Jan Köser

The coating makes the difference: Acute effects of iron oxide nanoparticles on Daphnia magna

The surface of nanoparticles (NP) is often functionalized with a capping agent to increase their colloidal stability. Having a strong effect on the characteristics of NP, the coating might already determine the risk from NP to organisms and the environment. In this study identical iron oxide nanoparticles (IONP; Ø 5-6nm) were functionalized with four different coatings: ascorbate (ASC-IONP), citrate (CIT-IONP), dextran (DEX-IONP), and polyvinylpyrrolidone (PVP-IONP). Ascorbate and citrate stabilize NP via electrostatic repulsion whereas dextran and polyvinylpyrrolidone are steric stabilizers. All IONP were colloidally stable over several weeks. Their acute effects on neonates of the waterflea Daphnia magna were investigated over 96h. The highest immobilizing effect was found for ASC- and DEX-IONP. In the presence of neonates, both agglomerated or flocculated and adsorbed to the carapace and filtering apparatuses, inducing high immobilization. Lower immobilization was found for CIT-IONP. Their effect was hypothesized to partly originate from an increased release of dissolved iron and the ability to form reactive oxygen species (ROS). Furthermore, incomplete ecdysis occurred at high concentrations of ASC-, DEX-, and CIT-IONP. PVP-IONP did not induce any negative effect, although high quantities were visibly ingested by the daphnids. PVP-IONP had the highest colloidal stability without any occurring agglomeration, adsorption, or dissolution. Only strong swelling of the PVP coating was observed in medium, highly increasing the hydrodynamic diameter. Each coating caused individual effects. Toxicity cannot be correlated to hydrodynamic diameter or the kind of stabilizing forces. Effects are rather linked to decreasing colloidal stability, the release of ions from the core material or the ability to form ROS, respectively.

Influences of use activities and waste management on environmental releases of engineered nanomaterials.

Engineered nanomaterials (ENM) offer enhanced or new functionalities and properties that are used in various products. This also entails potential environmental risks in terms of hazard and exposure. However, hazard and exposure assessment for ENM still suffer from insufficient knowledge particularly for product-related releases and environmental fate and behavior. This study therefore analyzes the multiple impacts of the product use, the properties of the matrix material, and the related waste management system (WMS) on the predicted environmental concentration (PEC) by applying nine prospective life cycle release scenarios based on reasonable assumptions. The products studied here are clothing textiles treated with silver nanoparticles (AgNPs), since they constitute a controversial application. Surprisingly, the results show counter-intuitive increases by a factor of 2.6 in PEC values for the air compartment in minimal AgNP release scenarios. Also, air releases can shift from washing to wearing activity; their associated release points may shift accordingly, potentially altering release hot spots. Additionally, at end-of-life, the fraction of AgNP-residues contained on exported textiles can be increased by 350% when assuming short product lifespans and globalized WMS. It becomes evident that certain combinations of use activities, matrix material characteristics, and WMS can influence the regional PEC by several orders of magnitude. Thus, in the light of the findings and expected ENM market potential, future assessments should consider these aspects to derive precautionary design alternatives and to enable prospective global and regional risk assessments.

Biodegradability of fluoroorganic and cyano-based ionic liquid anions under aerobic and anaerobic conditions

The present study deals with the primary biodegradability of ionic liquids in order to obtain a greater insight into their fate under different environmental conditions. The focus was thereby on the biodegradation potential of ionic liquid anions when undergoing aerobic and anaerobic biological waste water treatment. Five technologically relevant fluoroorganic and cyano-based ionic liquid anions were investigated as alkaline salts (Li (CF3SO2)2N, K (C2F5)3PF3 and Na N(CN)2, K C(CN)3, K B(CN)4 respectively). Their biodegradability was determined in activated sludge over a period of around 60 days by specific analysis of the anion using ion chromatography. Additionally, the antimicrobial activity of the test compounds towards the activated sludge organisms was tested in inhibition studies. Because of the technologically desirable chemical, thermal and electrochemical stability of these anions, their biodegradability is questioned. The results seem to support the hypothesis: although the concentrations used did not inhibit the inoculum, none of these anions could be biodegraded under either aerobic or denitrifying conditions. The present paper provides information concerning the biodegradability of ionic liquids in waste water treatment plants and gives a first systematic view of the aerobic and anaerobic biodegradability of fluoroorganic and cyano-based ionic liquid anions and therefore supports further hazard assessment.

