Uptake of Ag and TiO2 nanoparticles by zebrafish embryos in the presence of other contaminants in the aquatic environment

Toxicokinetics and Particle Number-Based Trophic Transfer of a Metallic Nanoparticle Mixture in a Terrestrial Food Chain

Herein, we investigated to which extent metallic nanoparticles (MNPs) affect the trophic transfer of other coexisting MNPs from lettuce to terrestrial snails and the associated tissue-specific distribution using toxicokinetic (TK) modeling and single-particle inductively coupled plasma mass spectrometry. During a period of 22 days, snails were fed with lettuce leaves that were root exposed to AgNO3 (0.05 mg/L), AgNPs (0.75 mg/L), TiO2NPs (200 mg/L), and a mixture of AgNPs and TiO2NPs (equivalent doses as for single NPs). The uptake rate constants (ku) were 0.08 and 0.11 kg leaves/kg snail/d for Ag and 1.63 and 1.79 kg leaves/kg snail/d for Ti in snails fed with NPs single- and mixture-exposed lettuce, respectively. The elimination rate constants (ke) of Ag in snails exposed to single AgNPs and mixed AgNPs were comparable to the corresponding ku, while the ke for Ti were lower than the corresponding ku. As a result, single TiO2NP treatments as well as exposure to mixtures containing TiO2NPs induced significant biomagnification from lettuce to snails with kinetic trophic transfer factors (TTFk) of 7.99 and 6.46. The TTFk of Ag in the single AgNPs treatment (1.15 kg leaves/kg snail) was significantly greater than the TTFk in the mixture treatment (0.85 kg leaves/kg snail), while the fraction of Ag remaining in the body of snails after AgNPs exposure (36%) was lower than the Ag fraction remaining after mixture exposure (50%). These results indicated that the presence of TiO2NPs inhibited the trophic transfer of AgNPs from lettuce to snails but enhanced the retention of AgNPs in snails. Biomagnification of AgNPs from lettuce to snails was observed in an AgNPs single treatment using AgNPs number as the dose metric, which was reflected by the particle number-based TTFs of AgNPs in snails (1.67, i.e., higher than 1). The size distribution of AgNPs was shifted across the lettuce-snail food chain. By making use of particle-specific measurements and fitting TK processes, this research provides important implications for potential risks associated with the trophic transfer of MNP mixtures.

Embryonic Toxicology Evaluation of Ginger- and Clove-mediated Titanium Oxide Nanoparticles-based Dental Varnish with Zebrafish

AIM

The aim of the study is to evaluate the embryonic toxicology of ginger- and clove-mediated titanium oxide (TiO2) nanoparticles (NPs)-based dental varnish with zebrafish (Danio rerio).

MATERIALS AND METHODS

Dental varnish was formulated using ginger, clove extract, and titanium dioxide NPs followed by the introduction of this test solution at concentrations of 1, 2, 4, 8, and 16 µL along with a control group with medium zebrafish embryos into a 6-well culture plate. After 2 hours of incubation, the embryos of zebrafish were tested and analyzed for hatchability and mortality rate using one-way ANOVA and post hoc Tukey's tests using statistical package for the social sciences (SPSS) software.

RESULTS

The hatching rate of zebrafish embryos was greatest at 1 µL in a declining order when compared to the control group, whereas the mortality rate was greatest at 16 µL compared to the control group. On intergroup comparisons, one-way analysis of variance (ANOVA) has revealed a significance (p = 0.00) between the concentrations and testing parameters such as hatchability and mortality.

CONCLUSION

Within the limitations of the study, the zebrafish embryos exposed acutely to TiO2 NPs at experimental doses have shown significant changes in their rate of deformity and capacity to hatch at 16- and 1-µL concentrations of the dental varnish formulation, respectively. Furthermore, studies are required to prove the efficacy of the formulation.

CLINICAL SIGNIFICANCE

Research and development of new formulations of various dental products is an ongoing process. One such segment is dental varnishes, wherein herbal resources and NPs mediated for improved efficacy against dental caries is an emerging alternative aiming to counteract the limitations posed by the traditional agents. To develop a new formulation of dental varnish, which is herbal resourced and NPs mediated, for an improved efficacy against dental caries.

Dispersion of Hydrophilic "Hedgehog" Microparticles in Liquid CO2 Mixtures

Liquid and supercritical CO₂ are nontoxic and nonflammable reaction media with pressure-variable physical properties. These states of CO₂ also have high solubility limits for gas and liquid hydrocarbons, making them good candidates for "green" hydrophobic solvents in sustainable chemical technologies. However, the dispersion of hydrophilic colloidal nanoscale and microscale particles in CO₂ is challenging due to the tendency of polar particles to aggregate in nonpolar media, limiting their available surface area and catalytic efficiencies. Here we show that native hydrophilic semiconductor particles can be effectively dispersed in a liquid CO₂ mixture with acetonitrile (ACN) without additional chemical or mechanical dispersion techniques. Using surface corrugation as a method to prevent aggregation, we find that geometrically complex particles with a halo of stiff nanoscale spikes disperse and remain suspended longer in liquid CO₂ than those without or with less prominent nanoscale corrugation. For the particles of this size and liquid CO₂ mixtures, individual particle mass remains a prominent factor determining particle sedimentation rate even in the absence of aggregation. Particle dispersion and structural stability are confirmed using a combination of UV-vis spectroscopy, finite-difference time-domain modeling, and electron microscopy. The necessity of the cosolvent (ACN) indicates that particle behavior in liquid CO₂ is vastly different than in traditional liquid-phase solvents and highlights the need for future studies to understand the wetting behavior of hydrophilic particles in high-pressure nonpolar environments.

