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Publications in peer reviewed journals

40 Publications found
  • About “Controls” in Pollution-Ecology Experiments in the Anthropocene

    Matthias C. Rillig, Shin Woong Kim, Andreas Schäffer, Gabriel Sigmund, Ksenia J. Groh, Zhanyun Wang
    2022 - Environ. Sci. Technol., 56: 11928-11930


    Controls are an essential component of experimental design, serving the purpose of accounting for all aspects of an experimental treatment except for the factor(s) under investigation in any given study. Especially in pollution ecology, proper controls are essential for attributing effects, describing dose–response relationships, and assessing risks. We here highlight that the interpretation of and communication about controls have become more complex, given the ubiquitous presence in the environment of a large number of anthropogenic factors, in part simultaneously affecting ecosystems. We therefore recommend a more conscious use of language when discussing effects in environmental matrices such as soil, water, or air.

  • Assessing the Lability and Environmental Mobility of Organically Bound Copper by Stable Isotope Dilution

    Ezzat R. Marzouk, Erica Donner, Frank von der Kammer, Elizabeth H. Bailey, Waleed H. Shetaya, Scott D. Young, Enzo Lombi
    2022 - Environ. Sci. Technol., 56: 5580-5589


    The environmental mobility of Cu and therefore its potential toxicity are closely linked to its attachment to natural organic matter (NOM). Geochemical models assume full lability of metals bound to NOM, especially under strong oxidizing conditions, which often leads to an overestimation of the lability of soil metals. Stable isotope dilution (SID) has been successfully applied to estimate the labile (isotopically exchangeable) pool of soil metals. However, its application to study the lability of NOM-Cu required development of a robust separation and detection approach so that free Cu ions can be discriminated from (the also soluble) NOM-Cu. We developed a SID protocol (with enriched 65Cu) to quantify the labile pool of NOM-Cu using size exclusion chromatography coupled to a UV detector (for the identification of different NOM molecular weights) and ICP-MS (for 65Cu/63Cu ratio measurement). The Cu isotopic-exchange technique was first characterized and verified using standard NOM (SR-NOM) before applying the developed technique to an “organic-rich” podzol soil extract. The developed protocol indicated that, in contrast to the common knowledge, significant proportions of SR-NOM-Cu (25%) and soil organic-Cu (55%) were not labile, i.e., permanently locked into inaccessible organic structures. These findings need to be considered in defining Cu interactions with the reactive pool of NOM using geochemical models and risk evaluation protocols in which complexed Cu has always been implicitly assumed to be fully labile and exchangeable with free Cu ions.

  • Assessment of geothermal impacts on urban aquifers using a polar coordinates-based approach

    Miguel Angel Marazuela, Alejandro García-Gil, Eduardo Garrido, Juan C. Santamarta, Noelia Cruz-Pérez, Thilo Hofmann
    2022 - Journal of Hydrology, 612: 128209


    The growing interest in shallow geothermal resources is compromising geothermal energy availability and groundwater quality in urban areas. This makes it necessary to search for new methodologies that facilitate urban geothermal resources management. In this work, a novel methodology based on polar coordinates to assess the geothermal impacts caused by shallow geothermal installations on urban aquifers is proposed and applied to a real case study. This methodology facilitated the definition of three key parameters (Tmax, Tmin and ANTI -Annual Net Thermal Impact-) for geothermal impact assessment and allowed classification of geothermal impacts on urban aquifers into five patterns (seasonally balanced, cooling/heating dominated impact, single cooling/heating impact, unrecovered cooling/heating impact and upward/downward linear impact).

    It was possible to establish the most frequent impact patterns in temperate to hot climates, where the use of the geothermal installations for cooling dominates, by applying this methodology to the Zaragoza city aquifer (Spain). The holistic view of the urban aquifer showed an average delay of four to five months between the production peak of the geothermal installations and the peak of the triggered thermal impact on the aquifer. The results showed that the increasing use of shallow geothermal energy is leading to an increase in temperature of aquifers which, in the case of the Zaragoza aquifer, was quantified at 0.20 °C/yr in the past five years. These results demonstrate the effectiveness of this methodology to assess thermal impacts on urban aquifers and facilitate thermal management in cities.

  • Bestimmung des elementaren Kohlenstoffs in Feststoffproben zur Beurteilung gemäß österreichischer Deponieverordnung

    Oliver Mann, Samet Coskuner, Thomas Klinger, Felix Maringer, Lisa Sappl, Marion Sappl, Marian Gazetovici, Klaus Wruss, Werner Wruss, Gabriel Sigmund
    2022 - Altlasten Spektrum, 4: 108-113


    In Österreich ist laut Deponieverordnung 2008 (DVO) die Ablagerung von Abfällen verboten, deren Anteil an organischem Kohlenstoff (TOC) im Feststoff mehr als fünf Masseprozent beträgt. Ausgenommen sind Abfälle, deren Kohlenstoffgehalt aus elementarem Kohlenstoff, Kohlen- oder Koksanteilen resultiert, sofern es sich nicht um beladene Aktivkohle oder beladenen Aktivkoks handelt, wenn diese Abfälle in einer Deponie für nicht gefährliche Abfälle abgelagert werden. Bei der Ablagerung organischer Abfallstoffe können durch mikrobiologischen Abbau Säuren entstehen, welche aus deponierten Abfällen Schwermetalle lösen, und diese dadurch in die Umwelt tragen. Durch den biologischen Zerfall können erhöhte TOC-Gehalte in deponierten Abfällen zur Bildung von Deponiegasen, wie zum Beispiel Methan führen. Diese Gase können durch ihre leichte Entzündbarkeit nach einer gewissen Zeit ein erhöhtes Gefahrenpotential entwickeln und dadurch zu einem Brand oder einer Explosion führen. Methan ist außerdem ein Treibhausgas und trägt zum Klimawandel bei. Der elementare Kohlenstoff (EC) wiederum ist einem mikrobiologischen Abbau nicht einfach zugänglich und hat somit keinen negativen Einfluss auf den Deponiekörper.

  • Broaden chemicals scope in biodiversity targets

    Gabriel Sigmund, Marlene Ågerstrand, Tomas Brodin, Miriam L. Diamond, Walter R. Erdelen, David C. Evers, Adelene Lai, Matthias C. Rillig, Andreas Schäffer, Anna Soehl, João Paulo M. Torres, Zhanyun Wang, Ksenia J. Groh
    2022 - Science, 376: 1280


    On 21 June, the next round of negotiations on the post-2020 global biodiversity framework will be held in Nairobi. In the draft document listing 21 targets, target 7 addresses chemical pollution by explicitly mentioning nutrients, pesticides, and plastic waste. Limiting this target’s scope to these three groups does not do justice to the immense variety of anthropogenic chemicals polluting the environment, which also include, for example, toxic metals, industrial chemicals, chemicals from consumer products, and pharmaceuticals, as well as the (often unknown) transformation products of substances from each group. We urge the negotiators to broaden the scope of target 7 to reflect the complexity of chemical pollution.

