Physical-chemical characterization of tungsten carbide nanoparticles as a basis for toxicological investigations

Cytotoxicity, Accumulation and Translocation of Silver and Silver Sulfide Nanoparticles in contact with Rainbow Trout Intestinal Cells

Silver nanoparticles (Ag NPs) are widely used in consumer products especially because of their antimicrobial properties. However, this wide usage of Ag NPs is accompanied by their release into the environment where they will be rapidly transformed to other silver species - especially silver sulfide (Ag₂S). In the present study, we synthesized Ag NPs and sulfidized them to obtain a core-shell system Ag@Ag₂S NPs. Both types of particles form stable dispersions with hydrodynamic diameters of less than 100 nm when diluted in water, but tend to form micrometer-sized agglomerates in biological exposure media. Application of Ag and Ag@Ag₂S NPs to rainbow trout intestinal cells (RTgutGC) resulted in a concentration-dependent cytotoxicity for both types of particles, as assessed by a three-endpoint assay for metabolic activity, membrane integrity and lysosomal integrity. The Ag NPs were shown to be slightly more toxic than the Ag@Ag₂S NPs. Adding Ag or Ag@Ag₂S NPs to RTgutGC cells, grown on a permeable membrane to mimic the intestinal barrier, revealed considerable accumulation of silver for both types of particles. Indeed, the cells significantly attenuated the NP translocation, allowing only a fraction of the metal to translocate across the intestinal epithelium. These findings support the notion that the intestine constitutes an important sink for Ag NPs and that, despite the reduced cytotoxicity of a sulfidized NP form, the particles can enter fish where they may constitute a long-term source for silver ion release and cytotoxicity.

Particle Size and Pre-Treatment Effects on Polystyrene Microplastic Settlement in Water: Implications for Environmental Behavior and Ecotoxicological Tests

Microplastic (MP) particle dispersions used in many recent publications covering adsorption or toxicological studies are not characterized very well. The size distribution of polydisperse dispersions is highly dependent on the agglomeration processes and influences experimental outcomes. Therefore, pre-treatment is a prerequisite for reproducibility. In this study, manual/automated shaking and ultrasonic treatment as different mechanical dispersion techniques were applied for the dispersion of cryomilled polystyrene (PS). Particle numbers and size distribution of dispersions were analyzed by a light extinction particle counter and the dispersion efficiency (ED) as the ratio between calculated volume and theoretical volume of suspended particles was used to compare techniques. PS dispersions (20 mg/L) treated for 90 min in an ultrasonic bath (120 W, 35 kHz) were evenly dispersed with a particle concentration of 140,000 particles/mL and a high reproducibility (rel. SD = 2.1%, n = 6). Automated horizontal shaking for 754 h (250 rpm) reached similar particle numbers (122,000/mL) but with a lower reproducibility (rel. SD = 9.1%, n = 6). Manual shaking by hand dispersed the lowest number of particles (55,000/mL) and was therefore found to be unsuitable to counteract homo-agglomeration. ED was calculated as 127%, 104% and 69% for ultrasonic treatment, horizontal shaking and manual shaking, respectively, showing an overestimation of volume assuming spherical shaped particles.

Assessing the bioactivity of crystalline silica in heated high-temperature insulation wools

