ИСТИНА

Some of zooplankton organisms (viz. several taxa of sea crustaceans) are found to accumulate lithium. Causes and mechanisms underlying this phaenomenon are unclear and interesting for marine biologists and oceanographers. The goal of this study was to establish correlations between analytical signals of elements and molecules in animal tissue using laser-induced breakdown spectroscopy (LIBS) and Raman scattering spectroscopy. These techniques are rapid and micro- or non-destructive. Bulk composition data, obtained by ICP-AES and ICP-MS after digestion, were also available. In total, 29 samples were analysed. The NMF is well suited for our purposes as it provides principal components (PCs) that have physical sense and are therefore relatively easy to interpret. Prior to processing Raman spectra, all remains of fluorescence background were carefully removed. We found that Raman PCs obtained by NMF correlate well with the available taxa (copepods, malacostracans, arrow worms, molluscs, and mixed samples). The number of PCs was found using the scree plot provided by the PCA. As copepods contain the highest amounts of Li, they were then considered as a separate sample subset. This subset could further be decomposed to give 3 PCs, the 1st containing carotenoid peaks, the 2nd exhibiting quite intensive amino acid signals, and the 3rd featuring bands of hydroxyl-containing compounds. Decomposition of LIBS data yields 4 PCs (lines of Mg, Sr and Ca; lines of Li, Na and K; molecular emission; Ca and Cu lines), while the copepod subset suggests that Li and K (but not Na) share the same component. NMF of fused datasets (composed from LIBS and Raman spectra) has suggested that Li accumulation is related to the content of amino acids. Indeed, Li content linearly depends on the area of tryptophan peak (R = 0.91, n = 8) for copepods containing less than 70 mg/kg of Li. It has also been found that high copper and lithium contents are not found simultaneously, Cu being more abundant in malacostracans than in copepods. The reported study was funded by the RFBR according to the research project No. 18-33-01297. ICP-AES and ICP-MS elemental analyses of zooplankton samples were funded by the Russian Science Foundation (research project No. 18-77-00064). The authors are grateful to Á. Bélteki, A. Kéri, P. Janovszky, D. Palásti, and Dr. K. Fintor (University of Szeged) for their valuable assistance.