Publications

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Publications in peer reviewed journals

12 Publications found
  • A critical evaluation of short columns for estimating the attachment efficiency of engineered nanomaterials in natural soils

    Knapp Karin Norrfors, Vesna Micić, Olga Borovinskaya, Frank von der Kammer, Thilo Hofmann, Geert Cornelis
    2021 - Environmental Science: Nano, in press

    Abstract: 

    Short, saturated packed columns are used frequently to estimate the attachment efficiency (α) of engineered nanomaterials (ENMs) in relatively homogeneous porous media, but a combined experimental and theoretical approach to obtain α-values for heterogeneous natural soils has not yet been agreed upon. Accurately determined α-values that can be used to study and predict ENM transport in natural soils should vary with ENM and soil properties, but not with experimental settings. We investigated the effect of experimental conditions, and used different methods to obtain soil parameters, essential to calculate α. We applied 150 different approaches onto 52 transport experiments using short columns with 5 different natural soils and 20 and 80 nm gold- or 27 nm silver sulphide ENMs. The choice of column end-filter material and pore size appeared critical to avoid overestimating α owing to filter – ENM interactions and/or incomplete saturation of the column. Using a low ionic strength (4.4 x 10-5 mol L-1) artificial rain water as an aqueous medium avoided ENM homo- or heteroaggregation in all soils, as confirmed by single-particle inductively coupled plasma - time of flight mass spectrometry. ENM breakthrough curves could be modelled using colloid filtration theory assuming irreversible attachment only. α-values calculated from this model, having the grain size represented by a single average size, accounting for dispersivity and effective porosity based on a prior inert tracer test, explained up to 42 % of the variance in α as revealed by partial least squares analysis. However, column length and dispersivity remained as important experimental parameters, which calls for further standardisation efforts of column tests with ENMs in natural soils, preferably cross-validated with batch tests.

  • Catalytic effects of photogenerated Fe(II) on the ligand-controlled dissolution of Iron(hydr)oxides by EDTA and DFOB

    Jagannath Biswakarma, KyounglimKang, Walter D.C.Schenkeveld, Stephan M.Kraemer, Janet G.Hering. Stephan J.Hug
    2021 - Chemosphere, 263: 128188

    Abstract: 

    Low bioavailability of iron due to poor solubility of iron(hydr)oxides limits the growth of microorganisms and plants in soils and aquatic environments. Previous studies described accelerated dissolution of iron(hydr)oxides under continuous illumination, but did not distinguish between photoreductive dissolution and non-reductive processes in which photogenerated Fe(II) catalyzes ligand-controlled dissolution. Here we show that short illuminations (5–15 min) accelerate the dissolution of iron(hydr)oxides by ligands during subsequent dark periods under anoxic conditions. Suspensions of lepidocrocite (Lp) and goethite (Gt) (1.13 mM) with 50 μM EDTA or DFOB were illuminated with UV-A light of comparable intensity to sunlight (pH 7.0, bicarbonate-CO2 buffered solutions). During illumination, the rate of Fe(II) production was highest with Gt-EDTA; followed by Lp-EDTA > Lp-DFOB > Lp > Gt-DFOB > Gt. Under anoxic conditions, photochemically produced Fe(II) increased dissolution rates during subsequent dark periods by factors of 10–40 and dissolved Fe(III) reached 50 μM with DFOB and EDTA. Under oxic conditions, dissolution rates increased by factors of 3–5 only during illumination. With DFOB dissolved Fe(III) reached 35 μM after 10 h of illumination, while with EDTA it peaked at 15 μM and then decreased to below 2 μM. The observations are explained and discussed based on a kinetic model. The results suggest that in anoxic bottom water of ponds and lakes, or in microenvironments of algal blooms, short illuminations can dramatically increase the bioavailability of iron by Fe(II)-catalyzed ligand-controlled dissolution. In oxic environments, photostable ligands such as DFOB can maintain Fe(III) in solution during extended illumination.

  • Environmentally persistent free radicals are ubiquitous in wildfire charcoals and remain stable for years

    Gabriel Sigmund, Cristina Santín, Marc Pignitter, Nathalie Tepe, Stefan H. Doerr, Thilo Hofmann
    2021 - Communications Earth & Environment, 2: 68

    Abstract: 

    Globally landscape fires produce about 256 Tg of pyrogenic carbon or charcoal each year. The role of charcoal as a source of environmentally persistent free radicals, which are precursors of potentially harmful reactive oxygen species, is poorly constrained. Here, we analyse 60 charcoal samples collected from 10 wildfires, that include crown as well as surface fires in forest, shrubland and grassland spanning different boreal, temperate, subtropical and tropical climate. Using electron spin resonance spectroscopy, we measure high concentrations of environmentally persistent free radicals in charcoal samples, much higher than those found in soils. Concentrations increased with degree of carbonization and woody fuels favoured higher concentrations. Moreover, environmentally persistent free radicals remained stable for an unexpectedly long time of at least 5 years. We suggest that wildfire charcoal is an important global source of environmentally persistent free radicals, and therefore potentially of harmful reactive oxygen species.

