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

Kovacheva, Petya and Todorov, Boyan and Djingova, Rumyana (2014) Geochemical fractionation and bioavailability of ²⁴¹Am, ⁶⁰Co and ¹³⁷Cs in Fluvisol soil after sharp temperature variation before the growing season. Central European Geology, 57 (2). pp. 153-163. ISSN 1788-2281

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Abstract

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.

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