Publications

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Publications in peer reviewed journals

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

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

    Abstract: 

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

  • Effect of Polymer Properties on the Biodegradation of Polyurethane Microplastics

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

    Abstract: 

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

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

    Charlotte Henkel, Thorsten Hüffer, Thilo Hofmann
    2022 - Environ. Sci. Technol., in press

    Abstract: 

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

  • Uptake, Metabolism, and Accumulation of Tire Wear Particle- Derived Compounds in Lettuce

    Stephanie Castan, Anya Sherman, Ruoting Peng, Michael Zumstein, Wolfgang Wanek, Thorsten Hüffer, Thilo Hofmann
    2022 - Environ. Sci. Technol., in press

    Abstract: 

    Tire wear particle (TWP)-derived compounds may be of high concern to consumers when released in the root zone of edible plants. We exposed lettuce plants to the TWP-derived compounds diphenylguanidine (DPG), hexamethoxymethylmelamine (HMMM), benzothiazole (BTZ), N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), and its quinone transformation product (6PPD-q) at concentrations of 1 mg L–1 in hydroponic solutions over 14 days to analyze if they are taken up and metabolized by the plants. Assuming that TWP may be a long-term source of TWP-derived compounds to plants, we further investigated the effect of leaching from TWP on the concentration of leachate compounds in lettuce leaves by adding constantly leaching TWP to the hydroponic solutions. Concentrations in leaves, roots, and nutrient solution were quantified by triple quadrupole mass spectrometry, and metabolites in the leaves were identified by Orbitrap high resolution mass spectrometry. This study demonstrates that TWP-derived compounds are readily taken up by lettuce with measured maximum leaf concentrations between ∼0.75 (6PPD) and 20 μg g–1 (HMMM). Although these compounds were metabolized in the plant, we identified several transformation products, most of which proved to be more stable in the lettuce leaves than the parent compounds. Furthermore, continuous leaching from TWP led to a resupply and replenishment of the metabolized compounds in the lettuce leaves. The stability of metabolized TWP-derived compounds with largely unknown toxicities is particularly concerning and is an important new aspect for the impact assessment of TWP in the environment.

  • 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.

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

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

    Abstract: 

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

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

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

    Abstract: 

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

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

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

    Abstract: 

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

  • Are we speaking the same language? Recommendations for a definition and categorisation framework for plastic debris

    Nanna B. Hartmann, Thorsten Hüffer, Richard C. Thompson, Martin Hassellv, Anja Verschoor, Anders E. Daugaard, Sinja Rist, Therese Karlsson, Nicole Brennholt, Matthew Cole, Maria P. Herrling, Maren C. Hess, Natalia P. Ivleva, Amy L. Lusher, Martin Wagner
    2019 - Environmental Science & Technology, 3: 1039-1047

    Abstract: 

    The accumulation of plastic litter in natural environments is a global issue. Concerns over potential negative impacts on the economy, wildlife, and human health provide strong incentives for improving the sustainable use of plastics. Despite the many voices raised on the issue, we lack a consensus on how to define and categorize plastic debris. This is evident for microplastics, where inconsistent size classes are used and where the materials to be included are under debate. While this is inherent in an emerging research field, an ambiguous terminology results in confusion and miscommunication that may compromise progress in research and mitigation measures. Therefore, we need to be explicit on what exactly we consider plastic debris. Thus, we critically discuss the advantages and disadvantages of a unified terminology, propose a definition and categorization framework, and highlight areas of uncertainty. Going beyond size classes, our framework includes physicochemical properties (polymer composition, solid state, solubility) as defining criteria and size, shape, color, and origin as classifiers for categorization. Acknowledging the rapid evolution of our knowledge on plastic pollution, our framework will promote consensus building within the scientific and regulatory community based on a solid scientific foundation.

  • Biochar particle aggregation in soil pore water: the influence of ionic strength and interactions with pyrene

    Stephanie Castan, Gabriel Sigmund, Thorsten Hüffer, Thilo Hofmann
    2019 - Environmental Science: Processes & Impacts, 21: 1722-1728

    Abstract: 

    The beneficial properties of biochar have led to its increasing application to soils for environmental management. Despite its stability in soil, biochar can physically disintegrate into smaller particles, which can then be relocated from the application area. Biochar transport is strongly dependent on the biochar particle size and aggregation, with the extent of aggregation depending on the chemistry of the soil pore water. Biochar has a strong sorption affinity for polyaromatic hydrocarbons (PAHs) such as pyrene, which can also affect its transport. We therefore investigated biochar particle aggregation in solutions of different ionic strengths (ultrapure water, 0.01 M CaCl2, and 0.1 M CaCl2) with suspensions of biochar particles, and with suspensions of biochar particles loaded with pyrene (0.2 and 3.6 g kg−1). Increasing the pyrene concentration in ultrapure water resulted in an increase in the biochar particle size, an effect that was more pronounced following equilibration for 28 days than following equilibration for only 24 hours. Biochar particle aggregation in solutions containing both pyrene and 0.01 M CaCl2 was greatly enhanced compared to aggregation in similar solutions with no pyrene. However, the influence of pyrene became negligible at high CaCl2 concentrations (0.1 M CaCl2). To determine the fate of biochar in soil, both the presence of PAHs and the influence of the pore water's ionic strength therefore need to be taken into account.

