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Monitoring of radionuclide concentration in natural samples is important for assessing environmental safety. The low concentration of long-lived radionuclides require concentration from large volumes of natural water samples. This paper presents a method for sequential separation and simultaneous determination of radioisotopes of U, Pu, Am and Tc in water samples. Actinides and technetium were pre-concentrated by coprecipitation with iron hydroxides from the aqueous sample. Separation of actinides and Tc was achieved by extraction chromatography. The developed method allows separation of actinide and technetium from 100 L water with chemical yields between 40 and 70%. [ABSTRACT FROM AUTHOR]

The extraction parameters and speciation of 137Cs and 241Am in bottom sediments of reservoir R-17 of the Mayak Production Assocation were studied. The extraction was performed with four solutions with different pH values (water simulating in its composition the groundwater from the investigated area, 0.1 M Na2CO3, acetate buffer solution, and 1 × 10−3 M HNO3). With the first solution, the degree of extraction of 137Cs and 90Sr becomes constant in 24 h. The desorption percentage did not depend on pH. The 137Cs distribution coefficients were calculated. The lowest values were observed in the buffer solution (27) and sodium carbonate solution (21), and the highest values, in water (9250). As shown by sequential extraction, the major fraction of cesium (90%) occurs in the insoluble form. Incorporation into the crystal lattice of clay minerals was found to be the main sorption mechanism. The 241Am sorption mainly occurs by the mechanism of complexation with carbonates. [ABSTRACT FROM AUTHOR]

The specific activities of natural (210Pb, 226Ra, and 232Th) and artificial (137Cs, 239,240Pu, and 241Am) radionuclides in the sediments of two North Caucasus lakes were determined. The two lakes, Lake Khuko and Lake Donguz-Orun, differ in their sedimentation conditions. Based on the use of unsupported 210Pb ex and both Chernobyl-derived and bomb-derived 137Cs as chronological markers, it was established that the sedimentation rates in Lake Khuko over the past 55–60 y did not exceed 0.017 cm y−1. Sedimentation rates in Lake Donguz-Orun were found to be more than an order of magnitude higher. In the latter case, the sedimentation rates for the period from 1986 to the present were over 1.5 times higher than they were for the period 1963–1986. The differences in sedimentation rates were due to differences in the rates of denudation of their respective catchment areas. The specific activities of artificial radionuclides (137Cs, 2600 Bq kg−1; 239,240Pu, 162 Bq kg−1; and 241Am, 36 Bq kg−1) and their ratios in the sediments of Lake Khuko show that their deposition was mainly due to global stratospheric fallout of technogenic radionuclides associated with nuclear bomb testing during 1954–1963—rather than fallout from the Chernobyl accident. Several factors, including the mode of precipitation, features of the surface runoff, and location of Lake Khuko, were responsible for the accumulation of artificial radionuclides. Image 1 • Both 137Cs and 210Pb ex were used for evaluation of sedimentation rates in the two Caucasus lakes. • Sedimentation rate in Donguz-Orun lake located in proglacial zone increase in 1,5 times since 1986. • Global warming is the main reason of increasing denudation rates in periglacial zone. • High concentrations of technogenic radionuclides were determined in sediments of Lake Khuko. • The possible contribution of different sources of Khuko lake sediment contamination is determined. Main finding: It was determined that global warming is the primary reason the denudation rates in the periglacial zone are increasing. The possible sources of the radioactive contamination of the Khuko lake sediment were also determined. [ABSTRACT FROM AUTHOR]

The purposes of this study are to determine the content and origin of anthropogenic fallout radionuclides (FRN) in soils of Mount Khuko, located in the western sector of the Caucasus Mountains and to assess the possibility to use them for evaluation of sediment redistribution for the alpine grasslands,. The field study was carried out in August 2019 near the top of Mount Khuko, located in the western part of the main Caucasus Mountain Ridge. Integral and incremental soil samples were collected from the different morphological units of the studied area. The content of 137Cs and 241Am in soil samples was evaluated using laboratory gamma-spectrometry. A part of samples was selected for Pu isotopes extraction and then alpha-spectrometric analysis. It was established that the 137Cs contamination of soils in the studied area has at least two sources of origin. The first source is the 137Cs bomb-derived fallout after the bomb tests in 1950–60th, which is widespread across the globe. The second source is 137Cs Chernobyl-derived fallout High random variability (Cv = 25–42%) was found within reference sites, located at the undisturbed areas on the local flat interfluves due to high variability of soil characteristics (grain size, density, organic matter content etc.). However minimum spatial variability (range 12,2–14,3 kBq/m2) was identified for the mean value of 137Cs inventories for all 5 reference sites located in the different parts of the studied area. It is difficult to separate individual peaks of the bomb-derived and Chernobyl-derived 137Cs falloutin sediment sinks with low sedimentation rates. Application 239,240Pu as an additional chronological marker allows to identify the origin of above mention peaks in the soils of alpine grasslands and of dry lake bottom. • Radioactive contamination with anthropogenic FRN of soils in the Western Caucasus has a heterogenous origin. • Variable deposition and lateral migration of 137Cs complicates interpretation of the vertical distribution. • 239,240Pu is implemented as an additional chronomarker for evaluation of sedimentation rates. [ABSTRACT FROM AUTHOR]