Fish exposure to nano-TiO2 under different experimental conditions: methodological aspects for nanoecotoxicology investigations

nano-TiO2 reduces bioavailability and biotransformation responses to crude oil WAF-associated PAHs in the European sea bass Dicentrachus labrax

The present study investigates the potential interaction between nano‑titanium dioxide (nano-TiO2) and the water accommodated fraction (WAF) of crude oil and associated chemicals on bioavailability and biotransformation responses in the European sea bass (Dicentrarchus labrax). An in vivo (48-h) waterborne exposure with nano-TiO2 (10 mgL-1), crude oil WAF (0.068 gL-1), alone and in combination was performed. Combined exposure significantly reduced levels of polycyclic aromatic hydrocarbons (PAH) in either seawater and fish fillets compared to WAF alone. A significant reduction in the expression of several biotransformation genes (cyp1a, gsta, erβ2, elmod2, abcb1 and abcc1) when nano-TiO2 was combined with WAF was observed in fish liver, compared to WAF alone. EROD and GST enzyme activities were also significantly reduced. Nano-TiO2 can reduce PAHs bioavailability in seawater and biological responses in European sea bass, suggesting a potential safe application of nano-TiO2 for the remediation of crude oil WAF in the marine environment.

Chronic toxicity and liver histopathology of mosquito fish (Gambusia holbrooki) exposed to natural and modified nanoclays

Nanoclays are found in the air, water, and soil, and modified nanoclays are being developed and used in several consumer products. For example, modified nanoclays are used to remove pollutants from wastewater. Ironically, however, nanoclays are now considered emerging contaminants. Indeed, release of modified nanoclays in aquatic systems, even as remediating agents, could adversely affect associated wildlife. However, aquatic organisms have interacted with natural nanoclays for millennia, and it is unclear if modified nanoclays induce stronger effects than the nanoclays that occur naturally. The concentrations over which nanoclays occur and illicit negative effects are not well studied. This study investigated the dose response of a natural nanoclay (Na+montmorillonite) relative to two modified nanoclays (Cloisite®30B and Novaclay™) on survival, body condition, and liver pathomorphology of Gambusia holbrooki after 14 days of exposure. Although none of the nanoclays affected survival and body condition of G. holbrooki over 14 days, each nanoclay induced histopathological changes in liver tissues at very low concentrations (LOAEL: 0.01 mgL-1). The effects of nanoclays on hepatic cell circulatory (blood cell aggregation with increased number of Kupffer cells and hemosiderin deposits), regressive (hepatocyte vacuolization), and degenerative (cell death) changes of mosquito fish varied among nanoclay types. Novaclay™ at low concentrations caused circulatory changes on hepatic tissues of G. holbrooki, whereas both natural nanoclays and Cloisite®30B showed little effect on circulatory endpoints. In contrast, all of the nanoclays induced regressive and degenerative changes on liver tissues of mosquito fish across all concentrations tested. This study clearly reveals that natural and modified nanoclays have important health implications for fish and other aquatic organisms. Consequently, the widespread use of modified nanoclays in several applications and increased release of natural nanoclays through erosion or other processes needs to be evaluated in more detail especially in the context of their safety for aquatic systems.

Toxicity enhancement of nano titanium dioxide to Brachionus calyciflorus (Rotifera) under simulated sunlight and the underlying mechanisms