  • Characterization of sorption properties of high-density polyethylene using the poly-parameter linearfree-energy relationships

    Tobias H. Uber, Thorsten Hüffer, Sibylle Planitz, Torsten C. Schmidt
    2019 - Environmental Pollution, 312-319

    Abstract: 

    High-density polyethylene (HDPE) is a known sorbent for non-ionic organic compounds in technical applications. Nevertheless, there is little information available describing sorption to industrial HDPE for a broad range of compounds. With a better understanding of the sorption properties of synthetic polymers, environmental risk assessment would achieve a higher degree of accuracy, especially for microplastic interactions with organic substances. Therefore, a robust methodology for the determination of sorbent properties for non-ionic organic compounds by HDPE is relevant for the understanding of molecular interactions for both technical use and environmental risk assessment.

    In this work, sorption properties of HDPE material used for water pipes were characterized using a poly-parameter linear free-energy relationship (ppLFER) approach. Sorption batch experiments with selected probe sorbates were carried out in a three-phase system (air/HDPE/water) covering an aqueous concentration range of at least three orders of magnitude. Sorption in the concentration range below 10−2 of the aqueous solubility was found to be non-linear and the Freundlich model was used to account for this non-linearity. Multiple regression analysis (MRA) using the determined distribution coefficients and literature-tabulated sorbate descriptors was performed to obtain the ppLFER phase descriptors for HDPE. Sorption properties of HDPE were then derived from the ppLFER model and statistical analysis of its robustness was conducted. The derived ppLFER model described sorption more accurately than commonly used single-parameter predictions, based i.e., on log Ko/w. The ppLFER predicted distribution data with an error 0.5 log units smaller than the spLFERs. The ppLFER was used for a priori prediction of sorption by the characterized sorbent material. The prediction was then compared to experimental data from literature and this work and demonstrated the strength of the ppLFER, based on the training set over several orders of magnitude.

  • NO2 and natural organic matter affect both soot aggregation behavior and sorption of S-metolachlor

    Gabriel Sigmund, Stephanie Castan, Christopher Wabnitz, Rani Bakkour, Thorsten Hüffer, Thilo Hofmann, Martin Elsner
    2019 - Environmental Science: Processes & Impacts, 21: 1729-1735

    Abstract: 

    Soot is an important carbonaceous nanoparticle (CNP) frequently found in natural environments. Its entry into surface waters can occur directly via surface runoff or infiltration, as well as via atmospheric deposition. Pristine soot is likely to rapidly undergo aggregation and subsequent sedimentation in aquatic environments. Further, soot can sorb a variety of organic contaminants, such as S-metolachlor (log KD = 3.25 ± 0.12). During atmospheric transport, soot can be chemically transformed by reactive oxygen species including NO2. The presence of natural organic matter (NOM) in surface waters can further affect the aquatic fate of soot. To better understand the processes driving the fate of soot and its interactions with contaminants, pristine and NO2-transformed model soot suspensions were investigated in the presence and absence of NOM. NO2-oxidized soot showed a smaller particle size, a higher number of particles remaining in suspension, and a decreased sorption of S-metolachlor (log KD = 2.47 ± 0.40). In agreement with findings for other CNPs, soot stability against aggregation was increased for both pristine and NO2 transformed soot in the presence of NOM.

  • Polyethylene microplastics influence the transport of organic contaminants in soil

    Thorsten Hüffer, Florian Metzelder, Gabriel Sigmund, Sophie Slawek, Torsten C. Schmidt, Thilo Hofmann
    2019 - Science of The Total Environment, 242-247

    Abstract: 

    Plastics are now found in all natural environments including soil. The effects of microplastics in terrestrial systems, however, remain largely unexplored. Polyethylene is one of the mass-manufactured polymers found in terrestrial environments. It is used in many different sectors, for example in agricultural mulches, composite materials, and packaging. The presence of microplastics in soil, including polyethylene, can affect the transport of hydrophobic organic pollutants including pesticides. The objective of this study was to investigate the influence of polyethylene microplastics (<250 μm) on the transport of two selected organic plant-protection agents (atrazine and 4-(2,4-dichlorophenoxy) butyric acid) in soil under different aqueous conditions, using inverse liquid chromatography. The distribution coefficients for the sorbates that were sorbed to pure polyethylene microplastic were found to be significantly smaller than those for the sorbates sorbed to pure soil. The addition of 10% (w/w) polyethylene to the soil therefore led to an overall reduction in sorption, but the sorption trends due to variations in pH and ionic strength were not affected. The results imply that the presence of polyethylene microplastics in soil may therefore increase the mobility of organic contaminants by reducing the sorption capacity of natural soils, which must be validated by further research.

