Chemical speciation of trivalent lanthanides and actinides in body fluids


Chemical speciation of trivalent lanthanides and actinides in body fluids

Barkleit, A.; Wilke, C.

In case of incorporation into the human body, heavy metals and radionuclides potentially represent serious health risks due to their chemo- and radiotoxicity. In order to assess their toxicological behavior, such as transport, metabolism, deposition, and elimination from the human organisms, the understanding of their in vivo chemical speciation on a molecular level is crucial. In order to improve our understanding of the behavior of trivalent actinides (An(III)) and lanthanides (Ln(III)) in the human body, the present study focuses on the chemical speciation of An(III) and Ln(III) in the gastrointestinal tract. The human gastrointestinal system was simulated by using an in vitro digestion model, which is part of an international unified bioaccessibility method (UBM), developed by the Bioaccessibility Research Group of Europe (BARGE) [1]. To verify the model, natural human saliva samples were included in the speciation investigation [2].
The speciation of curium(III) (Cm(III)) and europium(III) (Eu(III)) in the gastrointestinal tract as well as in human natural saliva has been studied by means of time-resolved laser-induced fluorescence spectroscopy (TRLFS). The standard model body fluids and the natural saliva samples were spiked in vitro with Cm(III) and Eu(III) in trace metal concentrations.
The dominant chemical species in the human saliva was identified by a comparison of the natural human sample spectra with reference spectra obtained for synthetic saliva and individual components of the body fluid. Linear combination fitting analysis on the sample spectra indicates the formation of 60-90% inorganic- and 10-40% organic species of Cm(III)/Eu(III) in the salivary media. Ternary M(III) complexes containing phosphate and carbonate anions with the additional counter-cation calcium are formed as the main inorganic species. Complexes with the digestive enzyme α-amylase and the protein mucin (to a minor extent) represent the major part of the organic species. When the M(III) reached the stomach, the metal complexes were dissociated due to the high acidic conditions. That is, Cm(III) and Eu(III) are mainly present as the aquo ion, and only a small part (about 20%) is coordinated by the protein pepsin. When entering the intestine the metal ions are strongly bound by the protective protein mucin (about 65%) and inorganic ligands (about 35%; mainly carbonate and phosphate).

References
[1] J. Wragg, M. Cave, H. Taylor, N. Basta, E. Brandon, S. Casteel, C. Gron, A. Oomen, T. van de Wiele, British Geological Survey Open Report OR/07/027, Keyworth, Nottingham (2009) 90 pp.
[2] A. Barkleit, C. Wilke, A. Heller, T. Stumpf, A. Ikeda-Ohno, Dalton Trans. 46 (2017), 1593-1605

  • Invited lecture (Conferences)
    2nd International Conference on Pollutant Toxic Ions and Molecules, PTIM2017, 06.-09.11.2017, Caparica, Portugal

Permalink: https://www.hzdr.de/publications/Publ-25212
Publ.-Id: 25212