  • Comparing biochar and hydrochar for reducing the risk of organic contaminants in polluted river sediments used for growing energy crops

    Snežana Maletić, Marijana Kragulj Isakovski, Gabriel Sigmund, Thilo Hofmann, Thorsten Hüffer, Jelena Beljin, Srđan Rončević
    2022 - Science of The Total Environment, 843: in press


    In Europe alone, >200 million m3 of river sediments are dredged each year, part of which are contaminated to such an extent that they have to be landfilled. This study compares the use of biochar and hydrochar for the remediation of sediment contaminated with pentachlorobenzene, hexachlorobenzene, lindane, trifluralin, alachlor, simazine, and atrazine with the motivation to make sediments contaminated by such priority substances usable as arable land for growing energy crops. Biochar and hydrochar originating from Miscanthus giganteus and Beta vulgaris shreds were compared for their potential to reduce contaminant associated risk in sediments. Specifically, by investigating the effects of sorbent amendment rate (1, 5, and 10 %) and incubation time (14, 30, and 180 d) on contaminant bioaccessibility, toxicity to the bacteria Vibrio fischeri, as well as toxicity and plant uptake in Zea mays. Biochar reduced contaminant bioaccessibility up to five times more than hydrochar. The bioaccessibility of contaminants decreased up to sevenfold with increasing incubation time, indicating that the performance of carbonaceous sorbents may be underestimated in short-term lab experiments. Biochar reduced contaminants toxicity to Vibrio fischeri, whereas hydrochar was itself toxic to the bacteria. Toxicity to Zea mays was determined by contaminant bioaccessibility but also sorbent feedstock with cellulose rich Beta vulgaris based sorbents exhibiting toxic effects. The plant uptake of all contaminants decreased after sorbent amendment.

  • 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, 9: 1406-1429


    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.

  • Effect of Polymer Properties on the Biodegradation of Polyurethane Microplastics

    Patrizia Pfohl, Daniel Bahl, Markus Rückel, Marion Wagner, Lars Meyer, Patrick Bolduan, Glauco Battagliarin, Thorsten Hüffer, Michael Zumstein, Thilo Hofmann, Wendel Wohlleben
    2022 - Environ. Sci. Technol., 56: 16873–16884


    The release of fragments from plastic products, that is, secondary microplastics, is a major concern in the context of the global plastic pollution. Currently available (thermoplastic) polyurethanes [(T)PU] are not biodegradable and therefore should be recycled. However, the ester bond in (T)PUs might be sufficiently hydrolysable to enable at least partial biodegradation of polyurethane particles. Here, we investigated biodegradation in compost of different types of (T)PU to gain insights into their fragmentation and biodegradation mechanisms. The studied (T)PUs varied regarding the chemistry of their polymer backbone (aromatic/aliphatic), hard phase content, cross-linking degree, and presence of a hydrolysis-stabilizing additive. We developed and validated an efficient and non-destructive polymer particle extraction process for partially biodegraded (T)PUs based on ultrasonication and density separation. Our results showed that biodegradation rates and extents decreased with increasing cross-linking density and hard-segment content. We found that the presence of a hydrolysis stabilizer reduced (T)PU fragmentation while not affecting the conversion of (T)PU carbon into CO2. We propose a biodegradation mechanism for (T)PUs that includes both mother particle shrinkage by surface erosion and fragmentation. The presented results help to understand structure–degradation relationships of (T)PUs and support recycling strategies.

  • Environmental Biodegradation of Water-Soluble Polymers: Key Considerations and Ways Forward

    Michael Zumstein, Glauco Battagliarin, Andreas Kuenkel, Michael Sander
    2022 - Accounts of Chemical Research, 55: 2163–2167


    Water-soluble polymers (WSPs) have unique properties that are valuable in diverse applications ranging from home and personal care products to agricultural formulations. For applications that result in the release of WSPs into natural environments or engineered systems, such as agricultural soils and wastewater streams, biodegradable as opposed to nonbiodegradable WSPs have the advantage of breaking down and, thereby, eliminating the risk of persistence and accumulation. In this Commentary, we emphasize central steps in WSP biodegradation, discuss how these steps depend on both WSP properties and characteristics of the receiving environment, and highlight critical requirements for testing WSP biodegradability.

  • Environmental Degradation of Microplastics: How to Measure Fragmentation Rates to Secondary Micro- and Nanoplastic Fragments and Dissociation into Dissolved Organics

    Patrizia Pfohl, Marion Wagner, Lars Meyer, Prado Domercq, Antonia Praetorius, Thorsten Hüffer, Thilo Hofmann
    2022 - Environ. Sci. Technol., 56: 11323–11334


    Understanding the environmental fate of microplastics is essential for their risk assessment. It is essential to differentiate size classes and degradation states. Still, insights into fragmentation and degradation mechanisms of primary and secondary microplastics into micro- and nanoplastic fragments and other degradation products are limited. Here, we present an adapted NanoRelease protocol for a UVdose-dependent assessment and size-selective quantification of the release of micro- and nanoplastic fragments down to 10 nm and demonstrate its applicability for polyamide and thermoplastic polyurethanes. The tested cryo-milled polymers do not originate from actual consumer products but are handled in industry and are therefore representative of polydisperse microplastics occurring in the environment. The protocol is suitable for various types of microplastic polymers, and the measured rates can serve to parameterize mechanistic fragmentation models. We also found that primary microplastics matched the same ranking of weathering stability as their corresponding macroplastics and that dissolved organics constitute a major rate of microplastic mass loss. The results imply that previously formed micro- and nanoplastic fragments can further degrade into water-soluble organics with measurable rates that enable modeling approaches for all environmental compartments accessible to UV light.

  • Estimation of the Water Table Position in Unconfined Aquifers with MODFLOW 6

    Paulo A. Herrera, Christian Langevin, Glenn Hammond
    2022 - Groundwater, in press


    The numerical estimation of the position of the water table in unconfined aquifers is important for many practical applications. Its determination through observations or analytical methods is restricted to a few cases. Therefore, it is often estimated through numerical simulations, which may be affected by numerical artifacts and/or poor stability. We use MODFLOW to estimate the position of the water table for a seemingly simple example problem and demonstrate difficulties that can be faced when performing this kind of numerical simulation. We explain the causes for the numerical challenges that originate from the properties of the mathematical equations that must be solved. Based on the results of more than 600 steady-state simulations, we show how the stability of the numerical solution can be affected by the values of physical parameters that define the problem (e.g., recharge rate, anisotropy ratio, and other parameters that control the numerical algorithm such as settings of the linear and nonlinear solution methods). Finally, we comment on some best practices to apply numerical simulations to estimate the water table position.

  • 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.

  • Factors affecting the radon (222Rn) emanation from aquifer rock materials: Implications for radiological and groundwater tracer studies

    Melanie Vital, Sebastián Grondona, Natasha Dimova, Daniel Martinez
    2022 - Applied Radiation and Isotopes, 189: 110433


    Groundwater discharge (GD) is an important component of the water budget in large urban areas with high water demands. Radon is a routinely used groundwater tracer in mass-balances for evaluating GD to surface water bodies. The diffusion of 222Rn from aquifers' sediments parameter is important for GD's assessments. Sediment equilibration experiments were employed with various sediment and rock materials, including sand, granite, gneiss and loess that constitute the Pampeano Aquifer (PA) in the Buenos Aires Province, Argentina. These experiments allowed the 222Rn concentration determination in pore fluids at secular equilibrium and to examine the factors affecting the magnitude of radon 222Rn emanation from the materials under study. We found that radon emanation decreases in a power function (R2 = 0.9, n = 6) with the particle size of the tested PA sediment and rock materials. Based on our results, loess sediments with the smallest particle size and the largest particle surface area have the highest radon emanation. This strongly suggests that these two parameters are the parameters that govern the radon diffusive fluxes' magnitude in the PA. On the other hand, we found that PA basement rocks, primarily granite and gneiss, showed an exhalation rate of radon of 8.1 ± 0.81 Bq∙m−2∙h−1 and 13.2 ± 1.32 Bq∙m−2∙h−1. These rates are two orders of magnitude higher than loess sediments (0.3 ± 0.1 Bq∙m−2∙h−1), owning to the higher natural content of radon's parent isotopes from the 238U natural decay series. These high radon levels are consistent with currently available radon concentrations measured in groundwater in contact with the PA basement rock formations. This study demonstrates the importance of considering site-specific aquifer properties in the radon diffusive fluxes when utilizing radon as a groundwater tracer in hydrological studies. This is the first quantitative study that examines the aquifer characteristics affecting radon emanations in this large hydrogeological system.

  • Freshwater suspended particulate matter—Key components and processes in floc formation and dynamics

    2022 - Water Research, 220: in press


    Freshwater suspended particulate matter (SPM) plays an important role in many biogeochemical cycles and serves multiple ecosystem functions. Most SPM is present as complex floc-like aggregate structures composed of various minerals and organic matter from the molecular to the organism level. Flocs provide habitat for microbes and feed for larger organisms. They constitute microbial bioreactors, with prominent roles in carbon and inorganic nutrient cycles, and transport nutrients as well as pollutants, affecting sediments, inundation zones, and the ocean. Composition, structure, size, and concentration of SPM flocs are subject to high spatiotemporal variability. Floc formation processes and compositional or morphological dynamics can be established around three functional components: phyllosilicates, iron oxides/(oxy)hydroxides (FeOx), and microbial extracellular polymeric substances (EPS). These components and their interactions increase heterogeneity in surface properties, enhancing flocculation. Phyllosilicates exhibit intrinsic heterogeneities in surface charge and hydrophobicity. They are preferential substrates for precipitation or attachment of reactive FeOx. FeOx form patchy coatings on minerals, especially on phyllosilicates, which increase surface charge heterogeneities. Both, phyllosilicates and FeOx strongly adsorb natural organic matter (NOM), preferentially certain EPS. EPS comprise various substances with heterogeneous properties that make them a sticky mixture, enhancing flocculation. Microbial metabolism, and thus EPS release, is supported by the high adsorption capacity and favorable nutrient composition of phyllosilicates, and FeOx supply essential Fe.

  • Getting in control of persistent, mobile and toxic (PMT) and very persistent and very mobile (vPvM) substances to protect water resources: strategies from diverse perspectives

    Sarah E. Hale, Michael Neumann, Ivo Schliebner, Jona Schulze, Frauke S. Averbeck, Claudia Castell-Exner, Marie Collard, Dunja Drmač, Julia Hartmann, Roberta Hofman-Caris, Juliane Hollender, Martin de Jonge, Thomas Kullick, Anna Lennquist, Thomas Letzel, Karsten Nödler, Sascha Pawlowski, Ninja Reineke, Emiel Rorije, Marco Scheurer, Gabriel Sigmund, Harrie Timmer, Xenia Trier, Eric Verbruggen, Hans Peter H. Arp
    2022 - Environmental Sciences Europe, 34: 22



    Safe and clean drinking water is essential for human life. Persistent, mobile and toxic (PMT) substances and/or very persistent and very mobile (vPvM) substances are an important group of substances for which additional measures to protect water resources may be needed to avoid negative environmental and human health effects. PMT/vPvM substances do not sufficiently biodegrade in the environment, they can travel long distances with water and are toxic (those that are PMT substances) to the environment and/or human health. PMT/vPvM substance research and regulation is arguably in its infancy and in order to get in control of these substances the following (non-exhaustive list of) knowledge gaps should to be addressed: environmental occurrence; the suitability of currently available analytical methods; the effectiveness and availability of treatment technologies; the ability of regional governance and industrial stewardship to contribute to safe drinking water while supporting innovation; the ways in which policies and regulations can be used most effectively to govern these substances; and, the identification of safe and sustainable alternatives.


    The work is the outcome of the third PMT workshop, held in March 2021, that brought together diverse scientists, regulators, NGOs, and representatives from the water sector and the chemical sector, all concerned with protecting the quality of our water resources. The online workshop was attended by over 700 people. The knowledge gaps above were discussed in the presentations given and the attendees were invited to provide their opinions about knowledge gaps related to PMT/vPvM substance research and regulation.


    Strategies to closing the knowledge, technical and practical gaps to get in control of PMT/vPvM substances can be rooted in the Chemicals Strategy for Sustainability Towards a Toxic Free Environment from the European Commission, as well as recent advances in the research and industrial stewardship. Key to closing these gaps are: (i) advancing remediation and removal strategies for PMT/vPvM substances that are already in the environment, however this is not an effective long-term strategy; (ii) clear and harmonized definitions of PMT/vPvM substances across diverse European and international legislations; (iii) ensuring wider availability of analytical methods and reference standards; (iv) addressing data gaps related to persistence, mobility and toxicity of chemical substances, particularly transformation products and those within complex substance mixtures; and (v) advancing monitoring and risk assessment tools for stewardship and regulatory compliance. The two most effective ways to get in control were identified to be source control through risk governance efforts, and enhancing market incentives for alternatives to PMT/vPvM substances by using safe and sustainable by design strategies.

  • Heterogeneity-Driven Hydrodynamics Conditions the Hydrochemistry of Spring Water in Volcanic Islands

    Alejandro García-Gil, Roberto Poncela Poncela, Elzbieta Skupien Balon, Angel Morales Gonzalez-Moro, Rafael J. Lario-Báscones, Miguel Angel Marazuela, Noelia Cruz-Pérez, Juan C. Santamarta
    2022 - Groundwater, 61: 375-388


    Perched aquifers represent significant unexploited groundwater reserves in volcanic islands and contain valuable freshwater resources. These water reserves provide critical resources to indigenous populations suffering water scarcity. Groundwater discharged from a perched aquifer into two adjacent (14 m) springs in the volcanic summits constituted by basaltic and pyroclastic deposits of Gran Canaria Island (Spain) was examined. Based on springs discharge data, a three-dimensional groundwater flow and solute transport model of the investigated perched aquifer was calibrated to reproduce its hydraulic regime, as well as to explain the hydrochemical and isotopic composition of its main discharge systems, the studied springs. Groundwater flow simulations effectively replicated flow paths of the two springs affected by the existing geological heterogeneities, with differential travel times of 246 and 130 years, respectively, and with a convergent flow toward them partially explaining the averaged differences in electrical conductivity, δ18O, and tritium observed between the springs. It can be concluded that, although water quality in both springs is similar and homogenous, as they come from the same aquifer system, geological heterogeneities in the upper elevation volcanic areas is likely the cause for the differences in the residence times of the two springs, which suggests that the flow regimes for the two springs are independent. The chemistry of the two springs, however, is essentially the same, with the exception of tritium, which is used to ascertain residence time.

  • 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.

  • Influence of dissolution on the uptake of bimetallic nanoparticles Au@Ag-NPs in soil organism Eisenia fetida

    Marta Baccaro, Manuel David Montano, X. Cui, Aiga Mackevica, Iseult Lynch, Frank von der Kammer, R.W. Lodge, A.N. Khlobystov, N.W. van den Brink
    2022 - Chemosphere, 302: 134909


    A key aspect in the safety testing of metal nanoparticles (NPs) is the measurement of their dissolution and of the true particle uptake in organisms. Here, based on the tendency of Ag-NP to dissolve and Au-NP to be inert in the environment, we exposed the earthworm Eisenia fetida to Au core-Ag shell NPs (Au@Ag-NPs, Ag-NPs with a Au core) and to both single and combined exposures of non-coated Au-NPs, Ag-NPs, Ag+ and Au+ ions in natural soil. Our hypothesis was that the Ag shell would partially or completely dissolve from the Au@Ag-NPs and that the Au core would thereby behave as a tracer of particulate uptake. Au and Ag concentrations were quantified in all the soils, in soil extract and in organisms by inductively coupled plasma mass spectrometry (ICP-MS). The earthworm exposed to Au@Ag-NPs, and to all the combinations of Ag and Au, were analyzed by single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) to allow the quantification of the metals that were truly part of a bimetallic particle. Results showed that only 5% of the total metal amounts in the earthworm were in the bimetallic particulate form and that the Ag shell increased in thickness, suggesting that biotransformation processes took place at the surface of the NPs. Additionally, the co-exposure to both metal ions led to a different uptake pattern compared to the single metal exposures. The study unequivocally confirmed that dissolution is the primary mechanism driving the uptake of (dissolving) metal NPs in earthworms. Therefore, the assessment of the uptake of metal nanoparticles is conservatively covered by the assessment of the uptake of their ionic counterpart.

  • Internal tree cycling and atmospheric archiving of mercury: examination with concentration and stable isotope analyses

    David S. McLagan, Harald Biester, Tomas Navrátil, Stephan M. Kraemer, Lorenz Schwab
    2022 - Biogeosciences, 19: 4415-4429


    Trees predominantly take up mercury (Hg) from the atmosphere via stomatal assimilation of gaseous elemental Hg (GEM). Hg is oxidised in leaves/needles and transported to other tree anatomy including bole wood, where it can be stored long-term. Using Hg associated with growth rings facilitates archiving of historical GEM concentrations. Nonetheless, there are significant knowledge gaps on the cycling of Hg within trees. We investigate Hg archived in tree rings, internal tree Hg cycling, and differences in Hg uptake mechanisms in Norway spruce and European larch sampled within 1 km of a HgCl2-contaminated site using total Hg (THg) and Hg stable isotope analyses. Tree ring samples are indicative of significant increases in THg concentrations (up to 521 µg kg−1) from the background period (BGP; facility closed; 1992–present) to secondary industrial period (2ndIP; no HgCl2 wood treatment; 1962–1992) to primary industrial period (1stIP; active HgCl2 wood treatment; ≈ 1900–1962). Mass-dependent fractionation (MDF) Hg stable isotope data are shifted negative during industrial periods (δ202Hg of 1stIP: −4.32 ± 0.15 ‰, 2ndIP: −4.04 ± 0.32 ‰, BGP: −2.83 ± 0.74 ‰; 1 SD). Even accounting for a ≈ −2.6 ‰ MDF shift associated with stomatal uptake, these data are indicative of emissions derived from industrial activity being enriched in lighter isotopes associated with HgCl2 reduction and Hg0 volatilisation. Similar MDF (δ202Hg: −3.90 ± 0.30 ‰; 1 SD) in bark Hg (137 ± 105 µg kg−1) suggests that stomatal assimilation and downward transport is also the dominant uptake mechanism for bark Hg (reflective of negative stomatal-uptake MDF shift) rather than deposition to bark. THg was enriched in sapwood of all sampled trees across both tree species. This may indicate long-term storage of a fraction of Hg in sapwood or xylem solution. We also observed a small range of odd-isotope mass-independent fractionation (MIF). Differences in Δ199Hg between periods of different industrial activities were significant (Δ199Hg of 1stIP: 0.00 ± 0.03 ‰, 2ndIP: −0.06 ± 0.04 ‰, BGP: −0.13 ± 0.03 ‰; 1 SD), and we suggest MIF signatures are conserved during stomatal assimilation (reflect source MIF signatures). These data advance our understanding of the physiological processing of Hg within trees and provide critical direction to future research into the use of trees as archives for historical atmospheric Hg.

  • 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.

  • Large extent of mercury stable isotope fractionation in contaminated stream sediments induced by changes of mercury binding forms

    Lorenz Schwab, Florian M. Rothe, David S. McLagan, Alexandra Alten, Stephan M. Kraemer, Harald Biester, and Jan G. Wiederhold
    2022 - Frontiers in Environmental Chemistry, 3: in press


    Mercury (Hg) release from contaminated legacy sites is a large contributor to riverine ecosystems and can represent a significant local and regional environmental issue even long after the initial site contamination. Understanding processes of in-stream species transformation is therefore important to assess the fate and bioavailability of the released Hg. In this study, we investigated in-stream Hg transformation processes with analyses of Hg binding forms and Hg stable isotopes. Stream sediments were collected downstream of a former kyanization facility (Black Forest, SW Germany), where highly soluble Hg(II)-chloride (HgCl2) was used as an anti-fouling agent to treat timber. Exfiltration of partly anoxic, contaminated groundwater with Hg concentrations of up to 700 μg L−1 into the adjacent Gutach stream is the main source of Hg to sediments. Total Hg concentrations in the stream bottom sediments (<2 mm) ranged from background values of 6.3 µg kg−1 upstream of the contaminated site to 77 mg kg−1 near the location of exfiltration of contaminated groundwater. A five-step sequential extraction procedure and Hg pyrolytic thermal desorption (PTD) analyses indicated changes in Hg binding forms in the sediments along the flow path towards a higher proportion of organically bound Hg. A large shift towards negative δ202Hg values was observed downstream of the contaminated site (change of ≈2‰) along with a minor offset in mass-independent fractionation. Binary mixing models based on Hg isotope ratios using one industrial and different natural background endmembers were tested to estimate their respective contribution of Hg to the sediments but failed to produce plausible allocations. Based on the observed changes in isotopic composition, total Hg concentrations and Hg binding forms, we propose that the large extent of fractionation observed in downstream sediments is the result of a combination of kinetic isotope effects during sorption, redistribution of Hg within the sediment and the preferential transport of Hg associated with the sediment fine fraction. These results highlight the importance of transformation processes when assessing the sources and fate of Hg in environmental systems and show limitations of using simple mixing models based on Hg stable isotopes.