High-Temperature Insulation Wools (HTIW), such as alumino silicate wools (Refractory Ceramic Fibers) and Alkaline Earth Silicate wools, are used in high-temperature industries for thermal insulation. These materials have an amorphous glass-like structure. In some applications, exposure to high temperatures causes devitrification resulting in the formation of crystalline species including crystalline silica. The formation of this potentially carcinogenic material raises safety concerns regarding after-use handling and disposal. This study aims to determine whether cristobalite formed in HTIW is bioactive in vitro. Mouse macrophage (J774A.1) and human alveolar epithelial (A549) cell lines were exposed to pristine HTIW of different compositions, and corresponding heat-treated samples. Cell death, cytokine release, and reactive oxygen species (ROS) formation were assessed in both cell types. Cell responses to aluminum lactate-coated fibers were assessed to determine if responses were caused by crystalline silica. DQ12 α-quartz was used as positive control, and TiO₂ as negative control. HTIW did not induce cell death or intracellular ROS, and their ability to induce pro-inflammatory mediator release was low. In contrast, DQ12 induced cytotoxicity, a strong pro-inflammatory response and ROS generation. The modest pro-inflammatory mediator responses of HTIW did not always coincide with the formation of cristobalite in heated fibers; therefore, we cannot confirm that devitrification of HTIW results in bioactive cristobalite in vitro. In conclusion, the biological responses to HTIW observed were not attributable to a single physicochemical characteristic; instead, a combination of physicochemical characteristics (cristobalite content, fiber chemistry, dimensions and material solubility) appear to contribute to induction of cellular responses.

Cellular uptake and intracellular localization of poly (acrylic acid) nanoparticles in a rainbow trout (Oncorhynchus mykiss) gill epithelial cell line, RTgill-W1

The ever-growing production of engineered nanoparticles (NPs) for use in many agricultural, commercial, consumer, and industrial applications will lead to their accidental or intentional release into the environment. Potential routes of environmental exposure include manufacturing or transport spills, disposal of NP-containing products down the drain and/or in landfills, as well as direct usage on agricultural land. Therefore, NPs will inevitably contaminate aquatic environments and interact with resident organisms. However, there is limited information regarding the mechanisms that regulate NP transport into fish from the environment. Thus, our primary objective was to elucidate the mechanism(s) underlying cellular uptake and intracellular fate of 3-9nm poly (acrylic acid) NPs loaded with the fluorescent dye Nile red using a rainbow trout (Oncorhynchus mykiss) gill epithelial cell line (RTgill-W1). In vitro measurements with NP-treated RTgill-W1 cells were carried out using a combination of laser scanning confocal microscopy, flow cytometry, fluorescent biomarkers (transferrin, cholera toxin B subunit, and dextran), endocytosis inhibitors (chlorpromazine, genistein, and wortmannin), and stains (4', 6-diamidino-2-phenylindole, Hoechst 33342, CellMask Deep Red, and LysoTracker Yellow). Clathrin-mediated endocytosis (CME), caveolae-mediated endocytosis and macropinocytosis pathways were active in RTgill-W1 cells, and these pathways were exploited by the non-cytotoxic NPs to enter these cells. We have demonstrated that NP uptake by RTgill-W1 cells was impeded when clathrin-coated pit formation was blocked by chlorpromazine. Furthermore, colocalization analysis revealed a moderate positive relationship between NPs and LysoTracker Yellow-positive lysosomal compartments indicating that CME was the dominant operative mechanism involved in NP internalization by RTgill-W1 cells. Overall, our results clearly show that fish gill epithelial cells internalized NPs via energy-dependent endocytotic processes. This study enhances our understanding of complex NP-cell interactions and the results obtained in vitro imply a potential risk to aquatic organisms.

From the sea to the laboratory: Characterization of microplastic as prerequisite for the assessment of ecotoxicological impact

The presence of microplastic (MP) in the aquatic environment is recognized as a global-scale pollution issue. Secondary MP particles result from an ongoing fragmentation process governed by various biotic and abiotic factors. For a reliable risk assessment of these MP particles, knowledge about interactions with biota is needed. However, extensive testing with standard organisms under reproducible laboratory conditions with well-characterized MP suspensions is not available yet. As MP in the environment represents a mixture of particles differing in properties (e.g., size, color, polymer type, surface characteristics), it is likely that only specific particle fractions pose a threat towards organisms. In order to assign hazardous effects to specific particle properties, these characteristics need to be analyzed. As shown by the testing of particles (e.g. nanoparticles), characteristics other than chemical properties are important for the emergence of toxicity in organisms, and parameters such as surface area or size distribution need consideration. Therefore, the use of "well-defined" particles for ecotoxicological testing (i.e., standard particles) facilitates the establishment of causal links between physical-chemical properties of MP particles and toxic effects in organisms. However, the benefits of well-defined particles under laboratory conditions are offset by the disadvantage of the unknown comparability with MP in the environment. Therefore, weathering effects caused by biological, chemical, physical or mechanical processes have to be considered. To date, the characterization of the progression of MP weathering based on powder and suspension characterization methods is in its infancy. The aim of this commentary is to illustrate the prerequisites for testing MP in the laboratory from 3 perspectives: (i) knowledge of particle properties; (ii) behavior of MP in test setups involving ecotoxicological test organisms; and (iii) accordingly, test conditions that may need adjustment. Only under those prerequisites will reliable hazard assessment of MP be feasible. Integr Environ Assess Manag 2017;13:500-504. © 2017 SETAC.