Comprehensive Review on the Degradation Chemistry and Toxicity Studies of Functional Materials

In recent decades there has been growing interest of material chemists in the successful development of functional materials for drug delivery, tissue engineering, imaging, diagnosis, theranostic, and other biomedical applications with advanced nanotechnology tools. The efficacy and safety of functional materials are determined by their pharmacological, toxicological, and immunogenic effects. It is essential to consider all degradation pathways of functional materials and to assess plausible intermediates and final products for quality control. This review provides a brief insight into chemical degradation mechanisms of functional materials like oxidation, photodegradation, and physical and enzymatic degradation. The intermediates and products of degradation were confirmed with analytical methods such as proton nuclear magnetic resonance (¹H NMR), gel permeation chromatography (GPC), UV-vis spectroscopy (UV-vis), infrared spectroscopy (IR), differential scanning calorimetry (DSC), mass spectroscopy, and other sophisticated analytical methods. These analytical methods are also used for regulatory, quality control, and stability purposes in industry. The assessment of degradation is important to predetermine the behavior of functional materials in specific storage conditions and can be relevant to their behavior during in vivo applications. Another important aspect is the evaluation of the toxicity of functional materials. Toxicity can be accessed with various methods using in vitro, in vivo, ex vivo, and in silico models. In vitro cell culture methods are used to determine mitochondrial damage, reactive oxygen species, stress responses, and cellular toxicity. In vitro cellular toxicity can be measured by MTT assay, LDH leakage assay, and hemolysis. In vivo studies are performed using various animal models involving zebrafish, rodents (mice and rats), and nonhuman primates. Ex vivo studies are also used for efficacy and toxicity determinations of functional materials like ex vivo potency assay and precision-cut liver slice (PCLS) models. The in silico tools with computational simulations like quantitative structure-activity relationships (QSAR), pharmacokinetics (PK) and pharmacodynamics (PD), dose and time response, and quantitative cationic-activity relationships ((Q)CARs) are used for prediction of the toxicity of functional materials. In this review, we studied the principle methods used for degradation studies, different degradation pathways, and mechanisms of functional material degradation with prototype examples. We discuss toxicity assessments with different toxicity approaches used for estimation of the safety and efficacy of functional materials.

Evaluation of Zebrafish DNA Integrity after Individual and Combined Exposure to TiO2 Nanoparticles and Lincomycin

Environmental contamination by nanoparticles (NPs) and drugs represents one of the most debated issues of the last years. The aquatic biome and, indirectly, human health are strongly influenced by the negative effects induced by the widespread presence of pharmaceutical products in wastewater, mainly due to the massive use of antibiotics and inefficient treatment of the waters. The present study aimed to evaluate the harmful consequences due to exposure to antibiotics and NPs, alone and in combination, in the aquatic environment. By exploiting some of their peculiar characteristics, such as small size and ability to bind different types of substances, NPs can carry drugs into the body, showing potential genotoxic effects. The research was conducted on zebrafish (Danio rerio) exposed in vivo to lincomycin (100 mg/L) and titanium dioxide nanoparticles (TiO₂ NPs) (10 µg/L) for 7 and 14 exposure days. The effects on zebrafish were evaluated in terms of cell viability, DNA fragmentation, and genomic template stability (GTS%) investigated using Trypan blue staining, TUNEL assay, and the random amplification of polymorphic DNA PCR (RAPD PCR) technique, respectively. Our results show that after TiO₂ NPs exposure, as well as after TiO₂ NPs and lincomycin co-exposure, the percentage of damaged DNA significantly increased and cell viability decreased. On the contrary, exposure to lincomycin alone caused only a GTS% reduction after 14 exposure days. Therefore, the results allow us to assert that genotoxic effect in target cells could be through a synergistic effect, also potentially mediated by the establishment of intermolecular interactions between lincomycin and TiO₂ NPs.

Effects of powdered activated carbon and calcium on trihalomethane toxicity of zebrafish embryos and larvae in hybrid membrane bioreactors

This study investigated the effect of powdered activated carbon and calcium on trihalomethane toxicity in zebrafish embryos and larvae in hybrid membrane bioreactors. Two hybrid membrane bioreactors were configured with the addition of powdered activated carbon or calcium to reduce the trihalomethane formation potential. Trihalomethane formation decreased by approximately 37.2% and 30.3% in membrane bioreactor-powdered activated carbon and membrane bioreactor-calcium, respectively. Additionally, the toxic effect of trihalomethane formation was examined on zebrafish embryos and larvae. About 35% of the embryos exposed to trihalomethanes (800 ppb) showed signs of deformation, with the majority displaying coagulation within 24 h after exposure. Color preference tests, which were conducted to identify any abnormal activities of the embryos, showed an increase in preference from short to longer wavelengths upon exposure to high levels of trihalomethanes. This may indicate damage to the optical organs in zebrafish when exposed to trihalomethanes. Behavioral analysis showed reduced mobility of zebrafish larvae under different trihalomethane concentrations, indicating a decrease in the average activity time with an increasing trihalomethane concentration. The membrane bioreactor effluents were toxic to zebrafish embryos and larvae in the presence of high trihalomethane concentrations. To understand the mechanism behind trihalomethane toxicity, further studies are needed.

