Publications

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Publications in peer reviewed journals

30 Publications found
  • A Large-Scale 3D Study on Transport of Humic Acid-Coated Goethite Nanoparticles for Aquifer Remediation

    Milica Velimirovic, Carlo Bianco, Natalia Ferrantello, Tiziana Tosco, Alessandro Casasso, Rajandrea Sethi, Doris Schmid, Stephan Wagner, Kumiko Miyajima, Norbert Klaas, Rainer U. Meckenstock, Frank von der Kammer, Bert Engelen, Thilo Hofmann
    2020 - Water, 12: 1207

    Abstract: 

    Humic acid-coated goethite nanoparticles (HA-GoeNPs) have been recently proposed as an effective reagent for the in situ nanoremediation of contaminated aquifers. However, the effective dosage of these particles has been studied only at laboratory scale to date. This study investigates the possibility of using HA-GoeNPs in remediation of real field sites by mimicking the injection and transport of HA-GoeNPs under realistic conditions. To this purpose, a three-dimensional (3D) transport experiment was conducted in a large-scale container representing a heterogeneous unconfined aquifer. Monitoring data, including particle size distribution, total iron (Fetot) content and turbidity measurements, revealed a good subsurface mobility of the HA-GoeNP suspension, especially within the higher permeability zones. A radius of influence of 2 m was achieved, proving that HA-GoeNPs delivery is feasible for aquifer restoration. A flow and transport model of the container was built using the numerical code Micro and Nanoparticle transport Model in 3D geometries (MNM3D) to predict the particle behavior during the experiment. The agreement between modeling and experimental results validated the capability of the model to reproduce the HA-GoeNP transport in a 3D heterogeneous aquifer. Such result confirms MNM3D as a valuable tool to support the design of field-scale applications of goethite-based nanoremediation.

  • Accurate quantification of TiO2 nanoparticles in commercial sunscreens using standard materials and orthogonal particle sizing methods for verification

    Milica Velimirovic, Stephan Wagner, Fazel Abdolahpur Monikh, Toni Uusimäki, Ralf Kaegi, Thilo Hofmann, Frank von der Kammer
    2020 - Talanta, 215: 120921

    Abstract: 

    The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO2 nanoparticles in sunscreens. Specifically, we used a combination of ultracentrifugation and hexane washing, thermal destruction of the matrix, and surfactant assisted particle extraction. The method accuracy was assessed by two internal reference samples: pristine TiO2 nanoparticles (NM104) and similar TiO2 nanoparticles dispersed in a sunscreen matrix. The PSDs were determined using an asymmetrical flow field-flow fractionation hyphenated with multi-angle light scattering and inductively coupled plasma-mass spectroscopy. Particle sizing was based on size calibration of the particle retention time in the AF4. Computation of radius of gyration from MALS data was used as an orthogonal particle sizing approach to verify ideal elution and particle size data from the AF4 calibration. Among the three tested sample preparation methods surfactant assisted particle extraction revealed TiO2 nanoparticle recoveries of above 90% and no increase in particle size due to sample preparation was observed. Finally, the sample preparation methods were applied to two commercial sunscreen samples revealing the existence of TiO2-NP < 100 nm. Conclusively, the surfactant assisted particle extraction method can provide valid data for TiO2-NPs in sunscreen and possibly for cosmetic samples of similar matrix.

  • Anthropogenic gadolinium in freshwater and drinking water systems

    Robert Brünjes and Thilo Hofmann
    2020 - Water Research, 182: 115966

    Abstract: 

    The increasing use of gadolinium-based contrast agents (GBCAs) for magnetic resonance imaging is leading to widespread contamination of freshwater and drinking water systems. Contrary to previous assumptions that GBCAs are stable throughout the water cycle, they can degrade. The stability of GBCAs depends largely on their organic ligands, but also on the physicochemical conditions. There is specific concern regarding UV end-of-pipe water treatments, which may degrade GBCAs. Degradation products in drinking water supplies can increase the risk of adverse health effects. This is of particular relevance where the raw water for drinking water production has a higher proportion of recycled wastewater. GBCAs concentrations in aquatic systems, often referred to as anthropogenic gadolinium, are determined using a variety of calculation methods. Where anthropogenic gadolinium concentrations are low, the inconsistent use of these methods results in high discrepancies and high levels of uncertainty. The current COVID-19 crisis will, in the short-term, drastically decrease the input of GBCAs to freshwater systems. Temporal variations in anthropogenic gadolinium concentrations in river water can be used to better understand river-aquifer interactions and groundwater flow velocities. Collecting urine from all patients following MRI examinations could be a way forward to halt the generally increasing concentrations of Gd in drinking water systems and recover this technologically critical element.

  • Carbonates and cherts as archives of seawater chemistry and habitability on a carbonate platform 3.35 Ga ago: Insights from Sm/Nd dating and trace element analysis from the Strelley Pool Formation, Western Australia

    Sebastian Viehmann. Joachim Reitner, NathalieTepe, Simon V. Hohl, Martin Van Kranendonk, Thilo Hofmann, Christian Koeberl, Patrick Meister
    2020 - Precambrian Research, 344: 105742

    Abstract: 

    Carbonates and cherts in the 3.35 billion-year-old Strelley Pool Formation (Fm.; Australia) host stromatolites that are among the oldest remnants of life on Earth. However, it is still not entirely clear whether these mineral phases are authigenic precipitates, and whether they represent reliable geochemical archives of early Earth environments. Here we present major/trace-element and Nd-isotope data of stromatolitic carbonates, associated crystal-fan carbonates, and cherts in the Strelley Pool Fm. (i) to assess the reliability of these chemical sediments as geochemical archives of the fluids from which they precipitated, (ii) to date the time of formation of carbonate and silica phases, and (iii) to trace the sources of elements prevailing in microbial habitats 3.35 Ga ago.

