University of Oulu

Eberle, A., Besold, J., León Ninin, J. M., Kerl, C. F., Kujala, K., & Planer-Friedrich, B. (2021). Potential of high pH and reduced sulfur for arsenic mobilization – Insights from a Finnish peatland treating mining waste water. Science of The Total Environment, 758, 143689.

Potential of high pH and reduced sulfur for arsenic mobilization : insights from a Finnish peatland treating mining waste water

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Author: Eberle, Anne1; Besold, Johannes1; Ninin, José M. León1;
Organizations: 1Department of Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
2Water Resources and Environmental Engineering Research Unit, University of Oulu, FI-90014 Oulu, Finland
Format: article
Version: accepted version
Access: open
Online Access: PDF Full Text (PDF, 2.7 MB)
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Language: English
Published: Elsevier, 2021
Publish Date: 2022-11-25


Peatlands, used for purification of mining waste waters, have shown efficient solid-phase sequestration of contaminants such as arsenic (As). However, contaminant re-mobilization may occur related to management changes or chemical alteration of original peatland conditions. For a treatment peatland in Finnish Lapland, we here confirm efficient As retention in near-surface peat layers close to the mining waste water inflow, likely due to binding to FeIII-phases. Seven years into operation of the treatment peatland, there appears to be further retention potential, as large areas downstream still had solid-phase As concentrations at background levels. However, via depth-resolved pore water analysis we observed a hotspot 170 m from the inflow at 10–50 cm depth, where As pore water concentrations exceeded input concentrations by a factor of 20, indicating substantial As re-mobilization. At the same spot, a peak of reduced sulfur (S) species was found. Arsenic species detected were arsenite and up to 26% methylated oxyarsenates, 15% methylated and 7.9% inorganic thioarsenates. We postulate that As mobilization is a result of short-term re-equilibration to a changed inflow chemistry after installation of a process water treatment plant and a long-term consequence of changing pore water pH from acidic to near-neutral, releasing reduced S and As. We infer that the co-occurrence of reduced S and As leads to formation of methylated and/or thiolated As species with known low sorption affinity, thereby further enhancing As mobility. Laboratory incubation studies with two peat cores confirmed a high S-induced As mobilization potential, especially when As-Fe-rich, oxic surface layers were incubated anoxically at near-neutral pH. Highest risk of As re-mobilization from this treatment peatland is expected in a scenario in which mining waste water inflow has stopped but the peatland remains flooded, and near-surface layers transition from oxic to anoxic conditions.

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Series: Science of the total environment
ISSN: 0048-9697
ISSN-E: 1879-1026
ISSN-L: 0048-9697
Volume: 758
Article number: 143689
DOI: 10.1016/j.scitotenv.2020.143689
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
Funding: This research was funded by the German Research Foundation [grant number DFG PL 302/20]. Fieldwork in Finland was supported by the Bavarian Research Alliance [grant number BayIntAn_UBT_2017_23, awarded to Britta Planer-Friedrich] and the Academy of Finland [project number 287397, awarded to Katharina Kujala].
Academy of Finland Grant Number: 287397
Detailed Information: 287397 (Academy of Finland Funding decision)
Copyright information: © 2020 Elsevier B.V. This manuscript version is made available under the CC-BY-NC-ND 4.0 license