Artificial radionuclides and, first of all, the most dangerous isotopes of transuranium elements(TUE) became constant and irreversible components of the biosphere because of the experimental nuclear explosions performed, the wrong concept of the disposal of radioactive wastes to open water reservoirs, and also process upsets and emergency situations at NFC enterprises .
It is known that many radionuclides can accumulate by biogeocenosis components and incorporate into food chains. However, only the behavior of gamma-emitting short-lived isotopes has been studied comprehensively at present. Bioaccumulation of alpha-emitting and the most toxic isotopes of actinide elements have been studied less due to methodological difficulties of radiochemical analysis. However, laboratory researches show a high degree of actinide sorption, primarily of neptunium, by microorganisms and plants.
The main problem of determining the coefficients of actinide accumulation by biota is the impossibility of direct detection of their content and the significant influence of the organic substance on the yield of the analyte during alpha-spectrometric determination. A method for determining actinides according to the luminescence of crystallophosphors was developed and tested in the Vernadsky Institute of Geochemistry and Analytic Chemistry of the Russian Academy of Sciences. A photometer and membrane modules for the separation of actinides in physicochemical forms, as well as for their concentration, were created. The method is particularly useful when analyzing natural objects, because it doesn’t require prior separation of actinide elements, as well as cleaning the sample from alkali and alkali-earth elements. Actinide luminescence is induced by the ultraviolet radiation of the crystallophosphor located at room temperature. Detection limit of the photometer for determining the neptunium contents in simulated groundwater is 3 pg/ml(0.3 pg of Np in a quarts crucible).
The present research studies the processes of bioaccumulation and biotransformation (changing of speciation) of the most toxic, alpha-emitting actinides on real biological objects, selected in the areas of Krasnoyarsk Mining and Chemical Combine (KMCC), and in the impact zone of the Kraton-3 underground nuclear explosion (Yakutia).
It has been established that the relative content of water-soluble and exchange forms of neptunium is 5-10 times higher than the relevant values for plutonium and americium. Among long-lived radionuclides only 90Sr has similar solubility. It was found that, for all of the studied soil types, the concentration of radionuclides in water-soluble and exchange forms,which are most mobile and determine in the series 237Np(39.1-75.4%) >241Am(3.9-21.7%) > 239Pu(4.1-
20.1%). In poorly soluble forms ( acid-soluble and residues) irrespectively of the soil type, the
Concentration of radionuclides changed in the inverse order : 239Pu(68.4-85.7%)> 241Am(19.6-
-36.2%) >237 Np (9.7-31.8%)
In the soil organic matter the main content of neptunium was found in the fulvic acids fraction and low molecular weight acids (below 43%), and moreover, up to 25% of neptunium is directly bonded to the low molecular weight substances of non-specific nature. This, apparently, provides its high bioavailability.
Neptunium is found in the aquatic vegetation of the Yenisei River. The water plant Fontinalis antipyretica (water moss), in the dry biomass of which the maximum specific activity of neptunium amounts up to 10 Bq/kg, accumulates it most actively.
The content of neptunium in the vegetation in the impact zone of the Kraton-3 underground nuclear explosion increases in the line: lingonberry (Vaccinium vitis-idaea) < mountain ash (Sorbus aucuparia) < sedge (Carex riparia) < lichen (Hypogymnia physodes) < larch needles (Larix sibirica) < moss (Cladonia rangiferina).