Characterizing the effects of titanium dioxide and silver nanoparticles released from painted surfaces due to weathering on zebrafish (Danio rerio)

Silver (nAg) and titanium dioxide nanoparticles (nTiO₂) are common engineered nanoparticles (ENPs) added into paint for their antimicrobial and whitening properties, respectively. Weathering of outdoor painted surfaces can release such ENPs, though little is known about the potential effects of released ENPs on aquatic species. The objective of this study was to characterize the toxicity of nAg and nTiO₂ released from painted panels using fish liver cells (CRL2643) and zebrafish embryos (OECD 236 embryotoxicity test). Cells and embryos were exposed to suspensions of pristine nAg or nTiO₂, panels (unpainted or painted with nAg or nTiO₂) or base paint, after sonication. Cell viability and gene expression were assessed using resazurin assay and qPCR, respectively, while embryo mortality and deformities were scored visually via microscopic examination. In the cell studies, both paint-released nanoparticles did not affect viability, but paint-released nAg resulted in differential expression of a few genes including gclc and ncf1. In embryos, paint-released nAg increased mortality and incidence of deformities, whereas paint-released nTiO₂ resulted in differential expression of several genes including gclc, ncf1, txnrd1, gpx1b, and cyp1c1 but without major phenotypic abnormalities. Comparing the two types of exposures, paint-released exposures affected both molecular (gene expression) and apical (embryotoxicity) endpoints, while pristine exposures affected the expression of some genes but had no apical effects. The differing effects of paint-released and pristine nanoparticle exposures suggest that further research is needed to further understand how paint coatings (and the products of their weathering and aging) may influence nanoparticle toxicity to aquatic organisms.

Catalytic ozonation of iohexol with α-Fe0.9Mn0.1OOH in water: Efficiency, degradation mechanism and toxicity evaluation

Iohexol, a widely used iodinated X-ray contrast media, is difficult to completely degrade with the traditional water treatment process. Catalytic ozonation with synthesized α-Fe_0.9Mn_0.1OOH as the catalyst can significantly promote the degradation of iohexol relative to that with ozonation alone. Hydroxyl radicals play a predominant role during the degradation of iohexol. The effect of various factors, including catalyst dose, ozone dose, iohexol concentration and water matrix factors, on the catalytic performance were investigated. The presence of α-Fe_0.9Mn_0.1OOH in the catalytic system can significantly promote the removal of iohexol and mineralization of the dissolved organic carbon in real water samples. The intermediate products were determined by high-resolution liquid chromatography, and the reaction site was predicted by frontier electron density (FED) calculations. The degradation mechanism of iohexol followed the processes of H-abstraction, amide hydrolysis, amide oxidation, and ·OH substitution. Higher exposure concentrations of iohexol had a negative effect on the survival and hatching rates in the development of zebrafish embryos. The autonomic movement process and heartbeat rate of the zebrafish larvae showed significant differences as the exposure concentration of iohexol increased. The catalytic ozonation process with α-Fe_0.9Mn_0.1OOH can decrease the toxicity of iohexol containing water.

Status Quo in Data Availability and Predictive Models of Nano-Mixture Toxicity

Co-exposure of nanomaterials and chemicals can cause mixture toxicity effects to living organisms. Predictive models might help to reduce the intensive laboratory experiments required for determining the toxicity of the mixtures. Previously, concentration addition (CA), independent action (IA), and quantitative structure–activity relationship (QSAR)-based models were successfully applied to mixtures of organic chemicals. However, there were few studies concerning predictive models for toxicity of nano-mixtures before June 2020. Previous reviews provided comprehensive knowledge of computational models and mechanisms for chemical mixture toxicity. There is a gap in the reviewing of datasets and predictive models, which might cause obstacles in the toxicity assessment of nano-mixtures by using in silico approach. In this review, we collected 183 studies of nano-mixture toxicity and curated data to investigate the current data and model availability and gap and to derive research challenges to facilitate further experimental studies for data gap filling and the development of predictive models.

The Crucial Role of Environmental Coronas in Determining the Biological Effects of Engineered Nanomaterials

In aquatic environments, a large number of ecological macromolecules (e.g., natural organic matter (NOM), extracellular polymeric substances (EPS), and proteins) can adsorb onto the surface of engineered nanomaterials (ENMs) to form a unique environmental corona. The presence of environmental corona as an eco-nano interface can significantly alter the bioavailability, biocompatibility, and toxicity of pristine ENMs to aquatic organisms. However, as an emerging field, research on the impact of the environmental corona on the fate and behavior of ENMs in aquatic environments is still in its infancy. To promote a deeper understanding of its importance in driving or moderating ENM toxicity, this study systemically recapitulates the literature of representative types of macromolecules that are adsorbed onto ENMs; these constitute the environmental corona, including NOM, EPS, proteins, and surfactants. Next, the ecotoxicological effects of environmental corona-coated ENMs on representative aquatic organisms at different trophic levels are discussed in comparison to pristine ENMs, based on the reported studies. According to this analysis, molecular mechanisms triggered by pristine and environmental corona-coated ENMs are compared, including membrane adhesion, membrane damage, cellular internalization, oxidative stress, immunotoxicity, genotoxicity, and reproductive toxicity. Finally, current knowledge gaps and challenges in this field are discussed from the ecotoxicology perspective.

Long-Term Effects of Copper Nanopesticides on Soil and Sediment Community Diversity in Two Outdoor Mesocosm Experiments

The use of novel pesticides containing nanomaterials (nanopesticides) is growing and is considered a promising approach to reduce the impacts of agriculture on the environment and human health. However, the environmental effects of these novel agrochemicals are not fully characterized, and more research is needed to determine the benefits and risks they confer. Here, we assessed the impacts of repeated exposures to a Cu(OH)₂ nanopesticide on the soil and sediment biodiversity of target (terrestrial) and nontarget (wetland) ecosystems by performing long-term outdoor mesocosm experiments. As pesticides are often used concomitantly with other agrochemicals, we also tested for interactive effects between nanopesticide exposure and fertilization treatments in both ecosystems. We used high-throughput sequencing on three marker genes to characterize effects on bacterial, fungal, and total eukaryotic community structure and diversity. Interestingly, we found limited effects of nanopesticide exposure on the terrestrial soil communities. Conversely, we found significant shifts in the sediment communities of the wetland mesocosms, especially for eukaryotes (protists, fungi, and algae). In the absence of fertilization, fungal and total eukaryotic community compositions exposed to nanopesticides for long periods of time were distinct from unexposed communities. We identified 60 taxa that were significantly affected by nanopesticide exposure, most of which were microeukaryotes affiliated to cercozoans, Gastrotricha, or unicellular algal taxa. Our study suggests that this nanopesticide has limited effects on the soil biodiversity of a target terrestrial agroecosystem, while nontarget aquatic communities are more sensitive, particularly among protists which are not targeted by this bactericide/fungicide.

