New insights into the biomineralization of mercury selenide nanoparticles through stable isotope analysis in giant petrel tissues

Tiemannite (HgSe) is considered the end-product of methylmercury (MeHg) demethylation in vertebrates. The biomineralization of HgSe nanoparticles (NPs) is understood to be an efficient MeHg detoxification mechanism; however, the process has not yet been fully elucidated. In order to contribute to the understanding of complex Hg metabolism and HgSe NPs formation, the Hg isotopic signatures of 40 samples of 11 giant petrels were measured. This seabird species is one of the largest avian scavengers in the Southern Ocean, highly exposed to MeHg through their diet, reaching Hg concentrations in the liver up to more than 900 mu g g(-1). This work constitutes the first species-specific isotopic measurement (delta Hg-202, Delta Hg-199) of HgSe NPs in seabirds and the largest characterization of this compound in biota. Similar delta Hg-202 values specifically associated to HgSe (delta Hg-202(HgSe)) and tissues (delta(202)Hgbulk) dominated by inorganic Hg species were found, suggesting that no isotopic fractionation is induced during the biomineralization step from the precursor (demethylated) species. In contrast, the largest variations between delta(202)Hg(bulk )and delta Hg-202(HgSe) were observed in muscle and brain tissues. This could be attributed to the higher fraction of Hg present as MeHg in these tissues. Hg-biomolecules screening highlights the importance of the isotopic characterization of these (unknown) complexes.

Automated summary

The study found that the formation of HgSe nanoparticles did not induce isotopic fractionation, and the presence of MeHg in tissues such as muscle and brain led to variations in Hg isotopic signatures. Screening of Hg biomolecules emphasized the importance of isotopic characterization of these complexes.