Nano titanium dioxide (nTiO₂) generally shows low toxicity to organisms under light-emitting diode (LED) light. However, nTiO₂ can induce production of reactive oxygen species (ROS) under ultraviolet (UV) light due to its photocatalytic activity. Therefore, it is reasonable to expect the enhancement of nTiO₂ toxicity under sunlight. To test this hypothesis, we compared the toxicity of nTiO₂ to Brachionus calyciflorus under simulated sunlight and LED light. The results showed that the 24 h-LC₅₀ of nTiO₂ to B. calyciflorus under LED light and simulated sunlight were 24.32 (95% CI: 14.54-46.81 mg/L) and 10.44 mg/L (95% CI: 6.74-17.09 mg/L), respectively. Compared with the blank control, treatments with nTiO₂ significantly affected life-table demographic parameters, population growth parameters and swimming linear speed under both simulated sunlight and LED light. However, life expectancy, net reproductive rate, average lifespan, maximal population density, and swimming linear speed in the treatments of nTiO₂ at 0.1, 1, and/or 10 mg/L showed markedly lower values under simulated sunlight than those under LED light, suggesting that simulated sunlight could enhance the toxicity of nTiO₂. In addition, markedly higher catalase (CAT) activity and malondialdehyde (MDA) content but lower glutathione (GSH) content were observed in treatment with 10 mg/L nTiO₂ under simulated sunlight than that under LED light. The results showed that compared with LED light, simulated sunlight significantly induced more oxidative stress in the presence of nTiO₂, and the ROS production was mainly localized to the corona and digestive tract of rotifers by confocal laser scanning microscope. Exposure to 10-50 μM of vitamin C, that is an effective ROS scavenger, could rescue the swimming linear speed of rotifers to the normal level in the blank control. These results suggested that oxidative damages on cell membrane might be the vital mechanism underlying the toxicity enhancement of nTiO₂ to rotifers under simulated sunlight. Thus, the previous publications under LED light may underestimate the real toxicity and environmental risk of nTiO₂ in natural conditions.

Considerations for bioaccumulation studies in fish with nanomaterials

Nanomaterials (NMs) pose challenges in performing bioaccumulation studies in fish and in regulatory interpretation of results. Therefore, a clear guidance is needed to obtain reliable, reproducible and comparable results. By analysing all the available literature, we aim in this manuscript to identify the critical aspects that should be addressed in these type of studies. Seventy-eight studies from a total of 67 published articles were identified in which a variety of approaches were used: aqueous exposure (49 studies), dietary exposure (19), and pre-exposed animals for trophic transfer studies (10). The NMs tested included TiO₂, Zn, ZnO, Cu, CuO, Ag, Au, CeO₂, Fe₂O₃, Fe₃O₄, Se, CdS, CdSe/ZnS-QDs, CdTe/ZnS-QDs, graphene, fullerenol and MWCNTs. In general, there is a scarcity of bioaccumulation studies for the different NMs. In particular, studies that use the dietary exposure route are lacking. TiO₂ NMs are the most studied for bioaccumulation potential in fish (20%), whereas very few data were available for CuO, FeO and carbon-based NMs. Different information gaps were identified in these studies that hamper overall conclusions to be made on the bioaccumulation potential of NMs. The main critical issues related to NM testing for bioaccumulation include: maintenance of stable exposure concentrations, the influence of feeding regimen on uptake and elimination, the use of appropriate feed spiking methodologies, the potential need for testing different concentrations, and the reporting of bioaccumulation endpoints (BCF/BMF). Each of these issues needs further guidance to allow proper use and reporting of NM bioaccumulation data for regulatory purposes.

Comparison of the Toxic Effects of Pristine and Photocatalytically Used TiO2 Nanoparticles in Mice

TiO2 nanoparticles used in the photocatalytic degradation of pollutants in water treatment processes undergo physiochemical changes; therefore, their toxicological effects may be potentially different from those of the pristine nanoparticles. This study compared the toxic effects of exposure to pristine and photocatalytically used TiO2 nanoparticles in mice. To obtain used TiO2, the nanoparticles were used for photocatalytic degradation of a model pollutant under UV irradiation several times. Two groups of mice were exposed to pristine (PT group) and photocatalytically used TiO2 (UT group) at three different concentrations (5-20 mg/m3) using whole-body exposure chambers (2 h/day, 5 days/weeks, 4 weeks). Exposure to both pristine and used TiO2 increased the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphate (ALP), lactate dehydrogenase (LDH), C-reactive protein (CRP), and creatine kinase (CK-MB) significantly. Both exposed groups showed higher levels of WBC, lymphocytes, platelets, hematocrits, hemoglobin, and mean corpuscular volume (MCV) and lower levels of RBC and mean corpuscular hemoglobin concentration (MCHC) in a concentration-dependent manner. In all analyses, there were small non-significant differences between the PT and UT groups. More pathological changes were observed in the lung, kidney, and brain of the UT group, while the PT group showed more pathological effects in the liver and heart. The histological observations indicated that damage was mostly in the form of vascular endothelial injury. These two types of TiO2 may activate different pathways to promote adverse effects. Further studies are required to evaluate and distinguish the mechanisms through which pristine and used TiO2 induce toxicity.

