Nanomaterial exposure, toxicity, and impact on human health

The use of engineered nanomaterials (ENM) has grown after the turn of the 21st century. Also, the production of ENM has globally grown, and exposure of workers especially via the lungs to ENM has increased. This review tackles with effects of ENM on workers' health because occupational environment is the main source of exposure to ENM. Assessment of exposure to ENM is demanding, and today there are no occupational exposure level (OEL) for ENM. This is partly due to challenges of such measurements, and in part to the unknown causality between ENM metrics and effects. There are also marked gaps in systematic knowledge on ENM hazards. Human health surveys of exposed workers, or human field studies have not identified specific effects of ENM linking them with a specific exposure. There is, however, a consensus that material characteristics such as size, and chemistry influence effects of ENM. Available data suggest that multiwalled carbon nanotubes (MWCNT) affect the immunological system and cause inflammation of the lungs, or signs of asthma whereas carbon nanofibers (CNF) may cause interstitial fibrosis. Metallic and metal oxide nanoparticles together with MWCNT induce genotoxicity, and a given type of MWCNT has been identified as a possible human carcinogen. Currently, lack of understanding of mechanisms of effects of ENM renders assessment of hazards and risks of ENM material-by-material a necessity. The so called "omics" approaches utilizing ENM-induced alterations in gene and protein expression may be useful in the development of a new paradigm for ENM hazard and risk assessment. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials.

Current Application of Capillary Electrophoresis in Nanomaterial Characterisation and Its Potential to Characterise the Protein and Small Molecule Corona

Due to the increasing use and production of nanomaterials (NMs), the ability to characterise their physical/chemical properties quickly and reliably has never been so important. Proper characterisation allows a thorough understanding of the material and its stability, and is critical to establishing dose-response curves to ascertain risks to human and environmental health. Traditionally, methods such as Transmission Electron Microscopy (TEM), Field Flow Fractionation (FFF) and Dynamic Light Scattering (DLS) have been favoured for size characterisation, due to their wide-availability and well-established protocols. Capillary Electrophoresis (CE) offers a faster and more cost-effective solution for complex dispersions including polydisperse or non-spherical NMs. CE has been used to rapidly separate NMs of varying sizes, shapes, surface modifications and compositions. This review will discuss the literature surrounding the CE separation techniques, detection and NM characteristics used for the analysis of a wide range of NMs. The potential of combining CE with mass spectrometry (CE-MS) will also be explored to further expand the characterisation of NMs, including the layer of biomolecules adsorbed to the surface of NMs in biological or environmental compartments, termed the acquired biomolecule corona. CE offers the opportunity to uncover new/poorly characterised low abundance and polar protein classes due to the high ionisation efficiency of CE-MS. Furthermore, the possibility of using CE-MS to characterise the poorly researched small molecule interactions within the NM corona is discussed.

Nanomaterial–microbe cross-talk: physicochemical principles and (patho)biological consequences

NPs’ characteristics impact their spontaneous binding to microbes, which may affect the (patho)biological identity of both NP and microbes.

Corrosion-Protected Hybrid Nanoparticles

Nanoparticles composed of functional materials hold great promise for applications due to their unique electronic, optical, magnetic, and catalytic properties. However, a number of functional materials are not only difficult to fabricate at the nanoscale, but are also chemically unstable in solution. Hence, protecting nanoparticles from corrosion is a major challenge for those applications that require stability in aqueous solutions and biological fluids. Here, this study presents a generic scheme to grow hybrid 3D nanoparticles that are completely encapsulated by a nm thick protective shell. The method consists of vacuum-based growth and protection, and combines oblique physical vapor deposition with atomic layer deposition. It provides wide flexibility in the shape and composition of the nanoparticles, and the environments against which particles are protected. The work demonstrates the approach with multifunctional nanoparticles possessing ferromagnetic, plasmonic, and chiral properties. The present scheme allows nanocolloids, which immediately corrode without protection, to remain functional, at least for a week, in acidic solutions.

