Tracing sources and fate of mercury in soils and groundwater at industrial contamination sites with stable mercury isotopes
- Author(s)
- Jan Georg Wiederhold, Flora Maria Brocza, Andrew Grigg, Stephan Krämer
- Abstract
Mercury (Hg) is a toxic pollutant of great environmental concern. The “Minamata Convention on Mercury”, a global treaty initiated by the United Nations Environment Programme and designed to reduce negative impacts of Hg on the environment, entered into force in August 2017. Although Hg is now being phased out in most industrial applications, a large number of legacy sites have been affected by historical industrial 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 at contaminated sites is thus essential for risk assessment and site management.
There are seven stable Hg isotopes (196Hg, 198Hg, 199Hg, 200Hg, 201Hg, 202Hg, and 204Hg) and recent studies have revealed that environmental processes can cause significant stable Hg isotope fractionations. Importantly, both mass-dependent (MDF) and mass-independent (MIF) fractionation can occur, affecting even-mass and odd-mass Hg isotopes to a different extent. This opens up the possibility of using Hg isotope signatures as two-dimensional tracer. High-precision Hg isotope analyses can be performed using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using a cold vapor introduction system and Tl addition for mass bias correction. With this method an analytical precision of about ±0.1‰ (2SD) for δ202Hg (MDF) and Δ199Hg (MIF) can be achieved. In the context of industrial contamination sites, variations in Hg isotope signatures may help identifying contamination sources and quantifying transformation processes of Hg species.
Here, we present data from two projects investigating Hg speciation and Hg isotope signatures in soil and groundwater collected at industrial legacy sites in Germany and Switzerland. Data from a former wood treatment facility, where Hg(II)-chloride had been used as preservative, demonstrate that significant Hg isotope variations exist between different depths of contaminated soil cores as well as between soil extracts targeting different Hg species. For instance, water-extractable Hg in the most contaminated zone is enriched in heavy Hg isotopes compared with the bulk soil suggesting that the initial Hg isotope fingerprint of the contamination source was altered during biogeochemical transformations in the subsurface. This finding is corroborated by groundwater samples collected downstream which also exhibit positive δ202Hg values. In contrast, data from a second contamination case, where Hg emissions from an industrial facility resulted in severe soil contamination adjacent to a drainage canal, exhibited no significant Hg isotope variations in soils collected downstream of the facility and between different soil extracts. This suggests that the source signature of the contamination source is preserved at this site. The implications of these results for using Hg isotope signatures as source and process tracer for industrial Hg emissions will be discussed.- Organisation(s)
- Publication date
- 11-2017
- Austrian Fields of Science 2012
- 105906 Environmental geosciences, 105105 Geochemistry, 104023 Environmental chemistry
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/08f3a71c-bebc-4708-9faa-0a703a7e0a74