  • Sorption of non-ionic organic compounds by polystyrene in water

    Tobias H. Uber, Thorsten Hüffer, Sibylle Planitz, Thorsten C. Schmidt
    2019 - Science of The Total Environment, 682: 348-355

    Abstract: 

    Polystyrene (PS) is a plastic material that is well known for its use in many different applications, e.g. as shock sensitive packaging.With its prevalence across society, PS contributes significantly to the overall plastic load in aqueous systems. Sorption of organic compounds by the plastics, especiallymicrometer-sized particles, in the environment has become a concern in the past years. The aim of this study was to improve the understanding of sorption properties of PS, one of the major plastic pollutants in the aqueous environment. Batch experiments with PS film (29 μmthickness)were performed for 4 days using a diverse set of 24 sorbates to account for varying molecular properties like polarity or molecular volume. Isotherms were evaluated using different sorption models to elucidate the sorption process of PS. Sorption to PS film was non-linear and absorption into the bulk materialwas the dominant sorption mode. A clear discrimination between the specific and non-specific interactions in the aqueous environment could be shown. The non-linear sorption to PS was shown to be controlled by themolar volume but also by the polarizability/dipolarity parameter (S) of the ppLFER model. The latter is influenced
    by the aromaticπ-π-interactions of PSwith the sorbate. Similar to other plastics like polyethylene, sorption to PS is driven by hydrophobic interactions but phase descriptors of pristine PS were significantly different than descriptors for other environmental relevant plastics.

  • Sorption of organic substances to tire wear materials: Similarities and differences with other types of microplastic

    Thorsten Hüffer, Stephan Wagner, Thorsten Reemtsma, Thilo Hofmann
    2019 - Trends in Analytical Chemistry, 113: 392-401

    Abstract: 

    Tire materials are a significant proportion of the (micro)plastics in the environment that until today have been clearly overlooked. These materials are released into the environment, either unintentionally as an abrasion product from tire wear, that reaches the environment via road runoff, or intentionally as, for example, shredded “tire crumble rubber” used as filling material for playgrounds. Although there are a few estimates available the amount of tire-wear material to be found in aquatic environments, investigations on the fate tire materials and especially their interaction with organic substances are missing. Although the sorption processes associated with the complex constituents of tires are an important aspect of any environmental risk assessment for tire-wear materials, they have yet to be thoroughly investigated. In this review we elucidate the sorption properties of the polymeric rubbers and carbon black that form the main components of tires, within the context of current microplastic research.

  • The composition of bacterial communities associated with plastic biofilms differs between different polymers and stages of biofilm succession

    Maria Pinto, Teresa M. Langer, Thorsten Hüffer, Thilo Hofmann, Gerhard J. Herndl
    2019 - PloS one, 14: 1-20

    Abstract: 

    Once in the ocean, plastics are rapidly colonized by complex microbial communities. Factors affecting the development and composition of these communities are still poorly understood. Additionally, whether there are plastic-type specific communities developing on different plastics remains enigmatic. We determined the development and succession of bacterial communities on different plastics under ambient and dim light conditions in the coastal Northern Adriatic over the course of two months using scanning electron microscopy and 16S rRNA gene analyses. Plastics used were low- and high-density polyethylene (LDPE and HDPE, respectively), polypropylene (PP) and polyvinyl chloride with two typical additives (PVC DEHP and PVC DINP). The bacterial communities developing on the plastics clustered in two groups; one group was found on PVC and the other group on all the other plastics and on glass, which was used as an inert control. Specific bacterial taxa were found on specific surfaces in essentially all stages of biofilm development and in both ambient and dim light conditions. Differences in bacterial community composition between the different plastics and light exposures were stronger after an incubation period of one week than at the later stages of the incubation. Under both ambient and dim light conditions, one part of the bacterial community was common on all plastic types, especially in later stages of the biofilm development, with families such as Flavobacteriaceae, Rhodobacteraceae, Planctomycetaceae and Phyllobacteriaceae presenting relatively high relative abundances on all surfaces. Another part of the bacterial community was plastic-type specific. The plastic-type specific fraction was variable among the different plastic types and was more abundant after one week of incubation than at later stages of the succession.

