Biological cycles of the Chernobyl originated cesium-137 (Cs-137, radiocesium) and the natural potassium (K) in oak, birch, and pine forest, and wheat cropland in Russian Federation, approximately 500 km northeast of the Chernobyl Nuclear Power Plant, were subject to a multiyear monitoring. By 2010, the annual return of Cs-137 from forest vegetation to the soil in dead tree components still exceeds its annual accumulation in the tree phytomass by a factor of 4-6, apparently due to residual surface contamination in the external bark and the ongoing process of tree stand decontamination following the initial fallout. In the cropland, both ascending and descending fluxes of Cs-137 are close to the steady state. The annual accumulation of Cs-137 in the tree biomass was the highest in the oak forest and the lowest in the pine forest. The annual K accumulation was the highest in the cropland and the lowest in the pine forest.

The paper integrates the results of 25-year monitoring study of 137 Cs and 90 Sr biogeochemical cycle in the forest ecosystems of Russia and Ukraine contaminated due to the Chernobyl accident. The monitoring network was established in 1986 as a number of long-term key sites (KS) located 5 to over 500 km from the Chernobyl NPP. The following components have been monitored: biota (trees, grass and shrubs, mosses, and fungi), soils (forest litter and mineral horizons), soil water, and throughfall. Presently, 25 years after the Chernobyl fallout, 137 Cs and 90 Sr uptake by vegetation exceed their infiltration through the soil, i.e. biogeochemical cycle currently plays an important role impeding the radionuclide infiltration through soil to the ground water. In wet, accumulative landscapes, biota is a leading factor of the radionuclide cycle, while in dry, eluvial landscapes, soil absorbing complex plays a more important role. The effect of landscape type is manifested for 137 Cs, yet less important for 90 Sr. 137 Cs is actively uptaken by the fungi complex, while 90 Sr is primarily accumulated in the arboreal vegetation. Biogeochemical fluxes of 137 Cs and 39 K in some ecosystems are still different, even 25 years after the fallout.

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.

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.

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.