Silver nanoparticles inhibit fish gill cell proliferation in protein-free culture medium

While short-term exposures of vertebrate cells, such as from fish, can be performed in defined, serum-free media, long-term cultures generally require addition of growth factors and proteins, normally supplied with a serum supplement. However, proteins are known to alter nanoparticle properties by binding to nanoparticles. Therefore, in order to be able to study nanoparticle-cell interactions for extended periods, the rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1, was adapted to proliferate in a commercial, serum-free medium, InVitrus VP-6. The newly adapted cell strain was named RTgill-W1-pf (protein free). These cells proliferate at a speed similar to the RTgill-W1 cells cultured in a fully supplemented medium containing 5% fetal bovine serum. As well, they were successfully cryopreserved in liquid nitrogen and fully recovered after thawing. Yet, senescence set in after about 10 passages in InVitrus VP-6 medium, revealing that this medium cannot fully support long-term culture of the RTgill-W1 strain. The RTgill-W1-pf cell line was subsequently applied to investigate the effect of silver nanoparticles (AgNP) on cell proliferation over a period of 12 days. Indeed, cell proliferation was inhibited by 10 μM AgNP. This effect correlated with high levels of silver being associated with the cells. The new cell line, RTgill-W1-pf, can serve as a unique representation of the gill cell-environment interface, offering novel opportunities to study nanoparticle-cell interactions without serum protein interference.

Towards sensible toxicity testing for nanomaterials: proposal for the specification of test design

During the last decade, nanomaterials (NM) were extensively tested for potential harmful effects towards humans and environmental organisms. However, a sound hazard assessment was so far hampered by uncertainties and a low comparability of test results. The reason for the low comparability is a high variation in the (1) type of NM tested with regard to raw material, size and shape and (2) procedures before and during the toxicity testing. This calls for tailored, nanomaterial-specific protocols. Here, a structured approach is proposed, intended to lead to test protocols not only tailored to specific types of nanomaterials, but also to respective test system for toxicity testing. There are existing standards on single procedures involving nanomaterials, however, not all relevant procedures are covered by standards. Hence, our approach offers a detailed way of weighting several plausible alternatives for e.g. sample preparation, in order to decide on the procedure most meaningful for a specific nanomaterial and toxicity test. A framework of several decision trees (DT) and flow charts to support testing of NM is proposed as a basis for further refinement and in-depth elaboration. DT and flow charts were drafted for (1) general procedure-physicochemical characterisation, (2) choice of test media, (3) decision on test scenario and application of NM to liquid media, (4) application of NM to the gas phase, (5) application of NM to soil and sediments, (6) dose metrics, (S1) definition of a nanomaterial, and (S2) dissolution. The applicability of the proposed approach was surveyed by using experimental data retrieved from studies on nanoscale CuO. This survey demonstrated the DT and flow charts to be a convenient tool to systematically decide upon test procedures and processes, and hence pose an important step towards harmonisation of NM testing.