    Stromatolitic carbonates plot together with the stratigraphically underlying Marble Bar cherts on a Sm-Nd regression line yielding 3253 ± 320 Ma. In contrast, associated crystal-fan carbonates together with altered Marble Bar cherts yield 2718 ± 220 Ma, suggesting that their Sm-Nd isotope system was reset after deposition. Both types of carbonates, as well as white cherts, show shale-normalized rare earth element and yttrium patterns (REYSN; with the exception of redox-sensitive Ce and Eu and heavy REYSN to middle REYSN depletion) that are parallel to those of modern seawater, indicating a predominantly seawater-derived origin. Positive EuSN anomalies (2.1–2.4), combined with heterogeneous ɛNd3.35Ga values between −3.2 and +5.8 within individual alternating stromatolite laminae, further support that the dissolved fraction of seawater on the ancient carbonate platform was variably affected by both continental weathering and high-temperature hydrothermal fluids contributing elements of both young mafic or older felsic rocks. In conclusion, trace element and Nd isotope data presented here match well with the depositional environment, as characterized based on lithological, geochemical, and stratigraphic relationships, on an early continent, showing at least episodic emergence above the sea level, supporting microbial life on a shallow marine platform.

     
  • Copper limiting threshold in the terrestrial ammonia oxidizing archaeon Nitrososphaera viennensis

    Carolina Reyes, Logan H.Hodgskiss, Oliver Baars, Melina Kerou, Barbara Bayer, Christa Schleper, Stephan M Kraemer
    2020 - Research in microbiology, 171: 134-142

    Abstract: 

    Ammonia oxidizing archaea (AOA) inhabiting soils have a central role in the global nitrogen cycle. Copper (Cu) is central to many enzymes in AOA including ammonia monooxygenase (AMO), the enzyme involved in the first step of ammonia oxidation. This study explored the physiological response of the AOA soil isolate, Nitrososphaera viennensis (EN76T) to Cu-limiting conditions in order to approach its limiting threshold under laboratory conditions. The chelator TETA (1,4,8,11-tetraazacyclotetradecane N, N′, N″, N‴-tetraacetic acid hydrochloride hydrate) with selective affinity for Cu2+ was used to lower bioavailable Cu2+ in culture experiments as predicted by thermodynamic speciation calculations. Results show that N. viennensis is Cu-limited at concentrations ≤10−15 mol L−1 free Cu2+ compared to standard conditions (10−12 mol L−1). This Cu2+ limiting threshold is similar to pure cultures of denitrifying bacteria and other AOA and AOB inhabiting soils, freshwaters and sewage (<10−16 mol L−1), and lower than pure cultures of the marine AOA Nitrosopumilus maritimus (<10−12.7 mol L−1), which also possesses a high amount of Cu-dependent enzymes.

  • Core–Shell Fe/FeS Nanoparticles with Controlled Shell Thickness for Enhanced Trichloroethylene Removal

    Miroslav Brumovský, Jan Filip, Ondřej Malina, Jana Oborná, Ondra Sracek, Thomas G. Reichenauer, Pavlína Andrýsková, Radek Zbořil
    2020 - ACS Applied Materials & Interfaces, 12: 35424–35434

    Abstract: 

    Zero-valent iron nanoparticles (nZVI) treated by reduced sulfur compounds (i.e., sulfidated nZVI, S-nZVI) have attracted increased attention as promising materials for environmental remediation. While the preparation of S-nZVI and its reactions with various groundwater contaminants such as trichloroethylene (TCE) were already a subject of several studies, nanoparticle synthesis procedures investigated so far were suited mainly for laboratory-scale preparation with only a limited possibility of easy and cost-effective large-scale production and FeS shell property control. This study presents a novel approach for synthesizing S-nZVI using commercially available nZVI particles that are treated with sodium sulfide in a concentrated slurry. This leads to S-nZVI particles that do not contain hazardous boron residues and can be easily prepared off-site. The resulting S-nZVI exhibits a core–shell structure where zero-valent iron is the dominant phase in the core, while the shell contains mostly amorphous iron sulfides. The average FeS shell thickness can be controlled by the applied sulfide concentration. Up to a 12-fold increase in the TCE removal and a 7-fold increase in the electron efficiency were observed upon amending nZVI with sulfide. Although the FeS shell thickness correlated with surface-area-normalized TCE removal rates, sulfidation negatively impacted the particle surface area, resulting in an optimal FeS shell thickness of approximately 7.3 nm. This corresponded to a particle S/Fe mass ratio of 0.0195. At all sulfide doses, the TCE degradation products were only fully dechlorinated hydrocarbons. Moreover, a nearly 100% chlorine balance was found at the end of the experiments, further confirming complete TCE degradation and the absence of chlorinated transformation products. The newly synthesized S-nZVI particles thus represent a promising remedial agent applicable at sites contaminated with TCE.

  • Deep Learning Neural Network Approach for Predicting the Sorption of Ionizable and Polar Organic Pollutants to a Wide Range of Carbonaceous Materials

    Gabriel Sigmund, Mehdi Gharasoo, Thorsten Hüffer, Thilo Hofmann
    2020 - Environmental Science & Technology, 54: 4583-4591

    Abstract: 

    Most contaminants of emerging concern are polar and/or ionizable organic compounds, whose removal from engineered and environmental systems is difficult. Carbonaceous sorbents include activated carbon, biochar, fullerenes, and carbon nanotubes, with applications such as drinking water filtration, wastewater treatment, and contaminant remediation. Tools for predicting sorption of many emerging contaminants to these sorbents are lacking because existing models were developed for neutral compounds. A method to select the appropriate sorbent for a given contaminant based on the ability to predict sorption is required by researchers and practitioners alike. Here, we present a widely applicable deep learning neural network approach that excellently predicted the conventionally used Freundlich isotherm fitting parameters log KF and n (R2 > 0.98 for log KF, and R2 > 0.91 for n). The neural network models are based on parameters generally available for carbonaceous sorbents and/or parameters freely available from online databases. A freely accessible graphical user interface is provided.

  • Enhanced chromium(VI) treatment in electroactive constructed wetlands: Influence of conductive material

    Pratiksha Srivastava, Rouzbeh Abbassi, Asheesh Kumar Yadav, Vikram Garaniya, Naresh Kumar, Stuart J.Khan, Trevor Lewis
    2020 - Journal of Hazardous Materials, 387: 121722

    Abstract: 

    A constructed wetland (CW) microcosm based on conductive graphite gravel was investigated for hexavalent chromium (Cr(VI)) treatment from synthetic wastewater. Its performance was evaluated and compared with a traditional gravel-based CW microcosm. The microcosms were operated at varying initial Cr(VI) concentrations (5−20 mg/L) and hydraulic retention times (HRT) (3–7.5 h). Near complete treatment (99.9 ± 0.06 %) was achieved in the graphite-based microcosm throughout the experiment. The performance was consistently high throughout with 42.9 % improvement in Cr (VI) treatment compared to a traditional gravel microcosm. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis indicated that chromium was adsorbed to microbial biofilms. Moreover, microbial diversity profiling suggested that the microbial population in both microcosms differed in diversity and communities. The results suggest that the use of conductive materials in CW significantly enhances the treatment of Cr(VI) and more importantly, allows microbial activity even at high levels of Cr(VI) in the CW.