Novel Multi-isotope Tracer Approach To Test ZnO Nanoparticle and Soluble Zn Bioavailability in Joint Soil Exposures

Here we use two enriched stable isotopes, ⁶⁸Zn_en and ⁶⁴Zn_en (>99%), to prepare ⁶⁸ZnO nanoparticles (NPs) and soluble ⁶⁴ZnCl₂. The standard LUFA 2.2 test soil was dosed with ⁶⁸ZnO NPs and soluble ⁶⁴ZnCl₂ to 5 mg kg^-1 each, plus between 0 and 95 mg kg^-1 of soluble ZnCl₂ with a natural isotope composition. After 0, 1, 3, 6, and 12 months of soil incubation, earthworms (Eisenia andrei) were introduced for 72 h exposures. Analyses of soils, pore waters, and earthworm tissues using multiple collector inductively coupled plasma mass spectrometry allowed the simultaneous measurement of the diagnostic ⁶⁸Zn/⁶⁶Zn, ⁶⁴Zn/⁶⁶Zn, and ⁶⁸Zn/⁶⁴Zn ratios, from which the three different isotopic forms of Zn were quantified. Eisenia andrei was able to regulate Zn body concentrations with no difference observed between the different total dosing concentrations. The accumulation of labeled Zn by the earthworms showed a direct relationship with the proportion of labeled to total Zn in the pore water, which increased with longer soil incubation times and decreasing soil pH. The ⁶⁸Zn_en/⁶⁴Zn_en ratios determined for earthworms (1.09 ± 0.04), soils (1.09 ± 0.02), and pore waters (1.08 ± 0.02) indicate indistinguishable environmental distribution and uptake of the Zn forms, most likely due to rapid dissolution of the ZnO NPs.

Structural Transformation of Biochar Black Carbon by C60 Superstructure: Environmental Implications

Pyrogenic carbon is widespread in soil due to wildfires, soot deposition, and intentional amendment of pyrolyzed waste biomass (biochar). Interactions between engineered carbon nanoparticles and natural pyrogenic carbon (char) are unknown. This study first employed transmission electron microscopy (TEM) and X-ray diffraction (XRD) to interpret the superstructure composing aqueous fullerene C₆₀ nanoparticles prepared by prolonged stirring of commercial fullerite in water (nC₆₀-stir). The nC₆₀-stir was a superstructure composed of face-centered cubic (fcc) close-packing of near-spherical C₆₀ superatoms. The nC₆₀-stir superstructure (≈100 nm) reproducibly disintegrated pecan shell biochar pellets (2 mm) made at 700 °C into a stable and homogeneous aqueous colloidal (<100 nm) suspension. The amorphous carbon structure of biochar was preserved after the disintegration, which only occurred above the weight ratio of 30,000 biochar to nC₆₀-stir. Favorable hydrophobic surface interactions between nC₆₀-stir and 700 °C biochar likely disrupted van der Waals forces holding together the amorphous carbon units of biochar and C₆₀ packing in the nC₆₀ superstructure.

Metallic bionanocatalysts: potential applications as green catalysts and energy materials

Microbially generated or supported nanocatalysts have potential applications in green chemistry and environmental application. However, precious (and base) metals biorefined from wastes may be useful for making cheap, low-grade catalysts for clean energy production. The concept of bionanomaterials for energy applications is reviewed with respect to potential fuel cell applications, bio-catalytic upgrading of oils and manufacturing 'drop-in fuel' precursors. Cheap, effective biomaterials would facilitate progress towards dual development goals of sustainable consumption and production patterns and help to ensure access to affordable, reliable, sustainable and modern energy.