The oxidized state of the nanocomposite Carbo-Iron® causes no adverse effects on growth, survival and differential gene expression in zebrafish

For degradation of halogenated chemicals in groundwater Carbo-Iron®, a composite of activated carbon and nano-sized Fe(0), was developed (Mackenzie et al., 2012). Potential effects of this nanocomposite on fish were assessed. Beyond the contaminated zone Fe(0) can be expected to have oxidized and Carbo-Iron was used in its oxidized form in ecotoxicological tests. Potential effects of Carbo Iron in zebrafish (Danio rerio) were investigated using a 48 h embryo toxicity test under static conditions, a 96 h acute test with adult fish under semi-static conditions and a 34 d fish early life stage test (FELST) in a flow-through system. Particle diameters in test suspensions were determined via dynamic light scattering (DLS) and ranged from 266 to 497 nm. Particle concentrations were measured weekly in samples from the FELST using a method based on the count rate in DLS. Additionally, uptake of particles into test organisms was investigated using microscopic methods. Furthermore, effects of Carbo-Iron on gene expression were investigated by microarray analysis in zebrafish embryos. In all tests performed, no significant lethal effects were observed. Furthermore, Carbo-Iron had no significant influence on weight and length of fish as determined in the FELST. In the embryo test and the early life stage test, growth of fungi on the chorion was observed at Carbo-Iron concentrations between 6.3 and 25mg/L. Fungal growth did not affect survival, hatching success and growth. In the embryo test, no passage of Carbo-Iron particles into the perivitelline space or the embryo was observed. In juvenile and adult fish, Carbo-Iron was detected in the gut at the end of exposure. In juvenile fish exposed to Carbo-Iron for 29 d and subsequently kept for 5d in control water, Carbo-Iron was no longer detectable in the gut. Global gene expression in zebrafish embryos was not significantly influenced by Carbo-Iron.

Toxicity of silver nanoparticles to a fish gill cell line: role of medium composition

In aqueous solutions, silver nanoparticle (AgNP) behavior is affected by a variety of factors which lead to altered AgNP size and toxicity. Our research aims to explore the effect of media composition on citrate-coated AgNP (cit-AgNP) behavior and toxicity to the cell line from rainbow trout (Oncorhynchus mykiss) gill, RTgill-W1. Three different exposure media (L15/ex, L15/ex w/o Cl and d-L15/ex) were used. These were characterized by varying ionic strength and chloride content, both of which had a dominant effect on the behaviour of cit-AgNP. Comparing the behaviour and toxicity of cit-AgNP in the different media, stronger agglomeration of cit-AgNP correlated with higher toxicity. Deposition of cit-AgNP on cells might explain the higher toxicity of agglomerated cit-AgNP compared to that of suspended cit-AgNP. The cit-AgNP concentration-response curves as a function of dissolved silver ions, and the limited prevention of toxicity by silver ligands, indicated that cit-AgNP elicited a particle-specific effect on the cells. Furthermore, the lysosomal membrane integrity was significantly more sensitive to cit-AgNP exposure than cellular metabolic activity or cell membrane integrity and showed the weakest protection by silver ligands. This revealed that cit-AgNP toxicity seems to particularly act on RTgill-W1 cell lysosomes. The newly developed low ionic strength medium, d-L15/ex, which can stabilize cit-AgNP and better mimic the freshwater environment, offers an excellent exposure solution to study cellular and molecular effects of NP to gill cells.

Quantification of Al2O3 nanoparticles in human cell lines applying inductively coupled plasma mass spectrometry (neb-ICP-MS, LA-ICP-MS) and flow cytometry-based methods

In order to quantify and compare the uptake of aluminum oxide nanoparticles of three different sizes into two human cell lines (skin keratinocytes (HaCaT) and lung epithelial cells (A549)), three analytical methods were applied: digestion followed by nebulization inductively coupled plasma mass spectrometry (neb-ICP-MS), direct laser ablation ICP-MS (LA-ICP-MS), and flow cytometry. Light and electron microscopy revealed an accumulation and agglomeration of all particle types within the cell cytoplasm, whereas no particles were detected in the cell nuclei. The internalized Al₂O₃ particles exerted no toxicity in the two cell lines after 24 h of exposure. The smallest particles with a primary particle size (x_BET) of 14 nm (Alu1) showed the lowest sedimentation velocity within the cell culture media, but were calculated to have settled completely after 20 h. Alu2 (x_BET = 111 nm) and Alu3 (x_BET = 750 nm) were calculated to reach the cell surface after 7 h and 3 min, respectively. The internal concentrations determined with the different methods lay in a comparable range of 2-8 µg Al₂O₃/cm² cell layer, indicating the suitability of all methods to quantify the nanoparticle uptake. Nevertheless, particle size limitations of analytical methods using optical devices were demonstrated for LA-ICP-MS and flow cytometry. Furthermore, the consideration and comparison of particle properties as parameters for particle internalization revealed the particle size and the exposure concentration as determining factors for particle uptake.