The zebrafish embryotoxicity test (ZET) for nanotoxicity assessment: from morphological to molecular approach

Nanotechnology and use of nanomaterials (NMs) improve life quality, economic growth and environmental health. However, the increasing production and use of NMs in commercial products has led to concerns about their potential toxicity on human and environment health, as well as its toxicological classification and regulation. In this context, there is an urgent need to standardize and validate procedures for nanotoxicity testing. Since the zebrafish embryotoxicity test (ZET) has been indicated as a suitable approach for the toxicity assessment of traditional and emergent pollutants, the aim of this review is to summarize the existing literature on embryotoxic and teratogenic effects of NMs on zebrafish. In addition, morphological changes in zebrafish embryos induced by NMs were classified in four reaction models, allowing classification of the mode of action and toxicity of different types of NM. Revised data showed that the interaction and bioaccumulation of NMs on zebrafish embryos were associated to several toxic effects, while the detoxification process was limited. In general, NMs induced delayed hatching, circulatory changes, pigmentation and tegumentary alterations, musculoskeletal disorders and yolk sac alterations on zebrafish embryos. Recommendations for nanotoxicological tests are given, including guidance for future research. This review reinforces the use of the ZET as a suitable approach to assess the health risks of NM exposure.

Effects of hydrophobicity of titanium dioxide nanoparticles and exposure scenarios on copper uptake and toxicity in Daphnia magna

Titanium dioxide (TiO₂) nanoparticles (NPs) encounter heavy metals in the environment under different scenarios. However, the mechanism of their joint toxicity effects on Daphnia magna remains vague. This study assessed the effects of hydrophobicity of TiO₂ NPs (TDONPs) and exposure scenarios on copper uptake and toxicity in Daphnia magna. In the individual exposure scenario, hydrophilic and hydrophobic TDONPs both showed no acute toxicity to Daphnia magna, whereas individual Cu²⁺ exposure resulted in a 30% mortality rate. Co-exposure and sequential exposure to the two types of TDONP and Cu²⁺ resulted in mortality rates of 40%-50%. The mechanisms of the increased Cu²⁺ toxicity caused by hydrophilic and hydrophobic TDONP were different. In the presence of hydrophobic TDONPs, the Cu toxicity could be attributed to the increased bioaccumulation of Cu and Ti, leading to high oxidative stress injury. The Cu toxicity due to hydrophilic TDONPs could be induced by intensified intestinal membrane damage. The obtained data suggest that the hydrophobicity of the TDONPs plays a critical role in regulating the toxicity of Cu²⁺.

Toxic Effects of TiO₂ NPs on Zebrafish

Titanium dioxide nanoparticles (TiO₂ NPs) have become a widely used nanomaterial due to the photocatalytic activity and absorption of ultraviolet light of specific wavelengths. This study investigated the toxic effects of rutile TiO₂ NPs on zebrafish by examining its embryos and adults. In the embryo acute toxicity test, exposure to 100 mg/L TiO₂ NPs didn’t affect the hatching rate of zebrafish embryos, and there was no sign of deformity. In the adult toxicity test, the effects of TiO₂ NPs on oxidative damage in liver, intestine and gill tissue were studied. Enzyme linked immunosorbent assay (ELISA) and fluorescence-based quantitative real-time reverse transcription PCR (qRT-PCR) were used to detect the three antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT) and glutathione S transferase (GSTs) in the above mentioned zebrafish organs at protein and gene levels. The results showed that long-term exposure to TiO₂ NPs can cause oxidative damage to organisms; and compared with the control group, the activity of the three kinds of enzyme declined somewhat at the protein level. In addition, long-term exposure to TiO₂ NPs could cause high expression of CAT, SOD and GSTs in three organs of adult zebrafish in order to counter the adverse reaction. The effects of long-term exposure to TiO₂ NPs to adult zebrafish were more obvious in the liver and gill.

Evidences of metabolic alterations and cellular damage in mussels after short pulses of Ti contamination

Mytilus galloprovincialis mussels were exposed to seawater contaminated with Ti. Initial concentrations were 4.1, 32, and 66 μg L^-1 that declined during the first 24 h of the experiments, and after 48 h values were <2 μg L^-1. Experiments were run in triplicate, under constant salinity and temperature. Mussels were fed every two days, and water renewed every seven days and Ti concentrations re-stabilized. During the first 28 days of experimental period, mussels were exposed to four short pulses of contamination, followed by few days of low Ti concentration between weekly contamination renewals. Then mussels were exposed to additional 14-day exposure to Ti uncontaminated seawater. Only residual Ti concentrations were measured in mussels' whole soft tissue after the four pulses of Ti contamination, indicating low Ti accumulation by the organisms. Nevertheless, the biomarkers related to mussels' metabolic capacity (electron transport system activity, ETS), oxidative damage (lipid peroxidation, LPO and reduced glutathione content, GSH), and defense mechanisms (antioxidant and biotransformation enzymes) evidenced the impact of Ti during the 28 days of experimental period. The biomarkers that better indicated the recovery of mussels' biochemical performance were the ETS, LPO, GSH, and the antioxidant enzyme glutathione peroxidase (GPx). LPO was the prime indicator among the analyzed biochemical responses. Organisms appear to hold coping mechanisms to lower the damage induced by Ti, and to recover, albeit the 14 days period of exposure to uncontaminated seawater following the four Ti pulses were not enough for full recovery, as evidenced by results on LPO levels and GSH concentrations. Despite the low solubility of Ti in seawater, the toxicity of this element to a model marine organism was demonstrated.