  • The leaching of phthalates from PVC can be determined with an infinite sink approach

    Charlotte Henkel, Thorsten Hüffer, Thilo Hofmann
    2019 - MethodsX, 6: 2729-2734

    Abstract: 

    Polyvinyl chloride (PVC) is the third most used polymer for plastic products in the European Union (+NO/ CH) and contains the highest amounts of additives, especially phthalic acid esters (phthalates). Leaching kinetics of additives from (micro-) plastics into aqueous environments are highly relevant for environmental risk assessment and modelling of the fluxes of plastics and its associated additives. Investigating the leaching of phthalates into aqueous environments in batch experiments is challenging due to their low solubility and high hydrophobicity and there are no standard methods to study release processes. Here we describe an infinite sink method to investigate the leaching of phthalates from PVC into the aqueous phase. Spiking and leaching experiments using bis(2-ethylhexyl)phthalate as a model phthalate enabled the validation and evaluation of the designed infinite sink method. The developed method offers:

    • a low-cost and simple approach to investigate leaching of phthalates from PVC into aqueous environments
    • the use of a high-surface activated carbon powder as an infinite sink
    • a tool to elucidate the transport fluxes of plastics and additives
  • Comparison of Sorption to Carbon-Based Materials and Nanomaterials Using Inverse Liquid Chromatography

    Florian Metzelder, Matin Funck, Thorsten Hüffer, Torsten C. Schmidt
    2018 - Environmental Science & Technology, 1: 9731-9740

    Abstract: 

    Sorption studies of carbon-based materials and nanomaterials are typically conducted using batch experiments, but the analysis of weakly sorbing compounds may be challenging. Column chromatography represents a promising complement as higher sorbent to solution ratios can be applied. The sorbent is packed in a column, and sorption data are calculated by relating sorbate retention times to that of a nonretarded tracer. In this study, sorption of heterocyclic organic compounds (pyrazole, pyrrole, furan, and thiophene) by carbon-based materials (activated carbon, biochar, and graphite) and nanomaterials (functionalized carbon nanotubes and graphene platelets) was compared for the first time using column chromatography. D2O was used as nonretarded tracer. Sorption isotherms were nonlinear and described well by the Freundlich model. Sorption differed between the materials regarding determined Freundlich coefficients (Kf) by more than two orders of magnitude for isotherms in a similar concentration range. Normalization of Kf with the surface area of the sorbent significantly reduced but did not remove the differences between the sorbents. Overall, column chromatography represents the opportunity to study sorption of weakly sorbing compounds to diverse carbon-based sorbent materials with a single experimental approach, which is challenging in batch experiments because of the very different sorption properties of some sorbent materials.

  • Data on sorption of organic compounds by aged polystyrene microplastic particles

    Thorsten Hüffer, Anne-Katrin Weniger, Thilo Hofmann
    2018 - Data in Brief, 474-479

    Abstract: 

    This article contains data on experimental sorption isotherms of 21 probe sorbates by aged polystyrene microplastics. The polymeric particles were subjected to an UV-induced photo-oxidation procedure using hydrogen peroxide in a custom-made aging chamber. Sorption data were obtained for aged particles. The experimental sorption data was modelled using both single- and poly-parameter linear free-energy relationships. For discussion and interpretation of the presented data, refer to the research article entitled “Sorption of organic compounds by aged polystyrene microplastic particles” (Hüffer et al., 2018) [1].

  • Sorption of organic compounds by aged polystyrene microplastic particles

    Thorsten Hüffer, Anne-Katrin Weniger, Thilo Hofmann
    2018 - Environmental Pollution, 218-225

    Abstract: 

    Microplastics that are released into the environment undergo aging and interact with other substances such as organic contaminants. Understanding the sorption interactions between aged microplastics and organic contaminants is therefore essential for evaluating the impact of microplastics on the environment. There is little information available on how the aging of microplastics affects their sorption behavior and other properties. We have therefore investigated the effects of an accelerated UV-aging procedure on polystyrene microplastics, which are used in products such as skin cleaners and foams. Physical and chemical particle characterizations showed that aging led to significant surface oxidation and minor localized microcrack formation. Sorption coefficients of organic compounds by polystyrene microplastics following aging were up to one order of magnitude lower than for pristine particles. Sorption isotherms were experimentally determined using a diverse set of probe sorbates covering a variety of substance classes allowing an in-depth evaluation of the poly-parameter linear free-energy relationship (ppLFER) modelling used to investigate the contribution of individual molecular interactions to overall sorption. The ppLFER modelling was validated using internal cross-validation, which confirmed its robustness. This approach therefore yields improved estimates of the interactions between aged polystyrene microplastics and organic contaminants.