Influence of CNTRENE® C100LM carbon nanotube material on the growth and regulation of Escherichia coli

The growing use of carbon nanotubes (CNTs) in industrial and consumer products raises important questions about their environmental fate and impact on prokaryotes. In the environment, CNTs are exposed to a variety of conditions (e.g., UV light) that could lead to decomposition and changes in their chemical properties. Therefore, the potential cytotoxic effect of both pristine and artificially aged carboxyl functionalized CNTRENE^® C100LM CNTmaterial at neutral and acidic conditions on Escherichia coli K12 was analyzed using a minimal inhibitory concentration (MIC) assay, which also allowed monitoring of non-lethal growth effects. However, there were no observable MIC or significant changes in growth behavior in E. coli K12 when exposed to pristine or aged CNTs. Exposure to pristine CNTRENE^® C100LM CNT material did not appear to influence cell morphology or damage the cells when examined by electron microscopy. In addition, RNA sequencing revealed no observable regulatory changes in typical stress response pathways. This is surprising considering that previous studies have claimed high cytotoxicity of CNTs, including carboxyl functionalized single-walled CNTs, and suggest that other factors such as trace heavy metals or other impurities are likely responsible for many of the previously reported cytotoxicity in E. coli and possibly other microorganisms.

Inhaled Nanoparticles Accumulate at Sites of Vascular Disease

The development of engineered nanomaterials is growing exponentially, despite concerns over their potential similarities to environmental nanoparticles that are associated with significant cardiorespiratory morbidity and mortality. The mechanisms through which inhalation of nanoparticles could trigger acute cardiovascular events are emerging, but a fundamental unanswered question remains: Do inhaled nanoparticles translocate from the lung in man and directly contribute to the pathogenesis of cardiovascular disease? In complementary clinical and experimental studies, we used gold nanoparticles to evaluate particle translocation, permitting detection by high-resolution inductively coupled mass spectrometry and Raman microscopy. Healthy volunteers were exposed to nanoparticles by acute inhalation, followed by repeated sampling of blood and urine. Gold was detected in the blood and urine within 15 min to 24 h after exposure, and was still present 3 months after exposure. Levels were greater following inhalation of 5 nm (primary diameter) particles compared to 30 nm particles. Studies in mice demonstrated the accumulation in the blood and liver following pulmonary exposure to a broader size range of gold nanoparticles (2-200 nm primary diameter), with translocation markedly greater for particles <10 nm diameter. Gold nanoparticles preferentially accumulated in inflammation-rich vascular lesions of fat-fed apolipoproteinE-deficient mice. Furthermore, following inhalation, gold particles could be detected in surgical specimens of carotid artery disease from patients at risk of stroke. Translocation of inhaled nanoparticles into the systemic circulation and accumulation at sites of vascular inflammation provides a direct mechanism that can explain the link between environmental nanoparticles and cardiovascular disease and has major implications for risk management in the use of engineered nanomaterials.

Bovine Serum Albumin Adsorption on TiO2 Colloids: The Effect of Particle Agglomeration and Surface Composition

Protein adsorption at nanostructured oxides strongly depends on the synthesis conditions and sample history of the material investigated. We measured the adsorption of bovine serum albumin (BSA) to commercial Aeroxide TiO₂ P25 nanoparticles in aqueous dispersions. Significant changes in the adsorption capacity were induced by mild sample washing procedures and attributed to the structural modification of adsorbed water and surface hydroxyls. Motivated by the lack of information about the sample history of commercial TiO₂ nanoparticle samples, we used vapor-phase-grown TiO₂ nanoparticles, a well-established model system for adsorption and photocatalysis studies, and performed on this material for the first time a systematic and quantitative BSA adsorption study. After alternating vacuum and oxygen treatment of the nanoparticle powders at elevated temperatures for surface purification, we determined size distributions covering both the size of the individualized nanoparticles and nanoparticle agglomerates using transmission electron microscopy (TEM), X-ray diffraction (XRD), and dynamic light scattering (DLS) in an aqueous dispersion. Quantitative BSA adsorption measurements at different pH values and thus variable combinations of surface-charged proteins and TiO₂ nanoparticles revealed a consistent picture: BSA adsorbs only at the outer agglomerate surfaces without penetrating the interior of the agglomerates. This process levels at coverages of single monolayers, which resist consecutive simple washing procedures. A detailed analysis of the protein-specific IR amide bands reveals that the adsorption-induced protein conformational change is associated with a decrease in the helical content. This study underlines that robust qualitative and quantitative statements about protein adsorption and corona formation require well-documented and controllable surface properties of the nanomaterials involved.

