umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Thermodynamic modelling of the chemical speciation of mercury and methylmercury under sulfidic conditions in boreal wetland soils
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
(English)Manuscript (preprint) (Other academic)
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-129243OAI: oai:DiVA.org:umu-129243DiVA: diva2:1058680
Available from: 2016-12-21 Created: 2016-12-21 Last updated: 2016-12-21
In thesis
1. Determination of mercury chemical speciation in the presence of low molecular mass thiols and its importance for mercury methylation
Open this publication in new window or tab >>Determination of mercury chemical speciation in the presence of low molecular mass thiols and its importance for mercury methylation
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Methylmercury (MeHg) is a neurotoxic compound that threatens the well-being of humans and wildlife. It is formed through the methylation of inorganic mercury (HgII) under suboxic/anoxic conditions in soils, sediment and waters. The chemical speciation of HgII, including specific HgII species in aqueous and solid/adsorbed phases, plays a key role in MeHg formation. Chemical forms of HgII which have been reported to be available for uptake in methylating bacteria include neutral HgII–sulfide complexes, HgII complexes with specific low molecular mass (LMM) thiols, and nanoparticulate HgS(s). Accurate determination of the chemical speciation of HgII is thus crucial when elucidating the mechanism of MeHg formation. The concentration of HgII–LMM thiols complexes is predicted to be extremely low (sub fM range). Current analytical methods do not allow direct quantification of HgII complexes due to the very low concentration of these complexes, and therefore determination rely on thermodynamic modeling. Accurate stability constants for HgII–LMM thiols complexes and quantification of LMM thiol ligands in environments are thus required to precisely determine the concentration of such complexes.

In this thesis, a novel analytical method was developed based on online pre-concentration coupled with liquid chromatography tandem mass spectrometry to determine the concentration of 16 LMM thiols (Paper I). This method was successful in detecting 8 LMM thiols in boreal wetland porewaters, with mercaptoacetic acid and cysteine being the most abundant. The total concentration of individual detected LMM thiols ranged from sub nM (LOD=0.1 nM) to 77 nM. Moreover, the stability constant (β2) for HgII complexes with 15 LMM thiols were directly determined for the first time by competing ligand exchange experiments combined with liquid chromatography ICPMS analysis (Paper II). Values of log β2 for the reaction Hg2+ + 2LMM-RS- = Hg(LMM-RS)2 ranged from 34.6 for. Based on the determined constants of Hg(LMM-RS)2 complexes and state-of-the-art constants from literature for other HgII complexes, we established comprehensive thermodynamic speciation models for MeHg and HgII in boreal wetlands (Paper III). The speciation of HgII was coupled with the HgII methylation rate constant (km) determined with different enriched Hg isotope tracers (Paper IV). There was a good correlation (R2=0.88) between the km determined by a HgII(aq) tracer added as Hg(NO3)2 with high bioavailability and a tracer where HgII was bond to thiol groups in natural organic matter (HgII-NOM(ads)) and has a lower bioavailability. The HgII(aq) tracer was consistently methylated at 5 times higher rate than the HgII-NOM(ads) tracer. A good correlation was observed between the concentration of biologically produced LMM thiols and km in the boreal wetlands. In a mesocosm study of estuarine sediment-brackish water systems, increased concentration of phytoplankton chlorophyll α due to macro nutrient additions led to an increase in HgII methylation rate of the HgII(aq) but not of the HgII-NOM(ads) tracer or ambient HgII species (Paper V). Furthermore, simulated newly deposited HgII species from atmospheric and terrestrial sources were exhibited significantly higher HgII methylation rates when compared with simulated aged sediment HgII pools. Through the development and adoption of novel analytical methods, this thesis reveals the significance of LMM thiols in Hg biogeochemistry by precise determination of HgII–LMM thiol complexes in natural environmental systems.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2016. 45 p.
Keyword
Mercury, methylmercury, LMM thiol, mass spectrometry, biogeochemistry, soil, sediment, ICP, WinSGW, modeling, S XANES, ligand exchange, stability constant, boreal wetlands
National Category
Analytical Chemistry
Research subject
Analytical Chemistry; biology, Environmental Science
Identifiers
urn:nbn:se:umu:diva-119938 (URN)978-91-7601-469-1 (ISBN)
Public defence
2016-06-08, KBC-huset, KB3A9, Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2016-05-18 Created: 2016-05-03 Last updated: 2016-12-21Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Liem-Nguyen, VanBjörn, Erik
By organisation
Department of Chemistry
Analytical Chemistry

Search outside of DiVA

GoogleGoogle Scholar

Total: 49 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf