Tracking and quantification of single-walled carbon nanotubes in fish using near infrared fluorescence

Shielding Effects Provide a Dominant Mechanism in J-Aggregation-Induced Photoluminescence Enhancement of Carbon Nanotubes

The unique photophysical properties of single-walled carbon nanotubes (SWCNTs) exhibit great potential for bioimaging applications. This led to extensive exploration of photosensitization methods to improve their faint shortwave infrared (SWIR) photoluminescence. Here, we report the mechanisms of SWCNT-assisted J-aggregation of cyanine dyes and the associated photoluminescence enhancement of SWCNTs in the SWIR spectral region. Surprisingly, we found that excitation energy transfer between the cyanine dyes and SWCNTs makes a negligible contribution to the overall photoluminescence enhancement. Instead, the shielding of SWCNTs from the surrounding water molecules through hydrogen bond-assisted macromolecular reorganization of ionic surfactants triggered by counterions and the physisorption of the dye molecules on the side walls of SWCNTs play a primary role in the photoluminescence enhancement of SWCNTs. We observed 2 orders of magnitude photoluminescence enhancement of SWCNTs by optimizing these factors. Our findings suggest that the proper shielding of SWCNTs is the critical factor for their photoluminescence enhancement, which has important implications for their application as imaging agents in biological settings.

Carbon nanotubes and nanofibers seen as emerging threat to fish: Historical review and trends

Since the discovery of the third allotropic carbon form, carbon-based one-dimensional nanomaterials (1D-CNMs) became an attractive and new technology with different applications that range from electronics to biomedical and environmental technologies. Despite their broad application, data on environmental risks remain limited. Fish are widely used in ecotoxicological studies and biomonitoring programs. Thus, the aim of the current study was to summarize and critically analyze the literature focused on investigating the bioaccumulation and ecotoxicological impacts of 1D-CNMs (carbon nanotubes and nanofibers) on different fish species. In total, 93 articles were summarized and analyzed by taking into consideration the following aspects: bioaccumulation, trophic transfer, genotoxicity, mutagenicity, organ-specific toxicity, oxidative stress, neurotoxicity and behavioral changes. Results have evidenced that the analyzed studies were mainly carried out with multi-walled carbon nanotubes, which were followed by single-walled nanotubes and nanofibers. Zebrafish (Danio rerio) was the main fish species used as model system. CNMs' ecotoxicity in fish depends on their physicochemical features, functionalization, experimental design (e.g. exposure time, concentration, exposure type), as well as on fish species and developmental stage. CNMs' action mechanism and toxicity in fish are associated with oxidative stress, genotoxicity, hepatotoxicity and cardiotoxicity. Overall, fish are a suitable model system to assess the ecotoxicity of, and the environmental risk posed by, CNMs.

Translocation of 14C-polystyrene nanoplastics into fish during a very-low concentration dietary exposure

Assessing the dietary accumulation of nanoplastics in animals following very-low exposure concentrations is restricted due to analytical limitations. This study adapted a method for synthesising semi-stable 14C-PS NPs (through styrene polymerisation) in small volumes for deployment in environmental studies. The method was developed with non-labelled material where the final polystyrene product had a primary particle size of 35 ± 8 nm (as measured by transmission electron microscopy). This method was then applied to 14C-labelled styrene to produce radiolabelled polystyrene nanoplastics (14C-PS NPs). The 14C-PS NPs were added (top-dressed) to a commercially available fish feed, with a measured concentration of 27.9 ± 2.1 kBq kg-1 (n = 5), equating to 5.9 μg polystyrene kg-1 feed. Fish (rainbow trout; Oncorhynchus mykiss) were fed this diet at a ration of 2% body weight per day for a period of two weeks. On day 3, 7 and 14, the fish were sampled for the mid intestine, hind intestine, kidney and liver, and measured for tissue radioactivity (determined by liquid scintillation counting). Some background activity was detected in the control samples (e.g., 1-16 and 4-11 Bq g-1 in the hind intestine and liver, respectively) which is due to natural background fluorescence. By the end of the experiment, the hind intestine and liver had significantly elevated radioactivity (25.3 and 15.0 Bq g-1, respectively) compared to the control, indicating the accumulation of nano polystyrene. In the liver, this equated to 1.8 μg polystyrene g-1 dry weight. This study confirms the accumulation of nano particles in vertebrates at low, environmentally relevant concentration, and highlights radiolabelling as a methodological approach suitable for exploring the bioaccumulation of nanoplastics and potential impacts.

Near-Infrared-II In Vivo Visualization and Quantitative Tracking of Micro/Nanoplastics in Fish

As emerging contaminants, micro/nanoplastics (MNPs) are widely present in aquatic environments and are often ingested by aquatic organisms. However, the in vivo trafficking and fate of MNPs remain largely unknown. Here, we developed near-infrared (NIR) aggregated-induced emission (AIE) fluorophore-labeled microplastics (2 μm) and nanoplastics (100 nm) as models of MNPs. This model was based on the NIR-AIE technique with strong emission at the second near-infrared (NIR-IIII) window, which overcomes the interference of autofluorescence and observation artifacts in the detection of commercial fluorescent-labeled particles. Due to its deep tissue penetration and noninvasiveness, the dynamic process of accumulation and transport of MNPs in individuals can be tracked with NIR imaging. We then directly visualized and quantified the uptake and depuration processes of MPs and NPs in zebrafish. The results showed that the MPs and NPs were mainly accumulated in the fish gut, and the distribution was heterogeneous. MPs tended to accumulate more in the fore and mid areas of the gut compared with NPs. Besides, both MPs and NPs could accumulate in large quantities locally in the gut and might cause intestinal obstruction. MNPs accumulated slowly during the initial exposure followed by rapid and sustained accumulation in gut. Based on these kinetic accumulation and depuration, we developed a refined toxicokinetic (TK) model to describe the dynamic changes in the uptake and depuration of MNPs. Overall, this study proposed a MNP model based on the NIR-AIE technique, which provided a reliable tracer technology for the visualization, tracking and quantification of MNPs in vivo.

