Eawag - Swiss Federal Institute of Aquatic Science and Technology

Dr. Ralf Kägi

About Me

Research Interests

Detection and fate of particulate contaminants (engineered (nano)particles, micro- and nanoplastic particles) in natural environments and engineered systems
Fluxes and impacts (nano)particulate of contaminants through and on urban (waste)water systems
Development of new analytical methods for (nano)particle detection and structural characterization
Mechanistic understanding of the plastic fragmentation to produe nanoplastic particles

Research statement
Nano-materials (including engineered nanoparticles(NP), as well as nano-structure materials) are increasingly used in many consumer products due to their ‘beneficial’ properties. However, while these materials are certainly beneficial regarding their respective application, they might not be as beneficial in the aquatic environment. The (unintended) release and the fate of these nano-materials in the aquatic environment are only poorly understood mainly due to the he lack of adequate analytical techniques to detect and characterize these materials in the environment. My research therefore, aims at combining well established standard characterization methods from colloidal sciences, with new methods from materials science and with own developments to detect, quantify and understand the effects of the ‘nano-materials’ in the aquatic environment. The following research areas are of particular interest:

Detection and fate of engineered nanoparticles in the natural environment and engineered systems.
Although a large variety of analytical methods exist to characterize nano scale materials (and especially nanoparticles) mainly developed for materials science applications. these methods are capable of detecting pure substances in high concentrations (such as Ag-NP in concentrated stock solutions), but cannot handle polydisperse and dilute systems. However, natural systems are polydispers and dilute; we therefore try to fractionate aquatic colloids, including engineered NP, into monodisperse size fractions using field flow fractionation techniques. Individual size fractions can be further be analyzed using light scattering, mass spectroscopic or microscopic techniques.

Development of new analytical techniques to detect NP
Commercially available particle detection systems are not designed to detect particles down to the nano scale. A very promising laser based method (Laser Induced Breakdown Detection, LIBD) capable of detecting particles down to about 10nm at low concentrations has been developed almost 20 years ago by Japanese researchers. The technique never had it huge break-through (for several reasons) and thus no commercial LIBD systems are available. However, for certain applications, such as drinking water monitoring, the technique seems to be well suited. We therefore developed our own LIBD prototype in collaboration with the FZ-Karlsruhe, which is being continuously refined.

Characterization of the structure of environmental colloids and particles using microscopic and spectroscopic methods
Within this branch of research I am using state-of-the-art electron
microscopes (SEM and TEM) to characterize particles, such as natural and
experimentally produced aquatic colloids, as well as particles recovered from
ice cores. This part of my research has the rather unspecific goal of seeking any
kind of information stored in the particles that was not accessible with
‘older’ instruments. This exploratory work is vital to my function as head of
the particle laboratory at the Eawag, where I support / advise different
‘users’ on a variety of different materials.

Experimental facilities

Wastewater

Conventional activated sludge system (nitrification, denitrification, secondary clarification)

Anaerobic digestion ('Apollo')

Surface water

Custom made drum sieve designed for collection of particulate matter (e.g., microplastics) (planning phase)

Weathering

UV-exposure (SunTESTER, CPS+) -> Photooxidation

Mechanical abrasion (Roller Mill, RM1) -> simulation of beach environments

Temperature fluctuations (computer controlled temperature baths) -> simulating freeze - thaw cycles (collaboration with Prof. Stephan Gruber, Carlton UNiversity, Ottawa, Canada)

Analytical facilities

Particle size analysis

Dynamic Light Scattering (DLS) Analyzer (Zetasizer, NanoZS, Malvern)

Laser Diffraction Particle Size Analyzer (LS 13 320, Beckman Coulter)

asymmetric flow field flow fractionation system (Eclipse, Wyatt) in-line coupled to UV-DAD detector. DLS - detector, static light scattering (SLS) detector (Helios, Waytt) and a fraction collector.

visible light microscope (VHX-7000, Keyence)
Fourier Transform Infrared (FT-IR) Spectroscopy

Focal plain array (FPA)-µ-FT-IR microscope (Cary 670-IR, FTIR, Cary 610 IR Mikroskop)

Electron microscopes

Scanning electron microscope (Gemini 460, equipped with 2 EDX detectors (Extreme and Ultrmate, Oxford) Zeiss). Shared with and operated by Empa

Transmission electron microscope (Talos, FEI and HD2700Cs, Hitachi). Both instruments are operated by ScopeM (access via user training).

Particle Laboratory

Apart from my own research outlined above I also run the particle laboratory at Eawag. The particle laboratory is a contact-point for all sorts of particle-related questions, especially concerning microscopic work. My engagement in different projects covers all ranges from simple advice over a few measurements for a feasibility study up to solid collaborations. Thanks to very good contacts to the electron microscopy centers at ETHZ and Empa, experts on any kind of materials can be consulted if necessary.

Affiliation with professional societies
Swiss Society for Optics and Microscopy (SSOM), American Geophysical Union (AGU), International Water Association (IWA), Society of Environmental Toxicology and Chemistry (SETAC)

Management Committee:

Chair of the IWA specialist group: ‘Nano and water, Nanotechnology for the water sector’ (2012 – 2014)
Chair of the Norman WG4: ‘Engineered nanoparticles in the environment’ (2012 – present)
Swiss delegate in the management committee of COST action ES1205: ‘Engineered Nanomaterials - from wastewater Treatment & StormwatEr to Rivers? (ENTER)’ (2012 – present).
Chair of the Cost action ES1205, WG1: Fate and behavior of ENMs. (2012 – present)

Conference and workshop organization

Conference chair of the IWA specialist conference: ‘Nano and water, Nanotechnology for the water sector’, 15.05. – 18.05.2011, Monte Verita, Switzerland (Organiser)
Workshop organizer ‘Engineered nanoparticles in the environment’ NORMAN WG4; Zurich 18. – 19. 10.2012
Member of the program committee of the IWA Symposium on Environmental Nanotechnology, Nanjing, China, 2013
Member of the scientific committee of the 8th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials. Aix en Provence, France, 2013
Member of the organizing committee of the Micropol & Ecohazard Conference, Zürich, Switzerland, 2013.
Convener of Session 18I: Environmental Application of Engineered Nanomaterials: Benefits and Risks, Goldschmidt Conference, Florence, Italy, 2013

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Curriculum Vitae

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Publications

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Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Aluminium substitution affects jarosite transformation to iron oxyhydroxides in the presence of aqueous Fe(II). Geochimica et Cosmochimica Acta, 374, 72-84. doi:10.1016/j.gca.2024.04.008, Institutional Repository

Jarosite is an abundant mineral in acidic environments, often found in acid sulfate soil (ASS) and acid-mine drainage (AMD). As a store of Fe, K, S and acidity, and a scavenger for major and trace elements, jarosite plays an important role in the biogeochemistry of acid sulfate environments. When ASS and AMD become anoxic, reducing conditions can set in, producing conditions that are outside the thermodynamic stability field of jarosite. In this study, we investigated the transformation of synthetic and natural jarosite with various degrees of Al-for-Fe substitution under circumneutral anoxic conditions in the presence of Fe(II), to understand the rates and pathways of jarosite and Al-jarosite transformation, the role of competing transformation pathways, the fate of Al during transformation and the different reactivity of natural and synthetic Al-jarosite. Synthetic jarosite (containing 0 %–7 % Al-for-Fe substitution) and a natural Al-substituted jarosite sample from an ASS in Thailand were suspended in solutions of ⁵⁷Fe(II) at pH 7 for 24 h under anoxic conditions. The chosen experimental conditions mimic the Fe(II) concentrations and pH found in flooded ASS under reducing conditions. Changes in mineral composition of the suspensions were determined by Rietveld analysis of X-ray diffraction patterns at six time points. The fate of Al was determined by XRD, Raman spectroscopy and energy dispersive X-ray spectroscopy analysis of the jarosite and product minerals. Different transformation pathways that occurred simultaneously were traced by using ⁵⁷Fe Mössbauer spectroscopy and aqueous Fe isotope composition. The analysis showed that 7 % Al-for-Fe substitution in jarosite more than halved the mineral transformation rate compared to unsubstituted jarosite, regardless of the Fe(II) concentrations. Indeed, 7 % Al-for-Fe substitution had a greater effect on the transformation rate than an order-of-magnitude decrease in the Fe(II) concentrations in all Al-for-Fe substitution treatments. The transformation products in all samples were goethite, lepidocrocite and ferrihydrite, with minor amounts of magnetite forming from jarosite with no or low Al-for-Fe substitution reacted with high Fe(II) concentrations. Lepidocrocite was the dominant product in reactors without aluminium, but lepidocrocite was not strongly enriched in ⁵⁷Fe, suggesting that it may not have formed exclusively from Fe in solution during the Fe(II)-catalysed transformation of other minerals. In high-Al systems, lepidocrocite appeared to be a sink for Al, although its formation in Al-rich samples was suppressed. Natural jarosite reacted more than an order of magnitude more slowly than the synthetic jarosite and Al-jarosite, indicating that the properties of the synthetic jarosite do not completely account for the stability of natural jarosite under anoxic circumneutral conditions. The results provide an important baseline for understanding the drivers of jarosite transformation or stability in ASS and AMD.

Grigg, A. R. C., Notini, L., Kaegi, R., ThomasArrigo, L. K., & Kretzschmar, R. (2024). Structural effects of aluminum and iron occupancy in minerals of the jarosite-alunite solid solution. ACS Earth and Space Chemistry, 8(2), 194-206. doi:10.1021/acsearthspacechem.3c00174, Institutional Repository

Stetten, L., Kaegi, R., Hofmann, T., & von der Kammer, F. (2024). Depth-dependent transformation of ZnO and Ag nanoparticles in sulfate-reducing sediments tracked using scanning transmission electron microscopy. Environmental Science: Nano, 11(1), 136-148. doi:10.1039/d3en00550j, Institutional Repository

la Cecilia, D., Philipp, M., Kaegi, R., Schirmer, M., & Moeck, C. (2024). Microplastics attenuation from surface water to drinking water: impact of treatment and managed aquifer recharge – and identification uncertainties. Science of the Total Environment, 908, 168378 (12 pp.). doi:10.1016/j.scitotenv.2023.168378, Institutional Repository

River water can be used to recharge aquifers exploited for drinking water production. Several recent studies reported microplastics (MPs) in river water, and therefore, the potential contamination of groundwater by MPs is a growing concern among stakeholders and citizens. In this research, we investigate the fate of MPs (> 20 μm) along six different stages of a major Managed Aquifer Recharge (MAR)-water supply system in Switzerland. About 20 l of water were filtered using steel meshes at each location in triplicates. In the laboratory, MPs deposited on the anodisc filters were identified using Focal Plane Array (FPA) micro-Fourier-Transform-InfraRed (μFTIR) spectroscopy. The obtained hyperspectral data were processed using the imaging software Microplastics Finder for MPs identification and classification. Our results revealed a 20-fold decrease in MPs concentration from the Rhine River bed water (112 ± 27.4 MPs/l) to after the coagulation, flocculation and sedimentation (5.5 ± 2.2 MPs/l), a further 3-fold decrease to after the sand-filtration system (1.8 ± 0.9 MPs/l), corresponding to an overall removal efficiency of 98.4 %. The MPs concentrations remained low following MAR (2.7 ± 0.7 MPs/l) through a Quaternary gravel aquifer. Activated carbon filters did not substantially further reduce MPs concentrations. The percentage of fragments (≈95 %) prevailed over fibers (≈5 %) at all locations, with fibers being longer and more abundant in the river water. Overall, this study demonstrates the effectiveness of the treatment systems to remove MPs larger than 20 μm. Finally, we calculated an uncertainty in MPs concentrations of one order of magnitude depending on the user-defined parameters inside the MPs identification and classification model. The Quality Assurance/Quality Control approach followed during laboratory analysis highlighted an accumulation of surrogate particles at the edges of the disc, which would have an impact for MPs number upscaling.

Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). First evidence of nanoparticle uptake through leaves and roots in beech (Fagus sylvatica L.) and pine (Pinus sylvestris L.). Tree Physiology, 43(2), 262-276. doi:10.1093/treephys/tpac117, Institutional Repository

Ballikaya, P., Brunner, I., Cocozza, C., Grolimund, D., Kaegi, R., Murazzi, M. E., … Cherubini, P. (2023). Nanoparticles are everywhere, even inside trees. Chimia, 77(4), 256. doi:10.2533/chimia.2023.256, Institutional Repository

Gottschalk, F., Debray, B., Klaessig, F., Park, B., Lacome, J. M., Vignes, A., … Kaegi, R. (2023). Predicting accidental release of engineered nanomaterials to the environment. Nature Nanotechnology, 18, 412-418. doi:10.1038/s41565-022-01290-2, Institutional Repository

Joëlle Kubeneck, L., ThomasArrigo, L. K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2023). Competitive incorporation of Mn and Mg in vivianite at varying salinity and effects on crystal structure and morphology. Geochimica et Cosmochimica Acta, 346, 231-244. doi:10.1016/j.gca.2023.01.029, Institutional Repository

Vivianite, a ferrous phosphate mineral, can be an important phosphorus (P) sink in non-sulfidic, reducing coastal sediments. The Fe in the crystal structure of vivianite can be substituted by other divalent metal cations such as Mn²⁺ or Mg²⁺. Since Mg is much more abundant in coastal porewaters than Mn, the more frequent reports of Mn substitution in vivianites of coastal sediments has been suggested to indicate a preferential incorporation of Mn over Mg into the crystal structure of vivianite. However, although both Mn and Mg substitution in vivianite are environmentally relevant, it is yet unknown whether Mn or Mg is preferentially incorporated and how these isomorphic substitutions alter the crystal structure and morphology of vivianite, parameters which may influence vivianite reactivity. Here, we studied the incorporation of Mn and/or Mg in vivianites formed by co-precipitation at pH 7 in the presence of varying dissolved Mn and/or Mg concentrations and solution salinities resembling an estuarine gradient from 0 to 9 psu. In total, 19 different vivianites were synthesized, with up to 50% of Fe substituted by Mn and Mg. Thermodynamic equilibrium calculations showed that aqueous Mg speciation was altered with increasing salinity, while Mn speciation was less affected, likely explaining the preferential incorporation of Mn in the vivianite structure at higher salinities. ⁵⁷Fe-Mössbauer spectroscopy revealed that both Mn and Mg were preferentially incorporated in the double-octahedral Fe position, at which intervalence charge transfer is possible during the oxidation of vivianite. In contrast to Mg, which is redox inactive, incorporated Mn can participate in heteronuclear intervalence charge transfer with Fe. Thus, incorporation of either cation may impact the reactivity of vivianite under oxidizing conditions in element specific ways. Results of complementary analyses including X-ray diffraction, electron microscopy and Fe K-edge X-ray absorption spectroscopy further showed that incorporation of Mn and/or Mg led to smaller particle size, increased crystal roughness and thinner crystals, as well as systematic changes in unit cell parameters. These observed changes in crystal morphology might impact the reactivity of vivianite in natural environments and thus the effect of cation incorporation in vivianite should be considered when studying Fe and P cycling in coastal sediments.

