the intrasoil flow generally took place in the 5–10 cm layer. Radionuclides were not absorbed by the soil in proportion to their ratio in lysimetrical water leached through the forest litter. The mobility of radionuclides in the intrasoil flow can be represented by the following series: Sr-90 > Ru-106 > Cs-134, 137 > Ce-144. Sr-90 and Cs-137 are absorbed by soil more intensively than their chemical macroanalogs—Ca and K.

Eco-economic approach to evaluation of agricultural lands polluted by chemicals and radionuclides.

A comparative analysis of the existing methods of land evaluation has shown that none of them ensures a comprehensive assessment of the diverse economic and ecological functions of soils. An original methodology developed by the authors includes the evaluation of the soil ecological quality in addition to the traditional cost assessment of land plots, and adequate correction coefficients accounting for the chemical and radioactive contamination of soils are suggested. The effect of changes in the market price of the land on the inflation processes is analyzed.

Content of some organic and inorganic pollutants in soils of southern part of Sakhalin Island

The article is dedicated to analyzing the content and distribution of oil hydrocarbons, benz(a)pyrene, and heavy metals in the soils of the southern part of Sakhalin Island. The investigations were conducted in 2003–2010. A dynamical increase in the content of ecotoxicants in soils has been shown. The similar character of the accumulation of oil hydrocarbons, benz(a)pyrene, and heavy metals in the soils has been determined and indicates the possibility of the aerial transmission of pollutants from existing nearby sources.

137Cs 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.