Geochemical fractionation and bioavailability of ²⁴¹Am, ⁶⁰Co and ¹³⁷Cs in Fluvisol soil after sharp temperature variation before the growing season

This paper deals with the influence of sharp temperature variations on the geochemical fractionation and bioavailability of 241Am, 60Co and 137Cs in Fluvisol soil. The study was performed using soil contaminated with aqueous solutions of 241Am, 60Co and 137Cs in the laboratory and stored for three years at temperatures within the range of 10–18 ºC and soil moisture from 20 to 30 wt %. Afterward the soil was divided into three equal parts and conditioned for one month at 10–18 ºC, −18 ºC and 40 ºC temperature regimes, respectively. The impact of the storage conditions on geochemical forms of the radionuclides was investigated using single extraction of exchangeable 137Cs with 1 M NH4NO3 and sequential extraction of 241Am and 60Co, and by gamma-spectrometric measurement. The influence of temperature rise up to 40 ºC over a period of one month on the transfer factors (TFs) of the radionuclides from the investigated soil to orchard grass (Dactylis glomerata L.) was evaluated. The results showed that deep freezing and a sharp temperature increase continuing for one month led to re-distribution of 241Amand 60Co between the soil phases and provoked an increase of the exchangeable 137Cs. Freezing led to a decrease of 241Am in the residual fraction and an increase of oxide-bound americium. The storage at frozen conditions led to decrease of oxide bounded 60Co and increased immobilization in the residual fraction. Conditioning at high temperature increased the migration ability of 241Amand 137Cs, while immobilization of 60Co was registered. Conditioning at a sharp temperature increase before the growing season led to higher values of the TFs of all the studied radionuclides. This effect was highest for 137Cs. The sharp temperature change of contaminated Fluvisol soil lasting one month was found to create a risk of increased migration and bioaccumulation of radionuclides

Effects of freezing and soil drought on the geochemical fractionation of americium in Fluvisol and Cambisol soils from Bulgaria

Abstract Extreme changes of environmental conditions can alter the soil properties and influence the migration ability and bioavailability of pollutants. Elucidation of the effects of the extreme weather conditions, such as sharp temperature change, drought and floods, on the fractionation of radionuclides in different soil types is especially important for adequate risk assessment after radioactive contamination. The effects of short-term and prolonged freezing and soil drought on the geochemical fractionation of americium in two soil types (Fluvisol and Cambisol, classified according to the World Reference Base for Soil Resources/FAO) from Bulgaria were studied. The changes of the physico-chemical forms of 241Am after storage under different conditions were determined by the sequential extraction procedure and gamma-spectrometric measurements. The impact of the sharp temperature decrease and drought on the association of the radionuclide with the various soil phases was considered in terms of the soil characteristics. The results showed that the risk of increased mobility and bioavailability of americium in the loamy-sand soil with acidic pH and very low cation exchange capacity (CEC) exists under the examined extreme environmental conditions. The soil with sand-loam texture tended to immobilize americium after freeze and drought storage