Toxicity beyond accumulation of Titanium after exposure of Mytilus galloprovincialis to spiked seawater

Mytilus galloprovincialis was exposed to seawater spiked with 5, 50 and 100 μg L^-1 of Titanium (Ti) for 14 days. Seawater was renewed after 96 h and new addition of Ti was done. A parallel experiment conducted in the absence of mussels showed that during the first 24 h after spiking, Ti concentrations in seawater rapidly decreased to values below 2 μg L^-1. For this reason, along the entire experimental period (14 days) mussels were exposed to Ti during two short periods, in the beginning of the experiment and after seawater renewal. At 96 h, mussels exhibited low Ti concentrations (<2.5 μg g^-1), close or not significantly different from a control condition (1.6 μg g^-1 in the absence of Ti). Despite the low accumulated Ti in mussels' tissues after both experimental periods (96 h and 14 days), biochemical markers indicated that mussels developed two main strategies: reduction of their metabolic capacity to avoid the uptake of Ti, and antioxidant and biotransformation defense mechanisms, such as the activation of SOD, CAT, GPx and GSTs enzymes that were triggered to prevent cellular damages. Nevertheless, oxidative stress occurred after 96 h or 14 days. The current study highlights that alterations of biological activity of M. galloprovincialis exposed to Ti goes beyond its accumulation in tissues.

The interactions of fullerene C60 and Benzo(α)pyrene influence their bioavailability and toxicity to zebrafish embryos

This study aimed to assess the toxicological consequences related to the interaction of fullerene nanoparticles (C₆₀) and Benzo(α)pyrene (B(α)P) on zebrafish embryos, which were exposed to C₆₀ and B(α)P alone and to C₆₀ doped with B(α)P. The uptake of pollutants into their tissues and intra-cellular localization were investigated by immunofluorescence and electron microscopy. A set of biomarkers of genotoxicity and oxidative stress, as well as functional proteomics analysis were applied to assess the toxic effects due to C₆₀ interaction with B(α)P. The carrier role of C₆₀ for B(α)P was observed, however adsorption on C₆₀ did not affect the accumulation and localization of B(α)P in the embryos. Instead, C₆₀ doped with B(α)P resulted more prone to sedimentation and less bioavailable for the embryos compared to C₆₀ alone. As for toxicity, our results suggested that C₆₀ alone elicited oxidative stress in embryos and a down-regulation of proteins involved in energetic metabolism. The C₆₀ + B(α)P induced cellular response mechanisms similar to B(α)P alone, but generating greater cellular damages in the exposed embryos.

Environmental mixtures of nanomaterials and chemicals: The Trojan-horse phenomenon and its relevance for ecotoxicity

The usage of engineered nanomaterials (NM) offers many novel products and applications with advanced features, but at the same time raises concerns with regard to potential adverse biological effects. Upon release and emission, NM may interact with chemicals in the environment, potentially leading to a co-exposure of organisms and the occurrence of mixture effects. A prominent idea is that NM may act as carriers of chemicals, facilitating and enhancing the entry of substances into cells or organisms, subsequently leading to an increased toxicity. In the literature, the term 'Trojan-horse effect' describes this hypothesis. The relevance of this mechanism for organisms is, however, unclear as yet. Here, a review has been performed to provide a more systematic picture on existing evidence. It includes 151 experimental studies investigating the exposure of various NM and chemical mixtures in ecotoxicological in vitro and in vivo model systems. The papers retrieved comprised studies investigating (i) uptake, (ii) toxicity and (iii) investigations considering both, changes in substance uptake and toxicity upon joint exposure of a chemical with an NM. A closer inspection of the studies demonstrated that the existing evidence for interference of NM-chemical mixture exposure with uptake and toxicity points into different directions compared to the original Trojan-horse hypothesis. We could discriminate at least 7 different categories to capture the evidence ranging from no changes in uptake and toxicity to an increase in uptake and toxicity upon mixture exposure. Concluding recommendations for the consideration of relevant processes are given, including a proposal for a nomenclature to describe NM-chemical mixture interactions in consistent terms.

Oocyte exposure to ZnO nanoparticles inhibits early embryonic development through the γ-H2AX and NF-κB signaling pathways

The impacts of zinc oxide nanoparticles on embryonic development following oocyte stage exposure are unknown and the underlying mechanisms are sparsely understood. In the current investigation, intact nanoparticles were detected in ovarian tissue in vivo and cultured cells in vitro under zinc oxide nanoparticles treatment. Zinc oxide nanoparticles exposure during the oocyte stage inhibited embryonic development. Notably, in vitro culture data closely matched in vivo embryonic data, in that the impairments caused by Zinc oxide nanoparticles treatment passed through cell generations; and both gamma-H2AX and NF-kappaB pathways were involved in zinc oxide nanoparticles caused embryo-toxicity. Copper oxide and silicon dioxide nanoparticles have been used to confirm that particles are important for the toxicity of zinc oxide nanoparticles. The toxic effects of zinc oxide nanoparticles emanate from both intact nanoparticles and Zn²⁺. Our investigation along with others suggests that zinc oxide nanoparticles are toxic to the female reproductive system [ovaries (oocytes)] and subsequently embryo-toxic and that precaution should be taken regarding human exposure to their everyday use.