Near-IR-Absorbing Gold Nanoframes with Enhanced Physiological Stability and Improved Biocompatibility for In Vivo Biomedical Applications

This paper describes the synthesis of near-infrared (NIR)-absorbing gold nanoframes (GNFs) and a systematic study comparing their physiological stability and biocompatibility with those of hollow Au-Ag nanoshells (GNSs), which have been used widely as photothermal agents in biomedical applications because of their localized surface plasmon resonance (LSPR) in the NIR region. The GNFs were synthesized in three steps: galvanic replacement, Au deposition, and Ag dealloying, using silver nanospheres (SNP) as the starting material. The morphology and optical properties of the GNFs were dependent on the thickness of the Au coating layer and the degree of Ag dealloying. The optimal GNF exhibited a robust spherical skeleton composed of a few thick rims, but preserved the distinctive LSPR absorbance in the NIR region-even when the Ag content within the skeleton was only 10 wt %, 4-fold lower than that of the GNSs. These GNFs displayed an attractive photothermal conversion ability and great photothermal stability, and could efficiently kill 4T1 cancer cells through light-induced heating. Moreover, the GNFs preserved their morphology and optical properties after incubation in biological media (e.g., saline, serum), whereas the GNSs were unstable under the same conditions because of rapid dissolution of the considerable silver content with the shell. Furthermore, the GNFs had good biocompatibility with normal cells (e.g., NIH-3T3 and hepatocytes; cell viability for both cells: >90%), whereas the GNSs exhibited significant dose-dependent cytotoxicity (e.g., cell viability for hepatocytes at 1.14 nM: ca. 11%), accompanied by the induction of reactive oxygen species. Finally, the GNFs displayed good biocompatibility and biosafety in an in vivo mouse model; in contrast, the accumulation of GNSs caused liver injury and inflammation. Our results suggest that GNFs have great potential to serve as stable, biocompatible NIR-light absorbers for in vivo applications, including cancer detection and combination therapy.

Genome-Wide DNA Methylation Variations upon Exposure to Engineered Nanomaterials and Their Implications in Nanosafety Assessment

Sublethal exposure of engineered nanomaterials (ENMs) induces the alteration of various cellular processes due to DNA methylation changes. DNA methylation variations represent a more sensitive fingerprint analysis of the direct and indirect effects that may be overlooked by traditional toxicity assays, and an understanding of the structure-activity relationship of DNA methylation upon ENMs would open a new path for their safer design.

A protein corona-enabled blood test for early cancer detection

Pancreatic cancer is a very aggressive malignancy that is often diagnosed in the advanced stages, with the implication that long-term survivors are extremely rare. Thus, developing new methods for the early detection of pancreatic cancer is an urgent task for current research. To date, nanotechnology offers unprecedented opportunities for cancer therapeutics and diagnosis. The aim of this study is the development of a new pancreatic cancer diagnostic technology based on the exploitation of the nano-bio-interactions between nanoparticles and blood samples. In this study, blood samples from 20 pancreatic cancer patients and 5 patients without malignancy were allowed to interact with designed lipid nanoparticles, leading to the formation of a hard "protein corona" at the nanoparticle surface. After isolation, the protein patterns were characterized by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE). We found that the protein corona of pancreatic cancer patients was much more enriched than that of healthy individuals. Statistical analysis of SDS-PAGE results allowed us to discriminate between healthy and pancreatic cancer patients with a total discriminate correctness rate of 88%.

Safety assessment of nanomaterials using an advanced decision-making framework, the DF4nanoGrouping