Nenonen, V. V., Kaegi, R., Hug, S. J., Göttlicher, J., Mangold, S., Winkel, L. H. E., & Voegelin, A. (2023). Formation and transformation of Fe(III)- and Ca-precipitates in aqueous solutions and effects on phosphate retention over time. Geochimica et Cosmochimica Acta, 360, 207-230. doi:10.1016/j.gca.2023.09.004, Institutional Repository

Exfiltration of anoxic phosphate-rich groundwater into surface water leads to the oxidation of dissolved Fe(II) and the formation of Fe(III)-precipitates that can retain phosphate (PO₄) and thereby attenuate eutrophication. Fresh Fe(III)-precipitates transform into more stable phases over time, and retained PO₄ may be released again. In parallel, CO₂ outgassing can promote the formation of Ca-phosphates or -carbonates that also sequester PO₄. In laboratory experiments, we studied the effects of Mg, Ca, silicate (SiO₄) and PO₄ on these processes. Fresh Fe(III)-precipitates were formed in bicarbonate-buffered aqueous solutions at pH ∼ 7.0 via the oxidation of 0.5 mM Fe(II) in the presence of 0.15 or 0.025 mM PO₄, at Mg or Ca concentrations of 0, 0.4, 1.2 or 4 mM and in the absence or presence of 0.5 mM SiO₄. After CO₂ outgassing, the suspensions were allowed to age for 100 d at pH ∼ 8. Changes in the composition and structure of Fe(III)- and Ca-precipitates over time were probed with spectroscopic and microscopic techniques and were linked to variations in the retention of PO₄. The oxidation of Fe(II) led to effective PO₄ removal via the formation of Fe(III)-precipitates that consisted of amorphous (Ca-)Fe(III)-phosphate ((Ca)FeP), ferrihydrite (Fh) and, in SiO₄-free treatments, lepidocrocite (Lp). During aging, FeP and Fh that had formed in the absence of Mg, Ca and SiO₄ rapidly and nearly completely transformed into Lp. Via effects on molecular- and nanoscale precipitate structure, Mg slowed down FeP transformation into Fh, stabilized Fh, and decreased the crystallinity of Lp (in SiO₄-free suspensions), Ca stabilized CaFeP against transformation into Fh, and SiO₄ stabilized Fh and (Ca)FeP. Core/shell CaFeP/Fh particles formed in electrolytes that contained Ca and SiO₄ hardly transformed within 100 d. Calcite only formed at low dissolved PO₄ concentrations and, by incorporation of PO₄, contributed to PO₄ retention. Higher levels of dissolved PO₄ inhibited calcite formation but could induce Ca-phosphate precipitation. Differences in precipitate formation and transformation pathways and kinetics were reflected in the extents of PO₄ release over the 100-d aging period, ranging from rapid release of 77% of the total PO₄ in the treatment without Mg, Ca and SiO₄ at 0.15 mM total PO₄ to slow release of only 0.1% of the total PO₄ at initial concentrations of 4 mM Ca, 0.5 mM SiO₄, and 0.025 mM PO₄. In summary, this study reveals the conditions and the extents and timescales over which Fe(III)- and Ca-precipitates form and transform and how these processes affect PO₄ immobilization in near-neutral natural waters. The detailed new insights into the coupling between Fe(III)- and Ca-precipitate formation and into the interdependent effects of Mg, Ca, SiO₄ and PO₄ are not only relevant with respect to PO₄ but also with respect to the cycling of trace elements in natural and engineered systems.

Pulido-Reyes, G., Bianco, C., Magherini, L., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2023). Rückhalt von Nanoplastik-Partikeln bei der Wasseraufbereitung. Aqua & Gas, 103(7-8), 30-35. , Institutional Repository

Sodnikar, K., Kaegi, R., Christl, I., Schroth, M. H., & Sander, M. (2023). Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries. Environmental Science: Processes and Impacts, 25(12), 2067-2080. doi:10.1039/d3em00294b, Institutional Repository

Xu, J., Chen, C., Hu, X., Chen, D., Bland, G., Wielinski, J., … Lowry, G. V. (2023). Particle-scale understanding of arsenic interactions with sulfidized nanoscale zerovalent iron and their impacts on dehalogenation reactivity. Environmental Science and Technology, 57(51), 21917-21926. doi:10.1021/acs.est.3c08635, Institutional Repository

Grigg, A. R. C., ThomasArrigo, L. K., Schulz, K., Rothwell, K. A., Kaegi, R., & Kretzschmar, R. (2022). Ferrihydrite transformations in flooded paddy soils: rates, pathways, and product spatial distributions. Environmental Science: Processes and Impacts, 24(10), 1867-1882. doi:10.1039/d2em00290f, Institutional Repository

Kocic, J., Dirin, D. N., Kägi, R., Kovalenko, M. V., Günther, D., & Hattendorf, B. (2022). Direct analysis of nanoparticles in organic solvents by ICPMS with microdroplet injection. Journal of Analytical Atomic Spectrometry, 37(8), 1738-1750. doi:10.1039/d1ja00358e, Institutional Repository

Murazzi, M. E., Cherubini, P., Brunner, I., Kägi, R., Saurer, M., Ballikaya, P., … Gessler, A. (2022). Can forest trees take up and transport nanoplastics?. iForest, 15(2), 128-132. doi:10.3832/ifor4021-015, Institutional Repository

Notini, L., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2022). Coexisting goethite promotes Fe(II)-catalyzed transformation of ferrihydrite to goethite. Environmental Science and Technology, 56(17), 12723-12733. doi:10.1021/acs.est.2c03925, Institutional Repository

Philipp, M., Bucheli, T. D., & Kaegi, R. (2022). The use of surrogate standards as a QA/QC tool for routine analysis of microplastics in sewage sludge. Science of the Total Environment, 835, 155485 (9 pp.). doi:10.1016/j.scitotenv.2022.155485, Institutional Repository

Pulido-Reyes, G., Magherini, L., Bianco, C., Sethi, R., von Gunten, U., Kaegi, R., & Mitrano, D. M. (2022). Nanoplastics removal during drinking water treatment: laboratory- and pilot-scale experiments and modeling. Journal of Hazardous Materials, 436, 129011 (13 pp.). doi:10.1016/j.jhazmat.2022.129011, Institutional Repository

Rhein, F., Nirschl, H., & Kaegi, R. (2022). Separation of microplastic particles from sewage sludge extracts using magnetic seeded filtration. Water Research X, 17, 100155 (11 pp.). doi:10.1016/j.wroa.2022.100155, Institutional Repository

Microplastic particles (MP) are efficiently retained in wastewater treatment plants and enriched in sewage sludge. For monitoring MP contents in wastewater systems, sewage sludge is thus well suited, but also requires an isolation of MP from the sludge matrix, as other sewage sludge components may interfere with the MP identification and quantification. Although organic matter in sludge samples can be removed through acid and enzymatic digestion procedures, cellulose - mainly from toilet paper - remains in the digests, due to its high chemical resistivity and similar density to MP. We apply the separation concept of magnetic seeded filtration to isolate MP through selective hetero-agglomeration with magnetic seed particles. MP and cellulose differ in their hydrophobic properties and we investigate to what extent these differences can be exploited to selectively form MP-magnetite hetero-agglomerates in the presence of cellulose. These hetero-agglomerates are subsequently separated using a magnet. Five MP types (Polyethylene terephthalate (PET), polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC) and polystyrene (PS)) and cellulose particles were mixed in different combinations with both hydrophilic and hydrophobic (silanized) magnetite particles. PET, PP, LDPE and PS only poorly agglomerated with pristine (hydrophilic) magnetite, but efficiently formed hetero-agglomerates with hydrophobic magnetite and were successfully removed from suspensions (80 - 100 %). PVC agglomerated more efficiently with pristine than with hydrophobic magnetite and cellulose only agglomerated to a limited extent with either hydrophilic or hydrophobic magnetite, resulting in a high process selectivity. Results from experiments conducted at different ionic strengths and with hydrophilic and hydrophobic magnetite suggests that the agglomeration process was dominated by hydrophobic interactions. Enzymatic and oxidative treatment of the MP only marginally affected the separation efficiencies and (treated) MP spiked to sewage sludge extracts were successfully recovered using magnetic seeded filtration.

Schwarzfischer, M., Niechcial, A., Lee, S. S., Sinnet, B., Wawrzyniak, M., Laimbacher, A., … Spalinger, M. R. (2022). Ingested nano- and microsized polystyrene particles surpass the intestinal barrier and accumulate in the body. NanoImpact, 25, 100374 (9 pp.). doi:10.1016/j.impact.2021.100374, Institutional Repository

Stetten, L., Hofmann, T., Proux, O., Landrot, G., Kaegi, R., & von der Kammer, F. (2022). Transformation of zinc oxide nanoparticles in freshwater sediments under oxic and anoxic conditions. Environmental Science: Nano, 9(11), 4255-4267. doi:10.1039/d2en00709f, Institutional Repository

Szakas, S. E., Lancaster, R., Kaegi, R., & Gundlach-Graham, A. (2022). Quantification and classification of engineered, incidental, and natural cerium-containing particles by spICP-TOFMS. Environmental Science: Nano, 9, 1627-1638. doi:10.1039/d1en01039e, Institutional Repository

Berg, M., Suess, E., Cayo, L., Bouchet, S., Hug, S. J., Kaegi, R., … Buser, A. M. (2021). Quecksilber im Schweizer Abwasser. Konzentrationen, Massenflüsse, Speziierung und Rückhalt. Aqua & Gas, 101(1), 14-20. , Institutional Repository

Etique, M., Bouchet, S., Byrne, J. M., Thomasarrigo, L. K., Kaegi, R., & Kretzschmar, R. (2021). Mercury reduction by nanoparticulate vivianite. Environmental Science and Technology, 55(5), 3399-3407. doi:10.1021/acs.est.0c05203, Institutional Repository

Kaegi, R., Gogos, A., Voegelin, A., Hug, S. J., Winkel, L. H. E., Buser, A. M., & Berg, M. (2021). Quantification of individual Rare Earth Elements from industrial sources in sewage sludge. Water Research X, 11, 100092 (11 pp.). doi:10.1016/j.wroa.2021.100092, Institutional Repository

Kaegi, R., Fierz, M., & Hattendorf, B. (2021). Quantification of nanoparticles in dispersions using transmission electron microscopy. Microscopy and Microanalysis, 27(3), 557-565. doi:10.1017/S1431927621000398, Institutional Repository

Kuehr, S., Diehle, N., Kaegi, R., & Schlechtriem, C. (2021). Ingestion of bivalve droppings by benthic invertebrates may lead to the transfer of nanomaterials in the aquatic food chain. Environmental Sciences Europe, 33(1), 35 (16 pp.). doi:10.1186/s12302-021-00473-3, Institutional Repository

Background: Manufactured nanomaterials (MNMs) are released into the environment in increasing quantities. Consequently, MNMs also reach the aquatic environment, where they can interact with different organisms. Previous studies have already shown that filter-feeding bivalves can ingest nanomaterials from the surrounding water leading to higher concentration of the material. Furthermore, they have been shown to be vectors for environmental chemicals and pathogens to other organisms, as their feces/pseudofeces (F/pF) play a crucial role as a food source for other species. We exposed bivalves (Corbicula sp.) to MNMs and performed experiments to investigate the possible transport of MNMs by their feces to the benthic amphipod Hyalella azteca. Silver (Ag) and gold (Au) nanoparticles (NPs) as well as fluorescent polystyrene nanoparticles were used in this study. They allowed the investigation of the metal content of the bivalves’ feces and the amphipods feeding on it, as well as the localization of the fluorescent particles in the body of the animals.
Results: Examination of the feces by fluorescence microscope and determination of the total metal content by inductively coupled plasma mass spectrometry (ICP-MS) showed a high accumulation of the exposed MNMs in the F/pF. The examination of fecal matter, using transmission electron microscopy confirmed the nanoparticulate character of the metals in the examined fecal matter. After exposure of amphipods to the MNMs containing fecal matter, the fluorescent MNMs were localized in the animals gut. The chronic exposure of juvenile amphipods over 21 days to feces enriched with Au MNMs caused significant effects on the growth of the amphipods. The transfer of both metals (Ag and Au) from the fecal matter to the amphipods was confirmed after total metal measurements.
Conclusion: Probably, for the first time, it has been shown that when exposed to MNMs bivalves can transfer these particles to other benthic species. Transfer is via released F/pF upon which the benthic species feed and thus could ingest the particles. The high concentrations of MNMs in the fecal matter raises concerns about the potential accumulation and transfer of the materials and associated ecotoxicological effects in invertebrates such as benthic amphipods.

Kuehr, S., Kaegi, R., Maletzki, D., & Schlechtriem, C. (2021). Testing the bioaccumulation potential of manufactured nanomaterials in the freshwater amphipod Hyalella azteca. Chemosphere, 263, 127961 (15 pp.). doi:10.1016/j.chemosphere.2020.127961, Institutional Repository

Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Emerging investigator series: automated single-nanoparticle quantification and classification: a holistic study of particles into and out of wastewater treatment plants in Switzerland. Environmental Science: Nano, 8(5), 1211-1225. doi:10.1039/d0en01066a, Institutional Repository

Mehrabi, K., Kaegi, R., Günther, D., & Gundlach-Graham, A. (2021). Quantification and clustering of inorganic nanoparticles in wastewater treatment plants across Switzerland. Chimia, 75(7-8), 642-646. doi:10.2533/chimia.2021.642, Institutional Repository

Schulz, K., ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2021). Stabilization of ferrihydrite and lepidocrocite by silicate during Fe(II)-catalyzed mineral transformation: impact on particle morphology and silicate distribution. Environmental Science and Technology, 56(9), 5929-5938. doi:10.1021/acs.est.1c08789, Institutional Repository

Wielinski, J., Gogos, A., Voegelin, A., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Release of gold (Au), silver (Ag) and cerium dioxide (CeO₂) nanoparticles from sewage sludge incineration ash. Environmental Science: Nano, 8(11), 3220-3232. doi:10.1039/D1EN00497B, Institutional Repository

Wielinski, J., Voegelin, A., Grobéty, B., Müller, C. R., Morgenroth, E., & Kaegi, R. (2021). Transformation of TiO₂ (nano)particles during sewage sludge incineration. Journal of Hazardous Materials, 411, 124932 (14 pp.). doi:10.1016/j.jhazmat.2020.124932, Institutional Repository

Al-Sid-Cheikh, M., Rowland, S. J., Kaegi, R., Henry, T. B., Cormier, M. A., & Thompson, R. C. (2020). Synthesis of ¹⁴C-labelled polystyrene nanoplastics for environmental studies. Communications Materials, 1(1), 97 (8 pp.). doi:10.1038/s43246-020-00097-9, Institutional Repository

Dörner, L., Schmutz, P., Kägi, R., Kovalenko, M. V., & Jeurgens, L. P. H. (2020). Electrophoretic deposition of nanoporous oxide coatings from concentrated CuO nanoparticle dispersions. Langmuir, 36(28), 8075-8085. doi:10.1021/acs.langmuir.0c00720, Institutional Repository

Frehland, S., Kaegi, R., Hufenus, R., & Mitrano, D. M. (2020). Long-term assessment of nanoplastic particle and microplastic fiber flux through a pilot wastewater treatment plant using metal-doped plastics. Water Research, 182, 115860 (9 pp.). doi:10.1016/j.watres.2020.115860, Institutional Repository

Geitner, N. K., Ogilvie Hendren, C., Cornelis, G., Kaegi, R., Lead, J. R., Lowry, G. V., … Wiesner, M. R. (2020). Harmonizing across environmental nanomaterial testing media for increased comparability of nanomaterial datasets. Environmental Science: Nano, 7(1), 13-36. doi:10.1039/c9en00448c, Institutional Repository

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.

Gogos, A., Wielinski, J., Voegelin, A., von der Kammer, F., & Kaegi, R. (2020). Quantification of anthropogenic and geogenic Ce in sewage sludge based on Ce oxidation state and rare earth element patterns. Water Research X, 9, 100059 (8 pp.). doi:10.1016/j.wroa.2020.100059, Institutional Repository

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.

