Natural restoration of radiopolluted ecosystems and impact on human health

The vertical migration velocity of radionuclides and the ability of soils components to immobilise them,
as the most important parameters of natural-restoration, was studied. The Dose Equivalent Rate
(DER) reduction of external ã-radiation was studied in order to assess its impact on human health. The
vertical migration velocities of 137Cs and 90Sr in typical soils of contaminated regions in Ukraine
(Chernobyl 30-km zone) and Belarus (Gomel region) have been evaluated annually during the last 8
or 10 years since the accident. In most of these soils the migration rate of 90Sr was found to be higher
than this of 137Cs and ranged from 0.71 to 1.54 cm year-1 and 0 to 1.16 cm year-1 respectively. At present
the main part of radionuclides is located in the upper 10 cm soil layer. The ability of the soil components
to immobilise the radionuclides was also investigated from 1989 to 1994 and was found that
approximately 57% of 137Cs was converted in fixed forms. It is expected that this percentage will
increase to 80% in the next years. Finally, we studied how the DER of ã-radiation, which changes with
the migration of radionuclides in the soil, affects the human health. In comparison with 1986, when
100% of 137Cs was distributed on the soil surface, a significant reduction of DER occurred in the studied
areas and about ten years after the Chernobyl accident, it ranges from 17.5% to 45%, depending
mainly on the level of initial contamination of soils and its migration velocity.