ARTICLE pubs.acs.org/crt
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 Anne Heller,* Astrid Barkleit, and Gert Bernhard Institute of Radiochemistry, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, Dresden 01314, Germany
bS Supporting Information ABSTRACT: Radionuclides represent a serious health risk to humans in the case of incorporation. To elucidate the potential of time-resolved laser-induced fluorescence spectroscopy (TRLFS) to determine the dominant radionuclide species in natural biofluids, we investigated the in vitro speciation of curium(III) in human urine samples. Because in speciation studies trivalent lanthanides are often used as analogues for trivalent actinides, we also probed the suitability of this theory by investigating the speciation of europium(III) in human urine. Comparison with reference spectra of both heavy metals in model urine and of their complexes with single organic and inorganic urine constituents then allowed for the determination of the dominant species. Furthermore, the chemical composition of all urine samples was analyzed, and the parameters affecting the speciation of the metals were determined. The pH was found to be the most important parameter because for both, the actinide and the lanthanide, two analogue species were identified in dependence on the pH. In samples with slightly acidic pH a curium(III) and europium(III) citrate complex dominates, respectively, whereas in samples with near-neutral pH a higher complex with phosphate and calcium as the main ligands and the additional participation of citrate and/or carbonate is formed in each case. Comparison with thermodynamic modeling yields some discrepancies, especially at higher pH, which is due to a lack of data for the complex formation of the higher species for both heavy metals. Nevertheless, TRLFS has proven to be a suitable method for the direct determination of the dominant heavy metal species in untreated natural human urine samples.
’ INTRODUCTION Trivalent actinides (An(III)) such as curium(III) and americium(III) are mainly produced within the nuclear fuel cycle in nuclear power plants. Accidental release of such elements harbors the inherent danger of internal human contamination following acute or chronic exposure. This poses a serious health risk, because they have the potential to induce both radiological and chemical toxicity. Furthermore, whereas the majority of organic contaminants and poisons can be detoxified in vivo via metabolic degradation pathways, the human organism has only two ways to handle such toxic metal ions: immobilization or excretion.1 No matter whether incorporation occurs via ingestion or inhalation or through the skin, the heavy metals are absorbed into and transported by the bloodstream prior to deposition in target organs. In the case of An(III), these are, in particular, the bones and liver with organ retentions of 30 and 50%, respectively.2,3 In contrast, the excretion of those elements is
