Mercury speciation and isotope signatures in soils and groundwater at a HgCl2 contaminated site - evidence for fractionation processes during species transformations controlling Hg mobility.
- Autor(en)
- Jan Georg Wiederhold, Flora Maria Brocza, Harald Biester, Jan-Helge Richard, Stephan Krämer
- Abstrakt
Even though Hg has now been phased out in most industrial applications, a large number of legacy sites exist that have been affected by historical Hg releases. Elevated Hg levels in soils and waters at these sites represent a serious threat for the environment at local and regional scales. The long-term fate, mobility, and bioavailability of Hg strongly depend on its speciation, which is determined by the initial Hg compound from the industrial contamination source as well as biogeochemical transformation processes after release into the environment. Understanding the governing processes and controls on Hg speciation in contaminated subsurface environments is essential for risk assessment and site management.
Transformations of Hg species cause mass-dependent and mass-independent fractionation of stable Hg isotopes. Thus, variations in Hg isotope signatures may help identifying and quantifying transformation processes of Hg species. Previous studies at contaminated sites have largely focused on Hg isotopes as source tracer, whereas the application as process tracer has not been sufficiently explored yet.
Here, we present Hg speciation and isotope data from soil and groundwater collected at a former industrial facility in SW-Germany where wood was preserved by HgCl2 treatment (kyanization). Up to 25 tons of HgCl2 have been released to soil and aquifer during operation, resulting in a groundwater contamination plume of 1.3 km length. However, fast flowing groundwater and high Hg concentrations contrast sharply with extremely slow plume movement. It is unclear whether sorption/desorption or species transformation processes control the strong Hg retardation in the subsurface.
Thermodesorption analyses indicated the presence of different Hg species and partial transformation of HgCl2 to Hg0 in the contaminated soil layers (up to 635 µg g-1 Hg). Isotope analyses by CV-MC-ICP-MS revealed significant d202Hg variations between sections of a soil core taken close to the contamination source and groundwater collected nearby. Most groundwater samples (up to 192 µg L-1 Hg) were enriched in heavy Hg isotopes (up to +0.75‰) relative to NIST-3133. The most contaminated soil layers exhibited d202Hg values of 0.4‰, consistent with signatures of industrial Hg sources, whereas layers with lower Hg contents were isotopically heavier. Sequential extractions revealed significant variations between different Hg soil pools, e.g., isotopically heavy water-extractable Hg relative to bulk soil in the most contaminated layers. Our findings provide evidence for Hg isotope fractionation in the subsurface of contaminated sites and indicate the potential of Hg isotope signatures as tracer for species transformation processes controlling Hg mobility.- Organisation(en)
- Externe Organisation(en)
- Technische Universität Carolo-Wilhelmina zu Braunschweig
- Publikationsdatum
- 07-2017
- ÖFOS 2012
- 105105 Geochemie, 105906 Umweltgeowissenschaften, 105904 Umweltforschung
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/c8330505-29ad-434d-8769-45a4b7fe6c87