Environmental Fate and Toxicity of Sunscreen-Derived Inorganic Ultraviolet Filters in Aquatic Environments: A Review

An increasing number of inorganic ultraviolet filters (UVFs), such as nanosized zinc oxide (nZnO) and titanium dioxide (nTiO2), are formulated in sunscreens because of their broad UV spectrum sunlight protection and because they limit skin damage. However, sunscreen-derived inorganic UVFs are considered to be emerging contaminants; in particular, nZnO and nTiO2 UVFs have been shown to undergo absorption and bioaccumulation, release metal ions, and generate reactive oxygen species, which cause negative effects on aquatic organisms. We comprehensively reviewed the current study status of the environmental sources, occurrences, behaviors, and impacts of sunscreen-derived inorganic UVFs in aquatic environments. We find that the associated primary nanoparticle characteristics and coating materials significantly affect the environmental behavior and fate of inorganic UVFs. The consequential ecotoxicological risks and underlying mechanisms are discussed at the individual and trophic transfer levels. Due to their persistence and bioaccumulation, more attention and efforts should be redirected to investigating the sources, fate, and trophic transfer of inorganic UVFs in ecosystems.

A review of the effects of metallic nanoparticles on fish

Many important discoveries have been made in the field of nanotechnology in the last 40 years. Since then, nanoparticles became nearly ubiquitous. With their spreading use, safety concerns have warranted extensive research of nanotoxicity. This paper offers information about the occurrence, transport, and behaviour of metallic nanoparticles in the aquatic environment. It further summarizes details about parameters that dictate the toxicity of nanoparticles and discusses the general/common mechanisms of their toxicity. This review also focuses on fish exposure to nanoparticles, including the possibility of trophic transport through the food chain. Information on some of the most frequently used metallic nanoparticles, such as silver, gold, and titanium dioxide, is further elaborated on.

Influence of Titanium Dioxide Nanoparticles on Human Health and the Environment

Nanotechnology has enabled tremendous breakthroughs in the development of materials and, nowadays, is well established in various economic fields. Among the various nanomaterials, TiO₂ nanoparticles (NPs) occupy a special position, as they are distinguished by their high availability, high photocatalytic activity, and favorable price, which make them useful in the production of paints, plastics, paper, cosmetics, food, furniture, etc. In textiles, TiO₂ NPs are widely used in chemical finishing processes to impart various protective functional properties to the fibers for the production of high-tech textile products with high added value. Such applications contribute to the overall consumption of TiO₂ NPs, which gives rise to reasonable considerations about the impact of TiO₂ NPs on human health and the environment, and debates regarding whether the extent of the benefits gained from the use of TiO₂ NPs justifies the potential risks. In this study, different TiO₂ NPs exposure modes are discussed, and their toxicity mechanisms—evaluated in various in vitro and in vivo studies—are briefly described, considering the molecular interactions with human health and the environment. In addition, in the conclusion of this study, the toxicity and biocompatibility of TiO₂ NPs are discussed, along with relevant risk management strategies.

Cytotoxicity and genotoxicity of coated-gold nanoparticles on freshwater algae Pseudokirchneriella subcapitata