  • FeS colloids – formation and mobilization pathways in natural waters

    Vincent Noël, Naresh Kumar, Kristin Boye, Lilia Barragan, Juan S. Lezama-Pacheco, Rosalie Chu, Nikola Tolic, Gordon E. Brown, Jr., John R. Bargar
    2020 - Environmental Science: Nano, 7: 2102-2116

    Abstract: 

    We have used synchrotron-based X-ray absorption spectroscopy (structure of Fe–S clusters), transmission electron microscopy (solid-phase crystallinity), Fourier-transform ion-cyclotron-resonance mass spectrometry (identity and composition of natural organic carbon compounds), inductively coupled plasma optical emission spectrometry (total aqueous Fe), and the revised ferrozine method (aqueous Fe(II) and Fe(III) concentrations) to determine the stability and nature of colloids generated by sulfidation of ferrihydrite nanoparticles in the absence and presence of organic compounds. We observed that reductive dissolution of ferrihydrite by aqueous sulfide generates nm-scale FeS clusters. Their subsequent aggregation, which promotes settling of FeS aggregates into the solid fraction, was directly correlated with sulfide/Fe ratio. At sulfide/Fe ratios ≤0.5, FeS clusters and larger colloids remained in suspension for at least 14 days (and up to several months). At sulfide/Fe ratios >0.5, sulfidation reaction rates were rapid and FeS cluster aggregation was accelerated. Moreover, the presence of organic compounds increased the time of suspension of FeS colloids, whereas increased ionic strength inhibited the generation of FeS colloids. We present a general conceptual model to predict when and where FeS colloids can form and enhance or inhibit the mobility of contaminants and nutrients associated with them. Our study indicates that in low-salinity fresh groundwater systems poor in sulfate (i.e. low sulfidation; lakes, floodplains, peatlands etc.), the ferrihydrite sulfidation reaction generates aqueous FeS clusters and larger colloids that remain suspended over long time periods, thus mobilizing a substantial fraction of the total aqueous Fe and S.

  • Genome wide transcriptomic analysis of the soil ammonia oxidizing archaeon Nitrososphaera viennensis upon exposure to copper limitation

    Carolina Reyes, Logan H. Hodgskiss, Melina Kerou, Thomas Pribasnig, Sophie S. Abby, Barbara Bayer, Stephan M. Kraemer, Christa Schleper
    2020 - The ISME journal, 14: 2659-2674

    Abstract: 

    Ammonia-oxidizing archaea (AOA) are widespread in nature and are involved in nitrification, an essential process in the global nitrogen cycle. The enzymes for ammonia oxidation and electron transport rely heavily on copper (Cu), which can be limited in nature. In this study the model soil archaeon Nitrososphaera viennensis was investigated via transcriptomic analysis to gain insight regarding possible Cu uptake mechanisms and compensation strategies when Cu becomes limiting. Upon Cu limitation, N. viennensis exhibited impaired nitrite production and thus growth, which was paralleled by downregulation of ammonia oxidation, electron transport, carbon fixation, nucleotide, and lipid biosynthesis pathway genes. Under Cu-limitation, 1547 out of 3180 detected genes were differentially expressed, with 784 genes upregulated and 763 downregulated. The most highly upregulated genes encoded proteins with a possible role in Cu binding and uptake, such as the Cu chelator and transporter CopC/D, disulfide bond oxidoreductase D (dsbD), and multicopper oxidases. While this response differs from the marine strain Nitrosopumilus maritimus, conserved sequence motifs in some of the Cu-responsive genes suggest conserved transcriptional regulation in terrestrial AOA. This study provides possible gene regulation and energy conservation mechanisms linked to Cu bioavailability and presents the first model for Cu uptake by a soil AOA.

  • Groundwater Chemistry Has a Greater Influence on the Mobility of Nanoparticles Used for Remediation than the Chemical Heterogeneity of Aquifer Media

    Vesna Micić, Nathan Bossa, Doris Schmid, Mark R. Wiesner, Thilo Hofmann
    2020 - Environmental Science & Technology, 54: 1250-1257

    Abstract: 

    The application of nanoscale zerovalent iron (nano-ZVI) particles for groundwater remediation has spurred research into the influence of the collector heterogeneity on the  nano-ZVI mobility. The chemical heterogeneity of surfaces within aquifer media affects their surface charge distribution and their affinity for nano-ZVI. The groundwater chemistry affects the properties of both aquifer surfaces and the nano-ZVI particles. Commercial poly(acrylic acid)-coated nano-ZVI (PAA−nano-ZVI) particles were tested in column experiments using two solution chemistries and silica collectors with different degrees of chemical heterogeneity, achieved by ferrihydrite coating. A porous media filtration model was used to determine the attachment efficiency of PAA−nano-ZVI particles, and the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory was used to describe the interactions between PAA−nano-ZVI particles and the aquifer “collectors”. The mobility of PAA−nano-ZVI particles suspended in ultrapure water depended on the extent of ferrihydrite coating on the collector surfaces. The mobility of PAA−nano-ZVI particles under environmentally relevant conditions was independent of the collector chemical heterogeneity. The size of PAA−nano-ZVI aggregates doubled, inducing gravitational sedimentation and possibly straining as mechanisms of particle deposition. There was no repulsive energy barrier between particles and collectors, and the DLVO theory was unable to explain the observed particle attachment. Our results suggest that the groundwater chemistry has a greater influence on the mobility of PAA−nano-ZVI particles than the collector chemical heterogeneity. A better understanding of polymer adsorption to nanoparticles and its conformation under natural groundwater conditions is needed to further elucidate nanoparticle−collector interactions.