Development of Comparative Toxicity Potentials of TiO2 Nanoparticles for Use in Life Cycle Assessment

Studies have shown that releases of nanoparticles may take place through the life cycle of products embedding nanomaterials, thus resulting in potential impacts on ecosystems and human health. While several life cycle assessment (LCA) studies have assessed such products, only a few of them have quantitatively addressed the toxic impacts caused by released nanoparticles, thus leading to potential biases in their conclusions. Here, we address this gap and aim to provide a framework for calculating characterization factors or comparative toxicity potentials (CTP) for nanoparticles and derive CTP values for TiO₂ nanoparticles (TiO₂-NP) for use in LCA. We adapted the USEtox 2.0 consensus model to integrate the SimpleBox4Nano fate model, and we populated the resulting model with TiO₂-NP specific data. We thus calculated CTP values for TiO₂ nanoparticles for air, water, and soil emission compartments for freshwater ecotoxicity and human toxicity, both cancer effects and noncancer effects. Our results appeared plausible after benchmarking with CTPs for other nanoparticles and substances present in the USEtox database, while large differences were observed with CTP values for TiO₂ nanoparticles published in earlier studies. Assumptions, which were performed in those previous studies because of lack of data and knowledge at the time they were made, primarily explain such discrepancies. For future assessment of potential toxic impacts of TiO₂ nanoparticles in LCA studies, we therefore recommend the use of our calculated CTP.

Engineered nanoparticles of titanium dioxide (TIO2): Uptake and biological effects in a sea bass cell line

With the rapid development of nanotechnology there has been a corresponding increase in the application of titanium dioxide nanoparticles (TiO₂-NPs) in various consumer and industrial products, consequently their potential health hazards and environmental effects are considered an aspect of great concern. In the present study, in order to assess the impact of TiO₂-NPs in the marine environment, the biological effects of TiO₂-NPs on a sea bass cell line (DLEC) were investigated. Cells were exposed for 24 h to different concentrations of TiO₂-NPs (1, 8, 40, 200 and 1000 μg/ml) or co-exposed with CdCl₂ (Cd). The effects of UV light irradiation were also investigated in cells treated with TiO₂-NPs and/or Cd. The internalization of TiO₂-NPs and the morphological cell modifications induced by the treatments were examined by transmission and scanning electron microscopy, this latter coupled with energy dispersive X-ray spectroscopy (EDS) for particle element detection. In addition, the effects of controlled exposures were studied evaluating the cytotoxicity, the DNA damage and the expression of inflammatory genes. Our study indicates that TiO₂-NPs were localized on the cell surface mainly as agglomerates revealed by EDS analysis and that they were uptaken by the cells inducing morphological changes. Photoactivation of TiO₂-NPs and/or co-exposure with Cd affects ATP levels and it contributes to induce acute cellular toxicity in DLEC cells dependent on Ti concentration. The inflammatory potential and the DNA damage, this latter displayed through a caspase-3 independent apoptotic process, were also demonstrated. Overall our data suggest that the interaction of TiO₂-NPs with marine water contaminants, such as cadmium, and the UV irradiation, may be an additional threat to marine organisms.

Environmental dynamics of metal oxide nanoparticles in heterogeneous systems: A review

Metal oxide nanoparticles (MNPs) have been used for many purposes including water treatment, health, cosmetics, electronics, food packaging, and even food products. As their applications continue to expand, concerns have been mounting about the environmental fate and potential health risks of the nanoparticles in the environment. Based on the latest information, this review provides an overview of the factors that affect the fate, transformation and toxicity of MNPs. Emphasis is placed on the effects of various aquatic contaminants under various environmental conditions on the transformation of metal oxides and their transport kinetics - both in homogeneous and heterogeneous systems - and the effects of contaminants on the toxicity of MNPs. The presence of existing contaminants decreases bioavailability through hetero-aggregation, sorption, and/or complexation upon an interaction with MNPs. Contaminants also influence the fate and transport of MNPs and exhibit their synergistic toxic effects that contribute to the extent of the toxicity. This review will help regulators, engineers, and scientists in this field to understand the latest development on MNPs, their interactions with aquatic contaminants as well as the environmental dynamics of their fate and transformation. The knowledge gap and future research needs are also identified, and the challenges in assessing the environmental fate and transport of nanoparticles in heterogeneous systems are discussed.

Effect of titanium dioxide nanoparticles on copper toxicity to Daphnia magna in water: Role of organic matter

Inevitably released into natural water, titanium dioxide nanoparticles (nano-TiO₂) may affect the toxicity of other contaminants. Ubiquitous organic matter (OM) may influence their combined toxicity, which has been rarely reported. This study investigated the effect of nano-TiO₂ on Cu toxicity to Daphnia magna and the role of OM (dissolved or particle surface bound) in inducing combined effects. The effect of nano-TiO₂ on heavy metal accumulation depended on the adsorption capacity for heavy metals of nano-TiO₂ and the uptake of nano-TiO₂-metal complexes by organisms. Nano-TiO₂ significantly decreased Cu accumulation in D. magna, but the reducing effect of nano-TiO₂ was eliminated in the presence of humic acid (HA, a model OM). In the Cu and HA solution, nano-TiO₂ slightly affected the bioavailability of Cu²⁺ and Cu-HA complexes and thus slightly influenced Cu toxicity. The nanoparticle surface-bound HA reduced the effect of nano-TiO₂ on the speciation of the accumulated Cu; therefore, the combined effects of nano-TiO₂ and Cu on biomarkers similarly weakened. HA-altered Cu speciation may be the main factor responsible for the influence of HA on the combined effects of nano-TiO₂ and Cu. This study provides insights into the combined effects of nano-TiO₂ and heavy metals in natural water.