Gold engineered nanoparticles (nAu) are increasingly detected in ecosystems, and this raises the need to establish their potential effects on aquatic organisms. Herein, cytotoxic and genotoxic effects of branched polyethylenimine (BPEI)- and citrate (cit)-coated nAu (5, 20, and 40 nm) on algae Pseudokirchneriella subcapitata were evaluated. The apical biological endpoints: growth inhibition and chlorophyll a (Chl a) content were investigated at 62.5-1000 µg/L over 168 h. In addition, the apurinic/apyrimidinic (AP) sites, randomly amplified polymorphic deoxyribonucleic acid (RAPD) profiles, and genomic template stability (GTS) were assessed to determine the genotoxic effects of nAu. The results show algal growth inhibition at 5 nm BPEI-nAu up to 96 h, and thereafter cell recovery except at the highest concentration of 1000 µg/L. Insignificant growth reduction for cit-nAu (all sizes), as well as 20 and 40 nm BPEI-nAu, was observed over 96 h, but growth promotion was apparent at all exposures thereafter except for 40 nm BPEI-nAu at 250 µg/L. A decrease in Chl a content following exposure to 5 nm BPEI-nAu at 1000 µg/L corresponded to significant algal growth reduction. In genotoxicity studies, a significant increase in AP sites content was observed relative to the control - an indication of nAu ability to induce genotoxic effects irrespective of their size and coating type. For 5 nm- and 20 nm-sized nAu for both coating types and exposure concentrations no differences in AP sites content were observed after 72 and 168 h. However, a significant reduction in AP sites was observed following algae exposure to 40 nm-sized nAu (irrespective of coating type and exposure concentration) at 168 h compared to 72 h. Thus, AP sites results at 40 nm-size suggest likely DNA damage recovery over a longer exposure period. The findings on AP sites content showed a good correlation with an increase in genome template stability and growth promotion observed after 168 h. In addition, RAPD profiles demonstrated that nAu can induce DNA damage and/or DNA mutation to P. subcapitata as evidenced by the appearance and/or disappearance of normal bands compared to the controls. Therefore, genotoxicity results revealed significant toxicity of nAu to algae at the molecular level although no apparent effects were detectable at the morphological level. Overall, findings herein indicate that long-term exposure of P. subcapitata to low concentrations of nAu may cause undesirable sub-lethal ecological effects.

Tinospora cordifolia ameliorated titanium dioxide nanoparticle-induced toxicity via regulating oxidative stress-activated MAPK and NRF2/Keap1 signaling pathways in Nile tilapia (Oreochromis niloticus)

Titanium dioxide nanoparticle (TNP) has been suggested for use in fish farms to prevent or alleviate bacterial diseases owing to its bactericidal property. Unfortunately, the interaction of TNP with cells impaired the host defenses of fish resulting in increased mortality during bacterial challenges. The present study evaluated the efficacy of the ethanolic extract of Tinospora cordifolia (TCE) as a dietary supplement in ameliorating TNP induced toxicity in Nile tilapia (Oreochromis niloticus). The fishes were exposed to environmentally relevant concentration (10 mg/L) of TNP for 14 days and the effect of TCE supplemented feed at 3 different doses (5, 10, and 15 g/kg) was studied. TCE signally increased the weight gain, specific growth rate, and decreased feed conversion ratio in fish. TCE significantly (P < 0.05) ameliorated the toxic effects caused by TNP by increasing the antioxidant (CAT, SOD, GPx) activity and decreasing the levels of serum enzymes (ALT, AST, ALP, ACP), macromolecular oxidation, excessive ROS production, and pro-inflammatory cytokines (IL-1β, IL-6, IL-8, INF-γ, TNF-α, PGE-2). TNP bioaccumulation and histopathological alterations in gill, liver, and kidney were also significantly alleviated by TCE supplementation. TCE perceptibly regulated the expression of heat shock proteins (HSP60, -70), MAPKs (pERK1/2, pp38), antioxidant (NRF2, Keap1, HO-1), apoptotic (p53, PDRG1), and anti-apoptotic (AKT, Bcl2) proteins in fish. Regarding disease resistance, the TCE co-treated groups showed reduced cumulative mortality and higher relative percent survival with A. hydrophila. Our results suggest that TNP-induced apoptosis is mediated by the MAPK/NRF2/Keap1 pathway and underlines the therapeutic potential of TCE in aqua-farming.

Toxic effect of some heavy metals on hematology and histopathology of major carp (Catla catla)

The current study was conducted to assess the hematological and histopathological changes in major carp (Catla catla) exposed to different concentrations of copper (Cu) and cadmium (Cd). For this purpose, Catla catla fish, weighing approximately 230-235 g, were randomly divided into four groups and then exposed to acute doses of Cu (1.25 ppm), Cd (4.5 ppm), and their mixture (2.25 ppm) for 96 h and then 20, 30, and 40% respectively for a period of 30 days. Results showed that red blood cells (RBCs), hemoglobin (Hb), hematocrit (Hct), lymphocyte, and monocyte decreased significantly, while the total white blood cell count and neutrophil population significantly increased in experimental groups as compared with the control one. Histopathological examination of liver tissues showed karyorrhexis, hepatic cells degeneration, congestion, and hemorrhages. Microscopic analysis of gills' sections revealed lamellar atrophy, telangiectasia, and necrosis of lamellar epithelial cells. In the kidneys, different histopathological ailments like atrophy of glomeruli, necrosis of renal tubular cells, increased urinary spaces, degeneration of renal tubules, and melanomacrophage aggregates were observed, while in the intestine, atrophy of villi, sloughing of epithelial villi, and congestion were seen after 30 days of exposure. In conclusion, the study indicates that exposure to Cu and Cd for longer period of time causes adverse hematological and histopathological changes in Catla catla fish.