  • Sorption of organic substances to tire wear materials: Similarities and differences with other types of microplastic

    Thorsten Hüffer, Stephan Wagner, Thorsten Reemtsma, Thilo Hofmann
    2018 - TrAC Trends in Analytical Chemistry, 392-401

    Abstract: 

    Tire materials are a significant proportion of the (micro)plastics in the environment that until today have been clearly overlooked. These materials are released into the environment, either unintentionally as an abrasion product from tire wear, that reaches the environment via road runoff, or intentionally as, for example, shredded “tire crumble rubber” used as filling material for playgrounds. Although there are a few estimates available the amount of tire-wear material to be found in aquatic environments, investigations on the fate tire materials and especially their interaction with organic substances are missing. Although the sorption processes associated with the complex constituents of tires are an important aspect of any environmental risk assessment for tire-wear materials, they have yet to be thoroughly investigated. In this review we elucidate the sorption properties of the polymeric rubbers and carbon black that form the main components of tires, within the context of current microplastic research.

  • Tire wear particles in the aquatic environment - A review on generation, analysis, occurrence, fate and effects

    Wagner S, Thorsten Hüffer, Klöckner P, Wehrhahn M, Thilo Hofmann, Reemtsma T
    2018 - Water Research, 83-100

    Abstract: 

    Tire wear particles (TWP), generated from tire material during use on roads have gained increasing attention as part of organic particulate contaminants, such as microplastic, in aquatic environments. The available information on properties and generation of TWP, analytical techniques to determine TWP, emissions, occurrence and behavior and ecotoxicological effects of TWP are reviewed with a focus on surface water as a potential receptor. TWP emissions are traffic related and contribute 5–30% to non-exhaust emissions from traffic. The mass of TWP generated is estimated at 1,327,000 t/a for the European Union, 1,120,000 t/a for the United States and 133,000 t/a for Germany. For Germany, this is equivalent to four times the amount of pesticides used. The mass of TWP ultimately entering the aquatic environment strongly depends on the extent of collection and treatment of road runoff, which is highly variable. For the German highways it is estimated that up to 11,000 t/a of TWP reach surface waters. Data on TWP concentrations in the environment, including surface waters are fragmentary, which is also due to the lack of suitable analytical methods for their determination. Information on TWP properties such as density and size distribution are missing; this hampers assessing the fate of TWP in the aquatic environment. Effects in the aquatic environment may stem from TWP itself or from compounds released from TWP. It is concluded that reliable knowledge on transport mechanism to surface waters, concentrations in surface waters and sediments, effects of aging, environmental half-lives of TWP as well as effects on aquatic organisms are missing. These aspects need to be addressed to allow for the assessment of risk of TWP in an aquatic environment.

  • Biochar total surface area and total pore volume determined by N2 and CO2 physisorption are strongly influenced by degassing temperature

    Gabriel Sigmund, Thorsten Hüffer, Thilo Hofmann, Melanie Kah
    2017 - Science of The Total Environment, 770-775

    Abstract: 

    The surface area and pore volume of carbonaceous materials, which are commonly determined by N2 and/or CO2 gas-physisorption, are important parameters when describing environmental processes such as adsorption. Their measurement requires prior degassing of samples, which can change the nature of the material. Current guidelines for biochar characterization recommend different degassing temperatures. To investigate how degassing temperatures affect gas-physisorption we systematically degassed a range of materials (four biochars, carbon nanotubes, and Al2O3 reference material) at different temperatures (105, 150, 200, 250 and 300 °C; for ≥ 14 h each). Degassing temperatures had no effect on Al2O3 or carbon nanotubes but the measured surface areas and pore volumes of biochars increased by up to 300% with degassing temperature. An equation is presented for predicting surface area obtained at different degassing temperatures. Elemental analysis and results from sorption batch experiments suggest that surface area and pore volume may increase as biochar components volatilize during degassing. Our results showed that degassing temperatures change material properties and influence gas-physisorption measurements, and therefore need to be standardized. These results may also apply to the characterization of other complex materials, including carbon nanotubes coated with natural organic matter and fouled activated carbon.