Evaluation of bioaccumulation of nanoplastics, carbon nanotubes, fullerenes, and graphene family materials

Bioaccumulation is a key factor in understanding the potential ecotoxicity of substances. While there are well-developed models and methods to evaluate bioaccumulation of dissolved organic and inorganic substances, it is substantially more challenging to assess bioaccumulation of particulate contaminants such as engineered carbon nanomaterials (CNMs; carbon nanotubes (CNTs), graphene family nanomaterials (GFNs), and fullerenes) and nanoplastics. In this study, the methods used to evaluate bioaccumulation of different CNMs and nanoplastics are critically reviewed. In plant studies, uptake of CNMs and nanoplastics into the roots and stems was observed. For multicellular organisms other than plants, absorbance across epithelial surfaces was typically limited. Biomagnification was not observed for CNTs and GFNs but were observed for nanoplastics in some studies. However, the reported absorption in many nanoplastic studies may be a consequence of an experimental artifact, namely release of the fluorescent probe from the plastic particles and subsequent uptake. We identify that additional work is needed to develop analytical methods to provide robust, orthogonal methods that can measure unlabeled (e.g., without isotopic or fluorescent labels) CNMs and nanoplastics.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

Internal Exposure and Distribution of Airborne Fine Particles in the Human Body: Methodology, Current Understandings, and Research Needs

Exposure to airborne fine particles (PM_2.5, particulate matter with aerodynamic diameter <2.5 μm) severely threatens global human health. Understanding the distribution and processes of inhaled PM_2.5 in the human body is crucial to clarify the causal links between PM_2.5 pollution and diseases. In contrast to extensive research on the emission and formation of PM_2.5 in the ambient environment, reports about the occurrence and fate of PM_2.5 in humans are still limited, although many studies have focused on the exposure and adverse effects of PM_2.5 with animal models. It has been shown that PM_2.5, especially ultrafine particles (UFPs), have the potential to go across different biological barriers and translocate into different human organs (i.e., blood circulation, brain, heart, pleural cavity, and placenta). In this Perspective, we summarize the factors affecting the internal exposure of PM_2.5 and the relevant analytical methodology and review current knowledge about the exposure pathways and distribution of PM_2.5 in humans. We also discuss the research challenges and call for more studies on the identification and characterization of key toxic species of PM_2.5, quantification of internal exposure doses in the general population, and further clarification of translocation, metabolism, and clearance pathways of PM_2.5 in the human body. In this way, it is possible to develop toxicity-based air quality standards instead of the currently used mass-based standards.

Impacts of ingested MWCNT-Embedded nanocomposites in Japanese medaka (Oryzias latipes)

Polymer nanocomposites combine the versatile, lightweight characteristics of polymers with the properties of nanomaterials. Polyethylene terephthalate glycol (PETG) is commonly used in polymer additive manufacturing due to its controllable transparency, high modulus, and mechanical properties. Multi-walled carbon nanotubes (MWCNTs) add tensile strength, electrical conductivity, and thermal stability. The increased use of nanocomposites has led to concern over potential human health risks. We assessed morphologic alterations to determine impacts of ingested abraded nanocomposites compared to its component materials, pristine MWCNTs (1000 mg/L) and PETG. Adult transparent Japanese medaka (Oryzias latipes) were administered materials via oral gavage in 7 doses over 16 days. In vivo observations revealed altered livers and gallbladders following exposure to pristine MWCNTs and nanocomposites. Subsequent histologic sections showed fish exposed to pristine MWCNTs had highly altered biliary structures, and exposure to nanocomposites resulted in hepatocellular alteration. Thyroid follicle proliferation was also observed in fish exposed to materials containing MWCNTs. Transmission electron microscopy of livers showed that hepatocytes of fish exposed to MWCNTs had widespread swelling of rough endoplasmic reticulum, pronounced lysosomal activity, and swelling of intrahepatic biliary passageways. Fish exposed to nanocomposites had areas of degenerated hepatocytes with interspersed cellular debris. Each analysis showed that fish exposed to pristine PETG were most similar to controls. These results suggest that MWCNTs are the source of toxicity in abraded nanocomposite materials but that nanocomposites may also have some unique effects. The similarities of many teleost and mammalian tissues are such that these findings may indicate human health risks.

Removal of Carbon Nanotubes from Aqueous Solutions by Sodium Hypochlorite: Effects of Treatment Conditions

The treatment of carbon nanotubes (CNTs) containing wastewater has become an important issue with increasing industrial application due to the risk CNTs may pose to the environment and human health. However, an effective method for treating wastewater containing CNTs has not been established. Recently, we proposed a method to remove CNTs from aqueous dispersions using sodium hypochlorite (NaClO). To explore the practical applications of this method, we herein investigate the influence of different conditions, such as NaClO concentration, reaction temperature, pH value, and CNT concentration, on the CNT degradation rate. The results showed that the degradation of CNTs depends strongly on temperature and NaClO concentration: the higher the temperature and NaClO concentration, the faster the degradation rate. The optimal temperature and NaClO concentration are 50-70 °C and 2-3 wt%, respectively. Lower pH accelerated the degradation rate but induced the decomposition of NaClO. Furthermore, dispersants and other substances in the solution may also consume NaClO, thus affecting the degradation of CNTs. These findings are of significance for establishing a standard technique for CNT-containing industrial wastewater treatment, and for advancing the environmental sustainability of the CNT industry.

Analysis of Single-Walled Carbon Nanotubes in Estuarine Sediments by Density Gradient Ultracentrifugation Coupled to Near-Infrared Fluorescence Spectroscopy Reveals Disassociation of Residual Metal Catalyst Nanoparticles

The continued growth of the nanotechnology industry and the incorporation of nanomaterials into consumer applications will inevitably lead to their release into environmental systems. Single-walled carbon nanotubes (SWCNTs) in particular have exhibited many attractive optical, mechanical, and electrical properties that lend themselves to new and exciting applications. Assessing their environmental impact upon release into the environment is contingent upon quantifying and characterizing SWCNTs in environmental matrixes. In this study, SWCNTs were isolated from estuarine sediments using density gradient ultracentrifugation (DGU), followed by online flow-through analysis of the density fractions via near-infrared spectroscopy. This approach yielded significant improvements in the quantitative detection limit, from 62 to 1.5 μg g^-1. In addition, fractions of the density gradient were also obtained for further analysis by bulk inductively coupled plasma mass spectrometry (ICP-MS) and single-particle ICP-MS. Using fluorescent, semiconductive SWCNTs, the primary fluorescent nanotube fraction was found to be separated from the sediment matrix during DGU; however, the residual metal catalyst particles that had been assumed to be physically bound to the SWCNTs were found to form a separate band in the density gradient apart from the fluorescent SWCNTs. This result was repeated for a number of SWCNT types regardless of the metal catalyst and synthesis method, with a 0.1 g cm^-3 density difference between most fractions. The apparent disconnect between the fluorescent fraction of SWCNTs and their metal-containing constituents potentially complicates CNT risk assessment as analysis techniques focusing solely on either CNT fluorescence or metal fingerprints may misrepresent exposure concentrations and their toxicological implications.