  • 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.

  • Mercury Removal from Contaminated Water by Wood-Based Biochar Depends on Natural Organic Matter and Ionic Composition

    Sampriti Chaudhuri, Gabriel Sigmund, Sharon E. Bone, Naresh Kumar, Thilo Hofmann
    2022 - Environ. Sci. Technol., 56: 11354–11362


    Biochars can remove potentially toxic elements, such as inorganic mercury [Hg(II)] from contaminated waters. However, their performance in complex water matrices is rarely investigated, and the combined roles of natural organic matter (NOM) and ionic composition in the removal of Hg(II) by biochar remain unclear. Here, we investigate the influence of NOM and major ions such as chloride (Cl-), nitrate (NO3-), calcium (Ca2+), and sodium (Na+) on Hg(II) removal by a wood-based biochar (SWP700). Multiple sorption sites containing sulfur (S) were located within the porous SWP700. In the absence of NOM, Hg(II) removal was driven by these sites. Ca2+ bridging was important in enhancing removal of negatively charged Hg(II)-chloro complexes. In the presence of NOM, formation of soluble Hg-NOM complexes (as seen from speciation calculations), which have limited access to biochar pores, suppressed Hg(II) removal, but Cl- and Ca2+ could still facilitate it. The ability of Ca2+ to aggregate NOM, including Hg-NOM complexes, promoted Hg(II) removal from the dissolved fraction (<0.45 μm). Hg(II) removal in the presence of Cl- followed a stepwise mechanism. Weakly bound oxygen functional groups in NOM were outcompeted by Cl-, forming smaller-sized Hg(II)-chloro complexes, which could access additional intraparticle sorption sites. Therein, Cl- was outcompeted by S, which finally immobilized Hg(II) in SWP700 as confirmed by extended X-ray absorption fine structure spectroscopy. We conclude that in NOM containing oxic waters, with relatively high molar ratios of Cl-: NOM and Ca2+: NOM, Hg(II) removal can still be effective with SWP700.

  • Microbially inoculated chars strongly reduce the mobility of alachlor and pentachlorobenzene in an alluvial sediment

    Irina Jevrosimov, Marijana Kragulj Isakovski, Tamara Apostolović, Dragana Tamindžija, Srđan Rončević, Gabriel Sigmund, Marija Ercegović, Snežana Maletić
    2022 - Integrated Environmental Assessment and Management, in press


    The objective of this study was to investigate the transport behavior of two organic and persistent contaminants (alachlor and pentachlorobenzene) on Danube alluvial sediment in the absence and in the presence of microbially inoculated biochar produced at 400 °C and three hydrochars produced at 180, 200, and 220 °C. Stainless steel columns were used for the sorption experiments in nonequilibrium conditions. Obtained results were modeled using the advective-dispersive equation under nonequilibrium conditions. Transport of these compounds through the alluvial sediment column showed that the retention time increased with increasing molecular hydrophobicity. Inoculated biochar increases the retardation of both compounds: twofold for pentachlorobenzene compared with alachlor as a consequence of a higher hydrophobicity. Obtained results indicate that the highest biodegradation coefficient was observed for pentachlorobenzene (λ = 10) in alluvial sediment with addition of an inoculated hydrochar, which is assumed to be a consequence of biosorption. Moreover, all experiments on the columns indicate that the addition of inoculated chars yields a significantly higher Rd coefficient for pentachlorobenzene than for alachlor. Bacterial counts increased in all of the column experiments, which indicates the successful adaptation of microorganisms to experimental conditions and their potential for the removal of a large number of organic pollutants. Thus, addition of inoculated chars to contaminated sediments has the potential as a remediation technique to inhibit the leaching of pollutants to groundwaters. I

  • Parameter estimation and uncertainty analysis in hydrological modeling

    Paulo A. Herrera, Miguel Angel Marazuela, Thilo Hofmann
    2022 - WIRES Water, 9: e1569


    Nowadays, mathematical models of hydrological systems are used routinely to guide decision making in diverse subjects, such as: environmental and risk assessments, design of remediation strategies for contaminated sites, and evaluation of the impact of climate change on water resources. The correct development and use of them is relevant beyond the realm of hydrology. The continuous improvement in computational power and data collection are leading to the development of increasingly complex models, which integrate multiple coupled physical processes to achieve a better representation of the modeled system. Most of the parameters included in models are difficult to measure directly, so they must be estimated from collected data through a calibration procedure. Furthermore, when models are used to make forecasts about future or hypothetical scenarios, it is important to bound the uncertainty of their results. Therefore, the application of systematic approaches for parameter estimation, sensitivity, and uncertainty analysis to integrate data and models and quantify potential errors, is more necessary now than it was in the past. Even though methodological frameworks for these purposes exist, they have had a slow adoption due to their high computational cost and the required technical knowledge to apply them. We analyze existing methodologies, discuss remaining challenges, and present a survey of emerging trends for the application of parameter estimation and uncertainty analysis in hydrological modeling. Thus, the main objective of this overview article is contributing to improving the quality of models and to their correct use as support tools for decision-making.

  • Pharmaceutical pollution of the world’s rivers

    John L. Wilkinson, Alistair B. A. Boxall, Dana W. Kolpin, Kenneth M. Y. Leung, Racliffe W. S. Lai, Cristobal Galban-Malagon, Aiko D. Adell, Julie Mondon, Marc Metian, Robert A. Marchant, Alejandra Bouzas-Monroy, Aida Cuni-Sanchez, Anja Coors, Pedro Carriquiriborde, Macarena Rojo, Chris Gordon, Magdalena Cara, Monique Moermond, Thais Luarte, Vahagn Petrosyan, Yekaterina Perikhanyan, Clare S. Mahon, Christopher J. McGurk, Thilo Hofmann, Tapos Kormoker, Volga Iniguez, Jessica Guzman-Otazo, Jean L. Tavares, Francisco Gildasio De Figueiredo, Maria T. P. Razzolini, Victorien Dougnon, Gildas Gbaguidi, Oumar Traore, Jules M. Blais, Linda E. Kimpe, Michelle Wong, Donald Wong, Romaric Ntchantcho, Jaime Pizarro, Guang-Guo Ying, Chang-Er Chen, Martha Paez, Jina Martinez-Lara, Jean-Paul Otamonga, John Pote, Suspense A. Ifo, Penelope Wilson, Silvia Echeverria-Saenz, Nikolina Udikovic-Kolic, Milena Milakovic, Despo Fatta-Kassinos, Lida Ioannou-Ttofa, Vladimira Belusova, Jan Vymazal, Maria Cardenas-Bustamante, Bayable A. Kas
    2022 - PNAS, 119: e2113947119