Hagemann, N., Schmidt, H. P., Kägi, R., Böhler, M., Sigmund, G., Maccagnan, A., … Bucheli, T. D. (2020). Wood-based activated biochar to eliminate organic micropollutants from biologically treated wastewater. Science of the Total Environment, 730, 138417 (11 pp.). doi:10.1016/j.scitotenv.2020.138417, Institutional Repository

Hoffmann, K., Bouchet, S., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effect of NOM on copper sulfide nanoparticle growth, stability, and oxidative dissolution. Environmental Science: Nano, 7(4), 1163-1178. doi:10.1039/c9en01448a, Institutional Repository

Hoffmann, K., Christl, I., Kaegi, R., & Kretzschmar, R. (2020). Effects of natural organic matter (NOM), metal-to-sulfide ratio and Mn²⁺ on cadmium sulfide nanoparticle growth and colloidal stability. Environmental Science: Nano, 7(11), 3385-3404. doi:10.1039/d0en00764a, Institutional Repository

Mast, J., Verleysen, E., Hodoroaba, V. D., & Kaegi, R. (2020). Characterization of nanomaterials by transmission electron microscopy: measurement procedures. In V. D. Hodoroaba, W. E. S. Unger, & A. G. Shard (Eds.), Micro and nano technologies. Characterization of nanoparticles. Measurement processes for nanoparticles (pp. 29-48). doi:10.1016/B978-0-12-814182-3.00004-3, Institutional Repository

Pulido-Reyes, G., Mitrano, D. M., Kägi, R., & von Gunten, U. (2020). The effect of drinking water ozonation on different types of submicron plastic particles. In M. Cocca, E. Di Pace, M. E. Errico, G. Gentile, A. Montarsolo, R. Mossotti, & M. Avella (Eds.), Springer Water. Proceedings of the 2nd international conference on microplastic pollution in the Mediterranean Sea (pp. 152-157). doi:10.1007/978-3-030-45909-3_24, Institutional Repository

Suess, E., Berg, M., Bouchet, S., Cayo, L., Hug, S. J., Kaegi, R., … Buser, A. M. (2020). Mercury loads and fluxes from wastewater: a nationwide survey in Switzerland. Water Research, 175, 115708 (10 pp.). doi:10.1016/j.watres.2020.115708, Institutional Repository

Svendsen, C., Walker, L. A., Matzke, M., Lahive, E., Harrison, S., Crossley, A., … Spurgeon, D. J. (2020). Key principles and operational practices for improved nanotechnology environmental exposure assessment. Nature Nanotechnology, 15, 731-742. doi:10.1038/s41565-020-0742-1, Institutional Repository

ThomasArrigo, L. K., Bouchet, S., Kaegi, R., & Kretzschmar, R. (2020). Organic matter influences transformation products of ferrihydrite exposed to sulfide. Environmental Science: Nano, 7(11), 3405-3418. doi:10.1039/d0en00398k, Institutional Repository

In redox-dynamic environments, sorption to poorly-crystalline, nanometer-sized Fe(_III)-(oxyhydr)oxides like ferrihydrite influences the biogeochemical cycling of nutrients and trace elements. Under sulfate-reducing conditions, the reductive dissolution of ferrihydrite leads to the release of associated constituents, which may be re-immobilized via sorption to secondary Fe minerals. To date, studies following the kinetics and transformation pathways of Fe(_III)-(oxyhydr)oxides upon exposure to dissolved sulfide (S(-_II)) have largely focused on pure Fe minerals. However, in nature, Fe(_III)-(oxyhydr)oxides are often found in association with organic matter (OM). Because ferrihydrite-OM associations exhibit characteristics and biogeochemical reactivity differing from those of pure ferrihydrite, in this study, we compared sulfidization kinetics and transformation pathways of a pure ferrihydrite to those of ferrihydrite coprecipitated with contrasting organic ligands; polygalacturonic acid, galacturonic acid, and citric acid (C/Fe molar ratio ~0.55). Incorporating aqueous- and solid-phase S and Fe speciation analyses (via wet chemistry techniques and S and Fe X-ray absorption spectroscopy) in addition to X-ray diffraction and electron microscopy, we studied both rapid (<7 days) and long-term (12 months) mineral transformations as well as the impact of varying S(-_II)/Fe molar ratios at neutral pH. Our results showed that at low S(-_II)/Fe molar ratios (=0.1), poorly-crystalline Fe sulfide minerals (e.g. mackinawite) did not form in any (co)precipitate. In contrast, at higher S(-_II)/Fe molar ratios (=0.5), mackinawite rapidly precipitated, with higher contributions detected in the coprecipitates than in the pure ferrihydrite. Aging of the samples led to further mineral transformations, including divergent pyrite and greigite precipitation, and an overall increase in the crystallinity of secondary mineral phases. Still, the fraction of residual ferrihydrite at 12 months was higher in the OM-containing coprecipitates, with the most ferrihydrite preservation observed in coprecipitates comprising carboxyl-poor ligands (galacturonic acid and citric acid). This suggests that the presence of OM inhibited S(-_II)-induced ferrihydrite mineral transformations and that the composition of the associated OM influenced mineral transformation pathways. Collectively, these results suggest that further studies regarding sulfidization pathways should include OM in order to better represent environmental conditions.

Urstoeger, A., Wimmer, A., Kaegi, R., Reiter, S., & Schuster, M. (2020). Looking at silver-based nanoparticles in environmental water samples: repetitive cloud point extraction bridges gaps in electron microscopy for naturally occurring nanoparticles. Environmental Science and Technology, 54(19), 12063-12071. doi:10.1021/acs.est.0c02878, Institutional Repository

Velimirovic, M., Wagner, S., Monikh, F. A., Uusimäki, T., Kaegi, R., Hofmann, T., & von der Kammer, F. (2020). Accurate quantification of TiO₂ nanoparticles in commercial sunscreens using standard materials and orthogonal particle sizing methods for verification. Talanta, 215, 120921 (10 pp.). doi:10.1016/j.talanta.2020.120921, Institutional Repository

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.

Wielinski, J. J. (2020). Investigations into the fate of engineered transition metal nano particles during sewage sludge incineration (Doctoral dissertation). doi:10.3929/ethz-b-000473625, Institutional Repository

Engineered nanoparticles (ENP) are applied in consumer products and industrial processes to increase profitability and sustainability through reduced resource consumption, e.g., TiO₂-NP in sun screens, ZnO-NP in cosmetics and paints or Ag-NP and CuO-NP as anti-microbial agents. However, critical discussions about unintended, adverse effects of ENP on humans, soil- and aquatic organisms have always accompanied their usage. Therefore, investigations into the fate of ENP after their use phase are necessary to enable a reliable assessment of the risks associated with the use of such novel materials. Previous research efforts showed that after usage, large shares of ENP applied in consumer products are discharged to wastewater and transported to wastewater treatment plants (WWTPs). WWTPs retain > 95% of ENP leading to their accumulation in sewage sludge. In Switzerland, sewage sludge is incinerated preferably in mono-combustion fluidized bed reactors (FBRs) and the resulting ashes are landfilled for resource recovery in the future. To contribute to a better understanding of the fate and behavior of ENP in the urban environment, the following research questions were addressed: (i) how can the kinetics of sewage sludge devolatilization be quantified, (ii) what chemical and physical transformations of ENP occur during the sewage sludge combustion, (iii) what are the possibilities of synchrotron hard X-ray chemical imaging to study transformation products of ENP, and lastly (iv) to what extent are ENP released from sewage sludge ash landfill sites? [...]

Künstlich produzierte Nanopartikel (NP) werden in Konsumgütern und industriellen Prozessen zur Steigerung von Effizienz und Nachhaltigkeit durch reduzierten Ressourceneinsatz verwendet, z.B. TiO₂-NP in Sonnencreme, ZnO-NP in Kosmetika und Farbe oder Ag-NP und CuO-NP zu antimikrobiellen Zwecken. Allerdings ist stets vor ungewollten, nachteiligen Effekten solcher NP gegenüber Menschen, sowie Boden- und Wasserorganismen gewarnt worden. Daher sind Studien über die Transformation und den Verbleib von NP nach ihrer Nutzungsphase notwendig um die oben genannten Risiken der Nutzung solcher neuartigen Materialen zuverlässig abschätzen zu können. Vorangegangene Studien haben gezeigt, dass ein grosser Teil der NP in Konsumgütern in Abwasserkanäle entlassen wird und in Abwasserreinigungsanlangen (ARAs) gelangt. ARAs halten über 95% der einkommenden NP zurück, welche folglich im Faulschlamm aufkonzentriert werden. In der Schweiz wird Faulschlamm vorzugsweise in speziell dafür errichteten Wirbelbettreaktoren verbrannt und die anfallende Asche wird von Asche aus anderen Brennstoffen getrennt deponiert um daraus in der Zukunft Ressourcen rückzugewinnen.
Um ein besseres Verständnis des Verhaltens von NP in städtischen Abwassersystemen und insbesondere während der Klärschlammverbrennung zu gewinnen, wurden die folgenden Forschungsfragen adressiert: (i)Wie lässt sich die Verbrennungskinetik von Klärschlamm quantifizieren, (ii) welche physikalischen und chemischen Transformationsprozesse unterlaufen NP während der Klärschlammverbrennung, (iii) wie können Transformationsprodukte von NP mithilfe synchrotronbasierter, chemische Bildgebung identifiziert werden und (iv) wie gross ist das Freisetzungspotential von NP aus Klärschlammaschedeponien? [...]

Wielinski, J., Marafatto, F. F., Gogos, A., Scheidegger, A., Voegelin, A., Müller, C. R., … Kaegi, R. (2020). Synchrotron hard X-ray chemical imaging of trace element speciation in heterogeneous samples: development of criteria for uncertainty analysis. Journal of Analytical Atomic Spectrometry, 35, 567-579. doi:10.1039/C9JA00394K, Institutional Repository

Wigger, H., Kägi, R., Wiesner, M., & Nowack, B. (2020). Exposure and possible risks of engineered nanomaterials in the environment - current knowledge and directions for the future. Reviews of Geophysics, 58(4), e2020RG000710 (25 pp.). doi:10.1029/2020RG000710, Institutional Repository

Xu, J., Avellan, A., Li, H., Clark, E. A., Henkelman, G., Kaegi, R., & Lowry, G. V. (2020). Iron and sulfur precursors affect crystalline structure, speciation, and reactivity of sulfidized nanoscale zerovalent iron. Environmental Science and Technology, 54(20), 13294-13303. doi:10.1021/acs.est.0c03879, Institutional Repository

Xu, J., Avellan, A., Li, H., Liu, X., Noël, V., Lou, Z., … Lowry, G. V. (2020). Sulfur loading and speciation control the hydrophobicity, electron transfer, reactivity, and selectivity of sulfidized nanoscale zerovalent iron. Advanced Materials, 32(17), 1906010 (10 pp.). doi:10.1002/adma.201906910, Institutional Repository

Zeumer, R., Hermsen, L., Kaegi, R., Kühr, S., Knopf, B., & Schlechtriem, C. (2020). Bioavailability of silver from wastewater and planktonic food borne silver nanoparticles in the rainbow trout Oncorhynchus mykiss. Science of the Total Environment, 706, 135695 (12 pp.). doi:10.1016/j.scitotenv.2019.135695, Institutional Repository

Aeppli, M., Vranic, S., Kaegi, R., Kretzschmar, R., Brown, A. R., Voegelin, A., … Sander, M. (2019). Decreases in iron oxide reducibility during microbial reductive dissolution and transformation of ferrihydrite. Environmental Science and Technology, 53(15), 8736-8746. doi:10.1021/acs.est.9b01299, Institutional Repository

Aeppli, M., Kaegi, R., Kretzschmar, R., Voegelin, A., Hofstetter, T. B., & Sander, M. (2019). Electrochemical analysis of changes in iron oxide reducibility during abiotic ferrihydrite transformation into goethite and magnetite. Environmental Science and Technology, 53(7), 3568-3578. doi:10.1021/acs.est.8b07190, Institutional Repository

Bakshi, M., Liné, C., Bedolla, D. E., Stein, R. J., Kaegi, R., Sarret, G., … Larue, C. (2019). Assessing the impacts of sewage sludge amendment containing nano-TiO₂ on tomato plants: a life cycle study. Journal of Hazardous Materials, 369, 191-198. doi:10.1016/j.jhazmat.2019.02.036, Institutional Repository

Dörner, L., Cancellieri, C., Rheingans, B., Walter, M., Kägi, R., Schmutz, P., … Jeurgens, L. P. H. (2019). Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area. Scientific Reports, 9, 11758 (15 pp.). doi:10.1038/s41598-019-48020-8, Institutional Repository

Gogos, A., Wielinski, J., Voegelin, A., Emerich, H., & Kaegi, R. (2019). Transformation of cerium dioxide nanoparticles during sewage sludge incineration. Environmental Science: Nano, 6, 1765-1776. doi:10.1039/C9EN00281B, Institutional Repository

Production volumes of cerium dioxide nanoparticles (CeO₂ NP) are predicted to increase in the near future, which will result in increasing amounts of CeO₂ NP discharged into wastewater systems and their accumulation in the sewage sludge. At the same time, thermal treatments of sewage sludge, especially incineration, are gaining in importance. Therefore, knowledge on the physical–chemical transformations of CeO₂ NP during wastewater treatment and sludge incineration is critical for assessing possible (eco-) toxicological effects related to the increased use of CeO₂ NP. We, thus, incinerated unspiked municipal sewage sludge as well as sludge spiked with CeO₂ of different particle sizes (4 nm (CeO₂-s1), 26 nm (CeO₂-s2) and >16 μm (CeO₂-s3)) in a pilot fluidized bed reactor to investigate the (size dependent) transformation of CeO₂ under conditions mimicking full-scale incineration facilities. We used Ce K- and LIII-edge X-ray absorption spectroscopy (XAS) complemented by analytical electron microscopy to assess the changes in Ce speciation and to characterize the morphology of the pristine and the transformed Ce-(nano)particles. After one week of incubation in digested sludge under anaerobic conditions, CeO₂-s1 already showed partial reduction (≈40%) to a Ce(III)-phase. Cerium dioxide of larger particle size (CeO₂-s2 and -s3) was less reactive and did not show any detectable reduction within the same reaction time. Incineration of the sludge in general led to a further reduction of Ce, irrespective of whether the Ce was spiked (CeO₂-s1, CeO₂-s2, CeO₂-s3) or already present in the sludge. Reduction during incineration was nearly complete for CeO₂-s1 but much less pronounced for CeO₂-s2 and -s3. Ce(IV) in larger (primary-) particle sizes thus was more resistant to reduction during anaerobic digestion and incineration. In addition, elemental distribution maps of the CeO₂-s1 fly ash revealed elevated Ce signal intensities evenly distributed over areas of several 100 nm. The complementary results obtained from spectroscopic and microscopic analyses indicate that incineration led to the reductive decomposition of the initial CeO₂-s1 NP and the sequestration of Ce(III) into a mineralogical phase with probably allanite-like local Ce(III) coordination. Our results, thus, highlight the importance of particle size and the surrounding matrix both affecting the transformation of CeO₂ during sewage sludge incineration.

Hagemann, N., Bucheli, T. D., Schmidt, H. P., Kägi, R., Böhler, M., & McArdell, C. S. (2019). Aktivkohle - Made in Switzerland!. Aqua & Gas, 99(1), 32-38. , Institutional Repository

Hoppe, M., Schlich, K., Wielinski, J., Köser, J., Rückamp, D., Kaegi, R., & Hund-Rinke, K. (2019). Long-term outdoor lysimeter study with cerium dioxide nanomaterial. NanoImpact, 14, 100170 (9 pp.). doi:10.1016/j.impact.2019.100170, Institutional Repository

Fate and impact of cerium dioxide nanomaterials (CeO₂ NM) in soil remains uncertain. Most of the recent environmental studies used high doses of CeO₂ NM in short-term laboratory experiments and stated soil as large sink for NM. Recent studies covering the life cycle of plants found evidence for particle uptake in crop plants, and triggered concern about NM entering the food chain. Here, we present a 25 months outdoor lysimeter study that investigates the translocation, biological impact, and transformation of CeO₂ NM in soils cultivated with different crops (wheat (Triticum aestivum L.), canola (Brassica napus L.), and barley (Hordeum vulgare L.)). Low doses of CeO₂ NM (NM-212, 10 and 50 mg CeO₂ NM kg⁻¹ soil) were applied to a Cambisol by sewage sludge or artificial rainwater. To simulate ploughing, the CeO₂ NM was mixed into the first 20 cm of the lysimeter soil. Three weeks after the NM application by sewage sludge and five days after the latest NM application by artificial rainwater wheat seeds were sown.
We found no vertical Ce translocation to deeper soil layers as well as negligible release of Ce into percolating water, confirming that soil is a sink for CeO₂ NM. Furthermore, no inhibition of the NM sensitive ammonium oxidizing bacteria (AOB) was observed which implies a low bioavailability of CeO₂ NM in soil. The detected Ce root uptake for canola (Ce < 35.7 mg kg⁻¹) and barley (Ce < 61.8 mg kg⁻¹) indicates that physico-chemical conditions in the rhizosphere or the aging of the NM in soil can remobilize the applied CeO₂ NM to some extent. One can speculate that the obtained reduction of Ce⁴⁺ to Ce³⁺ (≈ 50% after 25 months) was coupled to different conditions (ionic strength, pH, water content, soil organic matter content) in the rhizosphere and necessary for the root accumulation of Ce.
Due to negligible mobility in the soil-water interface, as well as non-toxicity to AOB, the environmental risk of the tested CeO₂ NM appears to be low, compared to other highly mobile emergent pollutants. Nonetheless, further long-term investigations need to focus on the speciation and localization of NM in plants to clarify uptake and impact of NM to crops.