Testing nanomaterial toxicity in unicellular eukaryotic algae and fish cell lines

Nanoecotoxicology as a sub-discipline of ecotoxicology aims to identify and predict effects elicited on ecosystems by nano-sized materials (NM). Two key groups of model organisms in this context are algae and fish. In this chapter, we present considerations for testing NM with respect to their impact on unicellular algae and cell lines derived from various organs of fish.Based on currently available literature on NM effects in unicellular algae and fish cell lines, and our own experience, we provide guidance on test design, including principle test considerations, materials, NM presentation to cells, exposure, bioavailability, and effect assessment. Assessment needs to be based on a meaningful choice of exposure scenario(s) related to the research question. As a first step, one needs to address whether effects of NMs are to be investigated under environmentally relevant or probable conditions, which may include processes such as agglomeration, or whether NM effects from mono-dispersed particles are of interest, which may require special steps to ensure stable NM suspension. Moreover, whether effects on cells are to be studied in the short- or long-term is important with regard to experimental design. Preparation of NM suspensions, which can be done in aqueous media different from the exposure medium, is addressed with regard to energy input, sterility (as required for algae and fish cell exposure) and particle purity.Specified for the two model systems, algae and fish cell lines, availability and choice of culture media are presented and discussed with regard to impact on NM behavior. Light, temperature, and agitation, which are variables during exposure, are discussed. We further provide guidance on the characterization of the NM in the chosen aqueous exposure media regarding size, zeta potential and electrophoretic mobility. The state of NM in exposure media is decisive for their bioavailability and therefore for potential particle effects. Therefore, we present ways of deriving a mass balance and quantitative/qualitative information on the uptake and distribution of NM in cells.As NM have a high surface-to-volume ratio and possess specific physical-chemical properties, which make them prone to interfere with various compounds and certain types of toxicity tests, potential interferences and appropriate controls are introduced. Furthermore, different types of dose metrics, which is still a strongly debated issue in nanotoxicology, are highlighted. We also consider laboratory safety regarding NM handling and disposal.

Comparative evaluation of particle properties, formation of reactive oxygen species and genotoxic potential of tungsten carbide based nanoparticles in vitro

Tungsten carbide (WC) and cobalt (Co) are constituents of hard metals and are used for the production of extremely hard tools. Previous studies have identified greater cytotoxic potential of WC-based nanoparticles if particles contained Co. The aim of this study was to investigate whether the formation of reactive oxygen species (ROS) and micronuclei would help explain the impact on cultured mammalian cells by three different tungsten-based nanoparticles (WC(S), WC(L), WC(L)-Co (S: small; L: large)). The selection of particles allowed us to study the influence of particle properties, e.g. surface area, and the presence of Co on the toxicological results. WC(S) and WC(L)/WC(L)-Co differed in their crystalline structure and surface area, whereas WC(S)/WC(L) and WC(L)-Co differed in their cobalt content. WC(L) and WC(L)-Co showed neither a genotoxic potential nor ROS induction. Contrary to that, WC(S) nanoparticles induced the formation of both ROS and micronuclei. CoCl(2) was tested in relevant concentrations and induced no ROS formation, but increased the rate of micronuclei at concentrations exceeding those present in WC(L)-Co. In conclusion, ROS and micronuclei formation could not be associated with the presence of Co in the WC-based particles. The contrasting responses elicited by WC(S) vs. WC(L) appear to be due to large differences in crystalline structure.