  • Harmonizing across environmental nanomaterial testing media for increased comparability of nanomaterial datasets

    Nicholas K. Geitner, Christine Ogilvie Hendren, Geert Cornelis, Ralf Kaegi, Jamie R. Lead, Gregory V. Lowry, Iseult Lynch, Bernd Nowack, Elijah Petersen, Emily Bernhardt, Scott Brown, Wei Chen, Camille de Garidel-Thoron, Jaydee Hanson, Stacey Harper, Kim Jones, Frank von der Kammer, Alan Kennedy, Justin Kidd, Cole Matson, Chris D. Metcalfe, Joel Pedersen, Willie J. G. M. Peijnenburg, Joris T. K. Quik, Sónia M. Rodrigues, Jerome Rose, Phil Sayre, Marie Simonin, Claus Svendsen, Robert Tanguay, Nathalie Tefenkji, Tom van Teunenbroek, Gregory Thies, Yuan Tian, Jacelyn Rice, Amalia Turner, Jie Liu, Jason Unrine, Marina Vance, Jason C. White, Mark R. Wiesner
    2020 - Environmental Science: Nano, 7: 13-36

    Abstract: 

    The chemical composition and properties of environmental media determine nanomaterial (NM) transport, fate, biouptake, and organism response. To compare and interpret experimental data, it is essential that sufficient context be provided for describing the physical and chemical characteristics of the setting in which a nanomaterial may be present. While the nanomaterial environmental, health and safety (NanoEHS) field has begun harmonization to allow data comparison and re-use (e.g. using standardized materials, defining a minimum set of required material characterizations), there is limited guidance for standardizing test media. Since most of the NM properties driving environmental behaviour and toxicity are medium-dependent, harmonization of media is critical. A workshop in March 2016 at Duke University identified five categories of test media: aquatic testing media, soil and sediment testing media, biological testing media, engineered systems testing media and product matrix testing media. For each category of test media, a minimum set of medium characteristics to report in all NM tests is recommended. Definitions and detail level of the recommendations for specific standardized media vary across these media categories. This reflects the variation in the maturity of their use as a test medium and associated measurement techniques, variation in utility and relevance of standardizing medium properties, ability to simplify standardizing reporting requirements, and in the availability of established standard reference media. Adoption of these media harmonization recommendations will facilitate the generation of integrated comparable datasets on NM fate and effects. This will in turn allow testing of the predictive utility of functional assay measurements on NMs in relevant media, support investigation of first principles approaches to understand behavioral mechanisms, and support categorization strategies to guide research, commercial development, and policy.

  • Identifying the reactive sites of hydrogen peroxide decomposition and hydroxyl radical formation on chrysotile asbestos surfaces

    Martin Walter, Walter D. C. Schenkeveld, Gerald Geroldinger, Lars Gille, Michael Reissner & Stephan M. Kraemer
    2020 - Particle and Fibre Toxicology, 17: 3

    Abstract: 

    Chrysotile asbestos is a carcinogenic mineral that has been abundantly used in different industrial and consumer applications. The fibers’ toxicity is partly goverend by the formation of highly reative radicals by active surface sites.

    Stephan Kraemer from EDGE together with the former PhD student Martin Walter and university assistant Walter Schenkeveld investigated these reactive sites on chrysotile asbestos surfaces, in cooperation with the collegues Lars Gille and Gerald Geroldinger from VetMed Vienna and Michael Reissner from TU Vienna.

    The authors identified tetrahedrally coordinated Fe on the surface of chrysotile asbestos as the only relevant site in the formation of the highly reactive and toxic hydroxyl radicals, which readily damage DNA, proteins and lipids and hence contribute to the pathogenicity of the fibers. Fe added to chrysotile fibers increased the formation of hydroxyl radicals only when it became incorporated and coordinated into tetrahedral vacancy sites on asbestos surfaces.

  • Importance of oxidation products in coumarin-mediated Fe(hydr)oxide mineral dissolution

    Matthias Baune, Kyounglim Kang.Walter D. C, Schenkeveld, Stephan M. Kraemer, Heiko Hayen, Gu ̈nther Weber
    2020 - Springer, 33: 305–321
  • Intra-laboratory assessment of a method for the detection of TiO2 nanoparticles present in sunscreens based on multi-detector asymmetrical flow field-flow fractionation

    Milica Velimirovic, Stephan Wagner, Robert Koeber, Thilo Hofmann, Frank von der Kammer
    2020 - NanoImpact, 19: 100233

    Abstract: 

    In this study, an intra-laboratory assessment was carried out to establish the effectiveness of a method for the detection of TiO2 engineered nanoparticles (ENPs) present in sunscreen containing nano-scale TiO2 and a higher nanometer-range (approx. 200–500 nm) TiO2, as well as iron oxide particles. Three replicate measurements were performed on five separate days to generate the measurement uncertainties associated with the quantitative asymmetrical flow field-flow fractionation (AF4) measurement of the hydrodynamic radius rh,mode1 (MALS), rh,mode1 (ICP-MS), rh,mode2 (ICP-MS), and calculated mass-based particle size distribution (d10, d50, d90). The validation study demonstrates that the analysis of TiO2 ENPs present in sunscreen by AF4 separation-multi detection produces quantitative data (mass-based particle size distribution) after applying the sample preparation method developed within the NanoDefine project with uncertainties based on the precision (uIP) of 3.9–8.8%. This method can, therefore, be considered as the method with a good precision. Finally, the bias data shows that the trueness of the method (ut = 5.5–52%) can only be taken as a proxy due to the lack of a sunscreen standard containing certified TiO2 ENPs.

