Screening the importance of soil micro-organisms on radionuclides mobility

Abstract

Abstract. In surface soils, the native physical and chemical properties of the abiotic components control most of the sorption-desorption processes. Moreover, micro-organisms may significantly modify the speciation of trace elements and/or radionuclides and subsequently determine their fate, to a large extent. Micro-organisms, mainly bacteria and fungi, develop many strategies that may affect indirectly or directly the behaviour of trace elements. Due to their activity, changes in the pore-water composition, e.g. pH, redox-potential, may occur in relation with organic acid production or solid phase alteration, reduction or oxidation of metallic oxi-hydroxides, and mineralization of organo-metallic complexes. Micro-organisms may also directly modify the speciation of radionuclides as a result of bio-accumulation in living cells, biosorption on cellular components, direct reduction or oxidation, biomethylation, etc. Each one of these microbial processes may either increase or decrease radionuclide mobility, depending on the element, the soil reactivity and the environmental conditions. The resulting effect of these processes is still poorly known. This literature review intends to present a comprehensive overview of the role of micro-organisms on radionuclide mobility. It aims at classifying these elements, regarding to their potential sensitivity to these microbial processes. It summarizes the theoretical effect of these mechanisms, resulting in a potential increase or decrease of the solid-liquid distribution. The environmental significance of such processes for various biogeochemical radionuclides cycles still remains to be confirmed by experiments. (This study is part of a research program supported by Andra).

Selenium bioavailability and uptake as affected by four different plants in a loamy clay soil with particular attention to mycorrhizae inoculated ryegrass

“…Selenium is one of the trace elements strongly affected by microbiologically mediated redox processes influencing its solubility and consequently its mobility, bioavailability and uptake in soileplant system (Roussel-Debet et al, 2005). Phototrophic and chemotrophic bacteria have been shown to reduce oxyanions of selenium (Se(VI) and Se(IV)), either to the less soluble and therefore less toxic Se(0), or to a volatile form Se(ÀII) (Fatoki, 1997;Kessi et al, 1999;Deneux-Mustin et al, 2003;Siddique et al, 2006).…”

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

“…Microorganisms directly and indirectly influence the speciation of elements in the soil (Roussel-Debet et al 2005;Borch et al 2010) and therefore are another important factor to be considered when the mobility of the radionuclides and their fate in the environment are to be assessed. Since microbiological activity depends on the environmental conditions and changes under different temperature and soil moisture conditions (Brady and Weil 2002) it is logical to expect that the changes of temperature and soil moisture affect the microbiologically-caused modifications of the fractionation of radionuclides in the soils.…”