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Root transfer of uranium (VI) solution in a higher plant life form: speciation in an hydroponic solution, plant uptake and induced biological effects.

Laëtitia LAROCHE, doctorate thesis of the University of Aix-Marseille I Speciality Biosciences of Environment, Chemistry and Health, 241p. Defended on the 21st January 2005.

Document type > *Mémoire/HDR/Thesis

Keywords > speciation, transfer, transfer model, uranium

Research Unit > IRSN/DEI/SECRE/LRE

Authors >

Publication Date > 21/01/2005

Summary

Uranium exists naturally in the environment, usually present in trace quantities. In soil solution and oxic conditions, uranium is present in the +VI oxidation state and forms a large number of inorganic and organic complexes. The exposure medium, an artificial soil solution, was designed in such a way as to control the uranium species in solution. The geochemical speciation code JCHESS was used to calculate the uranium aqueous species concentration and to define the domains of interest, each of them characterized by a limited number of dominant U species. These domains were defined as follows: pH 4.9 with uranyl ions as dominant species, pH 5.8 with hydroxyl complexes and pH 7 where carbonates play a major role. For each pH, short-duration (5 hours of exposure) well-defined laboratory experiments were carried out with Phaseolus vulgaris as plant model. The effect of competitive ions such as Ca2+ or the presence of ligands such as phosphate or citrate on root assimilation efficiency was explored. Results have shown that uranium transfer was not affected by the presence of calcium, phosphate or citrate (but was decreased of 60% with citrate (10uM) at pH 5.8) in our experimental conditions. Moreover, observation in Transmission Electronic Microscopy (TEM), equipped with an EDAX probe, have shown that uranium was associated with granules rich in phosphorus and that there were some chloroplastic anomalies. Finally, the presence of uranium affects root CEC by reducing it and stimulates root elongation at low uranium concentrations (100nM, 400nM and 2uM at PHs 4.9, 5.8 and 7 respectively) and inhibits it at high uranium concentrations.


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