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Publications in peer reviewed journals

7 Publications found
  • Demystifying mercury geochemistry in contaminated soil–groundwater systems with complementary mercury stable isotope, concentration, and speciation analyses

    David S. McLagan, Lorenz Schwab, Jan G. Wiederhold, Lu Chen, Jan Pietrucha, Stephan M. Kraemer, Harald Biester
    2022 - Environmental Science: Processes & Impacts, Advance Article


    Interpretation of mercury (Hg) geochemistry in environmental systems remains a challenge. This is largely associated with the inability to identify specific Hg transformation processes and species using established analytical methods in Hg geochemistry (total Hg and Hg speciation). In this study, we demonstrate the improved Hg geochemical interpretation, particularly related to process tracing, that can be achieved when Hg stable isotope analyses are complemented by a suite of more established methods and applied to both solid- (soil) and liquid-phases (groundwater) across two Hg2+-chloride (HgCl2) contaminated sites with distinct geological and physicochemical properties. This novel approach allowed us to identify processes such as Hg2+ (i.e., HgCl2) sorption to the solid-phase, Hg2+ speciation changes associated with changes in groundwater level and redox conditions (particularly in the upper aquifer and capillary fringe), Hg2+ reduction to Hg0, and dark abiotic redox equilibration between Hg0 and Hg(II). Hg stable isotope analyses play a critical role in our ability to distinguish, or trace, these in situ processes. While we caution against the non-critical use of Hg isotope data for source tracing in environmental systems, due to potentially variable source signatures and overprinting by transformation processes, our study demonstrates the benefits of combining multiple analytical approaches, including Hg isotope ratios as a process tracer, to obtain an improved picture of the enigmatic geochemical behavior and fate of Hg at contaminated legacy sites.

  • Exploring Nanogeochemical Environments: New Insights from Single Particle ICP-TOFMS and AF4-ICPMS

    Manuel D. Montaño, Chad W. Cuss, Haley M. Holliday, Muhammad B. Javed, William Shotyk, Kathryn L. Sobocinski, Thilo Hofmann, Frank von der Kammer, James F. Ranville
    2022 - ACS Earth & Space Chemistry, 6: 943–952


    Nanogeochemistry is an emerging focus area recognizing the role of nanoparticles in Earth systems. Engineered nanotechnology has cultivated advanced analytical techniques that are also applicable to nanogeochemistry. Single particle inductively coupled plasma ICP-time-of-flight-mass spectrometry (ICP-TOF-MS) promises a significant step forward, as time-of-flight mass analyzers enable simultaneous quantification of the entire atomic mass spectrum (∼7–250 m/z+). To demonstrate the utility of this approach, samples were collected and analyzed from a large, boreal river, and its surrounding tributaries. These samples provided us with a diversity of particle compositions and morphologies, while their interconnected nature allowed for an examination of the various nanogeochemical processes present in this system. To further expand on this effort, we combined this high-throughput technique with AF4-ICPMS, focusing on major carriers of trace elements. Using spICP-TOF-MS, Al, Si, and Fe were grouped into classes having all combinations of one or more of these elements. Particle-by-particle ICP-TOF-MS analysis found chemically heterogeneous populations, indicating the predominance of diverse mineralogy or heteroaggregates. The importance of suspended Fe and Mn for the speciation of Pb was observed by single particle ICP-TOF-MS and complemented by AF4-ICPMS analysis of dissolved organic matter and nanoparticulate Fe/Mn. Our study exploits the combination of spICP-TOF-MS and AF4-ICP-MS for studying isotopic and elemental ratios (mineralogy) of individual nanoparticles, which opens the door to further explore the mechanisms of colloid facilitated transport of trace elements.