Safe-by-Design CuO Nanoparticles via Fe-Doping, Cu–O Bond Length Variation, and Biological Assessment in Cells and Zebrafish Embryos

The safe implementation of nanotechnology requires nanomaterial hazard assessment in accordance with the material physicochemical properties that trigger the injury response at the nano/bio interface. Since CuO nanoparticles (NPs) are widely used industrially and their dissolution properties play a major role in hazard potential, we hypothesized that tighter bonding of Cu to Fe by particle doping could constitute a safer-by-design approach through decreased dissolution. Accordingly, we designed a combinatorial library in which CuO was doped with 1-10% Fe in a flame spray pyrolysis reactor. The morphology and structural properties were determined by XRD, BET, Raman spectroscopy, HRTEM, EFTEM, and EELS, which demonstrated a significant reduction in the apical Cu-O bond length while simultaneously increasing the planar bond length (Jahn-Teller distortion). Hazard screening was performed in tissue culture cell lines and zebrafish embryos to discern the change in the hazardous effects of doped vs nondoped particles. This demonstrated that with increased levels of doping there was a progressive decrease in cytotoxicity in BEAS-2B and THP-1 cells, as well as an incremental decrease in the rate of hatching interference in zebrafish embryos. The dissolution profiles were determined and the surface reactions taking place in Holtfreters solution were validated using cyclic voltammetry measurements to demonstrate that the Cu+/Cu2+ and Fe2+/Fe3+ redox species play a major role in the dissolution process of pure and Fe-doped CuO. Altogether, a safe-by-design strategy was implemented for the toxic CuO particles via Fe doping and has been demonstrated for their safe use in the environment.

Silver nanoparticle-doped zirconia capillaries for enhanced bacterial filtration

Abstract Membrane clogging and biofilm formation are the most serious problems during water filtration. Silver nanoparticle (Agnano) coatings on filtration membranes can prevent bacterial adhesion and the initiation of biofilm formation. In this study, Agnano are immobilized via direct reduction on porous zirconia capillary membranes to generate a nanocomposite material combining the advantages of ceramics being chemically, thermally and mechanically stable with nanosilver, an efficient broadband bactericide for water decontamination. The filtration of bacterial suspensions of the fecal contaminant Escherichia coli reveals highly efficient bacterial retention capacities of the capillaries of 8 log reduction values, fulfilling the requirements on safe drinking water according to the U.S. Environmental Protection Agency. Maximum bacterial loading capacities of the capillary membranes are determined to be 3×109 bacterialcells/750mm2 capillary surface until back flushing is recommendable. The immobilized Agnano remain accessible and exhibit strong bactericidal properties by killing retained bacteria up to maximum bacterial loads of 6×108 bacterialcells/750mm2 capillary surface and the regenerated membranes regain filtration efficiencies of 95–100%. Silver release is moderate as only 0.8% of the initial silver loading is leached during a three-day filtration experiment leading to average silver contaminant levels of 100μg/L.

Toxicity of dimercaptosuccinate-coated and un-functionalized magnetic iron oxide nanoparticles towards aquatic organisms

Magnetic iron oxide nanoparticles (IONP) have gained growing attention in recent years for their promising applications in medical treatment and environmental remediation. Among the IONP, dimercaptosuccinic acid coated-IONP (DMSA-IONP) have great potential because of their rapid uptake into cells and their potential to effectively adsorb heavy metals. The widespread use and potential release of IONP into the environment raises concern about their environmental impact. To date, little is known about the consequences of the exposure of aquatic organisms to such particles. In this context we investigated the colloidal stability of DMSA-IONP in different test media as well as their effects on green algae (Raphidocelis subcapitata), duckweed (Lemna minor) and water fleas (Daphnia magna). Moreover, a comparative analysis of stability and ecotoxicity data of DMSA-IONP with freshly prepared and aged uncoated IONP dispersions was performed, considering the importance of stability of particles in determining their toxicity. The green algae were the most sensitive organism with EC50 values (72 h) ranging between 0.86–2.27 μM Fe (i.e. 0.05 to 0.13 mg Fe L−1) for the three types of IONP. The observed flocculation and (co-)sedimentation of algae with IONP are assumed to reduce the access of cells to nutrients and light. Lemna was not affected by any of the IONP due to the low availability of IONP induced by fast aggregation of IONP in the medium. Minor toxic effects on Daphnia were found for uncoated IONP (EC50 between 374–1181 μM Fe, i.e. 21–66 mg Fe L−1) after 72 h. However, the ingestion and accumulation of coated and uncoated IONP in the gastrointestinal tract of daphnids was observed. Our evaluation of IONP has revealed a certain hazard potential to aquatic organisms. In this light it appears important to prevent the release of large amounts of IONP into the environment, which might limit their applicability.

A miniaturized solid contact test with Arthrobacter globiformis for the assessment of the environmental impact of silver nanoparticles.

