The Impact of Sharp Temperature Shift on the Water-Soluble Forms of Technogenic Radionuclides in Different Soil Types

Studying the impact of sharp temperature change on the migration ability of radioactive isotopes in nature is of significant importance when predicting the radioecological risk in case of nuclear contamination. The increase or decrease of the environmental temperature may affect the mobile forms of radionuclides and change their fate in the environment, especially in the first months after their release in the soils. This study presents the impact of freezing and sharp warming on the water-soluble forms of 241 Am, 60 Co, 137 Cs and 54 Mn in four soil types: Calcaric chernozem, Gleyic fluvisol, Salic fluvisol and Vertisol, classified according to World Reference Base for Soil Resources/FAO. The experiment is a case study, based on a scenario where the radionuclides have entered the soil in the form of aqueous solution, followed by a rapid change of environmental temperature. The soil samples, taken from the surface soil layer 0-10 cm were contaminated by radioactive solutions of 241 Am, 60 Co, 137 Cs and 54 Mn, separated into three subsamples and stored during two months at different temperature regimes: -18 o C, 18 and 40 with the use of a freezer and a climate chamber. The water-soluble forms of the radionuclides were determined by single extraction and gamma-spectrometric measurements. The sharp temperature shift led to the decrease of the watersoluble forms of 241 Am, 60 Co, 137 Cs and 54 Mn in the Salic fluvisol soil with acidic pH. The increase of water-soluble 60 Co and 54 Mn after sharp warming or freezing was determined in Calcaric chernozem, Gleyic fluvisol, and Vertisol soils. Water-soluble forms of 241 Am and 137 Cs decreased in Salic fluvisol and increased in Vertisol soil as the result of sharp temperature increase or decrease. The storage at freezing or "hot summer" conditions caused the decrease of watersoluble forms of 241 Am in Calcaric chernozem. The increase of water-soluble 137 Cs was registered in Calcaric chernozem after sharp warming and in Gleyic fluvisol after freezing.