Influence of thermodynamic database on the modelisation of americium(III) speciation in a simulated biological medium

Abstract

International audienceA first exercice was led, considering only the americium(III) species in solution. Even with different data sets, all the exercises are in relatively good agreement, concluding to successive complexation of the radioelement by phosphate (pH range from 0 to 3), citrate (pH range from 3 to 8) and hydroxo-carbonate (pH range from 8 to 14). Nevertheless, the speciation of americium differs for each pH range from one work to an other. These results are still observed when the speciation calculation includes the formation of solids. Nevertheless, some workers did not integrate in their data set the formation constant of Am(PO4). This solid is known to be very insoluble in typical biological media. All the calculations where Am(PO4) was not in the TDB presented a speciation where americium is solvated (mostly under citrate forms). When the formation of Am(PO4) is considered, the actinide is quantitatively present under this solid species. This work is a representative example of the impact of the thermodynamic data used in speciation exercises. Some exercices, using uncompleted TDB had wrong results and led to the conclusion of the necessity in the use of expertised and extended TDB

Preliminary speciation study of Co(II)-citrate system by ion pairing-reversed phase chromatography coupled to UV detector

“…Nevertheless, the existing thermodynamic data [22,[37][38][39] seem not to be reliable enough to propose a correct speciation of the system in our experimental conditions. This point will be the subject of a future work and our present work is reasonably in good agreement with the stoichiometries and reactivity concerning the cobalt (II)-citrate system.…”

Chemical Speciation of Trivalent Actinides and Lanthanides in Biological Fluids: The Dominant in Vitro Binding Form of Curium(III) and Europium(III) in Human Urine

“…[7][8][9] Our own speciation calculations for curium(III) in human urine resulted in predominant citrate species up to pH 6.5 as well as in citrate and phosphate coordination at higher pH values. 10 The results and accuracy of such predictions rely significantly on the database and model used for calculation.…”

“…10 The results and accuracy of such predictions rely significantly on the database and model used for calculation. 7 This means that if a naturally occurring species is unknown or the available data are incomplete, the calculation can be misleading and not coherent with the real speciation. Therefore, experimental studies with natural biological samples are essential.…”

A modelling exercise on the importance of ternary alkaline earth carbonate species of uranium(VI) in the inorganic speciation of natural waters

“…Moreover, the uncertainty on thermodynamic formation constants can result in considerable output uncertainty, particularly for species like uranium that undergoes a complex aqueous speciation [4]. Within the working group "Speciation" of the CETAMA (Analytical methods establishment committee of the French Atomic Energy commission, CEA) a modelling exercise was conducted about the U(VI) speciation in waters of known compositions as previously carried out for other chemical systems [5,6]. The objectives were: i) to test thermodynamic data bases; ii) to compare the modellers' methods in selecting data; and iii) to evaluate the effect of inorganic species on the U(VI) speciation and solubility.…”