  • Investigation of Siderophore-Promoted and Reductive Dissolution of Dust in Marine Microenvironments Such as Trichodesmium Colonies

    Nivi Kessler, Stephan M. Kraemer, Yeala Shaked, Walter D. C. Schenkeveld
    2020 - Front. Mar. Sci, 7: 2296-7745

    Abstract: 

    Desert dust is a major source of iron (Fe) to phytoplankton in many Fe-poor ocean regions. However, phytoplankton often struggle to obtain dust-bound Fe (dust-Fe) due to its low solubility and short residence time in the euphotic zone. Trichodesmium, a globally important nitrogen-fixing, cyanobacterium, is uniquely adapted for utilizing dust as a source of Fe. Trichodesmium colonies can actively collect and concentrate dust particles within the colony core and enhance dust-Fe dissolution rates via two bio-dissolution mechanisms: reduction and complexation by strong Fe-chelators termed siderophores. Here, mimicking bio-dissolution in Trichodesmium colonies, we studied the kinetics of desert dust dissolution by a siderophore and a reductant in seawater. By concurrent measurements of dissolved Fe, silica (Si), and aluminum (Al) we recognized two major mineral pools that released Fe into seawater over an 8-day period: Fe(hydr)oxides and aluminosilicates. In the presence of the siderophore desferrioxamine-B, we observed two stages of dissolution: a short stage of fast Fe dissolution followed by a lasting stage of slow Fe dissolution that was highly correlated to Al and Si dissolution. In the presence of the reductant, ascorbate, Fe dissolution was not correlated to Al and Si dissolution and was relatively slow. Based on these observations and on dust mineralogy, we constructed a conceptual model for dust-Fe dissolution by a siderophore and a reductant from two major mineral pools: reductive and siderophore-promoted dissolution of Fe(hydr)oxides and slow continuous dissolution of Fe-bearing clays in the presence of a siderophore. Our findings highlight the importance of clays as an Fe source to Trichodesmium and possibly to other marine phytoplankton and can be further used to assess the contribution of dust to the Fe requirements of natural Trichodesmium colonies. Combining our measured bio-dissolution rates with dust concentrations retained within colonies from the Gulf of Aqaba, we calculated the supply of dissolved Fe from dust to single Trichodesmium colonies. Applying published Fe-quotas and growth rates we calculated the Fe requirements of the colonies under Fe-limited and Fe-replete conditions. The calculated dissolved Fe supply from dust retained within colonies can fulfill the Fe requirements of slow growing Fe-limited colonies, but cannot support fast growth and/or higher cellular Fe quotas. We conclude that despite these bio-dissolution mechanisms, dust-Fe availability to Trichodesmium is low and propose that it employs additional mechanisms to actively mine Fe from dust.

  • Key principles and operational practices for improved nanotechnology environmental exposure assessment

    Claus Svendsen, Lee A. Walker, Marianne Matzke, Elma Lahive, Samuel Harrison, Alison Crossley, Barry Park, Stephen Lofts, Iseult Lynch, Socorro Vázquez-Campos, Ralf Kaegi, Alexander Gogos, Christof Asbach, Geert Cornelis, Frank von der Kammer, Nico W. van den Brink, Claire Mays, David J. Spurgeon
    2020 - Nature Nanotechnology, 15: 731–742

    Abstract: 

    Nanotechnology is identified as a key enabling technology due to its potential to contribute to economic growth and societal well-being across industrial sectors. Sustainable nanotechnology requires a scientifically based and proportionate risk governance structure to support innovation, including a robust framework for environmental risk assessment (ERA) that ideally builds on methods established for conventional chemicals to ensure alignment and avoid duplication. Exposure assessment developed as a tiered approach is equally beneficial to nano-specific ERA as for other classes of chemicals. Here we present the developing knowledge, practical considerations and key principles need to support exposure assessment for engineered nanomaterials for regulatory and research applications.

  • Linking Isotope Exchange with Fe(II)-Catalyzed Dissolution ofIron(hydr)oxides in the Presence of the Bacterial SiderophoreDesferrioxamine‑B

    Jagannath Biswakarma, Kyounglim Kang, Walter D. C. Schenkeveld, Stephan M. Kraemer, Janet G. Hering, Stephan J. Hug
    2020 - Environ. Sci. Technol., 54: 768-777

    Abstract: 

    Dissolution of Fe(III) phases is a key process in making iron available to biota and in the mobilization ofassociated trace elements. Recently, we have demonstrated that submicromolar concentrations of Fe(II) significantly acceleraterates of ligand-controlled dissolution of Fe(III) (hydr)oxides at circumneutral pH. Here, we extend this work by studyingisotope exchange and dissolution with lepidocrocite (Lp) and goethite (Gt) in the presence of 20 or 50μM desferrioxamine-B(DFOB). Experiments with Lp at pH 7.0 were conducted in carbonate-buffered suspensions to mimic environmentalconditions. We applied a simple empirical model to determine dissolution rates and a more complex kinetic model thataccounts for the observed isotope exchange and catalytic effect of Fe(II). The fate of added tracer57Fe(II) was stronglydependent on the order of addition of57Fe(II) and ligand. When DFOB was addedfirst, tracer57Fe remained in solution. When57Fe(II) was addedfirst, isotope exchange between surface and solution could be observed at pH 6.0 but not at pH 7.0 and 8.5where57Fe(II) was almost completely adsorbed. During dissolution of Lp with DFOB, ratios of released56Fe and57Fe werelargely independent of DFOB concentrations. In the absence of DFOB, addition of phenanthroline 30 min after tracer57Fedesorbed predominantly56Fe(II), indicating that electron transfer from adsorbed57Fe to56Fe of the Lp surface occurs on a timescale of minutes to hours. In contrast, comparable experiments with Gt desorbed predominantly57Fe(II), suggesting a longertime scale for electron transfer on the Gt surface. Our results show that addition of 15μM Fe(II) leads to dynamic chargetransfer between dissolved and adsorbed species and to isotope exchange at the surface, with the dissolution of Lp by ligandsaccelerated by up to 60-fold.