  • Methanol-based extraction protocol for insoluble and moderately water-soluble nanoparticles in plants to enable characterization by single particle ICP-MS

    Stephanie Laughton, Adam Laycock, Garret Bland, Frank von der Kammer, Thilo Hofmann, Elizabeth A. Casman, Gregory V. Lowry
    2021 - Analytical and Bioanalytical Chemistry, 413: 299–314

    Abstract: 

    The detection and characterization of soluble metal nanoparticles in plant tissues are an analytical challenge, though a scientific necessity for regulating nano-enabled agrichemicals. The efficacy of two extraction methods to prepare plant samples for analysis by single particle ICP-MS, an analytical method enabling both size determination and quantification of nanoparticles (NP), was assessed. A standard enzyme-based extraction was compared to a newly developed methanol-based approach. Au, CuO, and ZnO NPs were extracted from three different plant leaf materials (lettuce, corn, and kale) selected for their agricultural relevance and differing characteristics. The enzyme-based approach was found to be unsuitable because of changes in the recovered NP size distribution of CuO NP. The MeOH-based extraction allowed reproducible extraction of the particle size distribution (PSD) without major alteration caused by the extraction. The type of leaf tissue did not significantly affect the recovered PSD. Total metal losses during the extraction process were largely due to the filtration step prior to analysis by spICP-MS, though this did not significantly affect PSD recovery. The methanol extraction worked with the three different NPs and plants tested and is suitable for studying the fate of labile metal-based nano-enabled agrichemicals.

  • Microplastic extraction protocols can impact the polymer structure

    Patrizia Pfohl, Christian Roth, Lars Meyer, Ute Heinemeyer, Till Gruendling, Christiane Lang, Nikolaus Nestle, Thilo Hofmann, Wendel Wohlleben, Sarah Jessl
    2021 - Microplastics and Nanoplastics, 1: 8

    Abstract: 

    Although microplastics are ubiquitous in today’s natural environments, our understanding of the materials, quantities, and particle sizes involved remains limited. The recovery of microplastics from different types of environmental matrices requires standardized matrix digestion protocols that allow inter-laboratory comparisons and that have no effect on the polymers themselves. A number of commonly used digestion methods rely on oxidation with concentrated hydrogen peroxide solutions to remove organic matter from the matrix. However, this can alter the nature of polymers through hydrolysis and often does not lead to a complete matrix removal. We have therefore investigated the use of two altered matrix digestion protocols, an acidic (Fenton) protocol and a new alkaline (Basic Piranha) protocol, focusing mainly on the effect on biodegradable polymers (polylactide, polybutylene adipate terephthalate, polybutylene succinate) and polymers with known degradation pathways via hydrolysis (thermoplastic polyurethanes, polyamide). Comparing the initial surface textures, chemical compositions, and particle size distributions with those obtained after digestion revealed that the Fenton protocol left most of the polymers unchanged. The ferrous residue that remains following Fenton digestion had no effect on either the polymer composition or the particle size distribution, but could disturb further analytics (e.g. Raman microscopy due to auto-fluorescence). While increasing the chance of complete matrix removal, the more powerful Basic Piranha protocol is also more likely to affect the polymer properties: Polylactide polymers in particular showed signs of degradation under alkaline digestion (reduced polylactide content, holes in the polymer matrix), indicating the unsuitability of the Basic Piranha protocol in this specific case. Polyamide, however, remained stable during the Basic Piranha treatment, and the surface chemistry, the particle size as well as the molar mass distribution of the investigated thermoplastic polyurethanes were also not affected. Hence, this protocol offers a powerful alternative for microplastic analysis with focus on particle size in more complex environmental matrices (e.g. removal of cellulose in soil), while avoiding ferrous Fenton residue. Unexpectedly, also tire rubber, a frequent target analyte in microplastic monitoring, was found to be susceptible to artefact structures by both oxidation protocols. In summary, controls for the specific combination of polymer and sample preparation protocol are highly recommended to select the most fitting protocol. Here selected suitable combinations are reported.