    Environmental exposure to active pharmaceutical ingredients (APIs) can have negative effects on the health of ecosystems and humans. While numerous studies have monitored APIs in rivers, these employ different analytial methods, measure different APIs, and have ignored many of the countries of the world. This makes it difficult to quantify the scale of the problem from a global perspective. Furthermore, comparison of the existing data, generated for different studies/regions/continents, is challenging due to the vast differences between the analytical methodologies employed. Here, we present a global-scale study of API pollution in 258 of the world’s rivers, representing the environmental influence of 471.4 million people across 137 geographic regions. Samples were obtained from 1,052 locations in 104 countries (representing all continents and 36 countries not previously studied for API contamination) and analyzed for 61 APIs. Highest cumulative API concentrations were observed in sub-Saharan Africa, south Asia, and South America. The most contaminated sites were in low- to middle-income countries and were associated with areas with poor wastewater and waste management infrastructure and pharmaceutical manufacturing. The most frequently detected APIs were carbamazepine, metformin, and caffeine (a compound also arising from lifestyle use), which were detected at over half of the sites monitored. Concentrations of at least one API at 25.7% of the sampling sites were greater than concentrations considered safe for aquatic organisms, or which are of concern in terms of selection for antimicrobial resistance. Therefore, pharmaceutical pollution poses a global threat to environmental and human health, as well as to delivery of the United Nations Sustainable Development Goals.

  • Platinum Nanoparticle Extraction, Quantification, and Characterization in Sediments by Single-Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry

    Sara Taskula, Lucie Stetten, Frank von der Kammer, Thilo Hofmann
    2022 - 12: 3307


    Particulate emissions from vehicle exhaust catalysts are the primary contributors to platinum group elements (PGEs) being released into roadside environments, especially platinum (Pt) particles. With increasing traffic density, it is essential to quantify the emission, accumulation, and potential health effects of traffic-emitted Pt particles. In this study, three procedures were investigated to extract Pt nanoparticles (NPs) from sediments and characterize them by single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOF-MS). For this purpose, a reference sediment sample was spiked with manufactured Pt NPs. Pt NPs’ extraction recoveries reached from 50% up to 102%, depending on the extraction procedure and whether the particle mass or number was used as the metric. Between 17% and 35% of the Pt NPs were found as unassociated Pt NPs and between 31% and 78% as Pt NPs hetero-aggregated with other sediment particles. Multi-elemental analysis of Pt-containing NPs in the pristine sediment revealed frequently co-occurring elements such as Au, Bi, and Ir, which can be used to determine a natural background baseline. Our results demonstrated that spICP-TOF-MS elemental characterization allows for distinguishing anthropogenic Pt NPs from the natural background. In the future, this could enable the sensitive monitoring of PGE release from anthropogenic sources such as vehicle exhausts.

  • Polyvinyl Chloride Microplastics Leach Phthalates into the Aquatic Environment over Decades

    Charlotte Henkel, Thorsten Hüffer, Thilo Hofmann
    2022 - Environ. Sci. Technol., 56: 14507–14516


    Phthalic acid esters (phthalates) have been detected everywhere in the environment, but data on leaching kinetics and the governing mass transfer process into aqueous systems remain largely unknown. In this study, we experimentally determined time-dependent leaching curves for three phthalates di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, and diisononyl phthalate from polyvinyl chloride (PVC) microplastics and thereby enabled a better understanding of their leaching kinetics. This is essential for exposure assessment and to predict microplastic-bound environmental concentrations of phthalates. Leaching curves were analyzed using models for intraparticle diffusion (IPD) and aqueous boundary layer diffusion (ABLD). We show that ABLD is the governing diffusion process for the continuous leaching of phthalates because phthalates are very hydrophobic (partitioning coefficients between PVC and water log KPVC/W were higher than 8.6), slowing down the diffusion through the ABL. Also, the diffusion coefficient in the polymer DPVC is relatively high (∼8 × 10–14 m2 s–1) and thus enhances IPD. Desorption half-lives of the studied PVC microplastics are greater than 500 years but can be strongly influenced by environmental factors. By combining leaching experiments and modeling, our results reveal that PVC microplastics are a long-term source of phthalates in the environment.

  • Rapid analysis of gunshot residues with single-particle inductively coupled plasma time-of-flight mass spectrometry

    Robert Brünjes, Jan Schüürman, Frank von der Kammer, Thilo Hofmann
    2022 - Forensic Science International, 332: in press


    Gunshot residues (GSRs) from different types of ammunition have been characterized using a new method based on single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOF-MS). This method can analyze thousands of particles per minute enabling rapid sample screening for GSR detection with minimal sample preparation. GSR particles are multi-elemental nanoparticles that are mainly defined by the elements lead, barium, and antimony. Sp-ICP-TOF-MS was also used to identify other elements contained in GSR particles while standard particle classification protocols do not consider the complexities of GSR compositions and can therefore miss out on valuable information. The proposed method can be used to support existing GSR detection methods, especially when lead-free, antimony-free, or tagged ammunition has been used; it also provides a possibility for multi-elemental fingerprinting of GSR particles.

  • Refinement of the selection of physicochemical properties for grouping and read-across of nanoforms

    Frédéric Loosli, Kirsten Rasmussen, Hubert Rauscher, Richard K. Cross, Nathan Bossa, Willie Peijnenburg, Josje Arts, Marianne Matzke, Claus Svendsen, David Spurgeon, Per Axel Clausen, Emmanuel Ruggiero, Wendel Wohlleben, Frank von der Kammer
    2022 - NanoImpact, 25: 100375


    Before placing a new nanoform (NF) on the market, its potential adverse effects must be evaluated. This may e.g. be done via hazard and risk assessment. Grouping and read-across of NFs is a possible strategy to reduce resource consumption, maximising the use of existing data for assessment of NFs. The GRACIOUS project provides a framework in which possible grouping and read-across for NFs is mainly based on an evaluation of their similarity. The impact of NFs on human health and the environment depends strongly on the concentration of the NF and its physicochemical properties, such as chemical composition, size distribution, shape, etc. Hence, knowledge of the most relevant physicochemical properties is essential information for comparing similarity.

    The presented work aims to refine existing proposals for sets of descriptors (descriptor array) that are needed to describe distinct NFs of a material to identify the most relevant ones for grouping and read-across. The selection criteria for refining this descriptor array are explained and demonstrated. Relevant protocols and methods are proposed for each physicochemical property. The required and achievable measurement accuracies of the refined descriptor array are reviewed, as this information is necessary for similarity assessment of NFs based on individual physicochemical properties.