  • Interactions between aromatic hydrocarbons and functionalized C60 fullerenes insights from experimental data and molecular modelling

    Thorsten Hüffer, Huichao Sun, James D. Kubicki, Thilo Hofmann, Melanie Kah
    2017 - Environmental Science: Nano, 5: 1045-1053

    Abstract: 

    Understanding molecular interactions between organic compounds and carbon-based nanomaterials is crucial to the interpretation of phase transfer processes, both in technical applications and within the environment. There is, however, little information available on the interactions between organic compounds and C60 fullerenes, in particular regarding the effects of functionalization. Experimental sorption isotherms and molecular modelling have therefore been used to systematically investigate how these interactions are affected by functionalization of the sorbate (using one, two and four ring aromatics, with –OH or –NH2functional groups) and the sorbent (i.e., C60 and C60-OH). Functionalization of the sorbent, as well as hydroxyl- and amino-functionalization of the sorbate, had a significant effect on sorption. The enhanced sorption of hydroxyl- and amino-functionalized sorbates by C60 may be due to an increased contribution from π–π electron donor–acceptor interactions. Additional hydrogen bond interactions with C60-OH also appear to play an important role. Our results emphasize that the surface chemistry of C60 is of critical importance to their interactions with organic compounds. The ageing of C60 in technical applications, or in the environment, is therefore likely to significantly affect the molecular interactions, and hence sorption strength, for polar and non-polar organic compounds.

  • Investigation of carbon-based nanomaterials as sorbents for headspace in-tube extraction of polycyclic aromatic hydrocarbons

    Xochitli L. Osorio Barajas, Thorsten Hüffer, Pascal Mettig, Beat Schilling, Maik A. Jochmann, Torsten C. Schmidt
    2017 - Analytical and Bioanalytical Chemistry, 1: 3861-3870

    Abstract: 

    Carbon-based nanomaterials (CNM) represent promising materials for the application as sorbents in micro- and other extraction devices. In this work, we investigate the applicability of five different CNM (multi-walled carbon nanotubes (MWCNTs), fullerenes, carboxylic acid functionalized multi-walled carbon nanotubes (MWCNTs-COOH), graphene platelets, and carbon nanohorns) for their performance on PAH extraction from the aqueous phase by headspace in-tube extraction (HS-ITEX). Optimal extraction parameters for HS-ITEX were determined using a Box-Behnken experimental design. From the extraction yield response, central point analysis, fullerenes showed the best extraction properties for the eight selected headspace compatible PAHs (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene). Fullerenes were used for a further method validation including the linear range, limit of detection, precision, as well as recovery. Finally, extraction yields were compared to a commercial material (Tenax GR), demonstrating that fullerene represents a better option as sorbent in ITEX for PAH analysis. Method detection limits for the PAH on fullerene ranged from 10 to 300 ng L−1, with recoveries between 45 and 103%.

  • Microplastic Exposure Assessment in Aquatic Environments: Learning from Similarities and Differences to Engineered Nanoparticles

    Thorsten Hüffer, Antonia Praetorius, Stephan Wagner, Frank von der Kammer, Thilo Hofmann
    2017 - Environmental Science & Technology, 5: 2499-2507

    Abstract: 

    Microplastics (MPs) have been identified as contaminants of emerging concern in aquatic environments and research into their behavior and fate has been sharply increasing in recent years. Nevertheless, significant gaps remain in our understanding of several crucial aspects of MP exposure and risk assessment, including the quantification of emissions, dominant fate processes, types of analytical tools required for characterization and monitoring, and adequate laboratory protocols for analysis and hazard testing. This Feature aims at identifying transferrable knowledge and experience from engineered nanoparticle (ENP) exposure assessment. This is achieved by comparing ENP and MPs based on their similarities as particulate contaminants, whereas critically discussing specific differences. We also highlight the most pressing research priorities to support an efficient development of tools and methods for MPs environmental risk assessment.

  • Sorbent material characterization using in-tube extraction needles as inverse gas chromatography column

    Xochitli L. Osorio Barajas, Maik A. Jochmann, Thorsten Hüffer, Beat Schilling, Torsten C. Schmidt
    2017 - Journal of Separation Science, 1: 2390-2397

    Abstract: 

    In‐tube extraction is a full automated enrichment technique that consists of a stainless‐steel needle, packed with sorbent material for the extraction of volatile and semivolatile compounds. In principle, all particulate sorbents used for enrichment in air or headspace analysis can be used. However, the selection of the sorbents is merely based on empirical considerations rather than on experimental data, which is caused by a lack of knowledge about the relevant physicochemical properties of the sorbent. Especially, the knowledge of hydrostatic, advective, diffusive, and dispersion mechanisms in addition to sorption enthalpies are important for combined transport and sorption models. To provide these missing parameters, we developed and evaluated a method in which an ordinary in‐tube extraction needle was employed directly as column for sorbent characterization by inverse gas chromatography. As probe compounds, benzene, ethyl acetate, and 3‐methyl‐1‐butanol were used to determine thermodynamic parameters such as sorption enthalpy, partitioning constant between the solid and gas phase, and kinetic parameters such as the diffusion coefficient, dispersion coefficient, and apparent permeability, exemplarily. As sorbent, three commercially available phases were characterized to demonstrate the applicability of the method.

