Preliminary insight into the intracellular behaviour of rare earths and other technology-critical elements (TCEs) in northern pike liver: study of TCE-binding biomolecules <i>via</i> size-exclusion HPLC-ICP-MS

Technology-critical elements (TCEs) refer to the elements that play an important role in many emerging technologies and the production of advanced materials, and these include lanthanides, tungsten and vanadium. Actinides, Tl, and Pb, which also belong to TCEs, are abundantly used in power generation, industrial applications, and modern agricultural practices. The information on the influence of these elements on the aquatic environment and biota is still rather scarce. Thus, the distributions of the above-mentioned metals among cytosolic biomolecules of different molecular masses in the liver of the northern pike (<i>Esox lucius</i>) from the Mrežnica River (Croatia) were studied to obtain an insight into their intracellular behaviour and potential for toxicity. The applied method was a hyphenated system of size-exclusion high-performance liquid chromatography and inductively coupled plasma mass spectrometry. In the samples with lower cytosolic concentrations, the obtained distributions of several TCEs (lanthanides, W, Th, and U) and Pb, among biomolecules of a wide range of molecular masses, which covered the entire column separation range (<10 to >600 kDa), indicated their nonspecific binding to various intracellular components. In the sample with the highest cytosolic concentration, a shift towards the highest molecular masse (>600 kDa) was observed for lanthanides and actinides, which is a sign of their possible binding to protein aggregates. In contrast, W and Pb showed a preference for medium molecular mass biomolecules (30-100 kDa). Moreover, it was hypothesized that prominent elution of U and Pb observed in the low molecular mass region (<10 kDa) possibly indicated their partial detoxification. Potential Pb associations with metallothionein-like proteins were also recorded (∼6-7 kDa). The remaining two elements, V and Tl, exhibited more specific intracellular binding, as they were eluted within one/two narrow peaks in the high molecular mass region (575 kDa/100-400 kDa). The tendency of the studied TCEs and other potentially toxic elements to bind to medium and high molecular mass intracellular proteins necessitates further research of their specific targets.