Nanomaterial Transformations in the Environment: Effects of Changing Exposure Forms on Bioaccumulation and Toxicity

In the environment, nanomaterials (NMs) are subject to chemical transformations, such as redox reactions, dissolution, coating degradation, and organic matter, protein, and macromolecule binding, and physical transformations including homo or heteroagglomeration. The combination of these reactions can result in NMs with differing characteristics progressing through a functional fate pathway that leads to the formation of transformed NM functional fate groups with shared properties. To establish the nature of such effects of transformation on NMs, four main types of studies are conducted: 1) chemical aging for transformation of pristine NMs; 2) manipulation of test media to change NM surface properties; 3) aging of pristine NMs water, sediment, or soil; 4) NM aging in waste streams and natural environments. From these studies a paradigm of aging effects on NM uptake and toxicity can be developed. Transformation, especially speciation changes, largely results in reduced potency. Further reactions at the surface resulting in processes, such as ecocorona formation and heteroagglomeration may additionally reduce NM potency. When NMs of differing potency transform and enter environments, common transformation reaction occurring in receiving system may act to reduce the variation in hazard between different initial NMs leading to similar actual hazard under realistic exposure conditions.

Titanium dioxide nanoparticles-induced cytogenotoxicity and alterations in haematological indices of Clarias gariepinus (Burchell, 1822)

The application of titanium dioxide (TiO₂) nanoparticles (NPs) in the manufacturing of consumer products has increased tremendously and with the potential to induce deleterious effects on aquatic biota. There have been reports on metal oxide NP toxicity in aquatic organisms, however, information on cytotoxicity and genotoxicity of TiO₂ NPs on the African catfish, Clarias gariepinus, is scarce. In this study, we investigated the genotoxicity and haematotoxicity of TiO₂ NPs in C. gariepinus using the micronucleus (MN) assay and haematological analysis, respectively. Juvenile C. gariepinus were exposed to 6.25, 12.5, 25.0, 50.0 and 100.0 mg L^-1 concentrations of TiO₂ NPs for 7 and 28 days. Benzene (0.05 mL L^-1) and dechlorinated tap water were used as positive and negative controls, respectively. Data of the MN showed a significant (p < 0.05) concentration-dependent increase in the frequency of MN at both exposure periods in comparison to negative control. Red blood cells, haematocrit, platelets and heterophils significantly reduced with an increased mean corpuscular haemoglobin concentration and lymphocytes at the 7-day exposure period, while in the 28-day exposure period, mean cell volume, mean corpuscular haemoglobin and lymphocytes had a significant increase in comparison with the negative control. This study indicates that TiO₂ NPs induced cytogenetic and haematological alterations in C. gariepinus and is of relevance in biodiversity and aquatic health management.

Ecotoxicity of nano-metal oxides: A case study on daphnia magna

In Europe REACH framework directive imposes data acquisition concerning toxicity on acquatic species before the commercialization of chemicals to assess environmental risks. According to official methods, exposure tests are performed under in vitro and standardized conditions: OECD's guideline rules external variables such as water type, feeding conditions, and exposure time. As consequence, such obtained results could be different from effects observed in natural environments. This study collects effects within 24-96 h of exposure to nano metal-oxides (ZnO, TiO₂) on D. magna obtained by the exposure under standard OECD conditions comparing them with results obtained by the exposure under more similar conditions to natural environment (i.e. mixture, feeding). High doses exposure determines gas-bubble disease. Animals exposed to LC10 actively ingest nanoparticles under both fasting and feeding conditions. Furthermore, body burial by a coat of nanoparticles thicker in mixtures than in single dispersions was recorded. Furthermore, results show that: (i) effects increase over time; (ii) n-ZnO results less effective than n-TiO₂ in both single dispersion, and mixture; (iii) the presence of surfactant increases toxicity of nanoparticles; (iv) immobilization is a more sensitive endpoint than mortality; (v) feeding increases test sensitiveness improving differences among treated and controls till 96 h and allowing longer exposure times than standard OECD test. As general remark, this study provides evidence that in vitro ecotoxicological results obtained under standardized OECD conditions could be significant different to animals' responses under natural (feeding and mixtures) exposure conditions.