  • Kunststoffe in aquatischen Umweltsystemen - Vorstellung einer neuen Fachausschusses

    Thorsten Hüffer, Nicole, B., Heß, M., Ivleva, N., Klein, S., Laforsch, C., Wagner M.
    2016 - Vom Wasser - das Journal, 26: in press
  • Pyrolysis of waste materials: Characterization and prediction of sorption potential across a wide range of mineral contents and pyrolysis temperatures

    Melanie Kah, Huichao Sun, Gabriel Sigmund, Thorsten Hüffer, Thilo Hofmann
    2016 - Bioresource Technology, 225-233

    Abstract: 

    Sewage sludge (50% mineral), manure (29%) and wood (<1%) were pyrolyzed at 200, 350 and 500 °C with the aim to study the characteristics and sorption potential of materials undergoing pyrolysis across a wide range of mineral contents. A commercial plant-derived biochar (41% mineral) was also considered. The materials were extensively characterized and tested for their sorption towards the model sorbates benzene, naphthalene and pyrene. Plant-derived materials, regardless of their mineral content, developed micropores causing size exclusion of pyrene. Changes in properties and sorption behavior upon pyrolysis were generally consistent for the manure and wood series. A single regression equation developed on our data (including the sorbate hydrophobicity and sorbent polarity) provided excellent prediction of previously reported changes in sorption upon pyrolysis across a wide range of mineral content (up to 500 °C). The sewage sludge series, however, followed a particular behavior, possibly due to very high mineral content (up to 67%).

  • Sorption of non-polar organic compounds by micro-sized plastic particles in aqueous solution

    2016 - Environmental Pollution, 194-201

    Abstract: 

    The presence of microscale polymer particles (i.e., microplastics) in the environment has become a major concern in recent years. Sorption of organic compounds by microplastics may affect the phase distribution within both sediments and aqueous phases. To investigate this process, isotherms were determined for the sorption of seven aliphatic and aromatic organic probe sorbates by four polymers with different physico-chemical properties. Sorption increased in the order polyamide < polyethylene < polyvinylchloride < polystyrene. This order does not reflect the particle sizes of the investigated microplastics within the aqueous dispersions, indicating the influence of additional factors (e.g., π-π-interactions) on the sorption of aromatic compounds by polystyrene. Linear isotherms by polyethylene suggested that sorbate uptake was due to absorption into the bulk polymer. In contrast, non-linear isotherms for sorption by PS, PA, and PVC suggest a predominance of adsorption onto the polymer surface, which is supported by the best fit of these isotherms using the Polanyi-Manes model. A strong relationship between the sorption coefficients of the microplastics and the hydrophobicity of the sorbates suggests that hydrophobic interactions are of major importance.

  • Influence of humic acids on sorption of alkanes by carbon nanotubes Implications for the dominant sorption mode

    Thorsten Hüffer, Sarah Schroth, Torsten C. Schmidt
    2015 - Chemosphere, 1169-1175

    Abstract: 

    The presence of humic substances (HS) has previously been shown to alter sorption properties of multi-walled carbon nanotubes (MWCNTs). To systematically study this process, three alkane pairs were selected as molecular probe sorbates. The influence of HS on sorption affinity, sorption linearity, and the dominant sorption mode (i.e., ad- or absorption) by MWCNTs was investigated. The addition of HS led to a continuous decrease in sorption affinity and an increase in sorption linearity with increasing HS addition. Furthermore, the comparison of distribution coefficients of n- and cycloalkanes showed that the dominant sorption mode remains to be adsorption regardless of the presence of HS on MWCNT surface. From this, it can be concluded that instead of a change in sorption mode to absorption of sorbates into HS-coated MWCNT, HS blocks high-energy sorption sites for subsequently added sorbates and that sorbates continuously sorb on the MWCNT surface.

  • Prediction of sorption of aromatic and aliphatic organic compounds by carbon nanotubes using poly-parameter linear free-energy relationships

    Thorsten Hüffer, Satoshi Endo, Florian Metzelder, Sarah Schroth, Torsten C. Schmidt
    2014 - Water Research, 295-303

    Abstract: 