  • Identifying Functional Groups that Determine Rates of Micropollutant Biotransformations Performed by Wastewater Microbial Communities

    Stephanie L. Rich, Michael Zumstein, Damian E. Helbling
    2022 - Environmental Science & Technology, 56: 984–994


    The goal of this research was to identify functional groups that determine rates of micropollutant (MP) biotransformations performed by wastewater microbial communities. To meet this goal, we performed a series of incubation experiments seeded with four independent wastewater microbial communities and spiked them with a mixture of 40 structurally diverse MPs. We collected samples over time and used high-resolution mass spectrometry to estimate biotransformation rate constants for each MP in each experiment and to propose structures of 46 biotransformation products. We then developed random forest models to classify the biotransformation rate constants based on the presence of specific functional groups or observed biotransformations. We extracted classification importance metrics from each random forest model and compared them across wastewater microbial communities. Our analysis revealed 30 functional groups that we define as either biotransformation promoters, biotransformation inhibitors, structural features that can be biotransformed based on uncharacterized features of the wastewater microbial community, or structural features that are not rate-determining. Our experimental data and analysis provide novel insights into MP biotransformations that can be used to more accurately predict MP biotransformations or to inform the design of new chemical products that may be more readily biodegradable during wastewater treatment.

  • Iron Nitride Nanoparticles for Enhanced Reductive Dechlorination of Trichloroethylene

    Miroslav Brumovský, Jana Oborná, Vesna Micić, Ondřej Malina, Josef Kašlík, Daniel Tunega, Miroslav Kolos, Thilo Hofmann, František Karlický, Jan Filip
    2022 - Environmental Science & Technology, 56: 4425-4436


    Nitriding has been used for decades to improve the corrosion resistance of iron and steel materials. Moreover, iron nitrides (FexN) have been shown to give an outstanding catalytic performance in a wide range of applications. We demonstrate that nitriding also substantially enhances the reactivity of zerovalent iron nanoparticles (nZVI) used for groundwater remediation, alongside reducing particle corrosion. Two different types of FexN nanoparticles were synthesized by passing gaseous NH3/N2 mixtures over pristine nZVI at elevated temperatures. The resulting particles were composed mostly of face-centered cubic (γ′-Fe4N) and hexagonal close-packed (ε-Fe2–3N) arrangements. Nitriding was found to increase the particles’ water contact angle and surface availability of iron in reduced forms. The two types of FexN nanoparticles showed a 20- and 5-fold increase in the trichloroethylene (TCE) dechlorination rate, compared to pristine nZVI, and about a 3-fold reduction in the hydrogen evolution rate. This was related to a low energy barrier of 27.0 kJ mol–1 for the first dechlorination step of TCE on the γ′-Fe4N(001) surface, as revealed by density functional theory calculations with an implicit solvation model. TCE dechlorination experiments with aged particles showed that the γ′-Fe4N nanoparticles retained high reactivity even after three months of aging. This combined theoretical-experimental study shows that FexN nanoparticles represent a new and potentially important tool for TCE dechlorination.

  • Ligand-Induced U Mobilization from Chemogenic Uraninite and Biogenic Noncrystalline U(IV) under Anoxic Conditions

    Kyle J. Chardi, Anshuman Satpathy, Walter D. C. Schenkeveld*, Naresh Kumar, Vincent Noël, Stephan M. Kraemer, and Daniel E. Giammar
    2022 - Environmental Science and Technology, 56: 6369–6379


    Microbial reduction of soluble hexavalent uranium (U(VI)) to sparingly soluble tetravalent uranium (U(IV)) has been explored as an in situ strategy to immobilize U. Organic ligands might pose a potential hindrance to the success of such remediation efforts. In the current study, a set of structurally diverse organic ligands were shown to enhance the dissolution of crystalline uraninite (UO2) for a wide range of ligand concentrations under anoxic conditions at pH 7.0. Comparisons were made to ligand-induced U mobilization from noncrystalline U(IV). For both U phases, aqueous U concentrations remained low in the absence of organic ligands (<25 nM for UO2; 300 nM for noncrystalline U(IV)). The tested organic ligands (2,6-pyridinedicarboxylic acid (DPA), desferrioxamine B (DFOB), N,N′-di(2-hydroxybenzyl)ethylene-diamine-N,N′-diacetic acid (HBED), and citrate) enhanced U mobilization to varying extents. Over 45 days, the ligands mobilized only up to 0.3% of the 370 μM UO2, while a much larger extent of the 300 μM of biomass-bound noncrystalline U(IV) was mobilized (up to 57%) within only 2 days (>500 times more U mobilization). This work shows the potential of numerous organic ligands present in the environment to mobilize both recalcitrant and labile U forms under anoxic conditions to hazardous levels and, in doing so, undermine the stability of immobilized U(IV) sources.