Antioxidant imbalance and genotoxicity detected in fish induced by titanium dioxide nanoparticles (NpTiO2) and inorganic lead (PbII)

Titanium dioxide nanoparticles (NpTiO₂) are the most widely-used nanoparticle type and the adsorption of metals such as lead (PbII) onto their surface is a major source of concern to scientists. This study evaluated the effects of the associated exposure to both types of contaminant, i.e., lead (a known genotoxic metal) and NpTiO₂, in a freshwater fish (Astyanax serratus) through intraperitoneal injection for an acute assay of 96 h. The effects of this exposure were evaluated using the comet assay, DNA diffusion assay and piscine micronucleus test, as well as the quantification of antioxidant enzymes (SOD, CAT, and GST) and metallothioneins. Our findings indicate that co-exposure of PbII with NpTiO₂ can provoke ROS imbalances, leading to DNA damage in the blood and liver tissue of A. serratus, as well as modifying erythropoiesis in this species, inducing necrosis and changing the nuclear morphology of the erythrocytes.

Nanoparticle transport and sequestration: Intracellular titanium dioxide nanoparticles in a neotropical fish

Intracellular titanium dioxide nanoparticles (TiO₂-NP) with rutile crystalline form and dimensions varying from 43 to 67 nm × 64 to 93 nm are reported for the first time as being sequestered from the environment. TiO₂-NP were identified inside all organs/tissues (muscle, kidney, gonad, hepatopancreas and gill) in both the cytoplasm and nucleus of the neotropical fish Centropomus parallelus, captured in an area affected by metallurgical activity. Atmospheric particulate matter (PM) sampled in the same area showed the presence of TiO₂-NP with the same rutile crystalline form and dimensions varying from 16 to 93 nm × 45 to 193 nm, thus indicating the smelting and iron processing industries as the most probable source of TiO₂-NP. In any sample, chemical analyses identify and quantify Ti concentration and nanocrystallography identified the structure of TiO₂-NP. The Ti concentration in the sediment and atmospheric PM varied between years and it was mirrored by the Ti concentration in the fish organs. The gill has a higher Ti concentration varying from 5.50 to 14.57 μg g^-1 dry weight and the gonad was the organ with lowest Ti level, 0.25 to 0.87 μg g^-1 dry weight. In the muscles, Ti concentration varied from 0.85 to 3.34 μg g^-1 dry weight. This contamination may be likely to affect the surrounding biota and food uptake, including the humans living in the city close to the metallurgical complex. These findings emphasised the needs to improve methods to reduce PM (including nanoparticles) arising from human activities and to evaluate the toxicokinetic and effects of TiO₂-NP in the biota and human health.

Influence of extracellular polymeric substances on cell-NPs heteroaggregation process and toxicity of cerium dioxide NPs to Microcystis aeruginosa

The presence of abundant extracellular polymeric substances (EPS) play a vital role in affecting heteroaggregation process and toxicity of nanoparticles (NPs) to Microcystis aeruginosa. Interactions between n-CeO₂ and cyanobacteria with/without EPS and the toxicity of n-CeO₂ to M. aeruginosa were investigated in this study. Aggregation kinetics of n-CeO₂ under both soluble EPS (SEPS) and bound EPS (BEPS) indicated the presence of EPS could induced the formation of EPS-NPs aggregates. Heteroaggregation between cells and n-CeO₂ was confirmed through co-settling experiment and SEM-EDS observation. SEPS contributed to the observable heteroaggregation using spectral measurement. Heteroaggregation between cells and n-CeO2 under no BEPS was hardly obtained through spectral measurement, but SEM-EDS observation convinced this process. And the DLVO theory explained this heteroaggregation process under various EPS conditions, where the energy barrier decreased with gradual EPS extraction. In addition, the order for 96 h half growth inhibition concentration (IC₅₀) was Raw M9 > M9-SEPS > M9+BEPS > M9-BEPS. These results revealed that not all heteroaggregation between cell-NPs can lead to the NPs toxicity to cells. BEPS act more important role in buffering against the toxicity of NPs from ambient adverse factors, but SEPS increase the stability of NPs which could aggravate the adverse effects of NPs in the environment.