  • Quantification and Characterization of Nanoparticulate Zinc in an Urban Watershed

    Shaun Bevers, Manuel David Montano, Laya Rybicki, Thilo Hofmann, Frank von der Kammer, James F. Ranville
    2020 - Frontiers in Environmental Science, 8: 84

    Abstract: 

    The recent expansion in the use of nanomaterials in consumer and industrial applications has led to a growing concern over their behavior, fate, and impacts in environmental systems. However, engineered nanoparticles comprise only a small fraction of the total nanoparticle mass in aquatic systems. Human activities, particularly in urban watersheds, are increasing the population of incidental nanoparticles and are likely  altering the cycling of more abundant natural nanoparticles. Accurate detection, quantification, characterization, and tracking of these different populations is important for assessing both the ecological risks of anthropogenic particles, and their impact on environmental health. The urban portion of the South Platte watershed in Denver, Colorado (United States) was sampled for zinc to identify and quantify different nanomaterial sources. Single particle ICP-QMS was employed, to provide single elemental (Zn) signals arising from particle detection events. Coupling spICP-QMS to sample pre-fractionation (sedimentation, filtration) provided some insights into Zn association with nanoparticulate, colloidal, and suspended sediment phases. Single particle ICP-TOFMS (spICP-TOFMS) provided quantification across a large atomic mass range, yielding an even more detailed characterization (elemental ratios) on a particle-by-particle basis, providing some delineation of multiple sources of particles. Across the watershed, on average, 21% of zinc mass was present as zinc-only particles with a rather uniform mean size of 40.2 nm. Zinc that was detected with one or more other elements, primarily Al, Fe, and Si, is likely to be present as heteroagglomerates or within mineral colloids. Although spICP-TOFMS provides a substantial amount of information, it is still in its early stages as an analytical technique and currently lacks the requisite sensitivity to study the smallest of nanoparticles. As this technique continues to develop, it is anticipated that this methodology can be broadly applied to study sources, behavior and effects of a disparate variety of nanoparticles from both geogenic and anthropogenic origins.

  • Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns

    Alexander Gogos, Jonas Wielinski, Andreas Voegelin, Frank von der Kammer, Ralf Kaegi
    2020 - Water Research X, 9: 100059

    Abstract: 

    Emissions of Ce from anthropogenic activities (anthropogenic Ce) into urban wastewater systems and the environment result from its widespread industrial use (abrasives, catalysts, nanotechnology). Because Ce in sewage sludge can also be of geogenic origin, the quantification of anthropogenic Ce in sewage sludge remains elusive. In this study, we evaluated the suitability of Ce oxidation state and rare earth element (REE) patterns for the quantification of anthropogenic Ce fractions in sewage sludge. A diverse set of soil samples served to gain baseline information on geogenic Ce. Geogenic Ce in the soils was characterized by high Ce(III) fractions (≥70%) and their REE patterns were comparable to the REE patterns of the upper continental crust. The sewage sludges contained on average ∼80% Ce(IV) (range 18–108%), pointing to the importance of anthropogenic inputs of Ce(IV). The quantification of the anthropogenic Ce fraction based on Ce oxidation state, however, was associated with considerable uncertainty because geogenic and anthropogenic Ce cannot exclusively be assigned to Ce(III) and Ce(IV), respectively. The REE patterns of most sewage sludges indicated a clear enrichment of Ce compared to heavier REE. Based on the assumption that the industrially used Ce is free of (most) other REE, we estimated the fraction of anthropogenic Ce in the sludges based on individual Ce/REE ratios. For the individual sludges the anthropogenic contributions were very variable (10–100%) but consistent fractions were obtained for individual sludges when calculated based on Ce/Dy (dysprosium), Ce/Er (erbium) and Ce/Eu (europium) ratios. Electron microscopy analysis of sludges dominated by anthropogenic Ce revealed that the Ce was mostly contained in nanoscale particles devoid of elements characteristic of Ce-bearing minerals. Thus, anthropogenic Ce contents derived from REE patterns may be used to validate current mass flow models for engineered CeO2 nanoparticles.

  • Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments

    Naresh Kumar, Vincent Noël, Britta Planer-Friedrich, Johannes BesoldJ, uan Lezama-Pacheco, John R. Bargar, Gordon E. Brown Jr., Scott Fendorf, Kristin Boye
    2020 - Environmental Science & Technology, 54, 6, 3237–3244

    Abstract: 

    Groundwater contamination by As from natural and anthropogenic sources is a worldwide concern. Redox heterogeneities over space and time are common and can influence the molecular-level speciation of As, and thus, As release/retention but are largely unexplored. Here, we present results from a dual-domain column experiment, with natural organic-rich, fine-grained, and sulfidic sediments embedded as lenses (referred to as “reducing lenses”) within natural aquifer sand. We show that redox interfaces in sulfur-rich, alkaline aquifers may release concerning levels of As, even when sediment As concentration is low (<2 mg/kg), due to the formation of mobile thioarsenates at aqueous sulfide/Fe molar ratios <1. In our experiments, this behavior occurred in the aquifer sand between reducing lenses and was attributed to the spreading of sulfidic conditions and subsequent Fe reductive dissolution. In contrast, inside reducing lenses (and some locations in the aquifer) the aqueous sulfide/Fe molar ratios exceeded 1 and aqueous sulfide/As molar ratios exceeded 100, which partitioned As(III)–S to the solid phase (associated with organics or as realgar (As4S4)). These results highlight the importance of thioarsenates in natural sediments and indicate that redox interfaces and sediment heterogeneities could locally degrade groundwater quality, even in aquifers with unconcerning solid-phase As concentrations.

  • Remediation of fluoride contaminated water using encapsulated active growing blue-green algae, Phormidium sp.

    Yamini Mittal, Pratiksha Srivastav, Naresh Kumar, Asheesh KumarYadav
    2020 - Environmental Technology and Innovation, 19: 100855

    Abstract: 

    Elevated fluoride concentration in drinking water is a global concern that impacts health of millions. Developing low cost remediation methods empower communities with fewer resources available to protect their health.

    Together with colleagues from CSIR India, and University of Tasmania in Australia, we have demonstrated that fluoride can be removed by using common blue-green algae, Phormidium sp. Using Response Surface Methodology (RSM) we were able to optimize parameters for the highest fluoride removal in our system. Further work is currently ongoing on process optimization to develop a household level pilot scale experimental reactor in a small village in eastern India.

