The regularities of 137Cs accumulation in the aboveand underground parts of aerial-and-aquatic plants originated from various types of reservoirs in the Polissia and the Forest-Steppe of Ukraine

The aim of the study was to establish the regularities of 137Cs accumulation in the above- and underground parts of aerial-and-aquatic plants originated from various types of reservoirs in the Polissia and the Forest-Steppe of Ukraine, located in territories varying in the degrees of radioactive contamination. The studies were carried out in 2014–2018. Higher aquatic plants were sampled in eutrophic, oligotrophic, and dystrophic reservoirs including large and small ones as well as lakes and ponds used for various purposes. The reservoirs were located in the areas that are considered conditionally clean relative to the density of 137Cs contamination, or are classifed as zones of enhanced radiological control, guaranteed voluntary resettlement, unconditional (guaranteed) resettlement and exclusion zones. The objects of research were 8 species of aerial aquatic plants widespread in the fresh water reservoirs of the Polissya and the Forest-Steppe of Ukraine. The specifc content of 137Cs in the aboveground parts, rhizomes, and roots of the plants was determined by common gamma-spectrometric methods. The analysis of the obtained results revealed a common regularity typical of plants from all the studied reservoirs – the levels of 137Cs in the aboveground parts and the rhizomes did not differ signifcantly, but in the ground roots they were signifcantly higher. The specifc activity of 137Cs in ground roots of Phragmites australis exceeded its activity in above ground parts by 6–25 times, in Tupha angustifolia – by 5–20, Glyceria maxima by 7–10, Scirpus lacustris by 4–9, Alisma plantago-aquatica – by 3 times, Sagittaria saggitifolia - by 2, Butomus umbellatus – by 3, Iris pseudacorus - by 4 times. The levels of 137Cs content in aboveground parts and rhizomes in most of the studied plants did not differ signifcantly. The results of the study will further make it possible to assess the role of aerial-and-aquatic plants in the bottom sediments radioactive contamination and to improve the understanding of the role of higher aquatic plants in the processes of radioactive elements migration and redistribution in aquatic ecosystems. The revealed regularities of 137Cs levels formation in the underground parts of plants should be taken into account in determining the radiation dose of plants growing in radionuclides contaminated reservoirs. Key words: aerial-and-aquatic plants, aboveground parts, underground parts, roots, rhizomes, 137Cs, reservoirs, lakes, ponds.

Operative assessment of radioactive contamination of agricultural land for their return to use

Significant regression dependencies between ambient equivalent dose rate and 137Cs contamination density, as well as between 137Cs and 90Sr contamination densities were obtained. An economically inexpensive approach to estimating the density of soil contamination by 137Cs, 90Sr, and plutonium isotopes with controlled uncertainties has been proposed and tested. The approach allows also the immediate evaluation of the density of radionuclide soil contamination even if there is a contamination gradient within the agricultural land.

Cartographing of "spots" of radioactive pollution

The methodology was proposed and the algorithm was developed for mapping and delineating the "spots" of radioactive contamination territory by the 137Cs. The methodology is based on the principle of multi-stage (successive approximations) widely used in geological surveys. Herewith, the 137Cs contamination density at each point is considered as a random variable with a lognormal probability distribution. The implementation of the algorithm is based on optimization of the number of sampling points necessary for estimating the density of soil contamination with a given relative error at the identification of a "spot" of contamination. The results of testing the algorithm confirmed the effectiveness and stability of its operation, as well as the simplicity of practical application. The proposed methodology makes it possible to substantially minimize the costs of field work for sampling soil and measuring the content of radionuclides in them.