Co-exposure to titanium dioxide nanoparticles (NpTiO2) and lead at environmentally relevant concentrations in the Neotropical fish species Hoplias intermedius

Growing production and utilization of titanium dioxide nanoparticles (NpTiO2) invariably lead to their accumulation in oceans, rivers and other water bodies, thus increasing the risk to the welfare of this ecosystem. The progressive launch of these nanoparticles in the environment has been accompanied by concern in understanding the dynamics and the toxic effect of these xenobiotic in different ecosystems, either on their own or in tandem with different contaminants (such as organic compounds and heavy metals), possibly altering their toxicity. Nevertheless, it remains unknown if these combined effects may induce damage in freshwater organisms. Therefore, this study aimed to analyze the consequences caused by NpTiO2, after a waterborne exposure of 96 h to a Neotropical fish species Hoplias intermedius, as well as after a co-exposure with lead, whose effects for fish have already been well described in the literature. The characterization of NpTiO2 stock suspension was carried out in order to provide additional information and revealed a stable colloidal suspension. As a result, NpTiO2 showed some genotoxic effects which were observed by comet assay in gill, kidney and brain cells. Also, the activity of brain acetylcholinesterase (AChE) has not changed, but the activity of muscle AChE decreased in the group exposed only to PbII. Regarding the hepatic antioxidant system, catalase (CAT) did not show any change in its activity, whereas that of superoxide dismutase (SOD) intensified in the groups submitted only to PbII and NpTiO2 alone. As for lipid peroxidation, there was a decrease in the group exposed to the NpTiO2 alone and to the co-exposed group (NpTiO2+PbII). As far as metallothionein is concerned, its concentration rose for the co-exposed group (NpTiO2+PbII) and for the group exposed to PbII alone. Overall, we may conclude that NpTiO2 alone caused DNA damage to vital tissues. Also, some impairment related to the antioxidant mechanism was described but it is probably not related to the DNA damage observed, suggesting that the genotoxic effect observed may be due to a different mechanism instead of ROS production.

Reactive oxygen species and other biochemical and morphological biomarkers in the gills and kidneys of the Neotropical freshwater fish, Prochilodus lineatus, exposed to titanium dioxide (TiO2) nanoparticles

This study investigated the action of titanium dioxide nanoparticles (TiO₂-NPs), on the gills and kidneys of Neotropical freshwater fish, Prochilodus lineatus, with emphasis on reactive oxygen species (ROS) production, antioxidant responses, and morphological changes. Fish were exposed to 1, 5, 10, and 50 mg L^-1 nominal TiO₂-NPs suspended into water for 2 or 14 days. In gills, ROS decreased and glutathione (GSH) increased after 2 days, while ROS and GSH increased and superoxide dismutase activity decreased after 14 days. In kidneys, GSH and lipoperoxidation increased after 2 days and catalase activity decreased after 14 days. Common histopathologies in gills were epithelium hyperplasia, cellular hypertrophy, proliferation of mitochondria-rich cells (MRC), and lamellar stasis; in kidneys, there were cellular and nuclear hypertrophy, focal tubule degeneration, necrosis, and melanomacrophage (MM) proliferation. Although environmentally unlikely, high-dose exposures clarified biological effects of TiO₂-NPs, such as ROS formation and MRC responses in the gills, which may impair ionic balance. It was also found that MM are likely responsible for eliminating NPs in the kidney. These findings will help to regulate TiO₂-NP disposal, but longer-term studies are still needed.

