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Download fileIsotope Fractionation from In Vivo Methylmercury Detoxification in Waterbirds
dataset
posted on 2021-04-08, 19:17 authored by Brett A. Poulin, Sarah E. Janssen, Tylor J. Rosera, David P. Krabbenhoft, Collin A. Eagles-Smith, Joshua T. Ackerman, A. Robin Stewart, Eunhee Kim, Zofia Baumann, Jeong-Hoon Kim, Alain ManceauThe robust application
of stable mercury (Hg) isotopes for mercury
source apportionment and risk assessment necessitates the understanding
of mass-dependent fractionation (MDF) as a result of internal transformations
within organisms. Here, we used high energy-resolution X-ray absorption
near edge structure spectroscopy and isotope ratios of total mercury
(δ202THg) and methylmercury (δ202MeHg) to elucidate the chemical speciation of Hg and the resultant
MDF as a result of internal MeHg demethylation in waterbirds. In three
waterbirds (Clark’s grebe, Forster’s tern, and south
polar skua), between 17 and 86% of MeHg was demethylated to inorganic
mercury (iHg) species primarily in the liver and kidneys as Hg–tetraselenolate
[Hg(Sec)4] and minor Hg–dithiolate [Hg(SR)2] complexes. Tissular differences between δ202THg
and δ202MeHg correlated linearly with %iHg [Hg(Sec)4 + Hg(SR)2] and were interpreted to reflect a kinetic
isotope effect during in vivo MeHg demethylation.
The product–reactant isotopic enrichment factor (εp/r) for the demethylation of MeHg → Hg(Sec)4 was −2.2 ± 0.1‰. δ202MeHg values
were unvarying within each bird, regardless of Hg(Sec)4 abundance, indicating fast internal cycling or replenishment of
MeHg relative to demethylation. Our findings document a universal
selenium-dependent demethylation reaction in birds, provide new insights
on the internal transformations and cycling of MeHg and Hg(Sec)4, and allow for mathematical correction of δ202THg values as a result of the MeHg → Hg(Sec)4 reaction.
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Keywords
mercury source apportionmentchemical speciationrisk assessmentfindings documentmass-dependent fractionationδ 202 THgenergy-resolution X-ray absorptionMeHg demethylationVivo Methylmercury Detoxificationδ 202 MeHgMDFδ 202 THg valuesvivo MeHg demethylationselenium-dependent demethylation re...isotope ratiosIsotope Fractionationedge structure spectroscopyisotope effectTissular differences