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

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.

3,4,3-LI(1,2-HOPO): In vitro formation of highly stable lanthanide complexes translates into efficacious in vivo europium decorporation

“…In addition, citrate is a low molecular weight biological ligand that may play a predominant role in lanthanide in vivo 10 speciation. 31 However, the stabilities of citrate-lanthanide complexes (pM ranging from 8.3 for La III to 9.0 for Yb III ) 16 are substantially lower than those determined with 3,4,3-LI(1,2-HOPO). The octadentate hydroxypyridonate chelator can therefore form some of the strongest complexes so far identified with the trivalent metal ions of the lanthanide series, which makes it an excellent candidate for decorporation applications.…”

Interaction of Eu(III) with mammalian cells: Cytotoxicity, uptake, and speciation as a function of Eu(III) concentration and nutrient composition

“…In the presence of inorganic ions, the lanthanide ions are highly complexed and soluble (e.g., with chloride, sulfate, carbonate) as well as insoluble species (especially with phosphate) are formed. But also organic ligands (e.g., citrate) can complex lanthanides to a great extent, like was demonstrated for Eu(III) in human urine samples (Heller et al, 2011). The interactions of lanthanides with mammalian cells are only little studied up to now.…”

“…The experiments were performed as a function of the metal ion concentration and nutrient composition in order to correlate the behavior of the cells to the aqueous metal ion speciation. Besides the influence of fetal bovine serum (FBS) on the Eu(III) cytotoxicity and uptake, also that of citrate was studied because of its physiological relevance in all body fluids, especially in blood and urine (Boothby and Adams, 1934;Heller et al, 2011Heller et al, , 2012. The Eu(III) speciation in the nutrient media was investigated by thermodynamic modeling, solubility studies, ultrafiltration, ultracentrifugation, and time-resolved laser-induced fluorescence spectroscopy (TRLFS).…”

Micelle mediated extraction for preconcentration of Eu(III) prior to determination by flame atomic absorption spectrometry

“…It is a reactive radionuclide which is used as component in fluorescent lamps, lasers, ceramics and catalysts for oil and nuclear industries. Radionuclides represent a serious health risk to humans in the case of incorporation [3]. Europium toxicity results in a significant decrease of creatinine and a significant increase of urinary volume, N-acetyl-b-D-glucosaminidase, and b-2-microglobulin.…”

“…Schott et al [34] and Horvath et al [35] reported that the cloud point of an aqueous solution containing a nonionic surfactant could be lowered by the addition of a salt. This is because the water molecules surrounding the nonionic surfactant are more strongly oriented toward the salt anions (e.g., NO 3 There are a few reports on the cloud point extraction of Eu(III) using chelating agents such as 2-(3,5-dichloro-2-pyridylazo)-5-diethylaminophenol [38], 8-quinolinol [39], and calixarenes [40]. Ohashi used di(2-ethylhexyl)phosphoric acid (HDEHP) and Triton X-100 for the extraction of Eu(III) [41].…”