First-Time Isotopic Characterization of Seleno-Compounds in Biota: A Pilot Study of Selenium and Selenium Isotope Composition in Top Predator Seabirds.

This study pioneers the reporting of Se isotopes in marine top predators and represents the most extensive Se isotopic characterization in animals to date. A methodology based on hydride generation─multicollector inductively coupled plasma mass spectrometry─was established for such samples. The study was conducted on various internal organs of giant petrels ( Macronectes spp.), encompassing bulk tissues (δ 82/78 Se bulk ), distinct Se-specific fractions such as selenoneine (δ 82/78 Se SEN ), and HgSe nanoparticles (δ 82/78 Se NPs ). The δ 82/78 Se bulk results (2.0-5.6‰) offer preliminary insights into the fate of Se in key internal organs of seabirds, including the liver, the kidneys, the muscle, and the brain. Notably, the liver of all individuals was enriched in heavier Se isotopes compared to other examined tissues. In nanoparticle fraction, δ 82/78 Se varies significantly across individuals (δ 82/78 Se NPs from 0.6 to 5.7‰, n = 8), whereas it exhibits remarkable consistency among tissues and individuals for selenoneine (δ 82/78 Se SEN , 1.7 ± 0.3‰, n = 8). Significantly, there was a positive correlation between the shift from δ 82/78 Se bulk to δ 82/78 Se SEN and the proportion of Se present as selenoneine in the internal organs. This pilot study proves that Se species-specific isotopic composition is a promising tool for a better understanding of Se species fate, sources, and dynamics in animals.