  • Strategies for determining heteroaggregation attachment efficiencies of engineered nanoparticles in aquatic environments

    Antonia Praetorius, Elena Badetti, Andrea Brunelli, Arnaud Clavier, Julián Alberto Gallego-Urrea, Andreas Gondikas, Martin Hassellöv, Thilo Hofmann, Aiga Mackevica, Antonio Marcomini, Willie Peijnenburg, Joris T. K. Quik, Marianne Seijo, Serge Stoll, Nathalie Tepe, Helene Walch, Frank von der Kammer
    2020 - Environmental Science: Nano, 7: 351–367

    Abstract: 

    Heteroaggregation of engineered nanoparticles (ENPs) with suspended particulate matter (SPM) ubiquitous in natural waters often dominates the transport behaviour and overall fate of ENPs in aquatic environments. In order to provide meaningful exposure predictions and support risk assessment for ENPs, environmental fate and transport models require quantitative information about this process, typically in the form of the so-called attachment efficiency for heteroaggregation αhetero. The inherent complexity of heteroaggregation—encompassing at least two different particle populations, various aggregation pathways and several possible attachment efficiencies (α values)—makes its theoretical and experimental determination challenging. In this frontier review we assess the current state of knowledge on heteroaggregation of ENPs with a focus on natural surface waters. A theoretical analysis presents relevant equations, outlines the possible aggregation pathways and highlights different types of α. In a second part, experimental approaches to study heteroaggregation and derive α values are reviewed and three possible strategies are identified: i) monitoring changes in size, ii) monitoring number or mass distribution and iii) studying indirect effects, such as sedimentation. It becomes apparent that the complexity of heteroaggregation creates various challenges and no single best method for its assessment has been developed yet. Nevertheless, many promising strategies have been identified and meaningful data can be derived from carefully designed experiments when accounting for the different concurrent aggregation pathways and clearly stating the type of α reported. For future method development a closer connection between experiments and models is encouraged.

  • Technology readiness and overcoming barriers to sustainably implement nanotechnology-enabled plant agriculture

    Thilo Hofmann, Gregory Victor Lowry, Subhasis Ghoshal, Nathalie Tufenkji, Davide Brambilla, John Robert Dutcher, Leanne M. Gilbertson, Juan Pablo Giraldo, Joseph Matthew Kinsella, Markita Patricia Landry, Wess Lovell, Rafik Naccache, Mathews Paret, Joel Alexander Pedersen, Jason Michael Unrine, Jason Christopher White, Kevin James Wilkinson
    2020 - Nature food, 1: 416–425

    Abstract: 

    Nanotechnology offers potential solutions for sustainable agriculture, including increasing nutrient utilization efficiency, improving the efficacy of pest management, mitigating the impacts of climate change, and reducing adverse environmental impacts of agricultural food production. Many promising nanotechnologies have been proposed and evaluated at different scales, but several barriers to implementation must be addressed for technology to be adopted, including efficient delivery at field scale, regulatory and safety concerns, and consumer acceptance. Here we explore these barriers, and rank technology readiness and potential impacts of a wide range of agricultural applications of nanotechnology. We propose pathways to overcome these barriers and develop effective, safe and acceptable nanotechnologies for agriculture.

  • The importance of aromaticity to describe the interactions of organic matter with carbonaceous materials depends on molecular weight and sorbent geometry

    Stephanie Castan, Gabriel Sigmund, Thorsten Hüffer, Nathalie Tepe, Frank von der Kammer, Benny Chefetz, Thilo Hofmann
    2020 - Environmental Science.: Processes & Impacts, 22: 1888-1897

    Abstract: 

    Dissolved organic matter (DOM) is ubiquitous in aquatic environments where it interacts with a variety of particles including carbonaceous materials (CMs). The complexity of both DOM and the CMs makes DOM–CM interactions difficult to predict. In this study we have identified the preferential sorption of specific DOM fractions as being dependent on their aromaticity and molecular weight, as well as on the surface properties of the CMs. This was achieved by conducting sorption batch experiments with three types of DOM (humic acid, Suwannee River natural organic matter, and a compost extract) and three types of CMs (graphite, carbon nanotubes, and biochar) with different geometries and surface complexities. The non-adsorbed DOM fraction was analyzed by size exclusion chromatography and preferentially sorbed molecular weight fractions were analyzed by UV/vis and fluorescence spectroscopy. All three sorbent types were found to preferentially sorb aromatic DOM fractions, but DOM fractionation depended on the particular combination of sorbent and sorbate characteristics. Single-walled carbon nanotubes only sorbed the smaller molecular weight fractions (<1 kDa). The sorption of smaller DOM fractions was not accompanied by a preference for less aromatic compounds, contrary to what was suggested in previous studies. While graphite preferentially sorbed the most aromatic DOM fraction (1–3 kDa), the structural heterogeneity of biochar resulted in reduced selectivity, sorbing all DOM > 1 kDa. The results explain the lack of correlation found in previous studies between the amount of aromatic carbon in a bulk DOM and its sorption coefficient. DOM sorption by CMs was generally controlled by DOM aromaticity but complex sorbent surfaces with high porosity, curvatures and functional groups strongly reduced the importance of aromaticity.

  • The molecular interactions of organic compounds with tire crumb materials differ substantially from those with other microplastics

    2020 - Environmental Science: Processes & Impacts, 22: 121-130

    Abstract: 

    Tire materials are the most commonly found elastomers in the environment and they account for a significant fraction of microplastic pollution. In the discussions on the environmental impact of microplastics tire materials and their sorption properties have been largely overlooked. In this study we used experimental sorption data from six organic probe sorbates sorbing to two tire materials and their major components, styrene butadiene rubber and carbon black, to gain a better understanding of the underlying sorption processes of tire materials. Commonly applied models used to describe non-linear sorption processes were unable to fully explain sorption to tire materials but showed that absorption into the rubber fraction dominated the sorption process. Hydrophobicity was approximated using the hexadecane–water partitioning constant, which correlated very well with the distribution data obtained for styrene rubber, whereas the correlations between hydrophobicity of sorbates and the sorption data to the tire materials were poor. Although hydrophobicity plays an important role in sorption to tire materials, additional interactions must be taken into account. Overall, the processes involved in sorption to tire materials differed significantly from those governing sorption to other microplastics.

  • The removal of lead, copper, zinc and cadmium from aqueous solution by biochar and amended biochars

    Stuart Cairns, Ian Robertson, Gabriel Sigmund, Alayne Street-Perrott
    2020 - Environmental Science and Pollution Research, 27: 21702-21715

    Abstract: 

    The exponential growth in the use of motor vehicles is a key contributor to freshwater degradation. Current remediation techniques require prohibitively expensive contaminant treatment and extraction. Biochar represents an inexpensive option to ameliorate contaminants from motorway runoff. Biochar from Norway spruce (Picea abies (L.) Karst.) was produced under fast pyrolysis-gasification (450–500 °C for 90 s) and amended with wood ash and basaltic rock dust to evaluate sorption of Pb, Cu, Zn and Cd. The column study, designed to mimic field conditions, confirmed that unamended biochar can bind contaminants for short periods, but that the addition of amendments, particularly wood ash, significantly improves contaminant removal. Wood ash-amended biochar removed 98–100% of all contaminants during the study, driven by pH (r = 0.73–0.74; p < 0.01 dependent on metal species) and phosphorus levels causing precipitation (r = 0.47–0.59; p < 0.01, dependent on metal species). The contaminants’ progression through the biochar subsections in the column indicated that increasing the thickness of the biochar layer increased contaminant residence time and removal.

