Mercury Isotope Fractionation by Internal Demethylation and Biomineralization Reactions in Seabirds: Implications for Environmental Mercury Science

• Main Authors: Alain Manceau (1455781), Romain Brossier (10911893), Sarah E. Janssen (2887310), Tylor J. Rosera (6112607), David P. Krabbenhoft (1247130), Yves Cherel (213795), Paco Bustamante (288199), Brett A. Poulin (3838039)
• Format: Dataset
• Language: unknown
• Published: 2021
• Subjects: Cell Biology; Molecular Biology; Physiology; Sociology; Hematology; Biological Sciences not elsewhere classified; Chemical Sciences not elsewhere classified; macronectes spp .); equilibrium isotope effects; e .; changes; 69 ± 0; 6 ± 0; 37 ± 0; 18 ± 0; toxicological risk assessment; nuclear volume fractionation; individual birds reflects; 4 </ sub; 3 ‰); consistent; hgse differed isotopically; 202 </ sup; 199 </ sup; 1 ± 0; → hgse biomineralization; xanes spectroscopic data; mercury isotope fractionation; hg (+ 1; environmental mercury science; spectroscopic data; ≤ 0; toxicological applications; eight birds; biomineralization reactions; 1 ‰); 06 ‰); (− 4; (− 1; mercury selenide; isotopic fractionation; isotopic data; stepwise transformation; stable isotopes; specific redistribution; selenocysteine ); relevant tissues; published hr; mathematical inversion; ligand bonds; kinetic lability; kerguelen islands; internal demethylation; inorganic hg; independent anomalies; hg values; giant petrels; dependent fractionation; demethylation reaction; biological reactions; antarctica ); 23 tissues; 02 ‰); Kerguelen; Kerguelen Islands; Antarc*; Antarctica; Giant Petrels
• Online Access: https://doi.org/10.1021/acs.est.1c04388.s005

A prerequisite for environmental and toxicological applications of mercury (Hg) stable isotopes in wildlife and humans is quantifying the isotopic fractionation of biological reactions. Here, we measured stable Hg isotope values of relevant tissues of giant petrels (Macronectes spp.). Isotopic data were interpreted with published HR-XANES spectroscopic data that document a stepwise transformation of methylmercury (MeHg) to Hg-tetraselenolate (Hg­(Sec) 4 ) and mercury selenide (HgSe) (Sec = selenocysteine). By mathematical inversion of isotopic and spectroscopic data, identical δ 202 Hg values for MeHg (2.69 ± 0.04‰), Hg­(Sec) 4 (−1.37 ± 0.06‰), and HgSe (0.18 ± 0.02‰) were determined in 23 tissues of eight birds from the Kerguelen Islands and Adélie Land (Antarctica). Isotopic differences in δ 202 Hg between MeHg and Hg­(Sec) 4 (−4.1 ± 0.1‰) reflect mass-dependent fractionation from a kinetic isotope effect due to the MeHg → Hg­(Sec) 4 demethylation reaction. Surprisingly, Hg­(Sec) 4 and HgSe differed isotopically in δ 202 Hg (+1.6 ± 0.1‰) and mass-independent anomalies (i.e., changes in Δ 199 Hg of ≤0.3‰), consistent with equilibrium isotope effects of mass-dependent and nuclear volume fractionation from Hg­(Sec) 4 → HgSe biomineralization. The invariance of species-specific δ 202 Hg values across tissues and individual birds reflects the kinetic lability of Hg-ligand bonds and tissue-specific redistribution of MeHg and inorganic Hg, likely as Hg­(Sec) 4 . These observations provide fundamental information necessary to improve the interpretation of stable Hg isotope data and provoke a revisitation of processes governing isotopic fractionation in biota and toxicological risk assessment in wildlife.