Induced toxicity in early-life stage zebrafish (Danio rerio) and its behavioral analysis after exposure to non-doped, nitrogen-doped and nitrogen, sulfur-co doped carbon quantum dots

In this study, the effects of doping of CQDs with alternative functional groups (dopants) were evaluated through embryonic development of zebrafish (Danio rerio). The CQDs were synthesized using simple and low-cost sources: Non-doped (citric acid was used as the carbon source), nitrogen-doped (N-doped) and nitrogen, sulfur-co-doped (N,S-doped). The CQDs induced significant toxicity to zebrafish (>150 μg/mL) and the toxic effects were dose-dependent. The N,S-doped CQDs were the most toxic (LD50 = 149.92 μg/mL), followed by the N-doped CQDs (LD50 = 399.95 μg/mL) while the non-doped CQDs were the least toxic (LD50 = 548.48 μg/mL) of the three. The growth rate (GR) was affected following the toxicity pattern (GR_NS-doped<GR_N-doped<GR_non-doped <GR_blanc), which, in turn, greatly depends on the type of dopant. Morphological malformations, such as pericardial edema, yolk sac edema, tail and spinal curvature were observed to zebrafish embryos as the toxicity, concentration and exposure time to the nanomaterial increased. Behavioral analysis showed that locomotor activity increases as the toxicity of the nanomaterial rises. The differences in toxicity, growth rate and malfunctions of CQDs were attributed to their doping with different heteroatoms. The N,S-doped CQDs, unequivocally, exhibited the most pronounced effects.

Low level of polystyrene microplastics decreases early developmental toxicity of phenanthrene on marine medaka (Oryzias melastigma)

Microplastics (MPs) have become global environmental concern. However, the effects of environmental concentrations of MPs, singly or in combination with organic pollutants, on the early development of marine fish remain unclear. In this study, fertilized eggs of marine medaka (Oryzias melastigma) were exposed to polystyrene MPs (0, 2, 20, 200 μg/L) and/or phenanthrene (Phe, 50 μg/L) for 28 days. The results revealed that MPs were accumulated on the chorion and ingested by larvae from 2 days post-hatching. High levels of MPs (20 and 200 μg/L) decreased the hatchability, delayed the hatching time, and suppressed the growth, whereas Phe inhibited hatching and caused malformations in larvae. The presence of MPs at 20 and 200 μg/L did not alter the toxicity of Phe. By contrast, combined exposure to 2 μg/L MPs and Phe increased the hatchability by 25.8%, decreased malformation and mortality rates, and restored Phe-induced abnormal expressions of cardiac development-related genes. The reduced early developmental toxicity could be attributed to the decreased bioavailability and bioaccumulation of Phe by the low level of MPs. These findings contradicted the view that MPs would aggravate the toxicity of organic pollutants, and future studies are warranted to elucidate the ecological risks of marine MPs.

The missing link between carbon nanotubes, dissolved organic matter and organic pollutants

Ternary interactions between carbon nanotubes (CNTs), dissolved organic matter (DOM) and small organic molecules (namely low molecular mass organic pollutants) are of great importance since they can affect the reactivity and fate of all involved compartments in the environment. This review thoroughly assesses existing knowledge on the adsorption of DOM and small organic molecules by CNTs, while giving special attention to (i) the complex nature of DOM, (ii) the ternary rather than binary interactions between CNTs, DOM and the small organic molecules and (iii) the DOM-organic molecule interactions. We discuss in detail the main factors influencing DOM adsorption by CNTs and attempt to differentiate between the role of DOM composition and conformation. We then outline how the presence of DOM influences the adsorption of small organic molecules by CNTs, considering the introduction stage of DOM and the impact of the organic molecule's properties. DOM adsorption by CNTs is highly dependent on its composition and is governed by the size, hydrophobicity and aromaticity of DOM. DOM adsorption was found to alter the assembly of the CNTs, resulting in changes in the distribution of adsorption sites. Small organic molecules may adsorb to residual surface area on the CNTs, to DOM-coating the CNTs or remain in solution, possibly complexed with DOM. This results in their suppressed or enhanced adsorption in comparison to DOM-free media. The physicochemical properties of the organic molecules (hydrophobicity, size, structure and charge) also play a major role in this process. We present knowledge gaps that need clarification such as the extent of DOM desorption from CNTs, the amount of co-adsorbed DOM during competition with small organic molecules for adsorption sites on the CNTs and the behavior of CNTs under realistic conditions. More data generated from experiments using natural DOM rather than dissolved humic substances are required to improve our understanding of the interactions between CNTs and small organic molecules in realistic environmental scenarios. This review provides conclusions and research directions needed to evaluate the nature of interactions between CNTs, DOM and organic pollutants in aquatic systems affected by anthropogenic activities.

A Near-infrared Persistent Luminescence Imaging Technique for Tracking Nanoparticles in Zebrafish (Danio rerio)

The development of nanotechnology has drawn increased attention to the risks of nanoparticles (NPs). In this work, the near-infrared persistent luminescence imaging technique was used to track the biodistribution of NPs in vivo in zebrafish. Zebrafish were used as a vertebrate animal model to show NPs distribution and the effects of exposure. ZnGa₂O₄:Cr (ZGOC) was chosen as the probe in this work. In continuous exposure experiments, the results showed more particles accumulated in the intestines than in the gills in both groups. In both the gills and abdomen, the NPs contents were greater in the ZGOC-NH₂-treated groups than in the ZGOC groups, and the NPs caused damage to the gills and intestines. Removal exposure experiments indicated that ZGOC and ZGOC-NH₂ could be excreted from the body. The metabolism, excretion of NPs, the quantification and monitoring of NPs behavior in biological systems should be examined in further studies.

