Mercury isotope ratios as a tool to trace and quantify Hg species transformations in contaminated soils and aquifers (MIRACOSA)
Mineralogy, Petrology and Geochemistry
Final Report Abstract
In this project we investigated the relationship between Hg species and Hg isotope fractionation in soil and groundwater and stream sediments at two sites contaminated by HgCl2 as a result of wood impregnation (kyanisation). Besides comprehensive field investigations we carried out additional laboratory experiments to decipher the retention of HgCl2 by aquifer sediments and related Hg species transformation and Hg isotope fractionation. By combining Hg speciation analyses using pyrolysis-thermodesorption and selective extractions with Hg isotope analyses of total Hg and separated Hg pools of soil and groundwater samples, we were able to trace Hg species transformations at the studied contamination cases. These results are useful not only for future investigations of similar contaminated sites but can also be transferred to uncontaminated systems to better understand Hg isotope fractionation in natural soil and groundwater systems as a function of Hg species transformation reactions. With this novel combination of Hg concentration, Hg speciation, and Hg isotope analysis (using CV-MC-ICP-MS) of liquid and solid samples significant improvements of our capability to predict the behavior and fate of Hg not only for the studied field sites but also for other contaminated and pristine aquifer and soil systems in general were anticipated. The findings of this project provide insights into the applicability of Hg isotope ratios as process tracers and the benefits of combining multiple analytical approaches to assess the geochemical behavior of Hg at contaminated sites which also have implications for the general interpretation of Hg isotope ratios in natural samples. Despite the demonstrated advancements in Hg geochemical interpretations highlighted by the addition of Hg isotope analyses within such a comprehensive study, considerable uncertainties and distinct unknowns remain. System complexity (multiple groundwater bodies, complex terrain, and highly variable redox conditions) observed particularly at the TN site appear to limit our ability to identify processes. A major limiting factor remains our inability to identify all Hg2+ species in environmental solid- or liquid-phase samples, a task that is not advanced by analyses of Hg isotopes. The application of Hg isotopes in Hg geochemistry is still relatively new and many processes that might occur in the natural environment have not been examined in laboratory conditions to determine fractionation factors. This puts a limit on how much we can presently interpret Hg isotope signatures of environmental samples. It is critical that laboratory examination of fractionation factors for MDF and MIF of known and potential biogeochemical processes continue to be pursed and then examined via holistic field studies such as this. Equally as important is the need to continue to assess these processes in field-based studies as we have done here to determine if they are indeed relevant (do occur) and can be identified under environmentally relevant conditions.
Publications
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Combining mercury isotope signatures and species analysis for the investigation of creek sediments downstream of a Hg(II) chloride contaminated industrial legacy site. International Conference on Mercury as a Global Pollutant (ICMGP), Krakow 2019 (p. 127-128)
Schwab, L., Rothe, F., McLagan, D. S., Kraemer, S. M., Biester, H. & Wiederhold, J. G.
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Mercury isotope and species analyses as a tool to trace processes in contaminated soils and sediments. Poster presentation at Goldschmidt Conference, Barcelona 2019
Schwab L., McLagan D. S., Kraemer S. M., Biester H. & Wiederhold J. G.
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Mercury isotope fractionation and speciation in surface soils and drilling cores of industrial legacy sites contaminated by timber kyanisation with mercury(II) chloride. International Conference on Mercury as a Global Pollutant (ICMGP), Krakow 2019
McLagan, D. S., Schwab, L., Wiederhold, J. G., Brocza, F. M., Chen, L., Kraemer, S. M. & Biester, H.
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Mercury concentrations, redox state, and isotope ratios in consecutive water extracts of Hg(II)-chloride contaminated soils. Copernicus GmbH.
Kleindienst, Alina; Schwab, Lorenz; McLagan, David; Krämer, Stephan M.; Biester, Harald & Wiederhold, Jan G.