  • Uranium Budget and Leaching in Swiss Agricultural Systems

    Moritz Bigalke, Martin Imseng, Stephan Schneider, Lorenz Schwab, Matthias Wiggenhauser, Armin Keller, Michael Müller, Emmanuel Frossard and Wolfgang Wilcke
    2020 - Front. Environ. Sci., 8: in press

    Abstract: 

    Many mineral P fertilizers contain toxic uranium (U) in high concentrations. When the fertilizers are applied to agricultural sites, U can either accumulate in the soil or leach to ground and surface waters. We analyzed the U fluxes at three arable and three grassland agricultural sites on the Swiss plateau for 1 year. We calculated all inputs and outputs to the soils, modeled the speciation of U in the soil solution and investigated the possible leaching of U along preferential flow paths. We found that all sites showed positive U budgets (+0.9–6.6 g ha–1 y–1), indicating an accumulation of U. However, the accumulation of U was low and a doubling of U concentration in the surface soil would need 850–2,660 years assuming today’s U fluxes. Mineral P fertilizers were the quantitatively most important input, followed by manure application and mineral weathering (only important in the soils developed on limestone). While at sites with slightly acidic pH only little U (<0.01 μg L–1) was leached, the U leaching increased at neutral pH values, because of the formation of carbonato-U complexes. In all soil solutions, the U concentrations (≤0.8 μg L–1) were below legal threshold values and comparable to local drinking and surface waters. We found no indication for enhanced U leaching along preferential flow paths.

  • Vertical mobility of pyrogenic organic matter in soils: a column experiment

    Marcus Schiedung, Severin-Luca Bellè, Gabriel Sigmund, Karsten Kalbitz, Samuel Abiven
    2020 - Biogeosciences, 17: 6457–6474

    Abstract: 

    Pyrogenic organic matter (PyOM) is a major and persistent component of soil organic matter, but its mobility and cycling in soils is largely unknown. We conducted a column experiment with a topsoil and subsoil of a sand and a sandy loam to study the mobility of highly 13C labeled ryegrass PyOM (>2.8 at. %), applied as a layer on a 7 cm long soil column, under saturated conditions. Further, we used fresh and oxidized PyOM (accelerated aging with H2O2) to identify changes in its migration through the soil with aging and associated surface oxidation. Due to the isotopic signature, we were able to trace the PyOM carbon (PyOM-C) in the soil columns, including density fractions, its effect on native soil organic carbon (nSOC) and its total export in percolates sequentially sampled after 1000–18 000 L m−2. In total, 4 %–11 % of the added PyOM-C was mobilized and <1 % leached from the columns. The majority of PyOM-C was mobilized with the first flush of 1000 L m−2 (51 %–84 % of exported PyOM-C), but its export was ongoing for the sandy soil and the loamy subsoil. Oxidized PyOM showed a 2–7 times higher mobility than fresh PyOM. In addition, 2-fold higher quantities of oxidized PyOM-C were leached from the sandy soil compared to the loamy soil. Besides the higher mobility of oxidized PyOM, its retention in both soils increased due to an increased reactivity of the oxidized PyOM surfaces and enhanced the interaction with the soil mineral phase. Density fractionation of the upper 0–2.3 cm, below the PyOM application layer, revealed that up to 40 % of the migrated PyOM was associated with the mineral phase in the loamy soil, highlighting the importance of mineral interaction for the long-term fate of PyOM in soils. The nSOC export from the sandy soil significantly increased by 48 %–270 % with addition of PyOM compared to the control, while no effect was found for the loamy soil after the whole percolation. Due to its high sorption affinity towards the soil mineral phase, PyOM can mobilize mineral-associated soil organic matter in coarse-textured soils, where organo-mineral interactions are limited, while finer-textured soils have the ability to re-adsorb the mobilized soil organic matter. Our results show that the vertical mobility of PyOM in soils is limited to a small fraction. Aging (oxidation) increases this fraction but also increases the PyOM surface reactivity and thus its long-term retention in soils. Moreover, the migration of PyOM affects the cycling of nSOC in coarse soils and thus influences the carbon cycle of fire-affected soils.

  • Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater

    Nikolas Hagemann, Hans-Peter Schmidt, Ralf Kaegi, Mark Boehler, Gabriel Sigmund, Andreas Maccagnan, Christa S. McArdell, Thomas D. Bucheli
    2020 - Science of The Total Environment, 730: 138417

    Abstract: 

    Implementing advanced wastewater treatment (WWT) to eliminate organic micropollutants (OMPs) is a necessary step to protect vulnerable freshwater ecosystems and water resources. To this end, sorption of OMP by activated carbon (AC) is one viable technology among others. However, conventional AC production based on fossil precursor materials causes environmental pollution, including considerable emissions of greenhouse gases. In this study, we produced activated biochar (AB) from wood and woody residues by physical activation and evaluated their capability to eliminate OMPs in treated wastewater. Activated biochar produced under optimized conditions sorbed 15 model OMPs, of which most were dissociated at circumneutral pH, to the same or higher extent than commercial AC used as a reference. While wood quality played a minor role, the dosage of the activation agent was the main parameter controlling the capacity of ABs to eliminate OMP. Our results highlight the possibility for local production of AB from local wood or woody residues as a strategy to improve WWT avoiding negative side effects of conventional AC production.

Book chapters and other publications

1 Publication found
  • Comment on Predicting Aqueous Adsorption of Organic Compounds onto Biochars, Carbon Nanotubes, Granular Activated Carbons, And Resins with Machine Learning

    Gabriel Sigmund, Mehdi Gharasoo, Thorsten Hüffer, Thilo Hofmann
    2020 - Environmental Science & Technology, A-B