Utilization of Near Infrared Fluorescence Imaging to Track and Quantify the Pulmonary Retention of Single-Walled Carbon Nanotubes in Mice

As nanomaterials are used in a wide array of applications, investigations regarding health impacts associated with inhalation are a concern. Reports show that exposure to single-walled carbon nanotubes (SWCNTs) can induce fibrosis, allergic-type reactions, and pathogen susceptibility. Airway clearance is known to play a primary role in these disease states, yet SWCNT detection in biological systems is challenging. Common techniques, such as electron microscopy, lack spatial resolution and specificity to delineate SWCNTs in carbon-based organisms. Here we validated a near-infrared fluorescence imaging (NIRFI) system to track and semi-quantify SWCNTs over 21 days in tissues of mice exposed intratracheally to 1 dose of SWCNTs. In tandem, we optimized a NIRF-based spectrometry method to quantify SWCNTs, showing that NIRFI was consistent with SWCNT burdens quantified by NIRF spectroscopy in whole lung tissue homogenates. Finally, NIRFI was utilized to localize SWCNTs on lung tissue sections used for pathological analysis. Results revealed that SWCNTs remained in the lung over 21 days and were consistent with alveolar wall restructuring and granuloma formation. This study is the first to quantify SWCNTs in mouse lungs using both semi-quantitative tracking and quantitative mass measurements using NIRF, highlighting this as a sensitive and specific technique for assessing SWCNT clearance in vivo.

Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.

Detection and Quantification of Graphene-Family Nanomaterials in the Environment

An increase in production of commercial products containing graphene-family nanomaterials (GFNs) has led to concern over their release into the environment. The fate and potential ecotoxicological effects of GFNs in the environment are currently unclear, partially due to the limited analytical methods for GFN measurements. In this review, the unique properties of GFNs that are useful for their detection and quantification are discussed. The capacity of several classes of techniques to identify and/or quantify GFNs in different environmental matrices (water, soil, sediment, and organisms), after environmental transformations, and after release from a polymer matrix of a product is evaluated. Extraction and strategies to combine methods for more accurate discrimination of GFNs from environmental interferences as well as from other carbonaceous nanomaterials are recommended. Overall, a comprehensive review of the techniques available to detect and quantify GFNs are systematically presented to inform the state of the science, guide researchers in their selection of the best technique for the system under investigation, and enable further development of GFN metrology in environmental matrices. Two case studies are described to provide practical examples of choosing which techniques to utilize for detection or quantification of GFNs in specific scenarios. Because the available quantitative techniques are somewhat limited, more research is required to distinguish GFNs from other carbonaceous materials and improve the accuracy and detection limits of GFNs at more environmentally relevant concentrations.

Green Algae as Carriers Enhance the Bioavailability of 14C-Labeled Few-Layer Graphene to Freshwater Snails

The waterborne exposure of graphene to ecological receptors has received much attention; however, little is known about the contribution of food to the bioaccumulation potential of graphene. We investigated the effect of algal food on the uptake and distribution of ¹⁴C-labeled few-layer graphene (FLG) in freshwater snails, a favorite food for Asian people. In a water-only system, FLG (∼158 μg/L) was ingested by and accumulated in the snails. Adding algae to the water significantly enhanced FLG accumulation in the snails, with a bioaccumulation factor of 2.7 (48 h exposure). Approximately 92.5% of the accumulated FLG was retained in the intestine; in particular, the accumulated FLG in the intestine was able to pass through the intestinal wall and enter the intestinal epithelial cells. Of them, 1.3% was subsequently transferred/internalized to the liver/hepatocytes, a process that was not observed in the absence of the algae. Characterizations data further suggested that both of the extra- and intracellular FLG in the algae (the algae-bound fraction was 30.2%) significantly contributed to the bioaccumulation. Our results provide the first evidence that algae as carriers enhanced FLG bioavailability to the snails, as well as the potential of FLG exposure to human beings through consuming the contaminated snails.

Bioaccumulation of 14C-Labeled Graphene in an Aquatic Food Chain through Direct Uptake or Trophic Transfer

The growing applications of graphene materials warrant a careful evaluation of their environmental fate in aquatic food webs. Escherichia coli (Bacteria), Tetrahymena thermophila (protozoa), Daphnia magna (zooplankton), and Danio rerio (vertebrate) were used to build aquatic food chains to investigate the waterborne uptake and trophic transfer of ¹⁴C-labeled graphene. Body burden factor (BBF) and trophic transfer factor (TTF) were analyzed for each organism and food chain to assess the bioaccumulation and biomagnification of graphene. The test organisms have high potential of accumulating graphene via direct uptake from culture medium with log-transformed BBF (log BBF) values of 3.66, 5.1, 3.9, and 1.62 for each organism, respectively. In the food chain from E. coli to T. thermophila, the calculated TTFs of 0.2 to 8.6 indicate the high trophic transfer potential in this aquatic food chain. However, the TTFs calculated for the food chain from T. thermophila to D. magna and from D. magna to D. rerio are much lower than 1, indicating that biomagnification was unlikely to occur in these food chains. Body burden measured for dietary uptake by T. thermophila, D. magna, and D. rerio are higher than that via waterborne exposure in a similar nominal concentration, respectively, indicating that trophic transfer is a nonnegligible route for the bioaccumulation of graphene in organisms.

Trophic Transfer and Accumulation of Multiwalled Carbon Nanotubes in the Presence of Copper Ions in Daphnia magna and Fathead Minnow (Pimephales promelas)

The increase in use of nanomaterials such as multiwalled carbon nanotubes (MWCNTs) presents a need to study their interactions with the environment. Trophic transfer was measured between Daphnia magna and Pimephales promelas (fathead minnow, FHM) exposed to MWCNTs with different outer diameter (OD) sizes (MWCNT1 = 8-15 nm OD and MWCNT2 = 20-30 nm OD) in the presence and absence of copper. Pristine FHM were fed D. magna, previously exposed for 3 d to MWCNT1 or MWCNT2 (0.1 mg/L) and copper (0.01 mg/L), for 7 d. D. magna bioaccumulated less MWCNT1 (0.02 μg/g) than MWCNT2 (0.06 μg/g), whereas FHM accumulated more MWCNT1 (0.81 μg/g) than MWCNT2 (0.04 μg/g). In the presence of copper, MWCNT bioaccumulation showed an opposite trend. Mostly MWCNT1 (0.03 μg/g) bioaccumulated in D. magna, however less MWCNT1 (0.21 μg/g) than MWCNT2 (0.32 μg/g) bioaccumulated in FHM. Bioaccumulation factors were higher for MWCNT1s than MWCNT2. However, an opposite trend was observed when copper was added. Plasma metallothionein-2 was measured among treatments; however concentrations were not statistically different from the control. This study demonstrates that trophic transfer of MWCNTs is possible in the aquatic environment and further exploration with mixtures can strengthen the understanding of MWCNT environmental behavior.