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Mercury isotope fractionation during dark abiotic reduction of Hg(II) by dissolved and surface-bound Fe(II) species. Copernicus GmbH.
Schwab, Lorenz; McLagan, David S.; Kraemer, Stephan M.; Biester, Harald & Wiederhold, Jan G.
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Experimental determination of kinetic mercury isotope fractionation during reduction of Hg(II) by dissolved Fe(II) and Fe(II)-bearing minerals. Goldschmidt2021 abstracts, 2021). European Association of Geochemistry.
Schwab, Lorenz; Gallati, Niklas; McLagan, David; Kraemer, Stephan; Biester, Harald & Wiederhold, Jan
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High mercury sorption in low organic matter aquifer material using column experiments.. Goldschmidt2021 abstracts, 2021. European Association of Geochemistry.
McLagan, David; Esser, Carina; Schwab, Lorenz; Pietrucha, Jan; Wiederhold, Jan; Kraemer, Stephan & Biester, Harald
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Temporal and spatial assessment of gaseous elemental mercury concentrations and emissions at contaminated sites using active and passive measurements. Environmental Research Communications, 3(5), 051004.
McLagan, David S.; Osterwalder, Stefan & Biester, Harald
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Assessing within tree cycling and atmospheric archiving of mercury using mercury stable isotopes and concentrations. International Conference on Mercury as a Global Pollutant (ICMGP) 2022
McLagan, D. S., Biester, H., Navrátil, T., Kraemer, S. M. & Schwab, L.
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Demystifying mercury geochemistry in contaminated soil–groundwater systems with complementary mercury stable isotope, concentration, and speciation analyses. Environmental Science: Processes & Impacts, 24(9), 1406-1429.
McLagan, D. S.; Schwab, L.; Wiederhold, J. G.; Chen, L.; Pietrucha, J.; Kraemer, S. M. & Biester, H.
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How Hg isotope source signatures can be overprinted by biogeochemical processes in the subsurface of contaminated legacy sites. EGU General Assembly 2022
Schwab L., McLagan D. S., Chen, L., Pietrucha, J., Kraemer S. M., Biester H. & Wiederhold J. G.
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Internal tree cycling and atmospheric archiving of mercury: examination with concentration and stable isotope analyses. Biogeosciences, 19(17), 4415-4429.
McLagan, David S.; Biester, Harald; Navrátil, Tomas; Kraemer, Stephan M. & Schwab, Lorenz
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Kinetic versus Equilibrium Mercury Isotope Effects During Homogenous and Surface Catalyzed Mercury(II) Reduction by Iron(II). Goldschmidt2022 abstracts, 2022). European Association of Geochemistry.
Schwab, Lorenz; Gallati, Niklas; McLagan, David; Biester, Harald; Kraemer, Stephan & Wiederhold, Jan
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Large extent of mercury stable isotope fractionation in contaminated stream sediments induced by changes of mercury binding forms. Frontiers in Environmental Chemistry, 3.
Schwab, Lorenz; Rothe, Florian M.; McLagan, David S.; Alten, Alexandra; Kraemer, Stephan M.; Biester, Harald & Wiederhold, Jan G.
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Tracing geochemical processes governing the stationary behavior of a Hg plume in groundwater using Hg isotopes. International Conference on Mercury as a Global Pollutant (ICMGP) 2022
Schwab L., Kleindienst, A., Esser, C., McLagan, D. S., Biester, H., Kraemer S. M. & Wiederhold J. G.
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Mercury Isotope Fractionation during Dark Abiotic Reduction of Hg(II) by Dissolved, Surface-Bound, and Structural Fe(II). Environmental Science & Technology, 57(40), 15243-15254.
Schwab, Lorenz; Gallati, Niklas; Reiter, Sofie M.; Kimber, Richard L.; Kumar, Naresh; McLagan, David S.; Biester, Harald; Kraemer, Stephan M. & Wiederhold, Jan G.