    The accurate prediction of distribution coefficients of organic compounds from water to carbon-based nanomaterials (CNM) is of major importance for the understanding of environmental processes and a risk assessment of released CNM. Poly-parameter linear free-energy relationships (ppLFER) have previously been shown to offer such an accurate prediction of sorption processes. The aim of this study was to identify and quantify the contribution of individual molecular interactions to overall sorption by multi-walled carbon nanotubes (MWCNTs). To this end, a large data set of experimental sorption isotherms by MWCNTs of 20 aliphatic and 14 aromatic compounds covering various relevant molecular interactions was produced. A thermodynamic cycle was used to obtain MWCNT-air distribution coefficients (KMWCNT/a) for the interpretation of direct sorbate-MWCNTs interactions. The thereby derived ppLFER log KMWCNT/a = (0.59 ± 0.59)E + (2.23 ± 0.59)S + (3.90 ± 0.67)A + (3.23 ± 0.71)B + (0.98 ± 0.17)L − (0.05 ± 0.50) shows the contribution of non-specific interactions, represented by the hexadecane-air partitioning constant (L), and specific interactions related to the solute polarity (S) as well as the H-bond interactions (A, B). Measured MWCNT-water distribution coefficients were clearly more accurately calculated by the ppLFER equations (R20.85–0.86) compared to the classical prediction by single parameter model based on the octanol–water partitioning constant (R2 0.64–0.78). In addition, the ppLFER presented here allow a more accurately prediction of sorption by MWCNTs compared to literature ppLFER, especially for aliphatic compounds and at environmentally relevant concentrations.

  • How Redox Conditions and Irradiation Affect Sorption of PAHs by Dispersed Fullerenes (nC60)

    Thorsten Hüffer, Melanie Kah, Thilo Hofmann, Torsten C. Schmidt
    2013 - Environmental Science & Technology, 1: 6935-6942

    Abstract: 

    Surface properties, dispersion state, and sorption behavior of carbon-based nanomaterials will change after being released into the environment. To study these processes, five different scenarios were considered to probe the impact of changes in surface properties of dispersed fullerenes (nC60) on their sorption potential due to irradiation and presence of oxygen. Sorption isotherms of pyrene by nC60 were determined at environmentally relevant concentrations applying a passive sampling method. Isotherms of all dispersion scenarios were best fit with the Dubinin–Ashthakov model. Sorption was strongest for nC60 kept under anoxic condition. Both the presence of oxygen and irradiation significantly decreased the sorption capacity of nC60, while commercially available polyhydroxy fullerenes had the smallest sorption. In addition, competition for sorption sites was never observed in multiple sorbate experiments with four polycyclic aromatic hydrocarbons at small concentration. A strong relationship between sorption coefficients and hydrophobic properties of sorbates suggests that hydrophobic interactions are of major importance. The results emphasize that aging of released fullerenes results in a reduced strength of interactions with nonpolar compounds and, thus, reduces the impact on the environmental transport of hydrophobic pollutants.

  • Multi-walled carbon nanotubes as sorptive material for solventless in-tube microextraction (ITEX2)-a factorial design study

    Thorsten Hüffer, Xochitli L. Osorio, Maik A. Jochmann, Beat Schilling, Torsten C. Schmidt
    2013 - Analytical and Bioanalytical Chemistry, 2: 8387-8395

    Abstract: 

    Multi-walled carbon nanotubes were evaluated as sorptive packing material for in-tube microextraction (ITEX2) in combination with GC-MS for the analysis of benzene, toluene, ethylbenzene, xylenes, and naphthalene in aqueous samples. For method development, a three-level full factorial design of experiment (DoE) was performed incorporating extraction temperature, number of extraction strokes, and extraction flow. The statistical analysis of method development showed that all considered extraction parameters significantly affected the extraction yield. Furthermore, it was shown that some factors significantly interacted with each other, which indicates the advantage of using DoE for method development. The thereby optimized ITEX2 protocol was validated regarding its linear dynamic range, method detection limit (MDL), and precision. The MDLs of investigated analytes ranged between 2 ng L−1 for naphthalene and 11 ng L−1 for p-xylene. The relatively low MDL obtained for naphthalene, despite its comparably low air–water partitioning, can be explained by its strong interaction with carbon nanotubes. All obtained MDLs are at least comparable to previous reports on microextraction techniques, emphasizing both the quality of ITEX2 and the highly promising sorbent characteristics of carbon nanotubes. Furthermore, the method was applied to three real samples, which demonstrated good recoveries of analytes from tap water, a bank filtrate, and an effluent from a wastewater treatment plant.

Book chapters and other publications

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

    Gabriel Sigmund, Mehdi Gharasoo, Thorsten Hüffer, Thilo Hofmann
    2020 - Environmental Science & Technology, A-B
  • Response to the Letter to the Editor Regarding Our Feature “Are We Speaking the Same Language? Recommendations for a Definition and Categorization Framework for Plastic Debris”

    Nanna B. Hartmann, Thorsten Hüffer, Richard C. Thompson, Martin Hassellöv, Anja Verschoor, Anders E. Daugaard, Sinja Rist, Therese Karlsson, Nicole Brennholt, Matthew Cole, Maria P. Herrling, Maren C. Hess, Natalia P. Ivleva, Amy L. Lusher, Martin Wagner
    2019 - Environmental Science & Technology, 53: 4678−4679