Acute toxicity of dichloroacetonitrile (DCAN), a typical nitrogenous disinfection by-product (N-DBP), on zebrafish (Danio rerio)

Dichloroacetonitrile (DCAN) is a typical nitrogenous disinfection by-product (N-DBP) and its toxicity on aquatic animals is investigated for the first time. The present study was designed to investigate the potential adverse effects of DCAN on zebrafish. DCAN could induce developmental toxicity to zebrafish embryos. A significant decrease in hatchability and an increase in malformation and mortality occurred when DCAN concentration was above 100µg/L. Heart function alteration and neuronal function disturbance occurred at concentration higher than 500 and 100µg/L, respectively. Further, DCAN was easily accumulated in adult zebrafish. The rank order of declining bioconcentration factor (BCF) was liver (1240-1670)> gill (1210-1430)> muscle (644-877). DCAN caused acute metabolism damage to adult zebrafish especially at 8 days exposure, at which time the "Integrated Biomarker Response" (IBR) index value reached 798 at 1mg/L DCAN dose. Acute DNA damage was induced to adult zebrafish by DCAN even at 10µg/L dose.

Sequential assessment via daphnia and zebrafish for systematic toxicity screening of heterogeneous substances

Environment and organisms are persistently exposed by a mixture of various substances. However, the current evaluation method is mostly based on an individual substance's toxicity. A systematic toxicity evaluation of heterogeneous substances needs to be established. To demonstrate toxicity assessment of mixture, we chose a group of three typical ingredients in cosmetic sunscreen products that frequently enters ecosystems: benzophenone-3 (BP-3), ethylhexyl methoxycinnamate (EHMC), and titanium dioxide nanoparticle (TiO2 NP). We first determined a range of nominal toxic concentration of each ingredient or substance using Daphnia magna, and then for the subsequent organismal level phenotypic assessment, chose the wild-type zebrafish embryos. Any phenotype change, such as body deformation, led to further examinations on the specific organs of transgenic zebrafish embryos. Based on the systematic toxicity assessments of the heterogeneous substances, we offer a sequential environmental toxicity assessment protocol that starts off by utilizing Daphnia magna to determine a nominal concentration range of each substance and finishes by utilizing the zebrafish embryos to detect defects on the embryos caused by the heterogeneous substances. The protocol showed additive toxic effects of the mixtures. We propose a sequential environmental toxicity assessment protocol for the systematic toxicity screening of heterogeneous substances from Daphnia magna to zebrafish embryo in-vivo models.

The removal process of 2,2-dichloroacetamide (DCAcAm), a new disinfection by-product, in drinking water treatment process and its toxicity on zebrafish

The removal process of 2,2-dichloroacetamide (DCAcAm), a new disinfection by-product (DBP) in conventional drinking water treatment plant (C-DWTP) and advanced DWTP (ADWTP) was studied with newly maximum formation potential (MFP) process. It was demonstrated that the advanced treatment displayed greater removal efficiency towards DCAcAm formation potential (MFP) than the conventional treatment. The hydrophilic natural organic matter and natural organic matter with molecular weight <1 kDa or >10 kDa leaded to more DCAcAm formation, and the aromatic protein was inferred as one part of DCAcAm precursor. DCAcAm was found to cause delayed development and malformation to zebrafish embryos at embryonic growth stage. Compared with heart toxicity, it caused a significant neuron toxicity. It also could cause the acute DNA damage to adult zebrafish, which should be extremely cautioned.

Effects of metal-bearing nanoparticles (Ag, Au, CdS, ZnO, SiO2) on developing zebrafish embryos

Due to the increasing commercialization of consumer and industrial products containing nanoparticles (NPs), an increase in the introduction of these materials into the environment is expected. NP toxicity to aquatic organisms depends on multiple biotic and abiotic factors, resulting in an unlimited number of combinations impossible to test in practice. The zebrafish embryo model offers a useful screening tool to test and rank the toxicity of nanomaterials according to those diverse factors. This work aims to study the acute and sublethal toxicity of a set of metal-bearing NPs displaying different properties, in comparison to that of the ionic and bulk forms of the metals, in order to establish a toxicity ranking. Soluble NPs (Ag, CdS and ZnO) showed the highest acute and sublethal toxicity, with LC50 values as low as 0.529 mg Ag l(-1) for Ag NPs of 20 nm, and a significant increase in the malformation prevalence in embryos exposed to 0.1 mg Cd l(-1) of CdS NPs of ∼4 nm. For insoluble NPs, like SiO2 NPs, acute effects were not observed during early embryo development due to the protective effect of the chorion. But effects on larvae could be expected, since deposition of fluorescent SiO2 NPs over the gill lamella and excretion through the intestine were observed after hatching. In other cases, such as for gold NPs, the toxicity could be attributed to the presence of additives (sodium citrate) in the NP suspension, as they displayed a similar toxicity when tested separately. Overall, the results indicated that toxicity to zebrafish embryos depends primarily on the chemical composition and, thus, the solubility of the NPs. Other characteristics, such as size, played a secondary role. This was supported by the observation that ionic forms of the metals were always more toxic than the nano forms, and bulk forms were the least toxic to the developing zebrafish embryos.

