es9b00619_si_001.pdf (645.58 kB)
Mercury Isotope Fractionation in the Subsurface of a Hg(II) Chloride-Contaminated Industrial Legacy Site
journal contribution
posted on 2019-05-30, 00:00 authored by Flora M. Brocza, Harald Biester, Jan-Helge Richard, Stephan M. Kraemer, Jan G. WiederholdTo
understand the transformations of mercury (Hg) species in the subsurface
of a HgCl2-contaminated former industrial site in southwest
Germany, Hg isotope analysis was combined with an investigation of
Hg forms by a four-step sequential extraction protocol (SEP) and pyrolytic
thermodesorption. Data from two soil cores revealed that the initial
HgCl2 was partly reduced to metallic Hg(0) and that Hg
forms of different mobility and oxidation state coexist in the subsurface.
The most contaminated sample (K2-8, 802 mg kg–1 Hg)
had a bulk δ202Hg value of around −0.43 ±
0.06‰ (2SD), similar to published average values for industrial
Hg sources. Other sample signatures varied significantly with depth
and between SEP pools. The most Hg-rich samples contained mixtures
of Hg(0) and Hg(II) phases, and the water-extractable, mobile Hg pool
exhibited heavy δ202Hg values of up to +0.18‰.
Sequential water extracts revealed slow dissolution kinetics of mobile
Hg pools, continuously releasing isotopically heavy Hg into solution.
This was further corroborated by heavy δ202Hg values
of groundwater samples. Our results demonstrate that the Hg isotope
signature of an industrial contamination source can be significantly
altered during the transformations of Hg species in the subsurface,
which complicates source tracing applications but offers the possibility
of using Hg isotopes as process tracers in contaminated subsurface
systems.