Silver nanoparticles (AgNPs) are widely applied for their antibacterial activity. Their increasing use in consumer products implies that they will find their way into the environment via wastewater-treatment plants. The aim of the present study was to compare the ecotoxicological impact of 2 differently designed AgNPs using the solid contact test for the bacterial strain Arthrobacter globiformis. In addition, a miniaturized version of this test system was established, which requires only small-sized samples because AgNPs are produced in small quantities during the design level. The results demonstrate that the solid contact test can be performed in 24-well microplates and that the miniaturized test system fulfills the validity criterion. Soils spiked with AgNPs showed a concentration-dependent reduction of Arthrobacter dehydrogenase activity for both AgNPs and Ag ions (Ag(+)). The toxic effect of the investigated AgNPs on the bacterial viability differed by 1 order of magnitude and can be related to the release of dissolved Ag(+). The release of dissolved Ag(+) can be attributed to particle size and surface area or to the fact that AgNPs are in either metallic or oxide form. Environ

Light Scattering Simulation and Measurement of Monodisperse Spheroids using a Phase Doppler Anemometer

Mathematical tools are provided for the computation of the scattered field produced by non-spherical particles moving through the measurement volume of a phase Doppler anemometer. The phase distribution of a spheroid with random orientation is computed by using the rigorous extended boundary condition method and the ray theory. In a phase Doppler experiment the spheroid parameters are obtained by fitting the measured phase distribution with the simulated phase distribution. The numerical simulations are supported by experimental results on monodisperse spheroids.

Predictability of silver nanoparticle speciation and toxicity in ecotoxicological media

The use of silver nanoparticles (AgNPs) as an antimicrobial agent has increased significantly over the past decade which potentiates their release to the environment. The antimicrobial effect of AgNPs is generally considered to be due to the release of silver ions (Ag+). Here we describe their bioavailability under environmental conditions and demonstrate its influence on (eco-)toxicity for the AgNP NM-300K and a wide variety of aquatic organisms (green algae, plants and crustaceans), terrestrial organisms (soil bacteria) and mammalian cells. Since the bioavailability of AgNPs is largely determined by Ag speciation, this paper focuses on the Ag speciation in the test media for these organisms. We predicted the Ag speciation in aqueous test media by equilibrium speciation calculation and validated the results by comparison with experimental speciation using ultracentrifugation and membrane filtration. Silver amounts were quantified using GF-AAS, ICP-OES/MS and UV-vis. The dissolved Ag concentrations were controlled by the fast initial release of a limited amount of Ag+. After this initial release, the media components, chloride and proteins, controlled the available dissolved Ag by precipitation and complexation. Further release of Ag+ due to oxidation was not observed in the time frame of our experiments, except for media with very high chloride content. Apparently, the stabilisers of these AgNPs prevented any further release accounting for an enhanced redox stability. These findings facilitated the prediction of the bioavailability of Ag in the test media and, based on literature toxicity data, also of its toxic effects (EC50) on the respective organisms. The toxic effects of the AgNP NM-300K depended solely on the amount of Ag+ that was already present in the stock dispersion and not from further release due to later oxidation processes.

Collembola Reproduction Decreases with Aging of Silver Nanoparticles in a Sewage Sludge-Treated Soil

Silver nanoparticles (AgNP) are integrated into various products due to their antimicrobial characteristics and hence, the application of AgNP is increasing. During production, use and disposal AgNP are emitted and enter the environment via several pathways. Soils are considered a major sink of AgNP. The aim of the present study was to determine the toxic effect of AgNP on Folsomia candida reproduction to illustrate potential impact on terrestrial ecosystems. The AgNP-dependent reduction of F. candida reproduction was studied in RefeSol 01-A, LUFA 2.2 and OECD soil at 0.3 µg – 50 mg Ag kg-1. To simulate realistic exposure pathways, effects on F. candida reproduction after the application of AgNP via sewage sludge and after aging this treatment in the soil for up to 140 days were studied using environmentally relevant concentrations. The OECD representative AgNP, NM-300K, and AgNO3, as a metal salt reference, were used in all experiments. The generated data demonstrate that the presence of AgNP in the soil in the low mg Ag kg-1 concentration range results in significant, but concentration independent inhibition of F. candida reproduction in RefeSol 01-A and LUFA 2.2. Significant inhibition of F. candida reproduction due to AgNP was also observed for soil amended with AgNP treated sludge. An increase in inhibition with aging of the AgNP in the soil was evident. In conclusion, our results demonstrate that, at environmentally relevant concentrations, AgNP adsorption to sludge and subsequent aging in soil lead to a toxic effect on soil invertebrates.