Alexander P Borisov

Geoecological investigations of the Ob-Irtysh River Basin in the Khanty-Mansi Autonomous region: Yugra in 2006–2007

This paper reports the results of the investigations of 2006–2007 on the distribution and migration forms of artificial radionuclides and chemical elements in the Ob-Irtysh water system. Three regions were studied. One of them is a local segment of the Ob River upstream from the confluence with the Irtysh River; its investigation allowed us to estimate the general radioecological state of the aquatic environment affected by the activity of the Tomsk 7 plant. The second region is a local segment of the Irtysh River upstream from its confluence with the Ob River, where the influence of emissions from the NPO Mayak could be estimated. The third region is the water area of the Ob River after its confluence with the Irtysh River. It characterizes the real level of radioactive and chemical contamination of the middle reaches of the Ob River.In order to explain horizontal variations in the distribution of radionuclides in the upper layer of bottom sediments collected at various sites, the results of sorption-kinetic experiments with radioactive tracers in the precipitate-solution system were used. The investigation of the migration forms of trace elements and radionuclides occurring in river water was based on the method of tangential-flow membrane filtration.Chemical element contents were determined in 400-ml water samples. A set of Millipore polysulfone membranes with pore sizes of 8, 1.2, 0.45, 0.1, and 0.025 μm was employed. Taking into account the ultralow specific concentrations of radionuclides in the water, they were analyzed in 300–500 litre samples using Millipore polysulfone membranes with pore sizes of 0.45 μm and 15 kDa. This allowed us to estimate the percentages of cesium-137 and plutonium-239, 240 in the suspended particulate fraction, colloids, and dissolved species.

A Set of Analytical Methods for the Estimation of Elemental and Grain-Size Composition of Volcanic Ash

A combined approach to the analysis of volcanic ash (VA) was proposed. Ash particles were separated by size using a combination of vibration sieving on sieves (140, 70, 40 μm) and field-flow fractionation in a rotating coiled column (for separation of nano- and submicron particles). Initial samples and obtained fractions were characterized using scanning electron microscopy and static light scattering. Their elemental composition was determined using ICP-MS and ICP-AES methods. The radionuclide composition of the VA was studied by the low-background gamma spectrometry. The studies were carried out by the example of ashes from Puyehue volcano, the Puyehue Cordón Caulle volcanic group, Andes (Santiago, eruption on June, 2011), which were taken immediately after eruption and after first rain. It was shown that up to 15% of major elements (such as P, Ca, and К) and trace elements (such as Be, Hg, Tl, As, Sb, and Bi) could be extracted from the ash by rain and migrate into environment. It was also found that the content of radionuclides (U235, Th234, Pb214, Bi214, Be7) after rain decreases by 30–40%. Of special interest are ash nanoparticles (up to 200 nm), in which the contents of Cu, Pb, Tl, Bi, Sn, As, and Sb are over an order of magnitude higher than the bulk contents of these elements in the ash. This regularity was found in samples taken both prior to and after rain. The proposed methodology of fractionation, study, and analysis of ash particles may be applied for a wide range of soil, ash, and dust samples of different nature.