Intravenous injection of unfunctionalized carbon-based nanomaterials confirms the minimal toxicity observed in aqueous and dietary exposures in juvenile rainbow trout (Oncorhynchus mykiss)

Numerous ecotoxicology studies of carbon-based nanomaterials (CNMs) have been conducted in fishes; however, different approaches have been used to make CNM dispersions and dose tanks for aqueous exposures, and to prepare food containing CNMs for dietary studies. This diversity of experimental methods has led to conflicting results and difficulties in comparing studies. The objective of the present study was to evaluate intravenous injection of unfunctionalized CNMs in rainbow trout (Oncorhynchus mykiss), as a means of delivering a known internal dose, on tissue biochemistry and histopathological lesions; then, subsequently, to compare the results with our previous work on aqueous and dietary exposures of rainbow trout to CNMs. Rainbow trout were injected in the caudal vein with corn oil dispersions of 200 μg (approximately 1 μg g^-1) of either the fullerene C₆₀, single-walled carbon nanotubes (SWCNTs), or amorphous carbon black. After 96 h, injected fish were euthanized and tissue samples collected for biochemistry and histology. Histological examination of the kidney of fish injected intravenously indicated the presence of black material consistent with the injected carbon treatments. However, there were no additional lesions associated with CNM exposure compared to controls. There were also no significant changes in haematology, or ionoregulatory disturbance in blood plasma among the intravenously injected fish. Significant elevation in lipid peroxidation (thiobarbituric acid reactive substances TBARS) was detected only in kidney and spleen of fish injected with SWCNTs, but not the other carbon treatments. The elevated TBARS following injection contrasted with CNMs delivered via aqueous or dietary routes in our previous studies, suggesting that the latter exposure routes may not lead to absorption and toxicity in the internal tissues. Comparison of the effects of injected CNMs with aqueous and dietary CNMs exposures indicates that these materials are of minimal environmentally-relevant toxicity in rainbow trout.

Effect of single-wall carbon nanotubes on bioconcentration and toxicity of perfluorooctane sulfonate in zebrafish (Danio rerio)

The wide application of nanoparticles will lead its release into the aquatic environment, which may alter the bioavailability and toxicity of other contaminants to aquatic organisms. This work aimed to study the effects of perfluorooctane sulfonate (PFOS), single-wall carbon nanotubes (SWCNT), and their mixture on PFOS accumulation, antioxidant defenses and acetylcholinesterase (AChE) activity in zebrafish. The fish was dissected after being exposed (24, 48, 72 and 96h) separately to PFOS, SWCNT and PFOS+SWCNT co-exposure. The bioaccumulation of PFOS in fish tissues (liver, intestines, gills and brain) decreased with increasing dosage of SWCNT, however, the opposite trend was observed in fish skin, which indicated that the bioavailability of PFOS changed by adsorption on SWCNT. Meanwhile, co-exposure induced more reactive oxygen species (ROS) than PFOS alone and enhanced the effect of PFOS on the superoxide dismutase (SOD), and catalase (CAT) and AChE activities. Furthermore, the integrated biomarker response (IBR) showed that co-exposure was the most stressful circumstance.

Single-walled carbon nanotubes modulate pulmonary immune responses and increase pandemic influenza a virus titers in mice

Background

Numerous toxicological studies have focused on injury caused by exposure to single types of nanoparticles, but few have investigated how such exposures impact a host’s immune response to pathogen challenge. Few studies have shown that nanoparticles can alter a host’s response to pathogens (chiefly bacteria) but there is even less knowledge of the impact of such particles on viral infections. In this study, we performed experiments to investigate if exposure of mice to single-walled carbon nanotubes (SWCNT) alters immune mechanisms and viral titers following subsequent influenza A virus (IAV) infection.

Methods

Male C57BL/6 mice were exposed to 20 μg of SWCNT or control vehicle by intratracheal instillation followed by intranasal exposure to 3.2 × 10⁴ TCID₅₀ IAV or PBS after 3 days. On day 7 mice were euthanized and near-infrared fluorescence (NIRF) imaging was used to track SWCNT in lung tissues. Viral titers, histopathology, and mRNA expression of antiviral and inflammatory genes were measured in lung tissue. Differential cell counts and cytokine levels were quantified in bronchoalveolar lavage fluid (BALF).

Results

Viral titers showed a 63-fold increase in IAV in SWCNT + IAV exposed lungs compared to the IAV only exposure. Quantitation of immune cells in BALF indicated an increase of neutrophils in the IAV group and a mixed profile of lymphocytes and neutrophils in SWCNT + IAV treated mice. NIRF indicated SWCNT remained in the lung throughout the experiment and localized in the junctions of terminal bronchioles, alveolar ducts, and surrounding alveoli. The dual exposure exacerbated pulmonary inflammation and tissue lesions compared to SWCNT or IAV single exposures. IAV exposure increased several cytokine and chemokine levels in BALF, but greater levels of IL-4, IL-12 (P70), IP-10, MIP-1, MIP-1α, MIP-1β, and RANTES were evident in the SWCNT + IAV group. The expression of tlr3, ifnβ1, rantes, ifit2, ifit3, and il8 was induced by IAV alone but several anti-viral targets showed a repressed trend (ifits) with pre-exposure to SWCNT.

Conclusions

These findings reveal a pronounced effect of SWCNT on IAV infection in vivo as evidenced by exacerbated lung injury, increased viral titers and several cytokines/chemokines levels, and reduction of anti-viral gene expression. These results imply that SWCNT can increase susceptibility to respiratory viral infections as a novel mechanism of toxicity.

Electronic supplementary material

The online version of this article (10.1186/s12985-017-0909-z) contains supplementary material, which is available to authorized users.