Salas, P., Odzak, N., Echegoyen, Y., Kägi, R., Sancho, M. C., & Navarro, E. (2019). The role of size and protein shells in the toxicity to algal photosynthesis induced by ionic silver delivered from silver nanoparticles. Science of the Total Environment, 692, 233-239. doi:10.1016/j.scitotenv.2019.07.237, Institutional Repository

Surette, M. C., Nason, J. A., & Kaegi, R. (2019). The influence of surface coating functionality on the aging of nanoparticles in wastewater. Environmental Science: Nano, 6(8), 2470-2483. doi:10.1039/C9EN00376B, Institutional Repository

Efforts to predict the environmental fate of engineered nanomaterials (ENMs) are frequently based on the physiochemical properties and behavior of the ENMs in their pristine, “as-produced” state. However, it is well-established that ENMs can be physically, biologically, and chemically transformed, resulting in altered physiochemical properties and behavior. Wastewater treatment plants (WWTPs) represent an important stage in an ENM's life-cycle where they can be transformed. To better understand the properties of ENMs discharged from WWTPs into surface waters, we investigated how the transformation processes of aggregation and corona formation are influenced by the surface coating applied to ENMs during their manufacture. Using 40 nm gold nanoparticles coated with polyethylene glycol, lipoic acid, or branched polyethylenimine as model ENMs, batch experiments were performed to investigate aggregation and corona formation during the primary clarification and activated sludge treatment stages. A tangential flow filtration system was used to evaluate if the initial transformations were altered as the aquatic chemistry of the background matrix was changed, mimicking the varying conditions ENMs would experience during transport through a WWTP. Using a combination of corroborative techniques including dynamic light scattering, phase analysis light scattering, ultraviolet-visible light spectroscopy, and transmission electron microscopy, we find that the model ENMs aggregated in each wastewater matrix, regardless of the initial surface coating. Differences in the UV-vis spectra indicate that the nature of the corona acquired by the ENMs differed as a function of the surface coating of the pristine ENMs. In addition, initial ENM transformations during exposure to the influent wastewater persisted even as the background matrix changed. These results support the finding that ENMs discharged from WWTPs will not resemble their pristine analogs. Furthermore, the corona acquired by ENMs in WWTPs may vary in relation to their pristine properties and be dictated by conditions during early stage exposures.

ThomasArrigo, L. K., Kaegi, R., & Kretzschmar, R. (2019). Ferrihydrite growth and transformation in the presence of ferrous iron and model organic ligands. Environmental Science and Technology, 53(23), 13636-13647. doi:10.1021/acs.est.9b03952, Institutional Repository

Ferrihydrite (Fh) is a poorly crystalline Fe(III)-oxyhydroxide found in abundance in soils and sediments. With a high specific surface area and sorption capacity at circumneutral pH, ferrihydrite is an important player in the biogeochemical cycling of nutrients and trace elements in redox-dynamic environments. Under reducing conditions, exposure to Fe(II) induces mineral transformations in ferrihydrite; the extent and trajectory of which may be greatly influenced by organic matter (OM). However, natural OM is heterogeneous and comprises a range of molecular weights (MWs) and varied functional group compositions. To date, the impact that the chemical composition of the associated OM has on Fe(II)-catalyzed mineral transformations is not clear. To address this knowledge gap, we coprecipitated ferrihydrite with model organic ligands selected to cover a range of MWs (25 000–50 000 vs <200 Da) as well as carboxyl content (polygalacturonic acid (PGA) > citric acid (CA) > galacturonic acid (GA)). Coprecipitates (C:Fe ≈ 0.6) were reacted with 1 mM ⁵⁷Fe(II) for 1 week at pH 7, with time-resolved solid-phase analysis (via X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy) revealing that all ligands inhibited Fe(II)-catalyzed ferrihydrite mineral transformations and the formation of crystalline secondary mineral phases compared to a pure ferrihydrite. For carboxyl-rich coprecipitates (Fh-PGA and Fh-CA), mineral transformations were less inhibited than in the carboxyl poor Fh-GA, and a crystalline lepidocrocite "shell" was formed surrounding the residual ferrihydrite core. However, Fe isotope analysis revealed that all coprecipitates underwent near complete atom exchange. Collectively, our results highlight that ferrihydrite is indeed an active mineral phase in redox-dynamic environments, but that its stability under reducing conditions, and thus capacity for nutrient and trace element retention, depends on the chemical characteristic of the associated OM, specifically OM-induced changes in the particle surface charge and the distribution of organic functional groups.

Uusimaeki, T., Wagner, T., Lipinski, H. G., & Kaegi, R. (2019). AutoEM: a software for automated acquisition and analysis of nanoparticles. Journal of Nanoparticle Research, 21(6), 122 (11 pp.). doi:10.1007/s11051-019-4555-9, Institutional Repository

Verleysen, E., Wagner, T., Lipinski, H. G., Kägi, R., Koeber, R., Boix-Sanfeliu, A., … Mast, J. (2019). Evaluation of a TEM based approach for size measurement of particulate (nano)materials. Materials, 12(14), 2274 (20 pp.). doi:10.3390/ma12142274, Institutional Repository

Voegelin, A., Senn, A. C., Kaegi, R., & Hug, S. J. (2019). Reductive dissolution of As(V)-bearing Fe(III)-precipitates formed by Fe(II) oxidation in aqueous solutions. Geochemical Transactions, 20(2) (13 pp.). doi:10.1186/s12932-019-0062-2, Institutional Repository

Wielinski, J., Gogos, A., Voegelin, A., Müller, C., Morgenroth, E., & Kaegi, R. (2019). Transformation of nanoscale and ionic Cu and Zn during the incineration of digested sewage sludge (biosolids). Environmental Science and Technology, 53(20), 11704-11713. doi:10.1021/acs.est.9b01983, Institutional Repository

Xu, J., Wang, Y., Weng, C., Bai, W., Jiao, Y., Kaegi, R., & Lowry, G. V. (2019). Reactivity, selectivity, and long-term performance of sulfidized nanoscale zerovalent iron with different properties. Environmental Science and Technology, 53(10), 5936-5945. doi:10.1021/acs.est.9b00511, Institutional Repository

Zheng, Y., Mutzner, L., Ort, C., Kaegi, R., & Gottschalk, F. (2019). Modelling engineered nanomaterials in wet-weather discharges. NanoImpact, 16, 100188 (8 pp.). doi:10.1016/j.impact.2019.100188, Institutional Repository

Giese, B., Klaessig, F., Park, B., Kaegi, R., Steinfeldt, M., Wigger, H., … Gottschalk, F. (2018). Risks, release and concentrations of engineered nanomaterial in the environment. Scientific Reports, 8(1), 1565 (8 pp.). doi:10.1038/s41598-018-19275-4, Institutional Repository

Gogos, A., Voegelin, A., & Kaegi, R. (2018). Influence of organic compounds on the sulfidation of copper oxide nanoparticles. Environmental Science: Nano, 5(11), 2560-2569. doi:10.1039/C8EN00523K, Institutional Repository

Dissolved organic matter (DOM) influences the colloidal properties of engineered nanomaterials (ENMs) and impacts their transport and transformation in the environment. Sulfidation affects the fate and the ecological effects of released chalcophile ENMs. For copper oxide nanoparticles (CuO-NPs), the sulfidation and its kinetics have been described. However, the influence of DOM on this reaction has not been investigated yet. In wastewater systems, having high bisulfide contents, the DOM mainly consists of proteins, polysaccharides and humic substances. We therefore investigated the influence of the organic compounds bovine serum albumin (BSA, model protein), alginate (ALG, model polysaccharide), and polyacrylic acid (PAA, natural organic matter analogue) as well as that of natural humic acid (HA) and filtered wastewater (FW) on the sulfidation of CuO-NPs. Experiments were conducted in solutions buffered to pH 8.0 at concentrations of 1.3 mM CuO and ∼3.2 mM HS⁻. Increasing amounts of organic compounds were added to reach concentrations of 10–1000 mg L⁻¹. Reacted CuO-NPs were collected at selected time points and characterized using Cu K-edge X-ray absorption spectroscopy and analytical electron microscopy. The sulfidation of the CuO-NPs was complete after 3 h in all experiments, except in the presence of 1000 mg L⁻¹ BSA where ∼30% of CuO remained untransformed. Complete sulfidation of the CuO-NPs as observed in experiments conducted in FW suggests quantitative sulfidation of CuO-NPs in real wastewater. Without organic compounds, initially formed amorphous Cu_xS transformed into covellite over time. The presence of BSA, HA, ALG, and FW (but not PAA) hampered this transformation resulting in higher fractions of Cu_xS after sulfidation. Different amounts of Cu_xS with sizes of 10 kDa up to 10 nm formed during sulfidation depending on the type of organic compound. The properties of the Cu_xS-NPs formed by CuO-NP sulfidation must be considered when assessing their environmental impact.

Gondikas, A., Von Der Kammer, F., Kaegi, R., Borovinskaya, O., Neubauer, E., Navratilova, J., … Hofmann, T. (2018). Where is the nano? Analytical approaches for the detection and quantification of TiO₂ engineered nanoparticles in surface waters. Environmental Science: Nano, 5(2), 313-326. doi:10.1039/c7en00952f, Institutional Repository

Detecting and quantifying engineered nanoparticles (ENPs) in complex environmental matrices requires the distinction between natural nanoparticles (NNPs) and ENPs. The distinction of NNPs and ENPs for regulatory purposes calls for cost-efficient methods, but is hampered by similarities in intrinsic properties, such as particle composition, size, density, surface chemistry, etc. Titanium dioxide (TiO₂) ENPs, for instance, are produced in very large quantities but Ti also commonly occurs naturally in nano-scale minerals. In this work, we focus on utilizing particle size and composition to identify ENPs in a system with a significant background concentration of the target metal. We have followed independent approaches involving both conventional and state-of-the-art analytical techniques to detect and quantify TiO₂ ENPs released into surface waters from sunscreen products and to distinguish them from Ti-bearing NNPs. To achieve this, we applied single particle inductively coupled plasma mass spectrometry with single-element (spICPMS) and multi-element detection (time-of-flight) spICP-TOFMS, together with transmission electron microscopy (TEM), automated scanning electron microscopy (autoSEM), and bulk elemental analyses. A background concentration of Ti-bearing NPs (approximately 5 × 10³ particles per ml), possibly of natural origin, was consistently observed outside the bathing season. This concentration increased by up to 40% during the bathing season. Multi-element analysis of individual particles using spICP-TOFMS revealed that Al, Fe, Mn, and Pb are often present in natural Ti-bearing NPs, but no specific multi-element signatures were detected for ENPs. Our data suggests that TiO₂ ENPs enter the lake water during bathing activities, eventually agglomerating and sedimenting. We found adhesion of the TiO₂ ENPs to the air-water interface for short time periods, depending on wind conditions. This study demonstrates that the use of spICP-TOFMS and spICPMS in combination with other conventional analytical techniques offers significant advantages for discriminating between NNPs and ENPs. The quantitative data produced in this work can be used as input for modeling studies or as a benchmark for analysis protocols and model validations.

Hagemann, N., Spokas, K., Schmidt, H. P., Kägi, R., Böhler, M. A., & Bucheli, T. D. (2018). Activated carbon, biochar and charcoal: linkages and synergies across pyrogenic carbon's ABCs. Water, 10(2), 182 (19 pp.). doi:10.3390/w10020182, Institutional Repository

Kampe, S., Kaegi, R., Schlich, K., Wasmuth, C., Hollert, H., & Schlechtriem, C. (2018). Silver nanoparticles in sewage sludge: bioavailability of sulfidized silver to the terrestrial isopod Porcellio scaber. Environmental Toxicology and Chemistry, 37(6), 1606-1613. doi:10.1002/etc.4102, Institutional Repository

Neidhardt, H., Winkel, L. H. E., Kaegi, R., Stengel, C., Trang, P. T. K., Lan, V. M., … Berg, M. (2018). Insights into arsenic retention dynamics of Pleistocene aquifer sediments by in situ sorption experiments. Water Research, 129, 123-132. doi:10.1016/j.watres.2017.11.018, Institutional Repository

The migration of arsenic (As) enriched groundwater into Pleistocene aquifers as a consequence of extensive groundwater abstraction represents an increasing threat to the precious water resources in Asian delta regions. Pleistocene aquifer sediments are typically rich in FeIII-(hydr)oxides and are capable to adsorb high amounts of As. This results in a pronounced accumulation of As in Pleistocene aquifers, where high As groundwater infiltrates from adjacent Holocene aquifers. However, As retention by Pleistocene aquifers over long-term time scales remains largely unknown. We studied As sorption in situ by placing natural Pleistocene sediments and pure mineral phases directly inside groundwater monitoring wells at a study site near Hanoi (Vietnam). This in situ exposure allows for constant flushing of the samples with unaltered groundwater and the establishment of undisturbed sorption equilibria similar to those in local aquifer sediments, which is not readily attainable in traditional laboratory sorption experiments. The groundwaters in our experimental wells were characterized by different As concentrations (0.01–6.63 μmol/L) and redox states, reaching from suboxic to anoxic conditions (E_h of +159 to −4 mV). Results show that adsorption is the dominant As retention mechanism, independent from the respective groundwater chemistry (i.e. concentrations of dissolved P, HCO₃− and Si). Whilst most of the As sorbed within the first week, sorption further increased slowly but consistently by 6–189%, respectively, within six months. Hence, the As sorption behavior of Pleistocene aquifer sediments should be determined over longer periods to avoid an underestimation of the As sorption capacity. Accompanying desorption experiments revealed that about 51% of the sorbed As was remobilized within six months when exposed to low As groundwater. We therefore conclude that a considerable proportion of the As accumulated in the aquifer sediments is prone to remobilization once the As concentrations in migrating groundwater decline. Remobilization of As should be considered in local water management plans to avoid contamination of precious groundwater resources with this As legacy.

Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Larue, C., de Nolf, W., Reyes-Herrera, J., … Sarret, G. (2018). Searching for relevant criteria to distinguish natural vs. anthropogenic TiO₂ nanoparticles in soils. Environmental Science: Nano, 5(12), 2853-2863. doi:10.1039/c8en00386f, Institutional Repository

Nanosized TiO₂ is one of the most produced nanomaterials. Agricultural soils are a major compartment of accumulation of TiO₂-NPs after release from consumer products into the sewer system, due to the use of sewage sludge as a soil amendment. TiO₂ is naturally present in soils, and distinguishing between anthropogenic and natural TiO₂ in soils is thus important to assess the risks associated with the increased use of nano-TiO₂. Methods to distinguish these materials in complex matrices such as soils are currently lacking. The purpose of this study was, therefore, to search for characteristic physical and chemical properties of natural and engineered nano-TiO₂, based on a combination of bulk, micro and nanofocused X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, X-ray diffraction and chemical analyses. Digested sewage sludge, agricultural soil and sludge-amended soil were studied by these techniques. The particle size distribution was not a relevant criterion since the sludge and the sludge-amended soil contained a variety of nanometer- and micrometer sized Ti-containing particles. Both the sludge and the soil contained a mixture of rutile and anatase, with a minor proportion of amorphous TiO₂. In the sludge, there was no trend relating particle size and Ti mineralogy. The morphology of the TiO₂ particles proved to be different in the two matrices, with smooth faceted particles in the sludge and rough irregular ones in the soil. In addition, natural TiO₂ particles were included in micro and macroaggregates of the soil and formed intricate assemblages with minerals and organic compounds. In the sludge, TiO₂ formed homo and heteroaggregates of simpler structure, richer in organic matter. Thus, the study of the morphology of TiO₂ particles and their status in unperturbed mineral-organic assemblages may provide some insights into their origin. The observed differences may attenuate over time, due to the incorporation of the sludge material within the soil structure.

