Heterogeneity of soil contamination by 90Sr and its absorption by herbaceous plants in the East Ural Radioactive Trace area.

A nuclear accident occurred at the production association Mayak in the Urals in 1957. Approximately 74 PBq of radioactive substances were released into the environment, which resulted in the contamination of a vast area, named the East Ural Radioactive Trace (EURT). We have studied the current levels of contamination of soils and plants by 90Sr in the head part of the EURT. The heterogeneity of soil contamination (concentrations and contamination densities) in the EURT zone was considered at three scales. 1) At the macro-level, the soil contamination by 90Sr decreased by three orders of magnitude in the cross section of the zone. 2) At the meso-level, the variability of the soil contamination was estimated within several sectors, selected by the results of macro-scale mapping. 3) At the micro-level, differences in soil contamination between individual samples (0.01 m2) selected at the site (1000 m2) exceeded the one order of magnitude. The similarity of geometric mean (GM) values of the soil contamination was shown, based on the measurements of 3, 25 and 30 soil samples at the micro-level. In 57% of cases, the value of the GM obtained by 3 measurements differed by no >20% from the GM value by 25 measurements. In the most of cases, the differences in GM obtained by these two methods did not exceed 40%. Thus, in small sites it is possible to take only three soil samples to assess the level of soil contamination. We evaluated the absorption variability of 90Sr for six species of herbaceous plants (Rumex confertus, Leonurus quinquelobatus, Arctium tomentosum, Urtica dioica, Lathyrus pratensis, Bromopsis inermis). The range of concentration ratios (CRwo-soil) for 90Sr was 0.003-0.49, and the diapason of aggregated transfer factors (Tag) was 0.56-7.3. The 'plant species' factor determined about 55% of the total variability of CRwo-soil and Tag.

Radioactive contamination of the soil-plant cover at certain locations of Primorsky Krai, Sakhalin Island and Kamchatka Peninsula: Assessment of the Fukushima fallout.

The contamination densities of soil-plant cover at certain locations within the Primorsky Krai, Sakhalin Island and Kamchatka Peninsula attributable to 90Sr, 137Cs and 239,240Pu were 500-1390 Bq m-2, 980-2300 Bq m-2 and 37-74 Bq m-2, respectively. These values do not exceed average global background levels, typical for mid-latitudes of the Northern Hemisphere. The spatial distribution of radionuclides depends on the climatic conditions of the region. A positive dependence of the 90Sr and 137Cs contamination densities, as well as additional 137Cs from NPP "Fukushima" in the soil, was determined based on the sum of annual atmospheric precipitation within the study areas. No trends in the spatial distribution of Pu isotopes were observed. The 137Cs contribution from the "Fukushima" NPP constitutes 11-300 Bq m-2 in the Primorsky Krai, Sakhalin Island and at the Kamchatka peninsula, i.e., 1-22% of the total amount of radionuclides in the soil. The contribution of this radionuclide to the contamination of moss-lichen vegetation ranged from 7 to 42%.