Demystifying mercury geochemistry in contaminated soil–groundwater systems with complementary mercury stable isotope, concentration, and speciation analyses

David McLagan (Corresponding author), Lorenz Schwab, Jan Georg Wiederhold, Lu Chen, Jan Pietrucha, Stephan Krämer, Harald Biester (Corresponding author)

Publications: Contribution to journalArticlePeer Reviewed

Abstract

Interpretation of mercury (Hg) geochemistry in environmental systems remains a challenge. This is largely associated with the inability to identify specific Hg transformation processes and species using established analytical methods in Hg geochemistry (total Hg and Hg speciation). In this study, we demonstrate the improved Hg geochemical interpretation, particularly related to process tracing, that can be achieved when Hg stable isotope analyses are complemented by a suite of more established methods and applied to both solid- (soil) and liquid-phases (groundwater) across two Hg2+-chloride (HgCl2) contaminated sites with distinct geological and physicochemical properties. This novel approach allowed us to identify processes such as Hg2+ (i.e., HgCl2) sorption to the solid-phase, Hg2+ speciation changes associated with changes in groundwater level and redox conditions (particularly in the upper aquifer and capillary fringe), Hg2+ reduction to Hg0, and dark abiotic redox equilibration between Hg0 and Hg(II). Hg stable isotope analyses play a critical role in our ability to distinguish, or trace, these in situ processes. While we caution against the non-critical use of Hg isotope data for source tracing in environmental systems, due to potentially variable source signatures and overprinting by transformation processes, our study demonstrates the benefits of combining multiple analytical approaches, including Hg isotope ratios as a process tracer, to obtain an improved picture of the enigmatic geochemical behavior and fate of Hg at contaminated legacy sites.
Original languageEnglish
Pages (from-to)1406-1429
Number of pages24
JournalEnvironmental Science: Processes & Impact
Volume24
Issue number9
Early online dateJan 2022
DOIs
Publication statusPublished - 4 Jan 2022

Austrian Fields of Science 2012

  • 105105 Geochemistry
  • 104023 Environmental chemistry
  • 105906 Environmental geosciences

Keywords

  • Mercury Isotopes
  • Contaminated legacy sites
  • SPECIATION ANALYSIS
  • THERMAL-DESORPTION
  • ARID-ZONE SOILS
  • ELEMENTAL MERCURY
  • REDUCTION
  • HG-II
  • DISSOLVED ORGANIC-MATTER
  • ATMOSPHERIC MERCURY
  • MASS-INDEPENDENT FRACTIONATION
  • SEQUENTIAL EXTRACTION
  • NUCLEAR VOLUME

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