  • Microplastics and nanoplastics barely enhance contaminant mobility in agricultural soils

    Stephanie Castan, Charlotte Henkel, Thorsten Hüffer, Thilo Hofmann
    2021 - Communications Earth & Environment, 193: 1-9

    Abstract: 

    Farmland soils are prone to contamination with micro- and nanoplastics through a variety of agricultural practices. Concerns are recurrently raised that micro- and nanoplastics act as vector for organic contaminants to deeper soil layers and endanger groundwater resources. Whether and to what extent micro- and nanoplastics facilitate the transport of organic contaminants in soil remains unclear. Here we calculated the ratio between transport and desorption time scales using two diffusion models for micro- and nanoplastics between 100 nm and 1 mm. To identify micro- and nanoplastics bound contaminant transport we evaluated diffusion and partitioning coefficients of prominent agrochemicals and additives and of frequently used polymers e.g., polyethylene and tire material. Our findings suggest that the desorption of most organic contaminants is too fast for micro- and nanoplastics to act as transport facilitators in soil. Contaminant transport enabled by microplastics was found to be relevant only for very hydrophobic contaminants (logKow >5) under preferential flow conditions. While micro- and nanoplastics might be a source of potentially harmful contaminants in farmland soils this study suggests that they do not considerably enhance contaminant mobility.

  • New guidance brings clarity to environmental hazard and behaviour testing of nanomaterials

    Elijah Joel Petersen, Greg Gerard Goss, Frank von der Kammer, Alan James Kennedy
    2021 - Nature Nanotechnology, 16: 482–483
  • PAHs sorption to biochar colloids changes their mobility over time

    Yang Wen, Qu Ting, Flury Markus, Zhang Xin, Gabriel Sigmund, Shang Jianying, Li Baoguo
    2021 - Journal of Hydrology, 603: 126839

    Abstract: 

    Biochar is an efficient sorbent for polycyclic aromatic hydrocarbons (PAHs). However, little is known about PAHs sorption kinetics and the effect on the mobility of biochar colloids in saturated porous media. In this study, naphthalene (NAP) and phenanthrene (PHE) were chosen as typical PAHs. In different stages, different sorption sites of PAHs on biochar played a distinct role in affecting the transport of biochar colloids in saturated porous media. The biochar colloids showed less negative surface charge as the contact time between biochar colloids and PAHs increased from 0.017 h to 96 h, which led to the mobility of biochar colloids decreasing over time. But after 168 h contact time, the surface charge of biochar colloids became more negative again, and the inhibition effect of PAHs on biochar colloid transport was weakened. This was related to the sorption kinetics of PAHs on biochar colloids: (1) PAHs sorption onto outer biochar surface; and (2) adsorbed PAHs diffusion into internal biochar pores. PAHs sorption onto the outer biochar surface shielded the negative surface charge and then decreased the mobility of biochar colloids, and then the adsorbed PAHs diffusion into internal biochar pores increased their mobility again. Our results suggested that porous colloids-facilitated PAHs transport in porous media might be highly related to interaction time between PAHs and porous colloids.

  • Parameter estimation and uncertainty analysis in hydrological modeling

    Paulo A. Herrera, Miguel Angel Marazuela, Thilo Hofmann
    2021 - WIRES Water, e1569

    Abstract: 

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

  • Towards more Sustainable Peptide- based Antibiotics: Stable in Human Blood, Enzymatically Hydrolyzed in Wastewater?

    Michael Zumstein, Kathrin Fenner
    2021 - CHIMIA International Journal for Chemistry, 75: 267-271

    Abstract: 

    The emergence and spread of antibiotic resistance is a major societal challenge and new antibiotics are needed to successfully fight bacterial infections. Because the release of antibiotics into wastewater and downstream environments is expected to contribute to the problem of antibiotic resistance, it would be beneficial to consider the environmental fate of antibiotics in the development of novel antibiotics. In this article, we discuss the possibility of designing peptide-based antibiotics that are stable during treatment (e.g. in human blood), but rapidly inactivated through hydrolysis by peptidases after their secretion into wastewater. In the first part, we review studies on the biotransformation of peptide-based antibiotics during biological wastewater treatment and on the specificity of dissolved extracellular peptidases derived from wastewater. In the second part, we present first results of our endeavour to identify peptide bonds that are stable in human blood plasma and susceptible to hydrolysis by the industrially produced peptidase Subtilisin A.

