Project

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Redox-induced speciation changes and reductive mobilization of arsenic and iron in highly-contaminated river floodplains

Applicant Kretzschmar Ruben
Number 138003
Funding scheme Project funding (Div. I-III)
Research institution Institut für Biogeochemie und Schadstoffdynamik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Pedology
Start/End 01.01.2012 - 31.12.2014
Approved amount 379'696.00
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All Disciplines (4)

Discipline
Pedology
Mineralogy
Other disciplines of Environmental Sciences
Geochemistry

Keywords (6)

arsenic; soil pollution; speciation; redox; EXAFS; micro-spectroscopy

Lay Summary (English)

Lead
Arsenic is a highly toxic trace element which is enriched in many river floodplains due to past or current mining activities. The biogeochemical processes controlling As mobility and bioavailability in the soil environment are not fully understood, especially the coupling to microbial reduction of Fe and Mn. Our goal is to better understand these processes and thereby contribute to improved risk assessment and remediation strategies for contaminated river floodplains.
Lay summary

The alluvial sediments of the Ogosta River in NW-Bulgaria are strongly contaminated by arsenic (As) due to mining activities. In this project we study the microbial dissimilatory iron (Fe) and As reduction and subsequent speciation changes of both elements in the Ogosta River floodplain soils using controlled laboratory experiments.

The alluvial floodplains of the Ogosta River basin, covering 3,110 km2 in NW-Bulgaria are highly contaminated with As and other trace elements as a result of historic mining activities and a large tailing dam failure in 1964. Arsenic concentrations in Ogosta floodplain soils exceed the maximum permissible level of 50 mg/kg recommended by the World Health Organization by up to 940 times. The molar As/Fe ratio in the poorly-crystalline mineral fraction of these soils was found to be anomalously high. Since this fraction, potentially comprising Fe(III) arsenates in addition to poorly-crystalline Fe(III) oxyhydroxides, is hypothesized to be most bioavailable for microbial Fe and As reduction under anoxic conditions, its composition will have a significant effect on the dynamics of As and Fe release from soil solids during prolonged flooding.

The goals of this project are to (i) explore the speciation of As and Fe in Ogosta floodplain soils as a function of particle size and at the micrometer scale, and (ii) investigate the dynamics of microbial As and Fe reduction, resulting Fe mineral transformations, and As speciation changes induced by soil flooding.

The Ogosta River is a tributary of the Danube River, the second-largest river of Europe, and there is considerable contamination potential for the lower Danube system. The results of this project will provide essential scientific information needed to develop a sustainable river management and remediation strategy for the Ogosta River floodplain and similar mining-affected environments.

Direct link to Lay Summary Last update: 11.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Arsenic species formed from arsenopyrite weathering along a contamination gradient in circumneutral river floodplain soils.
Mandaliev Petar Nikolov, Mikutta Christian, Barmettler Kurt, Kotsev Tsvetan, Kretzschmar Ruben (2014), Arsenic species formed from arsenopyrite weathering along a contamination gradient in circumneutral river floodplain soils., in Environmental science & technology, 48, 208-217.
Bioaccessibility of arsenic in mining-impacted circumneutral river floodplain soils
Mikutta Christian, Mandaliev Petar Nikolov, Mahler Nina, Kotsev Tsvetan, Kretzschmar Ruben (2014), Bioaccessibility of arsenic in mining-impacted circumneutral river floodplain soils, in Environmental science & technology, 48, 13468-13477.
Impact of birnessite on arsenic and iron speciation during microbial reduction of arsenic-bearing ferrihydrite
Ehlert Katrin, Mikutta Christian, Kretzschmar Ruben (2014), Impact of birnessite on arsenic and iron speciation during microbial reduction of arsenic-bearing ferrihydrite, in Environmental science & technology, 48, 11320-11329.