  • Towards Standardization for Determining Dissolution Kinetics of Nanomaterials in Natural Aquatic Environments: Continuous Flow Dissolution of Ag Nanoparticles

    Lucie Stetten, Aiga Mackevica, Nathalie Tepe, Thilo Hofmann, Frank von der Kammer
    2022 - Nanomaterials, 12: 519


    The dissolution of metal-based engineered nanomaterials (ENMs) in aquatic environments is an important mechanism governing the release of toxic dissolved metals. For the registration of ENMs at regulatory bodies such as REACH, their dissolution behavior must therefore be assessed using standardized experimental approaches. To date, there are no standardized procedures for dissolution testing of ENMs in environmentally relevant aquatic media, and the Organisation for Economic Co-operation and Development (OECD) strongly encourages their development into test guidelines. According to a survey of surface water hydrochemistry, we propose to use media with low concentrations of Ca2+ and Mg2+ for a better simulation of the ionic background of surface waters, at pH values representing acidic (5 < pH < 6) and near-neutral/alkaline (7 < pH < 8) waters. We evaluated a continuous flow setup adapted to expose small amounts of ENMs to aqueous media, to mimic ENMs in surface waters. For this purpose, silver nanoparticles (Ag NPs) were used as model for soluble metal-bearing ENMs. Ag NPs were deposited onto a 10 kg.mol−1 membrane through the injection of 500 µL of a 5 mg.L−1 or 20 mg.L−1 Ag NP dispersion, in order to expose only a few micrograms of Ag NPs to the aqueous media. The dissolution rate of Ag NPs in 10 mM NaNO3 was more than two times higher for ~2 µg compared with ~8 µg of Ag NPs deposited onto the membrane, emphasizing the importance of evaluating the dissolution of ENMs at low concentrations in order to keep a realistic scenario. Dissolution rates of Ag NPs in artificial waters (2 mM Ca(NO3)2, 0.5 mM MgSO4, 0–5 mM NaHCO3) were also determined, proving the feasibility of the test using environmentally relevant media. In view of the current lack of harmonized methods, this work encourages the standardization of continuous flow dissolution methods toward OECD guidelines focused on natural aquatic environments, for systematic comparisons of nanomaterials and adapted risk assessments.

  • Tracking the legacy of early industrial activity in sediments of Lake Zurich, Switzerland: using a novel multi-proxy approach to find the source of extensive metal contamination

    Remo Luis Roethlin, Adrian Gilli, Bernhard Wehrli, Robin Sue Gilli, Jan Georg Wiederhold, Nathalie Dubois
    2022 - Environmental Science and Pollution Research, in press


    Historical industrial activities at the Horn Richterwil, on the shore of Lake Zurich (Switzerland), caused widespread metal contamination on land and in the adjacent lake sediments. This study provides an estimation of the age and source of the contamination by using XRF core scanning, ICP-OES, and Hg-AFS for quantitative measurements of trace metals and MC-ICP-MS for the stable isotope analysis of mercury. Radiometric dating ( 137Cs, 210Pb, and Pu dating) of two proximal cores and varve chronology in a distal core suggest two different contaminations, one stemming from around 1960 (Zn, Cd) and an earlier one from 1880 (Cr, Cu, Hg, Pb, Sn). The XRF data suggest two different contamination pathways: one by landfill of contaminated soil and another one by industrial wastewater effluents. Maximum concentrations found within all samples are in the range of per mil (dry weight) for Cr, Cu, Hg, Pb, Sn, and Zn and lie within the top 10 cm of the sediment cores. The analysis of the mercury isotopic composition ( 𝛿202 Hg and Δ199Hg) shows a significantly different signature for one of the cores, indicating a second mercury source. We could not identify the exact source or process leading to the isotopic fractionation of mercury, but the isotopic data confirm two different sources.

Book chapters and other publications

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