Exploring uptake and biodistribution of polystyrene (nano)particles in zebrafish embryos at different developmental stages

In ecotoxicology, it is continuously questioned whether (nano)particle exposure results in particle uptake and subsequent biodistribution or if particles adsorb to the epithelial layer only. To contribute to answering this question, we investigated different uptake routes in zebrafish embryos and how they affect particle uptake into organs and within whole organisms. This is addressed by exposing three different life stages of the zebrafish embryo in order to cover the following exposure routes: via chorion and dermal exposure; dermal exposure; oral and dermal exposure. How different nanoparticle sizes affect uptake routes was assessed by using polystyrene particles of 25, 50, 250 and 700nm. In our experimental study, we showed that particle uptake in biota is restricted to oral exposure, whereas the dermal route resulted in adsorption to the epidermis and gills only. Ingestion followed by biodistribution was observed for the tested particles of 25 and 50nm. The particles spread through the body and eventually accumulated in specific organs and tissues such as the eyes. Particles larger than 50nm were predominantly adsorbed onto the intestinal tract and outer epidermis of zebrafish embryos. Embryos exposed to particles via both epidermis and intestine showed highest uptake and eventually accumulated particles in the eye, whereas uptake of particles via the chorion and epidermis resulted in marginal uptake. Organ uptake and internal distribution should be monitored more closely to provide more in depth information of the toxicity of particles.

Interference of single walled carbon nanotubes (SWCNT) in the measurement of lipid peroxidation in aquatic organisms through TBARS assay

Nanomaterials (NM) exhibit unique properties due their size and relative area, but the mechanisms and effects in the living organisms are yet to be unfold in their totality. Potential toxicity mechanisms concerning NM as carbon nanotubes include oxidative stress generation. Several fluorimetric and colorimetric methods have been systematically used to measure NM toxicity, and controversial results have been reported. One of the problems can be related to the interference effects induced by NM, leading to artifacts that can lead to misleading conclusions. In present study, it was performed in vitro assays with two aquatic species: the zebrafish Danio rerio and the polychaete Laeonereis acuta to evaluate the potential interference capacity of single-wall carbon nanotubes (SWCNT) in a fluorometric method (TBARS assay) to measure lipid peroxidation. Obtained results indicated that gills and brain of zebrafish presented a lowered fluorescence only at extremely high concentrations (50 and 500mg/L). Determinations in anterior, middle, and posterior body regions of L. acuta showed a quite different pattern: high fluorescence at low SWCNT concentrations (0.5mg/L) and lowering at the highest (500mg/L). To eliminate matrix effect of biological samples, tests employing the standard for TBARS assay, 1,3,3-tetramethoxipropane, were run and the results showed again higher fluorescence values at low concentrations (0.5-5mg SWCNT/L), a technique artifact that could lead to misleading conclusions since higher fluorescence values implicate higher TBARS concentration, implying oxidative stress. Using the colorimetric FOX assay with cumene hydroperoxide as standard presented remarkable better results since no artifacts were observed in the same SWCNT concentration range that employed with the TBARS technique.

Reviews of the toxicity behavior of five potential engineered nanomaterials (ENMs) into the aquatic ecosystem

Presently, engineered nanomaterials (ENMs) are used in a wide variety of commercial applications, resulting in an uncontrolled introduction into the aquatic environment. The purpose of this review is to summarize the pathways and factors that controlling the transport and toxicity of five extensively used ENMs. These toxicological pathways are of great importance and need to be addressed for sustainable implications of ENMs without environmental liabilities. Here we discuss five potentially utilized ENMs with their possible toxicological risk factors to aquatic plants, vertebrates model and microbes. Moreover, the key effect of ENMs surface transformations by significant reaction with environmental objects such as dissolved natural organic matter (DOM) and the effect of ENMs surface coating and surface charge will also be debated. The transformations of ENMs are subsequently facing a major ecological transition that is expected to create a substantial toxicological effect towards the ecosystem. These transformations largely involve chemical and physical processes, which depend on the properties of both ENMs and the receiving medium. In this review article, the critical issues that controlling the transport and toxicity of ENMs are reviewed by exploiting the latest reports and future directions and targets are keenly discussed to minimize the pessimistic effects of ENMs.

Biological Uptake, Distribution, and Depuration of Radio-Labeled Graphene in Adult Zebrafish: Effects of Graphene Size and Natural Organic Matter

The exciting commercial application potential of graphene materials may inevitably lead to their increasing release into the environment where they may pose ecological risks. This study focused on using carbon-14-labeled few-layer graphene (FLG) to determine whether the size of graphene plays a role in its uptake, depuration, and biodistribution in adult zebrafish. After 48 h exposure to larger FLG (L-FLG) at 250 μg/L, the amount of graphene in the organism was close to 48 mg/kg fish dry mass, which was more than 170-fold greater than the body burden of those exposed to the same concentration of smaller FLG (S-FLG). The amount of uptake for both L-FLG and S-FLG increased by a factor of 2.5 and 16, respectively, when natural organic matter (NOM) was added in the exposure suspension. While the L-FLG mainly accumulated in the gut of adult zebrafish, the S-FLG was found in both the gut and liver after exposure with or without NOM. Strikingly, the S-FLG was able to pass through the intestinal wall and enter the intestinal epithelial cells and blood. The presence of NOM increased the quantity of S-FLG in these cells. Exposure to L-FLG or S-FLG also had a significantly different impact on the intestinal microbial community structure.

Influence of the Gastrointestinal Environment on the Bioavailability of Ethinyl Estradiol Sorbed to Single-Walled Carbon Nanotubes

Recent evidence suggests that, because of their sorptive nature, if single-walled carbon nanotubes (SWCNTs) make their way into aquatic environments, they may reduce the toxicity of other waterborne contaminants. However, few studies have examined whether contaminants remain adsorbed following ingestion by aquatic organisms. The objective of this study was to examine the bioavailability and bioactivity of ethinyl estradiol (EE2) sorbed onto SWCNTs in a fish gastrointestinal (GI) tract. Sorption experiments indicated that SWCNTs effectively adsorbed EE2, but the chemical was still able to bind and activate soluble estrogen receptors (ERs) in vitro. However, centrifugation to remove SWCNTs and adsorbed EE2 significantly reduced ER activity compared to that of EE2 alone. Additionally, the presence of SWCNTs did not reduce the extent of EE2-driven induction of vitellogenin 1 in vivo compared to the levels in organisms exposed to EE2 alone. These results suggest that while SWCNTs adsorb EE2 from aqueous solutions, under biological conditions EE2 can desorb and retain bioactivity. Additional results indicate that interactions with gastrointestinal proteins may decrease the level of adsorption of estrogen to SWCNTs by 5%. This study presents valuable data for elucidating how SWCNTs interact with chemicals that are already present in our aquatic environments, which is essential for determining their potential health risk.

