T. A. Goryachenkova

Forms of occurrence of plutonium in soils

The forms of Chemobyl plutonium were determined in soils with model laboratory and field experiments.

Behaviour of transuranium elements in the environment

The distribution and migration of Chenobyl plutonium have been studied in the ecosystem. Its behaviour is discussed.

Association of radionuclides with colloids in soil solutions

Association of Pu and Am with variously sized particles in soil extracts is studied by ultrafiltration. In aqueous extracts, the Pu and Am concentrations depend on the soil type and aqueous solution composition. In the aqueous extracts, from 60 to 100% of the radionuclides and organic carbon are associated with fine colloidal particles (<0.05 μm). The presence of humic acid increases the recovery of radionuclides by a factor of 4–8 depending on the soil type. The Pu and Am distribution among the groups and fractions of humus acids is studied. In the group of humic acids of chernozem, from 65 to 75% of the radionuclides are associated with the fraction with MW > 100 kDa; about 25%, with the fraction with MW 50–10 kDa; and 2–4%, with the low-molecular-weight fraction with MW < 3 kDa. In the group of fulvic acids, 44–49% of the radionuclides is found in the fraction with MW > 100 kDa, and 42–51%, in the fraction with MW < 3 kDa.

Migration of plutonium in soils

The goal of their work was to assess the migration features of plutonium in various types of soils and to compile a tentative long-term forecasting of the plutonium travel from the point of its entry. For this purpose, experimentally obtained vertical profiles of the plutonium distribution in the soils of the USSR and several countries of the Northern hemisphere were analyzed for various times ..delta..t, i.e., times which had passed between t/sub 0/ of the beginning of migration and the data t of sampling. In research on the migration of global plutonium, years 1954, when the observation of the environmental contamination by this element was initiated, and 1963, which is characterized by the maximum of the plutonium arrival from the atmosphere through radioactive fallout, were taken as t/sub 0/. The latter year was used in calculations for forecasting the /sup 137/Cs migration in soils. For the local technogenic contamination of soils, the time of the /sup 137/Cs arrival in the environment was taken as t/sub 0/.

Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

Associations of radionuclides with colloidal particles of various sizes, isolated from underground waters of the Lake Karachai contamination area, were studied. Analysis by photon correlation spectroscopy showed that the total content of colloidal matter in deeper horizons is higher by an order of magnitude than in near-surface horizons. The mean particle radius also increases with the depth. The major fraction of Pu, Am, and Cm is associated with colloids (40–90%). U and Np are associated with colloidal particles to a lesser extent (2–20%), which determines their higher migration mobility in underground waters. The amount of actinides associated with coarse colloidal particles of size from 450 to 200 nm is insignificant. A considerable fraction of actinides is in the deep-lying water (depth ≥40 m) is associated with colloidal particles of size from 200 to 50 nm. No more than 30% of Pu and Am in water of these horizons is associated with finer colloids (from 10 kDa to 50 nm). With approaching the surface, the amount of actinides in the fraction of nanometer-sized particles (50 nm-10 kDa) increases (to 50%).

Association of radionuclides with components of fulvic acids isolated from soils

The distribution of Pu and Am between specific and nonspecific components of various groups of the organic matter of soil was studied. For chernozem and soddy podzolic soil, 63 and 53% of Pu and only 1 and 8% of Am, respectively, are bound with fulvic acid purified to remove low-molecular-weight compounds by fractionation on BAU activated charcoal. Larger relative amount of Am, compared to Pu, in the form of low-molecular-weight nonspecific compounds is responsible for higher migration mobility of Am, compared to Pu, in the environment. The sorption of organic complexes of Pu and Am on carbon nanotubes was studied. The degree of Pu sorption only slightly depends on the nature of the organic substance, except solutions of humic acids from which the Pu sorption is appreciably higher. The degree of Am sorption regularly increases with a decrease in the molecular weight of the organic substances.

Membrane luminescence determination of technogenic actinides and their speciation in environmental objects

Researchers of the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences created a luminescence photometer of a new generation for the determination of trace amounts of uranium and transuranium elements (TUE). The limits of detection for actinides vary from 0.3 pg for uranium and neptunium to 2.0 pg for plutonium. For 237Np, the relative limit of detection is 0.008 Bq/L. The photometer was tested in the radioecological monitoring of a number of polluted zones in Russia. The dynamics of actinide migration in all of the studied zones enhanced in the series 239Pu < 241Am < 237Np. In this series, concentrations of radionuclides in water-soluble and exchange forms that are most mobile and determine the migration mobility of chemical elements increased in all of the studied soil types. In the group of fulvic acids, concentrations of radionuclides decreased in the series 237Np > 241Am > 239Pu irrespectively of the soil. In the group of humic acids, concentrations of radionuclides increased in the series 237Np < 239Pu < 241Am. The sorption coefficients of radionuclides by bottom sediments of the Markha River (Kraton-3 underground nuclear explosion site) and Lake Kyzyltash (East Urals Radioactive Trace) were calculated. Bioaccumulation factors of radionuclides by different plants in the impact area of the Kraton underground nuclear explosion were determined depending on the plant type.

Neptunium speciation in soils

The relative content of 237Np in the water-soluble form depends on the soil type and decreases in the following order: sandy loam soil > soddy podzolic soil > chernozem (black soil). The fraction of the most mobile forms of 237Np decreases with an increase in the content of organic carbon in soils. The major fraction of 237Np is associated with the fulvic acid (FA) group (90.3 and 71.0% of the total neptunium content for soddy podzolic soil and chernozem, respectively), with 8.6 and 18.7% of 237Np, respectively, associated with the humic acid (HA) group. In the FA group, the major fraction of 237Np is associated with low-molecular-weight organic compounds and with FA, free or bonded mainly with relatively mobile hydroxides of Fe, Al, Mn, etc. (R2O3·nH2O) (fractions 1a and 1).

Colloid transport of radionuclides in soils

Radionuclides undergo redistribution and change existence forms (and, therefore, migration dynamics) not only immediately after they enter into the environment, but also during migration. The latter can be associated with changes in the delivery medium (for example, as strongly contaminated wastewaters is diluted by natural), decrease in the concentration of radionuclides (during their sorption and coprecipitation on soil or host rock microparticles), or change in carrier forms (dissolution of fuel matrices). In view of the multifactor nature and complexity of these processes, we set ourselves the task to summarize results obtained at the GEOKHI RAS on the forms of existence and migration dynamics of radionuclides in radioactively contaminated soils. As objects for study we used soils typical of the forest-steppe zone of the Eastern Ural Radioactive Trace (EURT) and taken at a distance of 2 through 8 km from the Trace axis and 2–4 km from the accident place, as well as samples of the high-water bed soils and sediments of the Enisey River, taken 60 km downstream from the Mining Chemical Combine (MCC).

Model for Pu Migration in Soils

The term migration is understood as the movements of chemical elements in environmental components. One of the major tasks of radioecology is the elucidation of migration patterns and reliable long term prediction of the behavior of radionuclides in the environment. The migration mechanisms of radionuclides practically do no differ from those of any other chemical elements, and hence, the direction, intensity, and mechanisms of the migration of radionuclides are controlled, first of all, by their speciation and residence times in ecosys tems and by the natural conditions in these systems. It should be mentioned that the mobility of certain radio nuclides is greater than that of the corresponding stable isotopes and elements analogues [1, 2], because these radionuclides come to the environment in the form of more mobile species [3].