Senn, A. C., Hug, S. J., Kaegi, R., Hering, J. G., & Voegelin, A. (2018). Arsenate co-precipitation with Fe(II) oxidation products and retention or release during precipitate aging. Water Research, 131, 334-345. doi:10.1016/j.watres.2017.12.038, Institutional Repository

Thalmann, B., Kägi, R., & von Gunten, U. (2018). Metalle in der Ozonung. Verhalten von ausgewählten Metallen: Oxidation von Metallsulfiden und Metallkomplexen. Aqua & Gas, 98(4), 68-77. , Institutional Repository

Thalmann, B., von Gunten, U., & Kaegi, R. (2018). Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: kinetics and mechanisms. Water Research, 134, 170-180. doi:10.1016/j.watres.2018.01.042, Institutional Repository

Ozonation can be applied to mitigate the discharge of organic micropollutants from municipal wastewater treatment plants (WWTPs) to the aquatic environment. The toxicity of metals also present in WWTP effluents strongly depends on their speciation. Therefore, knowledge on the change of the metal speciation during ozonation of a WWTP effluent is essential to assess possible negative impacts. The kinetics and the stoichiometries of the reactions of ozone with three metal sulfides (ZnS, CuS and CdS) and metal-ethylenediaminetetraacetate (EDTA)/nitriloriacetic acid (NTA) complexes of Cu(II), Cd(II), Ni(II), Zn(II), Mg(II) and Pb(II) were investigated. With a stoichiometric factor of 2.6–3.9 moles of ozone per mole of sulfide and apparent second-order rate constants at pH 8 > 10⁴ M⁻¹ s⁻¹, a complete oxidation of the sulfides and a concomitant release of the respective metals is expected during ozonation of a WWTP effluent for enhanced micropollutant abatement. The apparent second-order rate constants at pH 8 for the reactions of metal-EDTA complexes with ozone ranged from 42 M⁻¹s⁻¹ to 2.0 × 10⁴ M⁻¹s⁻¹ and increased in the order Cd(II) < Cu(II) < Mg(II) < Ni(II) < Zn(II). Approximately 40% of Cd(II)-EDTA spiked to a WWTP effluent was oxidized at typical specific ozone doses of 0.5–0.7 g_O3/g_DOC. For the other metal-EDTA complexes a significantly higher fraction was oxidized. The bioavailable fraction determined by the diffusive-gradient thin films (DGT) method in the WWTP effluent increased during ozonation, due to the oxidative release of the metal ions. Algal toxicity (chlamynomodas reinhardtii) tests with CuS/CdS spiked WWTP effluent revealed a high tolerance toward Cu and Cd in the respective media. A toxic response was only observed at Cu concentrations above 10 μM, which is above typical WWTP effluent concentrations. Biological post-treatment after ozonation generally reduced the bioavailability of the metals, which resulted in a lower toxicity. Therefore, the biological post-treatment serves as an additional barrier to protect the downstream ecology of receiving waters.

Ulmer, P., Kaegi, R., & Müntener, O. (2018). Experimentally derived intermediate to silica-rich arc magmas by fractional and equilibrium crystallization at 1·0 GPa: an evaluation of phase relationships, compositions, liquid lines of descent and oxygen fugacity. Journal of Petrology, 59(1), 11-58. doi:10.1093/petrology/egy017, Institutional Repository

Differentiation of hydrous primary, mantle-derived magmas is a fundamental process to generate evolved intermediate to SiO₂-rich compositions forming the bulk of the continental and island arc crust. This study focuses on the results of equilibrium and fractional crystallization experiments at 1·0 GPa using two different primary magmas representing deep (90 km) and shallow (35 km) mantle extraction depths. Experiments on a hydrous high-Mg basalt were conducted at graphite-saturated and more oxidized conditions (NNO to NNO + 2, where NNO is nickel–nickel oxide buffer) to exploit the influence of fO₂ on phase assemblages and the evolution of derivative liquids. The liquid line of descent (LLD) was simulated from liquidus to near-solidus conditions ranging from 1330°C to 720°C. H₂O contents varied from about 2·0 to more than 10 wt %. The LLD covers the entire compositional range from high-Mg basalt to high-silica rhyolite and evolves from metaluminous to peraluminous compositions at 56–60 wt % SiO₂ under oxidizing conditions. The observed crystallization sequences and the LLD reveal contrasting behavior depending on oxidation state, H₂O content and equilibrium versus fractional crystallization. Equilibrium crystallization of high-Mg basalt under reducing conditions is initially dominated by olivine fractionation followed by Cr-rich spinel, clinopyroxene (cpx), and orthopyroxene (opx). Finally, between 1060 and 1000°C, amphibole formed by a peritectic reaction consuming cpx + olivine and forming amphibole + opx, resulting in 16% silica-undersaturated trachy-basaltic liquid. Equilibrium crystallization of the same composition under oxidizing conditions is characterized by strongly enhanced olivine and cpx fractionation and suppression of opx only occurring as a result of the peritectic amphibole-forming reaction at and below 1040°C. The liquid at 980°C is a peraluminous, alkali-poor, high-Al andesite representing ∼15% residual liquid. Fractional crystallization of the high-Mg basalt under oxidizing conditions evolves through fractionation of early olivine joined by cpx at 1200°C, followed by opx and hercynitic spinel (1140–1080°C) and amphibole at 1050°C coexisting with cpx (and spinel) to 980°C. At 950°C both garnet and plagioclase (plag) join amphibole as liquidus phases. This paragenesis (plus ilmenite and apatite) persists to 750°C with 16% residual liquid relative to the initial basaltic composition. Liquids evolve continuously from basalt to rhyolite, crossing the metaluminous–peraluminous boundary at about 60 wt % SiO₂. Fractional crystallization of the basaltic andesite starting material differs at high temperature, where opx and cpx are the liquidus phases (1200–1080°C), followed by amphibole at the expense of opx. Below 950°C the phase assemblage is identical except at the lowest temperature (720°C), where quartz saturates in a high-silica rhyolitic liquid representing 20% of the initial basaltic andesite. Liquid compositions of the two starting compositions converge below 950°C, with the exception of K₂O, which behaves incompatibly along the liquid line of descent. The H₂O-undersaturated fractional crystallization experiments on the high-Mg basaltic composition under relatively reducing conditions evolve towards tholeiitic or alkalic compositions owing to early plagioclase (at 1140°C) and abundant opx (at 1110°C) crystallization followed by garnet–cpx–plag–ilmenite at 1080°C. Closed-system equilibrium crystallization under relatively oxidized conditions is characterized by significant expansion of the olivine stability field (>250°C, 1280–1000°C) relative to more reducing conditions, causing depletion of the liquid in ferrous iron and increase of ferric iron. The resulting fO₂ of the coexisting basaltic liquids increases by more than 3 log units from about NNO + 2 to NNO + 5·5 over the temperature range >1200–1040°C, potentially offering an explanation for the more oxidized character of hydrous arc magmas as opposed to low-H₂O tholeiitic magmas.

Vriens, B., Voegelin, A., Hug, S., Kaegi, R., Berg, M., & Winkel, L. (2018). Spurenelemente in Schweizer Abwasser. Aktuelle Konzentrationen und Frachten. Aqua & Gas, 98(1), 40-46. , Institutional Repository

Wielinski, J., Müller, C., Voegelin, A., Morgenroth, E., & Kaegi, R. (2018). Combustion of sewage sludge: kinetics and speciation of the combustible. Energy and Fuels, 32(10), 10656-10667. doi:10.1021/acs.energyfuels.8b02106, Institutional Repository

Auvinen, H., Kaegi, R., Rousseau, D. P. L., & Du Laing, G. (2017). Fate of Silver Nanoparticles in Constructed Wetlands - a Microcosm Study. Water, Air, and Soil Pollution, 228(3) (11 pp.). doi:10.1007/s11270-017-3285-9, Institutional Repository

Gogos, A., Thalmann, B., Voegelin, A., & Kaegi, R. (2017). Sulfidation kinetics of copper oxide nanoparticles. Environmental Science: Nano, 4(8), 1733-1741. doi:10.1039/C7EN00309A, Institutional Repository

Kaegi, R., Englert, A., Gondikas, A., Sinnet, B., von der Kammer, F., & Burkhardt, M. (2017). Release of TiO₂ – (nano) particles from construction and demolition landfills. NanoImpact, 8, 73-79. doi:10.1016/j.impact.2017.07.004, Institutional Repository

A large fraction of engineered nanomaterials (ENM) will be deposited in landfills and it is assumed that ENM are securely locked in landfill sites and cannot leach into the environment (e.g. surface waters). However, experimental evidence supporting this assumption is lacking, as current production volumes of ENM are still too small and/or analytical techniques not sensitive enough to allow for the detection and quantification of ENM in landfill leachates. TiO₂ particles are currently used in large quantities, for example in construction materials such as paints and renders as white pigments and their sizes extend into the nano-size range. We, therefore, selected TiO₂ particles as a surrogate to assess the potential release of ENM from construction and demolition (C & D) landfill sites. We collected leachate samples from a landfill over one year and used complementary analytical techniques, including inductively coupled plasma (ICP) – optical emission spectroscopy (OES), automated scanning electron microscopy (auto SEM), transmission electron microscopy (TEM) and single particle ICP - mass spectrometry (spICPMS) to quantify TiO₂ particles in landfill leachates. Total elemental Ti contents were mostly around a few tens of μg L^{− 1} and were strongly correlated with total suspended solids. Based on the volumetric discharge of the landfill leachate water from the landfill, we estimate a total amount of ~ 0.5 kg of TiO₂ particles that are released annually from the landfill. Ti concentrations derived from ICP-OES measurements were in good agreement with quantifications based on TiO₂ particles detected by auto SEM analyses. spICPMS measurements indicated a number concentration of Ti-containing particles in the order of 105 mL− 1 and TEM analyses dominantly revealed nanoscale TiO₂ particles with a spherical shape typically observed for TiO₂ particles used as white pigments. In addition, angular TiO₂ particles with a well-defined crystal habitus were detected, suggesting that also natural TiO₂ particles of comparable sizes are present in the landfill leachates. The results from this study indicate that (nanoscale) TiO₂ particles are released from C & D landfill sites (~ 5 g/year). Although the amount of TiO₂ particles released from C & D landfill sites may still be rather low, these particles may serve as proxy for assessing the future release of ENM from C & D landfill sites, which may become relevant as an increasing use of ENM is predicted for construction materials in general.

Kraas, M., Schlich, K., Knopf, B., Wege, F., Kägi, R., Terytze, K., & Hund-Rinke, K. (2017). Long-term effects of sulfidized silver nanoparticles in sewage sludge on soil microflora. Environmental Toxicology and Chemistry, 36(12), 3305-3313. doi:10.1002/etc.3904, Institutional Repository

Praetorius, A., Gundlach-Graham, A., Goldberg, E., Fabienke, W., Navratilova, J., Gondikas, A., … von der Kammer, F. (2017). Single-particle multi-element fingerprinting (spMEF) using inductively-coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) to identify engineered nanoparticles against the elevated natural background in soils. Environmental Science: Nano, 4(2), 307-314. doi:10.1039/c6en00455e, Institutional Repository

Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2017). Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water. Geochimica et Cosmochimica Acta, 202, 341-360. doi:10.1016/j.gca.2016.12.033, Institutional Repository

Iron(III)-precipitates formed by Fe(II) oxidation in aqueous solutions affect the cycling and impact of Fe and other co-precipitated elements in environmental systems. Fresh Fe(III)-precipitates are metastable and their transformation into more stable phases during aging may result in the release of initially co-precipitated ions. Phosphate, silicate, Mg and Ca play key roles in determining the structure and composition of fresh Fe(III)-precipitates. Here we examine how these ions affect the structure and phosphate retention of Fe(III)-precipitates formed by oxidation of 0.5 mM dissolved Fe(II) at pH 7.0 after aging for 30 days at 40 °C.
Iron K-edge X-ray absorption spectroscopy (XAS) shows that aged precipitates consist of the same structural units as fresh precipitates: Amorphous Fe(III)- or Ca-Fe(III)-phosphate, ferrihydrite, and poorly crystalline lepidocrocite. Mg, Ca, and dissolved phosphate stabilize (Ca-)Fe(III)-phosphate against transformation into ferrihydrite. Silicate further attenuates (Ca-)Fe(III)-phosphate transformation. The crystallinity of lepidocrocite formed in phosphate- and silicate-free solutions slightly increases during aging. The transformation of Fe(III)- and Ca-Fe(III)-phosphate into ferrihydrite and ongoing ferrihydrite crystallization during aging result in the release of co-precipitated phosphate. Dissolved Ca on the other hand limits phosphate concentrations to values consistent with solubility control by octacalciumphosphate. Owing to the combined effects of Ca and silicate, phosphate is most effectively retained by Fe(III)-precipitates formed and aged in Ca- and silicate-containing solutions. The results from this study contribute to an improved understanding of the formation and transformation of Fe(III)-precipitates and emphasize that the complexity of Fe(III)-precipitate dynamics in the presence of multiple interfering solutes must be considered when addressing their impact on major and trace elements in environmental systems.

Vriens, B., Voegelin, A., Hug, S. J., Kaegi, R., Winkel, L. H. E., Buser, A. M., & Berg, M. (2017). Quantification of element fluxes in wastewaters: a nationwide survey in Switzerland. Environmental Science and Technology, 51(19), 10943-10953. doi:10.1021/acs.est.7b01731, Institutional Repository

Kaegi, R. (2016). Separation and analysis of nanoparticles (NP) in aqueous environmental samples. In B. Xing, C. D. Vecitis, & N. Senesi (Eds.), Wiley-IUPAC series in biophysico-chemical processes in environmental systems. Engineered nanoparticles and the environment. Biophysicochemical processes and toxicity (pp. 53-74). doi:10.1002/9781119275855.ch4, Institutional Repository

Meier, C., Voegelin, A., Pradas Del Real, A., Sarret, G., Mueller, C. R., & Kaegi, R. (2016). Transformation of silver nanoparticles in sewage sludge during incineration. Environmental Science and Technology, 50(7), 3503-3510. doi:10.1021/acs.est.5b04804, Institutional Repository

Petersen, E. J., Flores-Cervantes, D. X., Bucheli, T. D., Elliott, L. C. C., Fagan, J. A., Gogos, A., … Winchester, M. R. (2016). Quantification of carbon nanotubes in environmental matrices: current capabilities, case studies, and future prospects. Environmental Science and Technology, 50(9), 4587-4605. doi:10.1021/acs.est.5b05647, Institutional Repository

Pradas del Real, A. E., Castillo-Michel, H., Kaegi, R., Sinnet, B., Magnin, V., Findling, N., … Sarret, G. (2016). Fate of Ag-NPs in sewage sludge after application on agricultural soils. Environmental Science and Technology, 50(4), 1759-1768. doi:10.1021/acs.est.5b04550, Institutional Repository

Thalmann, B., Voegelin, A., Morgenroth, E., & Kaegi, R. (2016). Effect of humic acid on the kinetics of silver nanoparticle sulfidation. Environmental Science: Nano, 3(1), 203-212. doi:10.1039/c5en00209e, Institutional Repository

Vriens, B., Berg, M., Hug, S., Kägi, R., Voegelin, A., & Winkel, L. (2016). Ermittlung der Konzentrationsbereiche von Spurenelementen in Abwasserreinigungsanlagen. Zusammenfassender Schlussbericht. Dübendorf: Eawag. , Institutional Repository

Burkhardt, M., Dietschweiler, C., Schmidt, S., Englert, A., Hemmann, J., Sinnet, B., & Kägi, R. (2015). Titandioxid. Leitsubstanz für Nanopartikel im Deponiesickerwasser. Aqua & Gas, 95(12), 40-47. , Institutional Repository

Fedotova, N., Kaegi, R., Koch, J., & Günther, D. (2015). Influence of dispersion agents on particle size and concentration determined by laser-induced breakdown detection. Spectrochimica Acta B: Atomic Spectroscopy, 103-104(1), 92-98. doi:10.1016/j.sab.2014.12.002, Institutional Repository

Hofacker, A. F., Behrens, S., Voegelin, A., Kaegi, R., Lösekann-Behrens, T., Kappler, A., & Kretzschmar, R. (2015). Clostridium species as metallic copper-forming bacteria in soil under reducing conditions. Geomicrobiology Journal, 32(2), 130-139. doi:10.1080/01490451.2014.933287, Institutional Repository

Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Siegrist, H., & Burkhardt, M. (2015). Transformation of AgCl nanoparticles in a sewer system - a field study. Science of the Total Environment, 535, 20-27. doi:10.1016/j.scitotenv.2014.12.075, Institutional Repository

Müller, P., Mielke, J., Hodoroaba, V. D., Kägi, R., & Ryner, M. (2015). Assessment of different electron microscopy techniques for particle size quantification of potential nanomaterials. Microscopy and Microanalysis, 21(S3), 2403-2404. doi:10.1017/S1431927615012799, Institutional Repository

Senn, A. C., Kaegi, R., Hug, S. J., Hering, J. G., Mangold, S., & Voegelin, A. (2015). Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in water at near-neutral pH: interdependent effects of phosphate, silicate and Ca. Geochimica et Cosmochimica Acta, 162, 220-246. doi:10.1016/j.gca.2015.04.032, Institutional Repository

We studied the interdependent effects of phosphate, silicate and Ca on the formation of Fe(III)-precipitates by oxidation of 0.5 mM Fe(II) in near-neutral bicarbonate-buffered aqueous solutions at concentrations relevant for natural water resources. Complementary results obtained by a suite of analytical techniques including X-ray absorption spectroscopy and transmission electron microscopy showed that the ratio of initially dissolved phosphate over Fe(II) ((P/Fe)_init) had a major impact on precipitate formation. At (P/Fe)_init above a critical ratio ((P/Fe)_crit) of ∼0.5 in 8 mM NaHCO₃ and ∼0.8 in 4 mM Ca(HCO₃)₂ electrolyte, Fe(II) oxidation led to exclusive formation of amorphous basic Fe(III)-phosphate or Ca–Fe(III)-phosphate ((Ca-)Fe(III)-phosphate) with maximum precipitate P/Fe ratios ((P/Fe)_ppt) of ∼0.7 in Na and ∼1.1 in Ca electrolyte. Enhanced phosphate uptake in the presence of Ca was due to phosphate-Ca interactions coupled to Fe precipitation, mainly formation of mitridatite-like Ca–Fe(III)-phosphate polymers and Ca-phosphate polymers. At (P/Fe)_init < (P/Fe)_crit, in the absence of silicate, (Ca-)Fe(III)-phosphate precipitation was followed by the formation of poorly crystalline lepidocrocite and concomitant transformation of the (Ca-)Fe(III)-phosphate into a phosphate-rich ferrihydrite-type precipitate with a (P/Fe)_ppt of ∼0.25. In the presence of 0.5 mM silicate, initially formed (Ca-)Fe(III)-phosphate nanoparticles became coated with silicate-rich ferrihydrite during continuing Fe(II) oxidation and only limited transformation of the (Ca-)Fe(III)-phosphate occurred. The results from this study indicate the complexity of Fe(III)-precipitate formation in the presence of interfering solutes and its consequences for precipitate structure and phosphate sequestration. The findings provide a solid basis for further studies of the reactivity of different Fe(III)-precipitate types and for the systematic assessment of their impact on Fe, phosphate and trace elements dynamics in natural and engineered systems.

Thalmann, B., Voegelin, A., von Gunten, U., Behra, R., Morgenroth, E., & Kaegi, R. (2015). Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent. Environmental Science and Technology, 49(18), 10911-10919. doi:10.1021/acs.est.5b02194, Institutional Repository

Thalmann, B. A. D. (2015). Transformations of silver nanoparticles in urban wastewater and water systems (Doctoral dissertation). doi:10.3929/ethz-a-010579189, Institutional Repository

Metallic silver nanoparticles (AgNP) are increasingly applied in consumer products from which they are probably released to the urban wastewater and water system. Due to the antimicrobial activity of AgNP, they are of high ecotoxicological concern and an engineered nanomaterial of priority for environmental risk assessment. Transformations of AgNP can have large efects on their toxicity toward aquatic organism. Most importantly, the sulidation of AgNP is known to reduce the toxicity of Ag by several orders of magnitude. Thus, a proper understanding of the sulidation of AgNP in the urban wastewater and water system is crucial for in-depth environmental risk assessments. Furthermore, the ozonation of the eluent of wastewater treatment plant (WWTP) to mitigate micropollutants is likely to further change the Ag speciation. he irst objective of this thesis was to understand the sulidation kinetics of AgNP with bisulide (HS-) and metal sulides. The second objective was to study the impact of ozone treatment on sulidized AgNP. [...]

Silber Nanopartikel (AgNP) werden vermehrt in Konsumgütern angewandt, von welchen die Partikel durch den Gebrauch in das urbane Abwasser und Wasser ausgewaschen werden können. Aufgrund ihrer antimikrobieller Wirkung stellen sie ein potentielles Risiko für die Umwelt dar, welches abgeschätzt werden sollte. Durch Umwandlung in der Umwelt ändert sich die Speziierung der AgNP was die Toxizität gegenüber aquatischen Organismen und Planzen beeinlusst. Die Reaktion von AgNP mit Suliden, genannt Sulidierung, zum Beispiel reduziert die Ag Toxizität um mehrere Grössenordnungen. Deshalb ist es für eine Risikoeinschätzung der AgNP in der Umwelt wichtig die Sulidierung im urbanen Abwasser und Wasser zu verstehen. Im Abwasser ist die dominante Sulid Quelle Bisulid (HS-), welches in erhöhten Konzentrationen zu inden ist. Für das Oberlächengewässer hingegen ist die Sulidierung mit Metallsuliden wahrscheinlicher, da sie persistenter gegen die Oxidation mit Sauerstof sind. Das erste Ziel dieser Dissertation war deshalb die Sulidierung von AgNP mit HS- und Metallsuliden zu verstehen. [...]

Duester, L., Burkhardt, M., Gutleb, A. C., Kaegi, R., Macken, A., Meermann, B., & von der Kammer, F. (2014). Toward a comprehensive and realistic risk evaluation of engineered nanomaterials in the urban water system. Frontiers in Chemistry, 2, 39 (6 pp.). doi:10.3389/fchem.2014.00039, Institutional Repository

Gogos, A., Kaegi, R., Zenobi, R., & Bucheli, T. D. (2014). Capabilities of asymmetric flow field-flow fractionation coupled to multi-angle light scattering to detect carbon nanotubes in soot and soil. Environmental Science: Nano, 1(6), 584-594. doi:10.1039/c4en00070f, Institutional Repository

Grass, R. N., Schälchli, J., Paunescu, D., Soellner, J. O. B., Kaegi, R., & Stark, W. J. (2014). Tracking trace amounts of submicrometer silica particles in wastewaters and activated sludge using silica-encapsulated DNA barcodes. Environmental Science and Technology Letters, 1(12), 484-489. doi:10.1021/ez5003506, Institutional Repository

Kroll, A., Behra, R., Kaegi, R., & Sigg, L. (2014). Extracellular polymeric substances (EPS) of freshwater biofilms stabilize and modify CeO₂ and Ag nanoparticles. PLoS One, 9(10), e110709 (16 pp.). doi:10.1371/journal.pone.0110709, Institutional Repository

Neidhardt, H., Berg, M., Stengel, C., Winkel, L. H. E., Kaegi, R., Trang, P. T. K., … Viet, P. H. (2014). Arsenic adsorption on iron mineral phases under reducing conditions: results from an in-situ field experiment. In M. I. Litter, H. B. Nicolli, M. Meichtry, N. Quici, J. Bundschuh, P. Bhattacharya, & R. Naidu (Eds.), One century of the discovery of Arsenicosis in Latin America (1914-2014) (pp. 83-84). London: CRC Press. , Institutional Repository

Thalmann, B., Voegelin, A., Sinnet, B., Morgenroth, E., & Kaegi, R. (2014). Sulfidation kinetics of silver nanoparticles reacted with metal sulfides. Environmental Science and Technology, 48(9), 4885-4892. doi:10.1021/es5003378, Institutional Repository

Voegelin, A., Kaegi, R., Berg, M., Nitzsche, K. S., Kappler, A., Lan, V. M., … Steininger, R. (2014). Solid-phase characterisation of an effective household sand filter for As, Fe and Mn removal from groundwater in Vietnam. Environmental Chemistry, 11(5), 566-578. doi:10.1071/EN14011, Institutional Repository

Wenk, C. B., Kaegi, R., & Hug, S. J. (2014). Factors affecting arsenic and uranium removal with zero-valent iron: laboratory tests with Kanchan-type iron nail filter columns with different groundwaters. Environmental Chemistry, 11(5), 547-557. doi:10.1071/EN14020, Institutional Repository

Yang, Y., Doudrick, K., Bi, X., Hristovski, K., Herckes, P., Westerhoff, P., & Kaegi, R. (2014). Characterization of food-grade titanium dioxide: the presence of nanosized particles. Environmental Science and Technology, 48(11), 6391-6400. doi:10.1021/es500436x, Institutional Repository

Titanium dioxide (TiO₂) is widely used in food products, which will eventually enter wastewater treatment plants and terrestrial or aquatic environments, yet little is known about the fraction of this TiO₂ that is nanoscale, or the physical and chemical properties of TiO₂ that influence its human and environmental fate or toxicity. Instead of analyzing TiO₂ properties in complex food or environmental samples, we procured samples of food-grade TiO₂ obtained from global food suppliers and then, using spectroscopic and other analytical techniques, quantified several parameters (elemental composition, crystal structure, size, and surface composition) that are reported to influence environmental fate and toxicity. Another sample of nano-TiO₂ that is generally sold for catalytic applications (P25) and widely used in toxicity studies, was analyzed for comparison. Food-grade and P25 TiO₂ are engineered products, frequently synthesized from purified titanium precursors, and not milled from bulk scale minerals. Nanosized materials were present in all of the food-grade TiO₂ samples, and transmission electron microscopy showed that samples 1–5 contained 35, 23, 21, 17, and 19% of nanosized primary particles (<100 nm in diameter) by number, respectively (all primary P25 particles were <100 nm in diameter). Both types of TiO₂ aggregated in water with an average hydrodynamic diameter of >100 nm. Food-grade samples contained phosphorus (P), with concentrations ranging from 0.5 to 1.8 mg of P/g of TiO₂. The phosphorus content of P25 was below inductively coupled plasma mass spectrometry detection limits. Presumably because of a P-based coating detected by X-ray photoelectron spectroscopy, the ζ potential of the food-grade TiO₂ suspension in deionized water ranged from −10 to −45 mV around pH 7, and the iso-electric point for food-grade TiO₂ (2 (Si content of 0.026–0.062% and Al content of 0.0006–0.810%) was also different from the case for P25 and would influence the environmental fate of TiO₂. X-ray diffraction analysis confirmed the presence of anatase and/or rutile in the food-grade materials, and although the presence of amorphous TiO₂ could not be ruled out, it is unlikely on the basis of Raman analysis. The food-grade TiO₂ was solar photoactive. Cationic dyes adsorbed more readily to food-grade TiO₂ than P25, indicating very different potentials for interaction with organics in the environment. This research shows that food-grade TiO₂ contains engineered nanomaterials with properties quite different from those of P25, which has previously been used in many ecotoxicity studies, and because food-grade TiO₂ is more likely than P25 to enter the environment (i.e., potentially higher exposure levels), there is a need to design environmental (and human) fate and toxicity studies comparing food-grade to catalytic TiO₂.

Hofacker, A. F., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2013). Mercury mobilization in a flooded soil by incorporation into metallic copper and metal sulfide nanoparticles. Environmental Science and Technology, 47(14), 7739-7746. doi:10.1021/es4010976, Institutional Repository

Hofacker, A. F., Voegelin, A., Kaegi, R., Weber, F. A., & Kretzschmar, R. (2013). Temperature-dependent formation of metallic copper and metal sulfide nanoparticles during flooding of a contaminated soil. Geochimica et Cosmochimica Acta, 103, 316-332. doi:10.1016/j.gca.2012.10.053, Institutional Repository

Riparian floodplains in temperate regions are affected by pronounced seasonal variations in soil and water temperature. This affects the rates and interplay of microbial and abiotic geochemical processes that control the fate of metals in contaminated floodplain soils, including potential release into surface and groundwater during periodic flooding. Here, we investigated how temperature affects chalcophile trace metal contaminants (Cu, Cd, Pb) upon flooding of a riparian soil contaminated by past mining activities. In soil microcosms incubated at 23, 14, and 5 °C, the reductive dissolution of Mn(III,IV) and Fe(III) (oxyhydr)oxides and the release of dissolved Mn²⁺ and Fe²⁺ were significantly slower and less intense at the lower temperatures, which was reflected in a decrease of trace metal mobilization via the dissolution of metal oxide sorbents and cation competition for sorption sites. The onset of sulfate reduction was significantly delayed at lower temperatures and the apparent rate of sulfate reduction was decreased, especially at 5 °C. This resulted in elevated high dissolved Cu, Cd, and Pb concentrations over weeks of flooding at 5 °C, whereas colloidal metal sulfide formation dominated Cu, Cd, and Pb pore water dynamics at higher temperatures of 14 and 23 °C due to fast sulfate reduction. Cu K-edge X-ray absorption fine structure spectroscopy revealed metallic Cu(0) as the main colloidal Cu species prior to sulfate reduction at all three temperatures. Analytical electron microscopy showed that Cu(0) particles were associated with suspended bacteria, suggesting biomineralization of Cu(0). Upon onset of sulfate reduction, metallic Cu particles were transformed into Cu_xS with incorporation of smaller amounts of Cd and Pb. Concomitantly, freely dispersed mixed Cu–Cd–Pb sulfide nanoparticles precipitated in the pore water. Other metals with higher metal sulfide solubility products did not react with the limited amounts of biogenic sulfide. The median size of the mixed metal sulfide nanoparticles increased from 21 nm at 23 °C to 70 nm at 5 °C. During ∼30 days of soil flooding at 23 and 14 °C, Cu speciation in the soil matrix changed from Cu(II) bound to soil organic matter in the oxic soil to 66% Cu_xS, with intermittent formation of about 14% metallic Cu(0). In contrast, at 5 °C, sulfate reduction and formation of Cu(0) were strongly retarded. After ∼30 days of flooding at 23 and 14 °C, nearly all Cd and about 25% of total Pb in the soil, were precipitated in mixed metal sulfides. Our results demonstrate that temperature controls trace metal dynamics during soil flooding via its influence on microbial reduction of terminal electron acceptors. Even at low temperatures, soil flooding may trigger the release of chalcophile metals from contaminated floodplain soils by sorbent reduction, competitive sorption, and formation of nanoparticulate metal-bearing colloids.

Kaegi, R., Voegelin, A., Ort, C., Sinnet, B., Thalmann, B., Krismer, J., … Mueller, E. (2013). Fate and transformation of silver nanoparticles in urban wastewater systems. Water Research, 47(12), 3866-3877. doi:10.1016/j.watres.2012.11.060, Institutional Repository

Discharge of silver nanoparticles (Ag-NP) from textiles and cosmetics, todays major application areas for metallic Ag-NP, into wastewater is inevitable. Transformation and removal processes in sewers and wastewater treatment plants (WWTP) will determine the impact of Ag-NP on aquatic and terrestrial environments, via the effluents of the WWTP and via the use of digested sludge as fertilizer. We thus conducted experiments addressing the behavior of Ag-NP in sewers and in WWTP.
We spiked Ag-NP to a 5 km long main trunk sewer and collected 40 wastewater samples after 500 m, 2400 m and 5000 m each according to the expected travel times of the Ag-NP. Excellent mass closure of the Ag derived by multiplying the measured Ag concentrations times the volumetric flow rates indicate an efficient transport of the Ag-NP without substantial losses to the sewer biofilm. Ag-NP reacted with raw wastewater in batch experiments were sulfidized to roughly 15% after 5 h reaction time as revealed by X-ray absorption spectroscopy (XAS). However, acid volatile sulfide (AVS) concentrations were substantially higher in the sewer channel (100 μM) compared to the batch experiments (3 μM; still sufficient to sulfidize spiked 2 μM Ag) possibly resulting in a higher degree of sulfidation in the sewer channel. We further investigated the removal efficiency of 10 nm and 100 nm Ag- and gold (Au)-NP coated with citrate or polyvinylpyrrolidone in activated sludge batch experiments. We obtained very high removal efficiencies (∼99%) irrespective of size and coating for Ag- and Au-NP, the latter confirming that the particle type was of minor importance with respect to the degree of NP removal. We observed a strong size dependence of the sulfidation kinetics. We conclude that Ag-NP discharged to the wastewater stream will become sulfidized to various degrees in the sewer system and are efficiently transported to the WWTP. The sulfidation of the Ag-NP will continue in the WWTP, but primarily depending on the size the Ag-NP, may not be complete. Very high removal efficiencies in the WWTP will divert most of the Ag-NP mass flow to the digester and only a small fraction of the Ag will be released to surface waters.