Trophic transfer of nano-TiO2 in a paddy microcosm: A comparison of single-dose versus sequential multi-dose exposures

In the present study, replicated paddy microcosm systems were used to investigate the environmental fate and trophic transfer of titanium nanoparticles (NPs) over a period of 14 days. Most TiO2 NPs immediately settled down in the sediment, and high accumulations of nano TiO2 in the sandy loam sediment and biofilm were observed. The test organisms (quillworts, water dropworts, duckweeds, biofilms, river snails, and Chinese muddy loaches) and environmental media (freshwater, sandy loam sediment) were exposed to sequential low doses (2 mg/L at 1 h, 4 days, and 9 days) or a single high-dose (6 mg/L) of TiO2 NPs. The bioconcentration factors (BCFs) of nano-TiO2 in biofilms, quillworts, duckweeds, and Chinese muddy loaches were higher in the sequential multi-dose group than in the single-dose group. Chinese muddy loaches showed higher bioaccumulation factors (BAFs) over their prey than river snails. The difference in the carbon isotope ratios between Chinese muddy loaches and river snails was less than 2‰, and an approximately 4‰ difference in the stable nitrogen isotope ratio was observed in the two aquatic predators from their major prey (e.g., biofilms or particulate organic matter). The trophic levels between biofilms and river snails and between biofilms and Chinese muddy loaches were 2.8 and 2.4 levels, respectively. These results indicate that these two predators consumed biofilm and other alternative preys at a higher level than biofilm. Although the trophic transfer rates of TiO2 are generally low, relatively higher biomagnification factors (BMFs) were found in Chinese muddy loaches (0.04-0.05) than in river snails (0.01-0.02). These results suggest that TiO2 NPs show greater movement in the sediment than in the water and that TiO2 NPs can be retained through aquatic food chains more after a sequential low-dose exposure than after a single high-dose exposure.

In Vivo toxicological assessment of biologically synthesized silver nanoparticles in adult Zebrafish (Danio rerio)

The present study examines the deleterious effect of biologically synthesized silver nanoparticles in adult zebrafish. Silver nanoparticles (AgNPs) used in the study were synthesized by treating AgNO3 with aqueous leaves extract of Malva crispa Linn., a medicinal herb as source of reductants. LC50 concentration of AgNPs at 96 h was observed as 142.2 μg/l. In order to explore the underlying toxicity mechanisms of AgNPs, half of the LC50 concentration (71.1 μg/l) was exposed to adult zebrafish for 14 days. Cytological changes and intrahepatic localization of AgNPs were observed in gills and liver tissues respectively, and the results concluded a possible sign for oxidative stress. In addition to oxidative stress the genotoxic effect was observed in peripheral blood cells like presence of micronuclei, nuclear abnormalities and also loss in cell contact with irregular shape was observed in liver parenchyma cells. Hence to confirm the oxidative stress and genotoxic effects the mRNA expression of stress related (MTF-1, HSP70) and immune response related (TLR4, NFKB, IL1B, CEBP, TRF, TLR22) genes were analyzed in liver tissues and the results clearly concluded that the plant extract mediated synthesis of AgNPs leads to oxidative stress and immunotoxicity in adult zebrafish.

The toxicity of a new disinfection by-product, 2,2-dichloroacetamide (DCAcAm), on adult zebrafish (Danio rerio) and its occurrence in the chlorinated drinking water

The detection method of 2,2-dichloroacetamide (DCAcAm), a new disinfection by-product (DBP) in chlorinated drinking water, was established using a gas chromatograph coupled with a micro-electron capture detector. The chlorinated water samples were taken from ten drinking water treatment plants around Yangtze River or Taihu Lake in China. The concentration of DCAcAm was detected ranging from 0.5 to 1.8μg/L in the waterworks around Yangtze River, and 1.5-2.6μg/L around Taihu Lake. The toxicity of DCAcAm on adult zebrafish was assessed by investigating the metabolism damage with multiple metabolic biomarkers and the accumulation capability with bio-concentration factor. The results showed that DCAcAm could cause the acute metabolism damage and was easily accumulated in zebrafish, and should be extremely cautioned.

Titanium dioxide nanoparticles modulate the toxicological response to cadmium in the gills of Mytilus galloprovincialis

We investigated the influence of titanium dioxide nanoparticles (nano-TiO2) on the response to cadmium in the gills of the marine mussel Mytilus galloprovincialis in terms of accumulation and toxicity. Mussels were in vivo exposed to nano-TiO2, CdCl2, alone and in combination. Several cellular biomarkers were investigated in gills: ABC transport proteins and metallothioneins at gene/protein (abcb1, abcc-like and mt-20) and functional level, GST activity, NO production and DNA damage (Comet assay). Accumulation of total Cd and titanium in gills as in whole soft tissue was also investigated. Significant responses to Cd exposure were observed in mussel gills as up-regulation of abcb1 and mt-20 gene transcription, increases in total MT content, P-gp efflux and GST activity, DNA damage and NO production. Nano-TiO2 alone increased P-gp efflux activity and NO production. When combined with Cd, nano-TiO2 reduced the metal-induced effects by significantly lowering abcb1 gene transcription, GST activity, and DNA damage, whereas, additive effects were observed on NO production. A lower concentration of Cd was observed in the gills upon co-exposure, whereas, Ti levels were unaffected. A competitive effect in uptake/accumulation of nano-TiO2 and Cd seems to occur in gills. A confirmation is given by the observed absence of adsorption of Cd onto nano-TiO2 in sea water media.

Predicting the environmental impact of nanosilver

Silver nanoparticles (AgNPs) are incorporated into many consumer and medical products due to their antimicrobial properties; however, the potential environmental risks of AgNPs are yet to be fully understood. This mini-review aims to predict the environmental impact of AgNPs, thus supplementing previous reviews on this topic. To this end, the AgNP production, environmental release and fate, predicted environmental concentrations in surface water, sediment, and sludge-activated soil, as well as reported toxicity and proposed toxic mechanisms are discussed, focusing primarily on fish. Furthermore, knowledge gaps and recommendations for future research are addressed.