  • Reproducibility of methods required to identify and characterize nanoforms of substances

    Richard K. Cross, Nathan Bossa, Björn Stolpe, Frédéric Loosli, Nicklas Mønster Sahlgren, Per Axel Clausen, Camilla Delpivo, Michael Persson, Andrea Valsesia, Jessica Ponti, Dori Mehn, Didem Ag Seleci, Philipp Müller, Frank von der Kammer, Hubert Rauscher, Dave Spurgeon, Claus Svendsen, Wendel Wohlleben
    2022 - NanoImpact, 27: 100410


    Nanoforms (NFs) of a substance may be distinguished from one another through differences in their physicochemical properties. When registering nanoforms of a substance for assessment under the EU REACH framework, five basic descriptors are required for their identification: composition, surface chemistry, size, specific surface area and shape. To make the risk assessment of similar NFs efficient, a number of grouping frameworks have been proposed, which often require assessment of similarity on individual physicochemical properties as part of the group justification. Similarity assessment requires an understanding of the achievable accuracy of the available methods. It must be demonstrated that measured differences between NFs are greater than the achievable accuracy of the method, to have confidence that the measured differences are indeed real. To estimate the achievable accuracy of a method, we assess the reproducibility of six analytical techniques routinely used to measure these five basic descriptors of nanoforms: inductively coupled plasma mass spectrometry (ICP-MS), Thermogravimetric analysis (TGA), Electrophoretic light scattering (ELS), Brunauer–Emmett–Teller (BET) specific surface area and transmission and scanning electron microscopy (TEM and SEM). Assessment was performed on representative test materials to evaluate the reproducibility of methods on single NFs of substances. The achievable accuracy was defined as the relative standard deviation of reproducibility (RSDR) for each method.

    Well established methods such as ICP-MS quantification of metal impurities, BET measurements of specific surface area, TEM and SEM for size and shape and ELS for surface potential and isoelectric point, all performed well, with low RSDR, generally between 5 and 20%, with maximal fold differences usually <1.5 fold between laboratories. Applications of technologies such as TGA for measuring water content and putative organic impurities, additives or surface treatments (through loss on ignition), which have a lower technology readiness level, demonstrated poorer reproducibility, but still within 5-fold differences. The expected achievable accuracy of ICP-MS may be estimated for untested analytes using established relationships between concentration and reproducibility, but this is not yet the case for TGA measurements of loss on ignition or water content. The results here demonstrate an approach to estimate the achievable accuracy of a method that should be employed when interpreting differences between NFs on individual physicochemical properties.

  • Soil-pH and cement influence the weathering kinetics of chrysotile asbestos in soils and its hydroxyl radical yield

    Martin Walter, Gerald Geroldinger, Lars Gille, Stephan M. Kraemer, Walter D.C. Schenkeveld
    2022 - Journal of Hazardous Materials, 431: 128068


    Asbestos fibers are carcinogenic minerals that have abundantly been used in different industrial settings and in consumer applications. Much of the historically used asbestos has ended up in terrestrial environments where the fibers pose a health risk to residents.

    Stephan Kraemer from EDGE together with the former PhD student Martin Walter and university assistant Walter Schenkeveld, and colleagues from the University of Veterinary Medicine Vienna, investigated the weathering kinetics and hydroxyl radical yield of toxic chrysotile asbestos fibers in suspensions of (cement-amended) soils with different pH and organic carbon properties.

    Soil solution pH proved to be the major determinant of asbestos weathering in soil suspensions (with fiber weathering and soil solution pH being inversely related). Addition of cement to soils inhibited asbestos weathering because of its alkalinity. The hydroxyl radical yield of asbestos in soil suspensions decreased by maximally ≈75%, and fully decreased to background levels in soils to which cement has been added (due to precipitation of Fenton-inactive minerals on fibers). In low pH podzol suspensions, also increases in the fibers’ hydroxyl radical yield were observed, presumably because of an association of soil solution Fe with the asbestos fiber surface. 

  • Solving Familiar Problems: Leveraging Environmental Testing Methods for Nanomaterials to Evaluate Microplastics and Nanoplastics

    Elijah Joel Petersen, Alan James Kennedy, Thorsten Hüffer, Frank von der Kammer
    2022 - Nanomaterials, 12: 1332


    The potential environmental and human health risks from microplastic (1 µm to 1 mm) and nanoplastic (<1 µm) particles (MNPs) is receiving increasing attention from scientists and the public. Most particles in the environment are likely secondary particles formed from the degradation and weathering of larger pieces of plastic. These plastic particles have a large diversity of characteristics (e.g., size, density, shape, chemical composition, additives and degree of weathering).
    Currently, MNP environmental fate and hazard studies use a wide range of non-standardized methods, resulting in the low comparability of results. This hinders the generation of consistent and reliable hazard data, increases the uncertainty of risk determinations and limits the use of computational models. Examples of conflicting results in the literature include some studies suggesting that MNPs pose a serious ecotoxicological risk, while other studies report minimal toxicity after the removal of additives used in polymer processing or surfactants and antimicrobials added to MNP suspensions [9,10].
    Clearly, there is need for improved quality control in researching the environmental hazards of MNPs. One approach to resolve discrepancies is using existing standardized test methods. These methods were designed for dissolved substances and to avoid physical effects from particles [11]. However, MNPs at elevated concentrations could cause physical effects on organisms. This situation is similar to that confronted in research over the last decade studying the environmental behavior and toxicity of engineered nanomaterials (ENMs), where early publications also resulted in conflicting results. Given the particulate nature of both MNPs and ENMs, many concepts developed for the environmental risk assessment of ENMs may be adapted to improve MNP fate and hazard evaluations.
  • Sorption and Mobility of Charged Organic Compounds: How to Confront and Overcome Limitations in Their Assessment

    Gabriel Sigmund, Hans Peter H. Arp, Benedikt M. Aumeier, Thomas D. Bucheli, Benny Chefetz, Wei Chen, Steven T. J. Droge, Satoshi Endo, Beate I. Escher, Sarah E. Hale, Thilo Hofmann, Joseph Pignatello, Thorsten Reemtsma, Torsten C. Schmidt, Carina D. Schönsee, Martin Scheringer
    2022 - Environ. Sci. Technol., 56: 4702-2710


    Permanently charged and ionizable organic compounds (IOC) are a large and diverse group of compounds belonging to many contaminant classes, including pharmaceuticals, pesticides, industrial chemicals, and natural toxins. Sorption and mobility of IOCs are distinctively different from those of neutral compounds. Due to electrostatic interactions with natural sorbents, existing concepts for describing neutral organic contaminant sorption, and by extension mobility, are inadequate for IOC. Predictive models developed for neutral compounds are based on octanol–water partitioning of compounds (Kow) and organic-carbon content of soil/sediment, which is used to normalize sorption measurements (KOC). We revisit those concepts and their translation to IOC (Dow and DOC) and discuss compound and soil properties determining sorption of IOC under water saturated conditions. Highlighting possible complementary and/or alternative approaches to better assess IOC mobility, we discuss implications on their regulation and risk assessment. The development of better models for IOC mobility needs consistent and reliable sorption measurements at well-defined chemical conditions in natural porewater, better IOC-, as well as sorbent characterization. Such models should be complemented by monitoring data from the natural environment. The state of knowledge presented here may guide urgently needed future investigations in this field for researchers, engineers, and regulators.