Neumann, A., Kaegi, R., Voegelin, A., Hussam, A., Munir, A. K. M., & Hug, S. J. (2013). Arsenic removal with composite iron matrix filters in Bangladesh: a field and laboratory study. Environmental Science and Technology, 47(9), 4544-4554. doi:10.1021/es305176x, Institutional Repository

Schwyzer, I., Kaegi, R., Sigg, L., & Nowack, B. (2013). Colloidal stability of suspended and agglomerate structures of settled carbon nanotubes in different aqueous matrices. Water Research, 47(12), 3910-3920. doi:10.1016/j.watres.2013.01.057, Institutional Repository

Carbon nanotubes (CNTs) are often processed in suspended form and therefore a release of CNT-suspensions into the aquatic environment is plausible. In this study, the behaviour of two physico-chemically very different CNT types in the presence of varying, environmentally relevant calcium-containing media was investigated, including the long-term colloidal stability and the sedimentary structures of settled CNTs. Calcium induced CNT flocculation, however, the stability of the CNTs in the medium did not monotonously decrease with increasing calcium concentration. At intermediate calcium concentrations (0.5–1.5 mM Ca) pre-dispersed CNTs were stabilized in humic acid medium to similar, temporarily even to higher degree than in the absence of calcium. Between pH 5 and 8 only at the highest pH an influence on CNT stability was observed by either promoting flocculation or stabilisation depending on the CNT type. Humic acid stabilized CNTs much better than fulvic acid. Generally, the colloidal stability of the long, thick CNTs with higher surface oxygen content was less affected by the media composition.
An investigation of the settled CNT material using analytical electron microscopy revealed the presence of spheroidal, bundle-like and net like CNT-agglomerate structures. Calcium possibly acted as bridging agent linking CNTs in a network like manner, temporarily increasing the CNT concentrations stabilized in the supernatants due to the low density of these structures. With increasing settling time the CNTs formed a fluffy sediment layer at the bottom of the reaction vessels. Bundle-like CNT agglomerates were also observed within that layer of settled CNTs, possibly caused by calcium neutralizing the surface charges. Furthermore, the CNT suspensions contained spheroidal CNT agglomerates, most likely residues from the original dry powder that were not disaggregated. The analysis of settled CNT material is a novelty and illustrates CNT agglomerate structures possibly accumulating in the sediments of aquatic systems subsequent to CNT emissions.

Voegelin, A., Senn, A. C., Kaegi, R., Hug, S. J., & Mangold, S. (2013). Dynamic Fe-precipitate formation induced by Fe(II) oxidation in aerated phosphate-containing water. Geochimica et Cosmochimica Acta, 117, 216-231. doi:10.1016/j.gca.2013.04.022, Institutional Repository

Bonalumi, M. (2012). Effect of pumped-storage operations on temperature, turbidity and sedimentation in reservoirs and possible mitigation measures (Doctoral dissertation). doi:10.3929/ethz-a-007586451, Institutional Repository

Hagendorfer, H., Kaegi, R., Parlinska, M., Sinnet, B., Ludwig, C., & Ulrich, A. (2012). Characterization of silver nanoparticle products using asymmetric flow field flow fractionation with a multidetector approach - a comparison to transmission electron microscopy and batch dynamic light scattering. Analytical Chemistry, 84(6), 2678-2685. doi:10.1021/ac202641d, Institutional Repository

Mertens, J., Rose, J., Kägi, R., Chaurand, P., Plötze, M., Wehrli, B., & Furrer, G. (2012). Adsorption of arsenic on polyaluminum granulate. Environmental Science and Technology, 46(13), 7310-7317. doi:10.1021/es204508t, Institutional Repository

Schwyzer, I., Kaegi, R., Sigg, L., Smajda, R., Magrez, A., & Nowack, B. (2012). Long-term colloidal stability of 10 carbon nanotube types in the absence/presence of humic acid and calcium. Environmental Pollution, 169(1), 64-73. doi:10.1016/j.envpol.2012.05.004, Institutional Repository

Sternitzke, V., Kaegi, R., Audinot, J. N., Lewin, E., Hering, J. G., & Johnson, C. A. (2012). Uptake of fluoride from aqueous solution on nano-sized hydroxyapatite: examination of a fluoridated surface layer. Environmental Science and Technology, 46(2), 802-809. doi:10.1021/es202750t, Institutional Repository

Bonalumi, M., Anselmetti, F. S., Kaegi, R., & Wüest, A. (2011). Particle dynamics in high-Alpine proglacial reservoirs modified by pumped-storage operation. Water Resources Research, 47(9), 1-15. doi:10.1029/2010WR010262, Institutional Repository

Bukowiecki, N., Zieger, P., Weingartner, E., Jurányi, Z., Gysel, M., Neininger, B., … Baltensperger, U. (2011). Ground-based and airborne in-situ measurements of the Eyjafjallajökull volcanic aerosol plume in Switzerland in spring 2010. Atmospheric Chemistry and Physics, 11(19), 10011-10030. doi:10.5194/acp-11-10011-2011, Institutional Repository

The volcanic aerosol plume resulting from the Eyjafjallajökull eruption in Iceland in April and May 2010 was detected in clear layers above Switzerland during two periods (17–19 April 2010 and 16–19 May 2010). In-situ measurements of the airborne volcanic plume were performed both within ground-based monitoring networks and with a research aircraft up to an altitude of 6000 m a.s.l. The wide range of aerosol and gas phase parameters studied at the high altitude research station Jungfraujoch (3580 m a.s.l.) allowed for an in-depth characterization of the detected volcanic aerosol. Both the data from the Jungfraujoch and the aircraft vertical profiles showed a consistent volcanic ash mode in the aerosol volume size distribution with a mean optical diameter around 3 ± 0.3 μm. These particles were found to have an average chemical composition very similar to the trachyandesite-like composition of rock samples collected near the volcano. Furthermore, chemical processing of volcanic sulfur dioxide into sulfate clearly contributed to the accumulation mode of the aerosol at the Jungfraujoch. The combination of these in-situ data and plume dispersion modeling results showed that a significant portion of the first volcanic aerosol plume reaching Switzerland on 17 April 2010 did not reach the Jungfraujoch directly, but was first dispersed and diluted in the planetary boundary layer. The maximum PM₁₀ mass concentrations at the Jungfraujoch reached 30 μg m⁻³ and 70 μg m⁻³ (for 10-min mean values) during the April and May episode, respectively. Even low-altitude monitoring stations registered up to 45 μg m⁻³ of volcanic ash related PM₁₀ (Basel, Northwestern Switzerland, 18/19 April 2010). The flights with the research aircraft on 17 April 2010 showed one order of magnitude higher number concentrations over the northern Swiss plateau compared to the Jungfraujoch, and a mass concentration of 320 (200–520) μg m⁻³ on 18 May 2010 over the northwestern Swiss plateau. The presented data significantly contributed to the time-critical assessment of the local ash layer properties during the initial eruption phase. Furthermore, dispersion models benefited from the detailed information on the volcanic aerosol size distribution and its chemical composition.

Hagendorfer, H., Kaegi, R., Traber, J., Mertens, S. F. L., Scherrers, R., Ludwig, C., & Ulrich, A. (2011). Application of an asymmetric flow field flow fractionation multi-detector approach for metallic engineered nanoparticle characterization - prospects and limitations demonstrated on Au nanoparticles. Analytica Chimica Acta, 706(2), 367-378. doi:10.1016/j.aca.2011.08.014, Institutional Repository

In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system.
For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1–50 μg Au L⁻¹ in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle–membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup.
Figures of merit were obtained, by comparing the results from the multi detector approach outlined above, with results from batch-DLS and transmission electron microscopy (TEM). Furthermore, validation performed with certified NIST Au-NP showed excellent agreement. The developed methods show potential for characterization of other commonly used and important metallic engineered nanoparticles.

Kaegi, R., Voegelin, A., Sinnet, B., Zuleeg, S., Hagendorfer, H., Burkhardt, M., & Siegrist, H. (2011). Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant. Environmental Science and Technology, 45(9), 3902-3908. doi:10.1021/es1041892, Institutional Repository

Lorenz, C., Hagendorfer, H., von Goetz, N., Kaegi, R., Gehrig, R., Ulrich, A., … Hungerbühler, K. (2011). Nanosized aerosols from consumer sprays: experimental analysis and exposure modeling for four commercial products. Journal of Nanoparticle Research, 13, 3377-3391. doi:10.1007/s11051-011-0256-8, Institutional Repository

Schwyzer, I. I. (2011). Colloidal stability of carbon nanotubes in aqueous media of environmental relevance (Doctoral dissertation). doi:10.3929/ethz-a-007317859, Institutional Repository

Carbon nanotubes (CNTs) are engineered nanoparticles with unique physical and chemical properties making them promising for a broad range of industrial applications. Large scale synthesis and wide spread use of CNTs has increased the likelihood of the unintended release of CNTs into the environment. Environmental exposure of CNTs can occur during their whole life-cycle - production, use and disposal of CNTs, and CNTcontaining products. CNTs may reach the aquatic environment through waste water, runoff from contaminated areas, and aerosol-deposition. Knowledge about the partitioning of CNTs between the water column and the sediment is required to assess the potential impact of CNTs on the ecosystem. Depending on where (sediment or solution) and in which form (single CNTs or CNT agglomerates) CNTs are present in the aquatic environment, different organisms (benthic or pelagic) can be exposed and varying degrees of bioavailability would be expected, respectively. [...]

Kohlenstoffnanoröhrchen (CNTs) sind synthetisch hergestellte Nanopartikel mit einzigartigen physikalischen und chemischen Eigenschaften, was sie für vielfältigste Anwendungen attraktiv macht. CNT Synthese und Anwendung in grossem Stil birgt das Risiko, dass CNTs ungewollt in die Umwelt gelangen. Eine Freisetzung in die Umwelt ist dabei während des gesamten Lebenszyklus der CNTs möglich, d.h. während der Produktion, der Nutzung und der Entsorgung von CNTs und Produkten, die diese enthalten. Die aquatische Umwelt kann über Abwasser, über Abschwemmung von kontaminierten Stellen und über Aerosol-Deposition betroffen sein. Um potenzielle Risiken der CNTs auf das Ökosystem abschätzen zu können, ist es relevant zu wissen, ob der Verbleib der CNTs mehrheitlich im Sediment oder in der Wassersäule zu erwarten ist. Je nach dem wo (Sediment oder Wassersäule) und in welcher Form die CNTs (einzeln oder als Agglomerate) vorliegen, werden andere Organismen exponiert sein (benthische oder pelagische) und wird die Bioverfügbarkeit der Partikel variieren. [...]

Schwyzer, I., Kaegi, R., Sigg, L., Magrez, A., & Nowack, B. (2011). Influence of the initial state of carbon nanotubes on their colloidal stability under natural conditions. Environmental Pollution, 159(6), 1641-1648. doi:10.1016/j.envpol.2011.02.044, Institutional Repository

Burkhardt, M., Zuleeg, S., Kägi, R., Sinnet, B., Eugster, J., Boller, M., & Siegrist, H. (2010). Verhalten von Nanosilber in Kläranlagen und dessen Einfluss auf die Nitrifikationsleistung in Belebtschlamm. Fate of nanosilver in wastewater treatment plants and their impact on nitrification activity in sewage sludge. Umweltwissenschaften und Schadstoff-Forschung, 22(5), 529-540. doi:10.1007/s12302-010-0153-2, Institutional Repository

Background, aim and scope The application of nanosilver is increasing. Knowledge on the fate and behavior of nanosilver in wastewater and wastewater treatment plants is scarce. Studies under real world conditions are completely lacking. We studied (1) the impact of nanosilver on the nitrification of sewage sludge, (2) quantified the mass flow of nanosilver in a pilot-plant, and (3) verified the mass balance in a full-scale municipal wastewater treatment plant where nanosilver is introduced to the municipal plant by an indirect discharger.
Materials and Methods The addition of four different nanosilver additives on ammonia oxidation in activated sludge has been studied in batch-reactors at two concentrations (1, 100 mg/L Ag) with two exposure times (2 h, 6 days). The pilot-plant treating 70 population equivalents of domestic wastewater is operated with a 12 day sludge age. Nanosilver was applied to the activated sludge tank within two sludge ages. The silver concentrations were measured in sludge and effluent samples during dosing and the following two sludge ages. The adsorption and speciation of silver particles has been analyzed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Influent, effluent and sludge were sampled on a full-scale plant (60 000 equivalent inhabitants) and analyzed for silver.
Results Silver nitrate, metallic nanosilver, nano-scaled silver chloride and microcomposite silver did not show any effect on ammonia oxidation after the addition of 1 mg/L Ag to the activated sludge (corresponding to 250 mg Ag per kg solids). In contrast, 100 mg/L Ag inhibited the nitrification process by 100 % after the addition of silver nitrate and 20–30 % after addition of colloidal polymer-coated nanosilver. A complete mass balance of the pilot-plant, a steady-state system with known fluxes, demonstrates significant enrichment of silver in the sewage sludge (96 %) after the addition of silver chloride to the plant and small losses of silver into the secondary effluent (4 %). The mass fluxes are similar to metallic colloidal nanosilver investigated under the same conditions. The mass balance has been consistently confirmed by the full-scale study in a municipal wastewater treatment plant. The silver fluxes correspond to the fluxes of the suspended solids in sludge and effluent. Overall, it is estimated that from public wastewater treatment plants about 4–40 mg/a Ag per inhabitant equivalent are discharged annually to the receiving water. The analysis by SEM-EDX demonstrates adsorption and incorporation of nanosilver on biological flocs. This method yields first insight into complex building and transformation of silver associated with sulfide after adding metallic nanosilver and silver chloride to wastewater.
Discussion Silver ions released from nanosilver react immediately with large amounts of chloride present in wastewater to form silver chloride. Silver ions may react with organic ligands or sulfide groups additionally. Consequently, even silver nitrate added with 1 mg/L Ag (250 mg Ag/kg TS) to activated sludge did not inhibit nitrification activity. Very high amounts of nanosilver, i. e. 100 mg/L Ag, overburdened the system and equilibrium condition between silver ion release and ligands was not reached. The mass balance reflects the excellent attachment of nanosilver to activated sludge and biological flocs. Therefore, the main elimination process of nanosilver is attachment to the activated sludge. The elimination of nanosilver is high compared to organic and inorganic micro pollutants omnipresent in wastewater. Any further reduction of suspended solids in the effluent water will reduce the silver load.
Conclusions Generally, in wastewater nanosilver occurs bonded to activated sludge flocs and therefore the elimination of nanosilver is efficient under operation conditions typical for wastewater treatment plants. The major fraction of nanosilver is removed from the system by the excess sludge withdrawal. Nonetheless, the efficiency may be further improved by a tertiary filtration step. All analyses of influent, effluent and sludge confirmed that silver exists as silver sulfide. Due to a negligible water solubility of this silver species, silver ions are not subsequently released.
Recommendations and perspectives Nanosilver research should be driven to the identification of transformation processes in real environmental matrices and the influence of coatings on the adsorption behavior. There is no need for action to take special measures for nanosilver removal in the area of municipal wastewater treatment plants compared to ubiquitous hazardous organic pollutants may present in wastewater. Nevertheless, source control measures following the precautionary principle should be performed.