As presented at the 2016 TechConnect World Innovation Conference on 22-25 May 2016 in Washington DC, USA, the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) 'Nano Task Force' proposes a Decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping) consisting of three tiers to assign nanomaterials to four main groups with possible further subgrouping to refine specific information needs. The DF4nanoGrouping covers all relevant aspects of a nanomaterial's life cycle and biological pathways: intrinsic material properties and system-dependent properties (that depend upon the nanomaterial's respective surroundings), biopersistence, uptake and biodistribution, and cellular and apical toxic effects. Use, release, and exposure route may be applied as 'qualifiers' to determine if, e.g., nanomaterials cannot be released from products, which may justify waiving of testing. The four main groups encompass (1) soluble, (2) biopersistent high aspect ratio, (3) passive, and (4) active nanomaterials. The DF4nanoGrouping foresees a stepwise evaluation of nanomaterial properties and effects with increasing biological complexity. In case studies covering carbonaceous nanomaterials, metal oxide, and metal sulfate nanomaterials, amorphous silica and organic pigments (all nanomaterials having primary particle sizes below 100 nm), the usefulness of the DF4nanoGrouping for nanomaterial hazard assessment was confirmed. The DF4nanoGrouping facilitates grouping and targeted testing of nanomaterials. It ensures that sufficient data for the risk assessment of a nanomaterial are available, and it fosters the use of non-animal methods. No studies are performed that do not provide crucial data. Thereby, the DF4nanoGrouping serves to save both animals and resources.

Development of scalable and versatile nanomaterial libraries for nanosafety studies: polyvinylpyrrolidone (PVP) capped metal oxide nanoparticles

A simple synthesis protocol produced a library of PVP-capped metal oxide nanomaterials with systematically varied properties for hypothesis-driven nano(eco)toxicological studies.

Cellular Interactions and Formation of an Epithelial "Nanocoating-Like Barrier" with Mesoporous Silica Nanoparticles

Oral mucosa as the front-line barrier in the mouth is constantly exposed to a complex microenvironment with multitudinous microbes. In this study, the interactions of mesoporous silica nanoparticles (MSNs) with primary human gingival epithelial cells were analyzed for up to 72 h, and their diffusion capacity in the reconstructed human gingival epithelia (RHGE) and porcine ear skin models was further assessed at 24 h. It was found that the synthesized fluorescent mesoporous silica nanoparticles (RITC-NPs) with low cytotoxicity could be uptaken, degraded, and/or excreted by the human gingival epithelial cells. Moreover, the RITC-NPs penetrated into the stratum corneum of RHGE in a time-dependent manner, while they were unable to get across the barrier of stratum corneum in the porcine ear skins. Consequently, the penetration and accumulation of RITC-NPs at the corneum layers of epithelia could form a “nanocoating-like barrier”. This preliminary proof-of-concept study suggests the feasibility of developing nanoparticle-based antimicrobial and anti-inflammatory agents through topical application for oral healthcare.

Toxicity of copper nanoparticles to Daphnia magna under different exposure conditions

Although the risks of metallic nanoparticles (NPs) to aquatic organisms have already been studied for >10years, our understanding of the link between the fate of particles in exposure medium and their toxicity is still in its infancy. Moreover, most of the earlier studies did not distinguish the contribution of particles and soluble ions to the toxic effects caused by suspensions of metallic NPs. In this study, the toxicity of CuNPs to Daphnia magna upon modification of the exposure conditions, achieved by aging the suspensions of CuNPs and by altering water chemistry parameters like the pH and levels of dissolved organic carbon (DOC), was investigated. The LC50 values for CuNPs exposure decreased by about 30% after 7days of aging. The LC50 values increased >12-fold upon addition of DOC at concentrations ranging from 0 to 10mg/L to the exposure medium. Changing the pH from 6.5 to 8.5 resulted in a 3-fold higher LC50 value. Furthermore, it was found that during 7days of aging of the exposure medium (without addition of DOC and at pH7.8), the toxicity could be mostly ascribed to the particles present in the suspension (around 70%). However, adding DOC or decreasing the pH of the exposure medium reduced the contribution of the particles to the observed toxicity. We thus found that the effective concentration regarding the toxicity was mainly driven by the contribution of the soluble ions in the presence of DOC or at pH6.5. Our results suggest that the toxicity results of CuNPs obtained from laboratory tests may overestimate the risk of the particles in polluted waters due to the common absence of DOC in laboratory test solutions. Moreover, the role of the ions shedding from CuNPs is very important in explaining the toxicity in natural waters.