Increasing evidence indicates low bioaccumulation of carbon nanotubes

As the production of carbon nanotubes (CNTs) expands, so might the potential for release into the environment. The possibility of bioaccumulation and toxicological effects has prompted research on their fate and potential ecological effects. For many organic chemicals, bioaccumulation properties are associated with lipid-water partitioning properties. However, predictions based on phase partitioning provide a poor fit for nanomaterials. In the absence of data on the bioaccumulation and other properties of CNTs, the Office of Pollution Prevention and Toxics (OPPT) within the US Environmental Protection Agency (EPA) subjects new pre-manufacture submissions for all nanomaterials to a higher-level review. We review the literature on CNT bioaccumulation by plants, invertebrates and non-mammalian vertebrates, summarizing 40 studies to improve the assessment of the potential for bioaccumulation. Because the properties and environmental fate of CNTs may be affected by type (single versus multiwall), functionalization, and dosing technique, the bioaccumulation studies were reviewed with respect to these factors. Absorption into tissues and elimination behaviors across species were also investigated. All of the invertebrate and non-mammalian vertebrate studies showed little to no absorption of the material from the gut tract to other tissues. These findings combined with the lack of biomagnification in the CNT trophic transfer studies conducted to date suggest that the overall risk of trophic transfer is low. Based on the available data, in particular the low levels of absorption of CNTs across epithelial surfaces, CNTs generally appear to form a class that should be designated as a low concern for bioaccumulation.

Considerations of Environmentally Relevant Test Conditions for Improved Evaluation of Ecological Hazards of Engineered Nanomaterials

Engineered nanomaterials (ENMs) are increasingly entering the environment with uncertain consequences including potential ecological effects. Various research communities view differently whether ecotoxicological testing of ENMs should be conducted using environmentally relevant concentrations-where observing outcomes is difficult-versus higher ENM doses, where responses are observable. What exposure conditions are typically used in assessing ENM hazards to populations? What conditions are used to test ecosystem-scale hazards? What is known regarding actual ENMs in the environment, via measurements or modeling simulations? How should exposure conditions, ENM transformation, dose, and body burden be used in interpreting biological and computational findings for assessing risks? These questions were addressed in the context of this critical review. As a result, three main recommendations emerged. First, researchers should improve ecotoxicology of ENMs by choosing test end points, duration, and study conditions-including ENM test concentrations-that align with realistic exposure scenarios. Second, testing should proceed via tiers with iterative feedback that informs experiments at other levels of biological organization. Finally, environmental realism in ENM hazard assessments should involve greater coordination among ENM quantitative analysts, exposure modelers, and ecotoxicologists, across government, industry, and academia.

Quantification of Carbon Nanotubes in Environmental Matrices: Current Capabilities, Case Studies, and Future Prospects

Carbon nanotubes (CNTs) have numerous exciting potential applications and some that have reached commercialization. As such, quantitative measurements of CNTs in key environmental matrices (water, soil, sediment, and biological tissues) are needed to address concerns about their potential environmental and human health risks and to inform application development. However, standard methods for CNT quantification are not yet available. We systematically and critically review each component of the current methods for CNT quantification including CNT extraction approaches, potential biases, limits of detection, and potential for standardization. This review reveals that many of the techniques with the lowest detection limits require uncommon equipment or expertise, and thus, they are not frequently accessible. Additionally, changes to the CNTs (e.g., agglomeration) after environmental release and matrix effects can cause biases for many of the techniques, and biasing factors vary among the techniques. Five case studies are provided to illustrate how to use this information to inform responses to real-world scenarios such as monitoring potential CNT discharge into a river or ecotoxicity testing by a testing laboratory. Overall, substantial progress has been made in improving CNT quantification during the past ten years, but additional work is needed for standardization, development of extraction techniques from complex matrices, and multimethod comparisons of standard samples to reveal the comparability of techniques.

Carbon nanomaterials: multi-functional agents for biomedical fluorescence and Raman imaging

Carbon based nanomaterials have emerged over the last few years as important agents for biomedical fluorescence and Raman imaging applications. These spectroscopic techniques utilize either fluorescently labelled carbon nanomaterials or the intrinsic photophysical properties of the carbon nanomaterial. In this review article we present the utilization and performance of several classes of carbon nanomaterials, namely carbon nanotubes, carbon nanohorns, carbon nanoonions, nanodiamonds and different graphene derivatives, which are currently employed for in vitro as well as in vivo imaging in biology and medicine. A variety of different approaches, imaging agents and techniques are examined and the specific properties of the various carbon based imaging agents are discussed. Some theranostic carbon nanomaterials, which combine diagnostic features (i.e. imaging) with cell specific targeting and therapeutic approaches (i.e. drug delivery or photothermal therapy), are also included in this overview.

Toxicity assessment and bioaccumulation in zebrafish embryos exposed to carbon nanotubes suspended in Pluronic® F-108

Carbon nanotubes (CNTs) are often suspended in Pluronic® surfactants by sonication, which may confound toxicity studies because sonication of surfactants can create degradation products that are toxic to mammalian cells. Here, we present a toxicity assessment of Pluronic® F-108 with and without suspended CNTs using embryonic zebrafish as an in vivo model. Pluronic® sonolytic degradation products were toxic to zebrafish embryos just as they were to mammalian cells. When the toxic Pluronic® fragments were removed, there was little effect of pristine multi-walled CNTs (pMWNTs), carboxylated MWNTs (cMWNTs) or pristine single-walled carbon nanotubes (pSWNTs) on embryo viability and development, even at high concentrations. A gel electrophoretic method coupled with Raman imaging was developed to measure the bioaccumulation of CNTs by zebrafish embryos, and dose-dependent uptake of CNTs was observed. These data indicate that embryos accumulate pMWNTs, cMWNTs and pSWNTs yet there is very little embryo toxicity.