  • Stormwater management in urban areas using dry gallery infiltration systems

    Miguel Angel Marazuela, Alejandro García-Gil, Juan C. Santamarta, Samanta Gasco-Cavero, Noelia Cruz-Pérez, Thilo Hofmann
    2022 - Science of The Total Environment, 823: 153705


    The increase in the frequency of extreme precipitation events due to climate change, together with the continuous development of cities and surface sealing that hinder water infiltration into the subsoil, is accelerating the search for new facilities to manage stormwater. The Canary Islands (Spain) are taking advantage of the knowledge acquired in the construction of water mines to exploit a novel stormwater management facility, which we have defined as a dry gallery. Dry galleries are constituted by a vertical well connected to a horizontal gallery dug into highly permeable volcanic layers of the vadose zone, from where infiltration takes place. However, the lack of scientific knowledge about these facilities prevents them from being properly dimensioned and managed. In this work, we simulate for the first time the infiltration process and the wetting front propagation from dry galleries based on a 3D unsaturated flow model and provide some recommendations for the installation and sizing of these facilities. The fastest advance of the wetting front takes place during the earliest times of infiltration (<2 h), with plausible propagation velocities and infiltration rates higher than 1000 m∙d−1 and 2 m3∙s−1. As time progresses, the propagation velocity and infiltration rate decrease as a consequence of the hydraulic gradient attenuation between the gallery and the aquifer. Therefore, stormwater infiltration is a highly transient process in which a sizing underestimation of 100% may be committed if unsaturated conditions or geological configuration are neglected.

  • The potential contribution of hexavalent chromium to the carcinogenicity of chrysotile asbestos

    Martin Walter, Walter D.C. Schenkeveld*, Maura Tomatis, Karin Schelch, Barbara Peter-Vörösmarty, Gerald Geroldinger, Lars Gille, Maria C. Bruzzoniti, Francesco Turci, Stephan M. Kraemer, and Michael Grusch
    2022 - Chemical Research in Toxicology, 35: 2335–2347


    Asbestos fibers are carcinogenic minerals that induce non-malignant and malignant diseases after inhalation.

    In this publication, Stephan Kraemer from EDGE together with the former PhD student Martin Walter and university assistant Walter Schenkeveld investigated whether Cr in chrysotile asbestos leaches from the fiber surface in its genotoxic hexavalent redox state upon oxidation by H2O2 (as found in inflamed asbestos-burdened tissues) at the physiological lung pH 7.4. These investigations were contemplated by collaborations with colleagues of the Medical University and the University of Veterinary Medicine in Vienna, and the University of Turin. Apart from Cr leaching from chrysotile, we also investigated the potential of cells from typical asbestos-burdened tissues and cancers to take up Cr(VI). Finally, we investigated the potential contribution of Cr on chrysotile surfaces to the fiber-mediated generation of highly toxic hydroxyl radicals out of H2O2.

    Chromium readily dissolved from chrysotile fibers in its genotoxic and carcinogenic hexavalent redox state upon oxidation by H2O2. All investigated cells of typically asbestos-burdened tissues and cancers readily took up Cr(VI). However, chromium associated with chrysotile did not contribute to fiber-mediated hydroxyl radical generation.

  • Towards an effective application of parameter estimation and uncertainty analysis to mathematical groundwater models

    Paulo A. Herrera, Miguel Angel Marazuela, Giovanni Formentin, Thilo Hofmann
    2022 - SN Applied Sciences, 4: 213


    Groundwater models serve as support tools to among others: assess water resources, evaluate management strategies, design remediation systems and optimize monitoring networks. Thus, the assimilation of information from observations into models is crucial to improve forecasts and reduce uncertainty of their results. As more information is collected routinely due to the use of automatic sensors, data loggers and real time transmission systems; groundwater modelers are becoming increasingly aware of the importance of using sophisticated tools to perform model calibration in combination with sensitivity and uncertainty analysis. Despite their usefulness, available approaches to perform this kind of analyses still present some challenges such as non-unique solution for the parameter estimation problem, high computational burden and a need of a deep understanding of the theoretical basis for the correct interpretation and use of their results, in particular the ones related to uncertainty analysis. We present a brief derivation of the main equations that serve as basis for this kind of analysis. We demonstrate how to use them to estimate parameters, assess the sensitivity and quantify the uncertainty of the model results using an example inspired by a real world setting. We analyze some of the main pitfalls that can occur when performing such kind of analyses and comment on practical approaches to overcome them. We also demonstrate that including groundwater flow estimations, although helpful in constraining the solution of the inverse problem as shown previously, may be difficult to apply in practice and, in some cases, may not provide enough information to significantly constrain the set of potential solutions. Therefore, this article can serve as a practitioner-oriented introduction for the application of parameter estimation and uncertainty analysis to groundwater models.

  • 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.

  • Transformation of Zinc Oxide Nanoparticles in Freshwater Sediments Under Oxic and Anoxic Conditions

    Lucie Stetten, Thilo Hofmann, Olivier Proux, Gautier Landrot, Ralf Kaegi, Frank von der Kammer
    2022 - Environ. Sci.: Nano, in press


    This study improves the understanding of ZnO NP transformation and Zn behavior in redox-dynamic slightly alkaline freshwater sediments. , The transformation of zinc oxide nanoparticles (ZnO NPs) has been largely investigated in wastewater treatment plants, recognized as important intermediates before the discharge of NPs into the environment. However, considering direct releases of the pristine ZnO NP forms, additional studies on ZnO NP fate in different environmental compartments are encouraged. In this work, we investigated ZnO NP transformation in lacustrine sediments under defined redox conditions. Using X-ray absorption spectroscopy and wet chemical analyses, we followed ZnO NP and Zn 2+ fate over a three-month period in sediments incubated under oxic or anoxic sulfide-rich conditions. Under oxic conditions, ZnO NPs were dissolved within a few hours. By contrast, ZnO NP dissolution under anoxic conditions was much slower, with ∼19% of ZnO NPs remaining at the end of the incubation, together with ∼41% of ZnS, ∼15% of Zn adsorbed onto phyllosilicates and ∼27% of Zn-phyllosilicate-like species. The transient formation of Zn–organic complexes under oxic conditions supports that ZnO NP dissolution is driven by organic compounds, followed by Zn adsorption onto phyllosilicates and the subsequent formation of Zn-layered minerals. Under anoxic conditions, ZnO NP dissolution is inhibited by the precipitation of amorphous ZnS and controlled by the progressive growth of ZnS NPs. These results improve the understanding of ZnO NP transformation in slightly alkaline freshwater sediments and highlight the need to assess NP fate under environmentally relevant conditions.

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