Mercury isotope signatures of digests and sequential extracts from industrially contaminated soils and sediments

Author(s)

Andrew R.C. Grigg, Ruben Kretzschmar, Robin S. Gilli, Jan Georg Wiederhold

Abstract

Environmental mercury (Hg) pollution is a matter of global concern. Mercury speciation controls its environmental behaviour, and stable isotope ratios can potentially trace Hg movement through environmental compartments. Here we investigated Hg in industrially contaminated soils and sediments (Visp, Valais, Switzerland) using concentration and stable isotope analysis (CV-MC-ICP-MS) of total digests, and a four-step sequential extraction procedure. The sequential extraction employed (1) water (labile Hg species), (2) NaOH or Na

₄P

₂O

₇ (organically-bound Hg), (3) hydroxylamine-HCl (Hg bound to Mn and Fe (oxyhydr)oxides), and (4) aqua regia (residual Hg pools). The majority of Hg was extracted in step 4 and up to 36% in step 2. Mercury bound to organic matter was the dominant source of Hg in water, NaOH and Na

₄P

₂O

₇ extracts. Sulfides and colloidal oxide minerals were possible additional sources of Hg in some samples. The inconsistent comparative performance of NaOH and Na

₄P

₂O

₇ extractions showed that these classical extractants may not extract Hg exclusively from the organically-bound pool. Samples taken at the industrial facility displayed the greatest isotopic variation (δ

²⁰²Hg: −0.80‰ ± 0.14‰ to 0.25‰ ± 0.13‰, Δ

¹⁹⁹Hg: −0.10‰ ± 0.03‰ to 0.02‰ ± 0.03‰; all 2SD) whereas downstream of the facility there was much less variation around average values of δ

²⁰²Hg = −0.47‰ ± 0.11‰ and Δ

¹⁹⁹Hg = −0.05‰ ± 0.03‰ (1SD, n = 19). We interpret the difference as the result of homogenisation by mixing of canal sediments containing Hg from the various sources at the industrial facility with preservation of the mixed industrial Hg signature downstream. In contrast to previous findings, Hg isotopes in the sequential extracts were largely similar to one another (2SD < 0.14‰), likely demonstrating that the Hg speciation was similar among the extracts. Our results reveal that Hg resides in relatively stable soil pools which record an averaged isotope signature of the industrial sources, potentially facilitating source tracing studies with Hg isotope signatures at larger spatial scales further downstream.

Organisation(s)

External organisation(s)

Eidgenössische Technische Hochschule Zürich, University of Vienna

Journal

Science of the Total Environment

Volume

636

Pages

1344-1354

No. of pages

11

ISSN

0048-9697

DOI

https://doi.org/10.1016/j.scitotenv.2018.04.261

Publication date

05-2018

Peer reviewed

Yes

Austrian Fields of Science 2012

105105 Geochemistry, 104023 Environmental chemistry, 105906 Environmental geosciences

Keywords

ASJC Scopus subject areas

Pollution, Waste Management and Disposal, Environmental Engineering, Environmental Chemistry

Portal url

https://ucrisportal.univie.ac.at/en/publications/154c9dc7-b172-4a4f-bc24-a5ec448ba3d6