Examination of Single-Walled Carbon Nanotubes Uptake and Toxicity from Dietary Exposure: Tracking Movement and Impacts in the Gastrointestinal System

Previous studies indicate that exposure of fish to pristine single-walled carbon nanotubes (SWCNTs) by oral gavage, causes no overt toxicity, and no appreciable absorption has been observed. However, in the environment, SWCNTs are likely to be present in dietary sources, which may result in differential impacts on uptake and biological effects. Additionally, the potential of these materials to sorb nutrients (proteins, carbohydrates, and lipids) while present in the gastrointestinal (GI) tract may lead to nutrient depletion conditions that impact processes such as growth and reproduction. To test this phenomenon, fathead minnows were fed a commercial diet either with or without SWCNTs for 96 h. Tracking and quantification of SWCNTs using near-infrared fluorescence (NIRF) imaging during feeding studies showed the presence of food does not facilitate transport of SWCNTs across the intestinal epithelia. Targeting genes shown to be responsive to nutrient depletion (peptide transporters, peptide hormones, and lipases) indicated that pept2, a peptide transporter, and cck, a peptide hormone, showed differential mRNA expression by 96 h, a response that may be indicative of nutrient limitation. The results of the current study increase our understanding of the movement of SWCNTs through the GI tract, while the changes in nutrient processing genes highlight a novel mechanism of sublethal toxicity in aquatic organisms.

Single-walled carbon nanotubes increase pandemic influenza A H1N1 virus infectivity of lung epithelial cells

Background

Airborne exposure to nanomaterials from unintended occupational or environmental exposures or as a consequence of product use may lead to adverse health effects. Numerous studies have focused on single-walled carbon nanotubes (SWCNTs) and their ability to cause pulmonary injury related to fibrosis, and cancer; however few studies have addressed their impact on infectious agents, particularly viruses that are known for causing severe disease. Here we have demonstrated the ability of pristine SWCNTs of diverse electronic structure to increase the susceptibility of small airway epithelial cells (SAEC) to pandemic influenza A H1N1 infection and discerned potential mechanisms of action driving this response.

Methods

Small airway epithelial cells (SAEC) were exposed to three types of SWCNTs with varying electronic structure (SG65, SG76, CG200) followed by infection with A/Mexico/4108/2009 (pH1N1). Cells were then assayed for viral infectivity by immunofluorescence and viral titers. We quantified mRNA and protein levels of targets involved in inflammation and anti-viral activity (INFβ1, IL-8, RANTES/CCL5, IFIT2, IFIT3, ST3GAL4, ST6GAL1, IL-10), localized sialic acid receptors, and assessed mitochondrial function. Hyperspectral imaging analysis was performed to map the SWCNTs and virus particles in fixed SAEC preparations. We additionally performed characterization analysis to monitor SWCNT aggregate size and structure under biological conditions using dynamic light scattering (DLS), static light scattering (SLS).

Results

Based on data from viral titer and immunofluorescence assays, we report that pre-treatment of SAEC with SWCNTs significantly enhances viral infectivity that is not dependent on SWCNT electronic structure and aggregate size within the range of 106 nm – 243 nm. We further provide evidence to support that this noted effect on infectivity is not likely due to direct interaction of the virus and nanoparticles, but rather a combination of suppression of pro-inflammatory (RANTES) and anti-viral (IFIT2, IFIT3) gene/protein expression, impaired mitochondrial function and modulation of viral receptors by SWCNTs.

Conclusions

Results of this work reveal the potential for SWCNTs to increase susceptibility to viral infections as a mechanism of adverse effect. These data highlight the importance of investigating the ability of carbon-nanomaterials to modulate the immune system, including impacts on anti-viral mechanisms in lung cells, thereby increasing susceptibility to infectious agents.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0066-0) contains supplementary material, which is available to authorized users.

Accumulation and distribution of multiwalled carbon nanotubes in zebrafish (Danio rerio)

No data on the bioaccumulation and distribution of multiwalled carbon nanotubes (MWCNTs) in aquatic vertebrates is available until now. We quantified uptake and elimination of dispersed radiolabeled MWCNTs ((14)C-MWCNT; 1 mg/L) by zebrafish (Danio rerio) over time. The influences of the feeding regime and presence of dissolved organic carbon (DOC) on accumulation of the nanomaterial were determined. The partitioning of radioactivity to different organs and tissues was measured in all experiments. A bioaccumulation factor of 16 L/kg fish wet weight was derived. MWCNTs quickly associated with the fish, and steady state was reached within 1 day. After transfer to clear medium, MWCNTs were quickly released to the water phase, but on average 5 mg of MWCNTs/kg fish dry weight remained associated with the fish. The nanomaterial mainly accumulated in the gut of all fish. Feeding led to lower internal concentrations due to facilitated elimination via the digestive tract. In the presence of DOC, 10-fold less was taken up by the fish after 48 h of exposure compared to without DOC. Quick adhesion to and detachment from superficial tissues were observed. Remarkably, little fractions of the internalized radioactivity were detected in the blood and muscle tissue of exposed fish. The part accumulated in these fish compartments remained constant during the elimination phase. Hence, biomagnification of MWCNTs in the food chain is possible and should be a subject of further research.

Emergent Properties and Toxicological Considerations for Nanohybrid Materials in Aquatic Systems

Conjugation of multiple nanomaterials has become the focus of recent materials development. This new material class is commonly known as nanohybrids or "horizon nanomaterials". Conjugation of metal/metal oxides with carbonaceous nanomaterials and overcoating or doping of one metal with another have been pursued to enhance material performance and/or incorporate multifunctionality into nano-enabled devices and processes. Nanohybrids are already at use in commercialized energy, electronics and medical products, which warrant immediate attention for their safety evaluation. These conjugated ensembles likely present a new set of physicochemical properties that are unique to their individual component attributes, hence increasing uncertainty in their risk evaluation. Established toxicological testing strategies and enumerated underlying mechanisms will thus need to be re-evaluated for the assessment of these horizon materials. This review will present a critical discussion on the altered physicochemical properties of nanohybrids and analyze the validity of existing nanotoxicology data against these unique properties. The article will also propose strategies to evaluate the conjugate materials' safety to help undertake future toxicological research on the nanohybrid material class.