Collaboration

Group / person Country
Types of collaboration
Synchrotron radiation facilities United States of America (North America)
- Research Infrastructure
Prof. Andreas Kappler/Eberhard Karls University Tübingen Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Dr. Tsvetan Kotsev/Bulgarian Academy of Sciences (BAS) Bulgaria (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
SSSA International Annual Meeting Talk given at a conference Impact of birnessite on arsenic and iron speciation during microbial reduction of arsenic-bearing ferrihydrite 02.11.2014 Long Beach, CA, United States of America Mikutta Christian; Ehlert Katrin; Kretzschmar Ruben;
Monte Verita Conference on Iron Biogeochemistry Poster Influence of birnessite on reductive transformations of Fe and As: A microcosm study 03.03.2013 Ascona, Switzerland Mikutta Christian; Ehlert Katrin; Kretzschmar Ruben; Mandaliev Petar Nikolov;
EMC2012, First European Mineralogical Conference Talk given at a conference Biogeochemistry of arsenic in a mining-affected river floodplain 02.09.2012 Frankfurt a.m., Germany Kretzschmar Ruben; Mandaliev Petar Nikolov; Mikutta Christian;
Eurosoil 2012, 4th International Congress of the European Soil Science Societies Talk given at a conference Arsenic speciation and mobility in mining-affected river floodplain soils: X-ray absorption spectroscopy and column studies 02.07.2012 Bari, Italy Kretzschmar Ruben; Mandaliev Petar Nikolov; Mikutta Christian;
Invited Seminar, Laboratory of Hydrology and Geochemistry of Strasbourg Individual talk Micro-spectroscopic arsenic speciation in a highly contaminated, mining affected river floodplain 29.06.2012 Strasbourg, France Kretzschmar Ruben; Mikutta Christian; Mandaliev Petar Nikolov;
NIGGG-BAS Seminar, "Mining impact to the Riverine Environment in Bulgaria – Geoecological Issues Related to Ogosta River Valley" Individual talk Micro-XRF/XAS studies on arsenic speciation in Ogosta floodplain soils 08.06.2012 Sofia, Bulgaria Mandaliev Petar Nikolov; Mikutta Christian; Kretzschmar Ruben;


Awards

Title Year
Soil & Environmental Quality Graduate Student Award 2014

Associated projects

Number Title Start Funding scheme
117933 Dynamics of Trace Metal Speciation in Periodically Reduced Soils 01.03.2008 Project funding (Div. I-III)
155890 Redox-induced speciation changes and reductive mobilization of arsenic, manganese, and iron in highly-contaminated river floodplains 01.01.2015 Project funding (Div. I-III)
156392 Mobility of trace metals in periodically flooded soils: Influence of reduced iron, manganese, and sulfur 01.05.2015 Project funding (Div. I-III)
142978 Arsenic contamination of Ogosta river: Linking biogeochemical processes in floodplain soils with river system dynamics 01.11.2012 Bulgarian-Swiss Research Programme (BSRP)
141562 Structure analysis of nanocrystalline iron arsenates and phosphates 01.02.2012 International short research visits
113654 Arsenic Contamination of Paddy Soils through Irrigation Water in Bangladesh: Field Evidence and Investigation of Relevant Processes 01.01.2007 Project funding (Div. I-III)

Abstract

The alluvial floodplains of the Ogosta River in NW Bulgaria, a tributary to the lower Danube River, are highly contaminated with arsenic (As) and other trace elements as a result of historic mining activities and a large tailing dam failure in 1964. In a preliminary study, we detected As concentrations up to 47`000 mg/kg in floodplain soils, exceeding the EU guideline values for As in soils by a factor of 940. Despite the high iron (Fe) concentrations in these extremely contaminated soils, which are also a result of mining impacts, the molar As/Fe ratio in the poorly-crystalline mineral fraction of the soils (as assessed by oxalate or ascorbate extraction) was found to be anomalously high, reaching values of 0.5 in some soils. Since these poorly-crystalline Fe oxyhydroxide fractions are most bioavailable for microbial Fe reduction under anoxic conditions, the composition of this Fe and As pool will have a significant effect of the dynamics of As and Fe release from soil solids during prolonged flooding. To date, no studies have been published on the As speciation in the circum-neutral to alkaline, extremely As contaminated soils of the Ogosta river floodplain. The goals of our proposed research are to (i) provide the first detailed spectroscopic study on the speciation of As and Fe in Ogosta floodplain soils sampled along contamination gradients, (ii) characterize the distribution of As species as a function of particle size and at the micrometer scale, (iii) investigate the dynamics of As and Fe reduction and resulting Fe mineral transformations and speciation changes of As under anoxic conditions induced by soil flooding. We are particularly interested in understanding the influence of molar As/Fe ratios in the poorly-crystalline mineral fraction of soils on As and Fe reduction. We hypothesize, that very high As/Fe ratios suppress microbial Fe reduction and Fe mineral transformations. This will in turn limit As(V) reduction and release into solution. Thus, the mobility of As in extremely contaminated soils may be lower than expected based on the total elemental concentrations.The speciation of As and Fe in the Ogosta soils will be investigated by synchrotron X-ray absorption fine structure spectroscopy (XAFS). Micro-focussed X-ray fluorescence (µ-XRF) and µ-XAFS will be used to study the spatial distribution of As, Fe, Mn, and other elements at the micrometer scale. “Chemical imaging” using hard X-ray micro-spectroscopy will be used to visualize the distribution of major As species in the soils.The microbial reduction and subsequent release of As and Fe in the Ogosta soils will be studied by different types of controlled laboratory experiments (“slurry”, “column”, “microcosm”). Overall, the results will provide essential scientific information needed to develop a sustainable river management and remediation strategy for Ogosta and similar mining-affected floodplains.
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