Radionuclides in the liquid phase of the forest soils at the Chernobyl accident zone.

The relative content (alpha) of 137Cs (1987-1991), 106Ru, 134Cs, 144Ce (1987) and the chemical speciation of radionuclides in the liquid phase of forest soils at different plots in the 30-km Chernobyl zone were studied. One year after the accident, substantial variations in the alpha-value between the different plots and a variation in alpha along the soil profile were observed due to unequal physico-chemical properties of nuclear fallout and soils. The alpha-value calculated for the total contaminated layer (alpha av) at different plots varied within relatively narrow limits. Between 77 and 97% of 137Cs in soil solution was shown to be included in organic compounds (MMw, 10(2)-10(4) Da), the latter making a major contribution to the radionuclide transport from soil to plant. The alpha-value for 137Cs for all plots in the Chernobyl 30-km zone and the differences in alpha value between plots had a tendency to decrease with time. These data indicate that the process of 137Cs fixation by the soil solid phase was prevalent. Now, the 'soil-soil solution' system is approaching equilibrium for the radionuclide distribution between solid and liquid phases.