Quantitative analysis of nanoparticle transport through in vitro blood-brain barrier models

Nanoparticle transport through the blood-brain barrier has received much attention of late, both from the point of view of nano-enabled drug delivery, as well as due to concerns about unintended exposure of nanomaterials to humans and other organisms. In vitro models play a lead role in efforts to understand the extent of transport through the blood-brain barrier, but unique features of the nanoscale challenge their direct adaptation. Here we highlight some of the differences compared to molecular species when utilizing in vitro blood-brain barrier models for nanoparticle studies. Issues that may arise with transwell systems are discussed, together with some potential alternative methodologies. We also briefly review the biomolecular corona concept and its importance for how nanoparticles interact with the blood-brain barrier. We end with considering future directions, including indirect effects and application of shear and fluidics-technologies.

Effect of silver nanoparticles on the standard soil arthropod Folsomia candida (Collembola) and the eukaryote model organism Saccharomyces cerevisiae

BACKGROUND

Because of their antimicrobial properties, silver nanoparticles (AgNPs) have been widely used and have come into contact with the environment. In the present work, an effect of AgNPs on a standard soil organism, Folsomia candida, was studied (in comparison to silver nitrate) focusing on molecular and cellular alterations as ecotoxicological endpoints.

RESULTS

At the molecular level, an up-regulation of metallothionein-containing protein (MTC) mRNA in AgNP-treated groups indicated toxic heavy metal stress effects caused by the release of silver ions from AgNPs, which is similar to animal groups treated with silver nitrate. Alteration of the steady-state level of glutathione S-transferase (GST) mRNA was detected in animal treated with AgNPs and AgNO₃. At the cellular level, the relation between GST activity and the size of the glutathione (GSH) was examined. Change of GST activity from different animal groups was not significant, whereas the GSH pool (reduced and oxidized forms) decreased with increasing concentration of AgNPs. In order to obtain direct evidence whether AgNPs cause oxidative stress, treated animals were incubated with the non-fluorescent probe, 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). A fluorescence signal was observed in both AgNPs- and AgNO₃-treated groups pointing to the production of reactive species (RS). Since RS formation in F.candida is difficult to quantify, yeast strain BY4742 (wild-type) and mutants lacking of oxidative stress-related protective enzymes were exploited as a further eukaryote model organism. AgNPs and AgNO₃ were found to also affect growth of yeast and induced oxidative stress.

CONCLUSIONS

An effect of AgNPs on Collembola and yeast strains is similar to the one from AgNO₃. However, AgNPs is less toxic due to the slow release of silver ions. In summary, the toxic effect of AgNPs on F. candida is caused by the combination of the release of silver ions from AgNPs and the formation of reactive species.

Effect of sonication on particle dispersion, administered dose and metal release of non-functionalized, non-inert metal nanoparticles

ABSTRACT

In this study, we elucidate the effect of different sonication techniques to efficiently prepare particle dispersions from selected non-functionalized NPs (Cu, Al, Mn, ZnO), and corresponding consequences on the particle dose, surface charge and release of metals. Probe sonication was shown to be the preferred method for dispersing non-inert, non-functionalized metal NPs (Cu, Mn, Al). However, rapid sedimentation during sonication resulted in differences between the real and the administered doses in the order of 30-80 % when sonicating in 1 and 2.56 g/L NP stock solutions. After sonication, extensive agglomeration of the metal NPs resulted in rapid sedimentation of all particles. DLVO calculations supported these findings, showing the strong van der Waals forces of the metal NPs to result in significant NP agglomeration. Metal release from the metal NPs was slightly increased by increased sonication. The addition of a stabilizing agent (bovine serum albumin) had an accelerating effect on the release of metals in sonicated solutions. For Cu and Mn NPs, the extent of particle dissolution increased from <1.6 to ~5 % after sonication for 15 min. A prolonged sonication time (3-15 min) had negligible effects on the zeta potential of the studied NPs. In all, it is shown that it is of utmost importance to carefully investigate how sonication influences the physico-chemical properties of dispersed metal NPs. This should be considered in nanotoxicology investigations of metal NPs.