Radiation and migration characteristics of the Chernobyl radionuclides causing environmental contamination in various provinces in the European sector of the USSR

The radionuclide composition of the Chernobyl fallout has been studied over practically the whole European sector of the Union of Soviet Socialist Republics using soil sampling methods, the upper turf layer of the soil being treated as a natural planchet. Regular observation of the migration of radionuclides in the soil-plant system has been in progress since July 1986 at a stationary network of landscape-geochemical testing sites and sampling grounds; two types of natural ecosystem have been looked at - meadowland and forest. The behaviour of individual radionuclides is evaluated using the coefficient of fractionation in relation to 95Zr or 144Ce. The migration characteristics of individual radionuclides were revealed to depend both on soil conditions and on the type of radionuclide composition. The main features of the vertical profile of radionuclide concentrations in soils were clear 2-3 months after the contamination occurred. During subsequent years the migrational profiles changed depending on the individual characteristics of the radionuclides and soil conditions. Information on the radionuclide composition and evolution of the vertical distribution of radionuclides in soils was used to calculate and predict exposure gamma radiation dose from the Chernobyl fallout in various provinces in the European sector of the Soviet Union. When monitoring forest sampling grounds, samples were taken of the soil (litter, humus, mineral layer), the phytomasses of ligneous species (pine needles, leaves, bark, wood), moss and lichens. The main aim of monitoring surveys from 1986 to 1989 was to evaluate the distribution of Chernobyl radionuclides in the compartments of the forest ecosystem. In particular, 60-80% of the total amount of 137Cs was bound with the humus layer of the forest soil. 4 refs, 6 figs, 3 tabs