  • Wildfire-Derived Pyrogenic Carbon Modulates Riverine Organic Matter and Biofilm Enzyme Activities in an In Situ Flume Experiment

    Lukas Thuile Bistarelli, Caroline Poyntner, Cristina Santín, Stefan Helmut Doerr, Matthew V. Talluto, Gabriel Singer, Gabriel Sigmund
    2021 - ACS EST Water, 1648–1656

    Abstract: 

    Wildfires produce large amounts of pyrogenic carbon (PyC), including charcoal, known for its chemical recalcitrance and sorption affinity for organic molecules. Wildfire-derived PyC can be transported to fluvial networks. Here it may alter the dissolved organic matter (DOM) concentration and composition as well as microbial biofilm functioning. Effects of PyC on carbon cycling in freshwater ecosystems remain poorly investigated. Employing in-stream flumes with a control versus treatment design (PyC pulse addition), we present evidence that field-aged PyC inputs to rivers can increase the dissolved organic carbon (DOC) concentration and alter the DOM composition. DOM fluorescence components were not affected by PyC. The in-stream DOM composition was altered due to leaching of pyrogenic DOM from PyC and possibly concurrent sorption of riverine DOM to PyC. Decreased DOM aromaticity indicated by a lower SUVA245 (−0.31 unit) and a higher pH (0.25 unit) was associated with changes in enzymatic activities in benthic biofilms, including a lower recalcitrance index (β-glucosidase/phenol oxidase), suggesting preferential usage of recalcitrant over readily available DOM by biofilms. The deposition of particulate PyC onto biofilms may further modulate the impacts of PyC due to direct contact with the biofilm matrix. This study highlights the importance of PyC for in-stream biogeochemical organic matter cycling in fire-affected watersheds. It was featured on the journal front cover.

  • Wood ash amended biochar for the removal of lead, copper, zinc and cadmium from aqueous solution

    Stuart Cairns, Sampriti Chaudhuri, Gabriel Sigmund, Iain Robertson, Natasha Hawkins, Tom Dunlop, Thilo Hofmann
    2021 - Environmental Technology & Innovation, 24: 1-11

    Abstract: 

    Heavy metals in motorway adjoined aqueous environments have increased at an alarming rate over recent years. This increase has been primarily attributed to anthropogenic activities such as the increase of motor vehicle use. Current remediation techniques, such as balancing ponds have the potential to leave toxic residue with the associated removal costs often proving prohibitive. In this study biochar and wood ash amended biochar were evaluated as remediators of inorganic vehicular pollutants found in motorway runoff, specifically Pb, Cu, Zn and Cd. Biochar from European larch (Larix decidua (L.) Karst.) was produced via fast pyrolysis-gasification (485–530 °C for 90 s) and amended with wood ash post pyrolysis. Pristine larch biochar (BC), larch biochar cold mixed with wood ash (WA) and larch biochar sintered with wood ash (WAS) were studied to evaluate metal immobilisation mechanisms and maximum removal capacities. This study demonstrates that the amendment of biochar with wood ash increases Pb, Cu, Zn, and Cd immobilisation by an order of magnitude compared to BC. The addition of wood ash increases pH whilst adding minerals causing precipitation. Precipitation and ion exchange dominate metal immobilisation and were not correlated to surface area. Sustainability of feedstock, low feedstock/production costs and maximum measured contaminant removal (61.5 mg/g, 38.9 mg/g, 12.1 mg/g and 10.2 mg/g for Pb, Cu, Zn and Cd respectively) indicate that wood ash amended biochar is a viable option to immobilise Pb, Cu, Zn and Cd from motorway runoff.

Book chapters and other publications

2 Publications found
  • Nanoparticle inventory in a sediment core from the Iron Gate I reservoir

    2021 - JDS4 Scientific Report, 501-510

    Abstract: 

    River sediments are a sink for natural and anthropogenic nanoparticles. Given their risk to harm ecosystems and humans the latter are among contaminants of emerging concern. Here we present multi-element single-particle data of a Danube sediment core, aiming to identify anthropogenic nanoparticles and elucidate their occurrence at different sediment depths. A fly ash dump near Kostolac, Serbia, on the right bank of the Danube River is a likely point source of anthropogenic fly ash particles. Kostolac fly ash particles are enriched in elements such as Cu, Ni, and V. The signatures of these elements within nanoparticles of the sediment core reveal four potential events of fly ash release into the Danube.

  • Natürliche Schwebstoffe in Flüssen: Zusammensetzung, Schlüsselkomponenten und Dynamiken

    2021 - Vom Wasser - das Journal, 51-53