Glaus, R., Kaegi, R., Krumeich, F., & Günther, D. (2010). Phenomenological studies on structure and elemental composition of nanosecond and femtosecond laser-generated aerosols with implications on laser ablation inductively coupled plasma mass spectrometry. Spectrochimica Acta B: Atomic Spectroscopy, 65(9–10), 812-822. doi:10.1016/j.sab.2010.07.005, Institutional Repository

In laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), the properties of laser-generated aerosols, such as size and composition, are crucial for matrix-independent quantification. In this study, the aerosol particle morphology and elemental composition generated by two state-of-the-art laser systems (ArF excimer nanosecond-UV laser and Ti:sapphire femtosecond-IR laser) were investigated by electron microscopic techniques. Electrostatic sampling of the aerosols directly onto transmission electron microscopy (TEM) grids allowed us to study the morphology and elemental composition of the aerosols using TEM and TEM–EDX (energy dispersive X-ray spectroscopy) analyses, respectively. The results of the electron microscopic studies were finally compared to the LA-ICPMS signals of the main matrix components. The investigations were carried out for non-conducting materials (glass and zircon), metallic samples (steel and brass) and semiconductors (sulfides). The studies confirm that ns-LA-generated aerosols dominantly consist of nanoparticle agglomerates while conducting samples additionally contain larger spherical particles (diameter typically 50 to 500 nm). In contrast to ns-laser ablation, fs-LA-generated aerosols consist of a mixture of spherical particles and nanoparticle agglomerates for all investigated samples. Surprisingly, the differences in elemental composition between nanoparticle agglomerates and spherical particles produced with fs-LA were much more pronounced than in the case of ns-LA, especially for zircon (Si/Zr fractionation) and brass (Cu/Zn fractionation). These observations indicate different ablation and particle formation mechanisms for ns- and fs-LA. The particle growth mechanism for ns-LA is most likely a gas-to-particle conversion followed by agglomeration and additional hydrodynamic sputtering for conducting samples. On the other hand, phase explosion is assumed to be responsible for the mixture of large spherical particles and nanoparticle agglomerates as found for fs-LA-generated aerosols. Based on these mechanisms, the overall temporal elemental fractionation effects in ns-LA-ICPMS seem to occur mainly during the ablation. This effect was not observed for fs-LA-ICPMS despite the element separation into different particle fractions, which, on the other hand, could induce severe ICP-induced fractionation.

Hagendorfer, H., Lorenz, C., Kaegi, R., Sinnet, B., Gehrig, R., Goetz, N. V., … Ulrich, A. (2010). Size-fractionated characterization and quantification of nanoparticle release rates from a consumer spray product containing engineered nanoparticles. Journal of Nanoparticle Research, 12(7), 2481-2494. doi:10.1007/s11051-009-9816-6, Institutional Repository

Kaegi, R., Voegelin, A., Folini, D., & Hug, S. (2010). Effect of phosphate, silicate, and Ca on the morphology, structure and elemental composition of Fe(III)-precipitates formed in aerated Fe(II) and As(III) containing water. Geochimica et Cosmochimica Acta, 74(20), 5798-5816. doi:10.1016/j.gca.2010.07.017, Institutional Repository

We investigated Fe(III)-precipitates formed from Fe(II) oxidation in water at pH 7 as a function of dissolved Fe(II), As(III), phosphate, and silicate in the absence and presence of Ca. We used transmission electron microscopy (TEM), including selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) to characterize the morphology, structure and elemental composition of the precipitates. Results from our companion X-ray absorption spectroscopy (XAS) study suggested that the oxidation of Fe(II) leads to the sequential formation of distinct polymeric units in the following order: Fe(III)–phosphate oligomers in the presence of phosphate, silicate-rich hydrous ferric oxide (HFO-Si) at high Si/Fe (>0.5) or 2-line ferrihydrite (2L-Fh) at lower Si/Fe (0.1–0.5), and lepidocrocite (Lp) in the absence of phosphate at low Si/Fe (<0.1). Results from this study show that the size of the polymeric units increased along the same sequence and that the aggregation of these polymeric units resulted in spherical particles with characteristic surface textures changing from smooth to coarse. The diameter of the spherical particles increased from 15 to 380 nm as the molar ratio (P + Si + As)/Fe(II) in the starting solution decreased and larger spherical particles precipitated from Ca-containing than from Ca-free solutions. These trends suggested that the size of the spherical particles was controlled by the charge of the polymeric units. Spherical particles coagulated into flocs whose size was larger in the presence than in the absence of Ca. Further observations pointed to the importance of Fe(II) oxidation and polymerization versus polymer aggregation and floc formation kinetics in controlling the spatial arrangement of the different polymeric units within Fe(III)-precipitates. The resulting structural and compositional heterogeneity of short-range-ordered Fe(III)-precipitates likely affects their colloidal stability and their chemical reactivity and needs to be considered when addressing the fate of co-transformed trace elements such as arsenic.

Kaegi, R., Sinnet, B., Zuleeg, S., Hagendorfer, H., Mueller, E., Vonbank, R., … Burkhardt, M. (2010). Release of silver nanoparticles from outdoor facades. Environmental Pollution, 158(9), 2900-2905. doi:10.1016/j.envpol.2010.06.009, Institutional Repository

Latkoczy, C., Kägi, R., Fierz, M., Ritzmann, M., Günther, D., & Boller, M. (2010). Development of a mobile fast-screening laser-induced breakdown detection (LIBD) system for field-based measurements of nanometre sized particles in aqueous solutions. Journal of Environmental Monitoring, 12(7), 1422-1429. doi:10.1039/c002020f, Institutional Repository

Leisinger, S. M., Lothenbach, B., Saout, G. L., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Solid solutions between CrO₄- and SO₄-ettringite Ca₆(Al(OH)₆)₂[(CrO₄)_x(SO₄)_1-_x]₃*26 H₂O. Environmental Science and Technology, 44(23), 8983-8988. doi:10.1021/es100554v, Institutional Repository

Leisinger, S., Lothenbach, B., Lesaout, G., Kägi, R., Wehrli, B., & Johnson, C. A. (2010). Sulphate and chromate-AFt solid solutions; characterization and thermodynamic modeling (p. (4 pp.). Presented at the International RILEM symposium on concrete modelling – CONMOD'10. Lausanne, Switzerland. , Institutional Repository

Mikutta, C., Frommer, J., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2010). Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation. Geochimica et Cosmochimica Acta, 74(19), 5574-5592. doi:10.1016/j.gca.2010.06.024, Institutional Repository

In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, ‘2-line’ Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0–50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH)₆ octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe–O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe–O, 3.03 Å for Fe–Fe1, and 3.45 Å for Fe–Fe2. Likewise, citrate had no effect on the As–Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear (²C) As(V) surface complexes and (ii) combinations of ²C, monodentate mononuclear (¹V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing ¹V/²C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3–6.6, I 0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios 25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.

Voegelin, A., Kaegi, R., Frommer, J., Vantelon, D., & Hug, S. J. (2010). Effect of phosphate, silicate, and Ca on Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water studied by X-ray absorption spectroscopy. Geochimica et Cosmochimica Acta, 74(1), 164-186. doi:10.1016/j.gca.2009.09.020, Institutional Repository

We studied the local coordination and structure of Fe(III)-precipitates formed in aerated Fe(II)- and As(III)-containing water (buffered to pH 7 by 8 mM bicarbonate) using synchrotron-based X-ray absorption spectroscopy (XAS) at the K-edges of Fe, P, Ca, and As. Dissolved phosphate, silicate, and Ca at different ratios relative to each other and to Fe affect the forming Fe(III)-phases in a complex manner. The high affinity of phosphate for Fe(III) results in the predominant precipitation of Fe(III)-phosphate as long as dissolved phosphate is present, with Fe(III) polymerization limited to small oligomers. In Ca-containing solution, Ca uptake by Fe(III)–Ca-phosphate involves the linkage and coagulation of negatively charged Fe(III)-phosphate oligomers via Ca–O–P bonds. In the absence of phosphate, dissolved silicate at Si/Fe ratios above ~0.5 results in the formation of hydrous ferric oxide (HFO) with mainly edge-sharing Fe–Fe linkage. At lower Si/Fe ratios of ~0.5–0.1, mainly 2-line ferrihydrite (2L-Fh) with both edge- and corner-sharing Fe–Fe linkage forms. Only in the absence of phosphate at low Si/Fe ratio, lepidocrocite (Lp) forms. In solutions containing sufficient Fe(II), aeration results in the sequential precipitation of Fe(III)-(Ca-)phosphate, HFO or 2L-Fh (depending on solution Si/Fe), and finally Lp. The amount and oxidation state of As co-precipitated with Fe(III) are controlled by the co-oxidation of As(III) with Fe(II), which increases with initial Fe/As ratio, and the competitive uptake of phosphate, As(V) and less strongly sorbing silicate and As(III). This study demonstrates that the diversity and sequence of short-range-ordered Fe(III)-precipitates forming by Fe(II) oxidation in near-neutral natural waters depend on water chemistry. Because differences in the colloidal stability and biogeochemical reactivity of these phases will affect the fate of associated major and trace elements, the different Fe(III)-precipitates and their specific biogeochemical properties must be taken into account when addressing nutrient and contaminant dynamics at redox boundaries in natural and engineered systems.

Behra, R., Kägi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Effects of engineered nanoparticles. Eawag News [engl. ed.], 67, 22-24. , Institutional Repository

Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Les nanoparticules synthétiques et leurs effets. Eawag News [éd. fr.], 67, 22-24. , Institutional Repository

Behra, R., Kaegi, R., Navarro, E., Burkhardt, M., & Sigg, L. (2009). Synthetische Nanopartikel und ihre Wirkung. Eawag News [dtsch. Ausg.], 67, 22-24. , Institutional Repository

Burkhardt, M., Zuleeg, S., Etter, B., Marti, T., Landert, J., Eugster, J., … Vonmont, H. (2009). Nanosilber in Fassadenbeschichtungen. Auswaschung im Vergleich mit Titandioxid und organischen Bioziden. Dübendorf: Eawag; Empa. , Institutional Repository

Hassellöv, M., & Kaegi, R. (2009). Analysis and characterization of manufactured nanoparticles in aquatic environments. In J. R. Lead & E. Smith (Eds.), Environmental and human health impacts of nanotechnology (pp. 211-266). doi:10.1002/9781444307504.ch6, Institutional Repository

Kaegi, R., Wenk, C., & Hug, S. (2009). Elimination de l'arsenic par le fer colloïdal. Eawag News [éd. fr.], 66, 13-15. , Institutional Repository

Kaegi, R. (2009). Les nanoparticules dans l'eau potable. Eawag News [éd. fr.], 66, 7-9. , Institutional Repository

Kaegi, R., & Sinnet, B. (2009). Nanoparticles in drinking water. Eawag News [engl. ed.], 66, 7-9. , Institutional Repository

Kägi, R., Wenk, C., & Hug, S. (2009). Arsenentfernung mittels Eisenkolloiden. Eawag News [dtsch. Ausg.], 66, 13-15. , Institutional Repository

Kägi, R., Wenk, C., & Hug, S. (2009). Arsenic removal using iron colloids. Eawag News [engl. ed.], 66, 13-15. , Institutional Repository

Kägi, R., & Sinnet, B. (2009). Nanopartikel im Trinkwasser. Eawag News [dtsch. Ausg.], 66, 7-9. , Institutional Repository

Vernooij, M. G. C., Mohr, M., Tzvetkov, G., Zelenay, V., Huthwelker, T., Kaegi, R., … Grobéty, B. (2009). On source identification and alteration of single diesel and wood smoke soot particles in the atmosphere; an X-Ray microspectroscopy study. Environmental Science and Technology, 43(14), 5339-5344. doi:10.1021/es800773h, Institutional Repository

Weber, F. A., Voegelin, A., Kaegi, R., & Kretzschmar, R. (2009). Contaminant mobilization by metallic copper and metal sulphide colloids in flooded soil. Nature Geoscience, 2, 267-271. doi:10.1038/NGEO476, Institutional Repository

Zuleeg, S., Burkhardt, M., Boller, M., Kägi, R., Sinnet, B., Eugster, J., & Siegrist, H. (2009). Charakterisierung und Bilanzierung von Silber im Abwasser einer Wäscherei. Dübendorf: Eawag: Das Wasserforschungs-Institut des ETH-Bereichs. , Institutional Repository

Zuleeg, S., Burkhardt, M., Boller, M., Kägi, R., Sinnet, B., Eugster, J., & Siegrist, H. (2009). Charakterisierung und Bilanzierung von Silberpartikeln in Abwasserreinigungsanlagen. Dübendorf: Eawag: Das Wasserforschungs-Institut des ETH-Bereichs. , Institutional Repository

von Gunten, U., Egli, T., Hammes, F., Helbing, J., Kaegi, R., & Pronk, W. (2009). Wave21. Drinking water for the 21^st century. Final report. Schriftenreihe der Eawag: Vol. 20. Retrieved from http://www.lib4ri.ch/institutional-bibliography/eawag/schriftenreihe-der-eawag.html, Institutional Repository

Burkhardt, M., Kägi, R., Sinnet, B., Zuleeg, S., Simmler, H., Vonbank, R., … Boller, M. (2008). Biozide - Suche nach Alternativen. Nanopartikel in Fassadenbeschichtungen. Coviss, 4, 14-17. , Institutional Repository

Jermann, D., Pronk, W., Kägi, R., Halbeisen, M., & Boller, M. (2008). Influence of interactions between NOM and particles on UF fouling mechanisms. Water Research, 42(14), 3870-3878. doi:10.1016/j.watres.2008.05.013, Institutional Repository

Kaegi, R., Wagner, T., Hetzer, B., Sinnet, B., Tzvetkov, G., & Boller, M. (2008). Size, number and chemical composition of nanosized particles in drinking water determined by analytical microscopy and LIBD. Water Research, 42(10–11), 2778-2786. doi:10.1016/j.watres.2008.02.009, Institutional Repository

Kaegi, R., Ulrich, A., Sinnet, B., Vonbank, R., Wichser, A., Zuleeg, S., … Boller, M. (2008). Synthetic TiO₂ nanoparticle emission from exterior facades into the aquatic environment. Environmental Pollution, 156(2), 233-239. doi:10.1016/j.envpol.2008.08.004, Institutional Repository

Navarro, E., Piccapietra, F., Wagner, B., Marconi, F., Kaegi, R., Odzak, N., … Behra, R. (2008). Toxicity of silver nanoparticles to Chlamydomonas reinhardtii. Environmental Science and Technology, 42(23), 8959-8964. doi:10.1021/es801785m, Institutional Repository

Burkhardt, M., Kägi, R., Simmler, H., Ulrich, A., & Boller, M. (2007). Nanopartikel auf Fassaden erforschen. Thema Umwelt, 2, 12-13. , Institutional Repository

Fierz, M., Kaegi, R., & Burtscher, H. (2007). Theoretical and experimental evaluation of a portable electrostatic TEM sampler. Aerosol Science and Technology, 41(5), 520-528. doi:10.1080/02786820701253327, Institutional Repository

Lorenzo, R., Kaegi, R., Gehrig, R., Scherrer, L., Grobéty, B., & Burtscher, H. (2007). A thermophoretic precipitator for the representative collection of atmospheric ultrafine particles for microscopic analysis. Aerosol Science and Technology, 41(10), 934-943. doi:10.1080/02786820701581834, Institutional Repository

Yang, T., Holzer, L., Kägi, R., Winnefeld, F., & Keller, B. (2007). In situ nanomanipulators as a tool to separate individual tobermorite crystals for AFM studies. Ultramicroscopy, 107(10–11), 1068-1077. doi:10.1016/j.ultramic.2007.02.042, Institutional Repository

Kaegi, R., & Gasser, P. (2006). Application of the focused ion beam technique in aerosol science: detailed investigation of selected, airborne particles. Journal of Microscopy, 224(2), 140-145. doi:10.1111/j.1365-2818.2006.01669.x, Institutional Repository

Mavrocordatos, D., Kaegi, R., & Schmatloch, V. (2002). Fractal analysis of wood combustion aggregates by contact mode atomic force microscopy. Atmospheric Environment, 36(36-37), 5653-5660. doi:10.1016/S1352-2310(02)00702-1, Institutional Repository

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E-Mail:	ralf.kaegi@cluttereawag.ch
Phone:	+41 58 765 5273
Fax:	+41 58 765 5802
Address:	Eawag Überlandstrasse 133 8600 Dübendorf
Office:	BU B17

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