Mitochondria-rich cells adjustments and ionic balance in the Neotropical fish Prochilodus lineatus exposed to titanium dioxide nanoparticles

Manufactured titanium dioxide nanoparticles (TiO₂-NP) have been intensely applied in numerous industrial products and may be a risk for aquatic systems as they are not completely removed from domestic and industrial wastes after water treatment. This study evaluated the osmo- and ionic balance, Na⁺/K⁺-ATPase, H⁺-ATPase and carbonic anhydrase activities and the mitochondria-rich cells (MRC) in the gills and kidney of the Neotropical fish Prochilodus lineatus after 2 (acute) and 14 (subchronic) days of exposure to nominal 0, 1, 5, 10 and 50 mg L^-1 TiO₂-NP. The nominal concentrations corresponded to 0.0, 0.6, 1.6, 2.7 and 18.1 mg L^-1 suspended TiO₂-NP, respectively, in the water column one hour after NP introduction and were maintained for at least 24 h. Acute exposure to TiO₂-NP decreased plasma osmolality and Ca²⁺ levels. Na⁺/K⁺-ATPase, H⁺-ATPase and carbonic anhydrase activities were inhibited in the gills, but not in the kidney. Total MRC density did not change in gills and kidneys. At gill surface, total MRC density decreased in fish exposed to 50 mg L^-1 TiO₂-NP and the total MRC fractional surface area unchanged although, there were some changes in the fractional area of MRC with apical microvilli (MRCm) and MRC with apical sponge-like structure (MRCs). MRCm was more abundant than MRCs. After subchronic exposure, there was no change in plasma osmolality, ionic balance and enzyme activities. Total gill MRC density increased in the filament epithelium and renal tubules. In the gills, MRC contacting water exhibited some adjustments. Total MRC and fractional surface area unchanged, but there was an increase of MRCs contacting water at gill surface after exposure to10 and 50 mg L^-1 TiO₂-NP. MRC proliferation in filament epithelium and in renal tubules as well as the increasing MRCs at gill surface may have contributed to avoid change in plasma osmolality, ionic balance and enzyme activities and suggested a cellular physiological and morphological response to restore and maintain osmotic and ionic homeostasis after subchronic exposure.

Maternal exposure to nanosized titanium dioxide suppresses embryonic development in mice

Although nanoscale titanium dioxide (nano-TiO2) has been extensively used in industrial food applications and daily products for pregnant women, infants, and children, its potential toxicity on fetal development has been rarely studied. The main objective of this investigation was to establish the effects of maternal exposure of nano-TiO2 on developing embryos. Female imprinting control region mice were orally administered nano-TiO2 from gestational day 0 to 17. Our findings showed that Ti concentrations in maternal serum, placenta, and fetus were increased in nano-TiO2-exposed mice when compared to controls, which resulted in reductions in the contents of calcium and zinc in maternal serum, placenta, and fetus, maternal weight gain, placental weight, fetal weight, number of live fetuses, and fetal crown-rump length as well as cauda length, and caused an increase in the number of both dead fetuses and resorptions. Furthermore, maternal nano-TiO2 exposure inhibited development of the fetal skeleton, suggesting a significant absence of cartilage, reduced or absent ossification, and an increase in the number of fetuses with dysplasia, including exencephaly, spina bifida, coiled tail, scoliosis, rib absence, and sternum absence. These findings indicated that nano-TiO2 can cross the blood-fetal barrier and placental barrier, thereby delaying the development of fetal mice and inducing skeletal malformation. These factors may be associated with reductions in both calcium and zinc in maternal serum and the fetus, and both the placenta and embryos may be major targets of developmental toxicity following maternal exposure to nano-TiO2 during the prenatal period. Therefore, the application of nano-TiO2 should be carried out with caution.

Genotoxicity of metal based engineered nanoparticles in aquatic organisms: A review

Engineered nanoparticles (ENPs) are an emerging class of environmental contaminants, but are generally found in very low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. In this review, we: (i) highlight key mechanisms of metal-based ENP-induced genotoxicity, (ii) identify key nanoparticle and environmental factors which influence the observed genotoxic effects, and (iii) highlight the challenges involved in interpreting reported data and provide recommendations on how these challenges might be addressed. We review the application of eight different genotoxicity assays, where the Comet Assay is generally preferred due to its capacity to detect low levels of DNA damage. Most ENPs have been shown to cause genotoxic responses; e.g., DNA or/and chromosomal fragmentation, or DNA strand breakage, but at unrealistic high concentrations. The genotoxicity of the ENPs was dependent on the inherent physico-chemical properties (e.g. size, coating, surface chemistry, e.tc.), and the presence of co-pollutants. To enhance the value of published genotoxicity data, the role of environmental processes; e.g., dissolution, aggregation and agglomeration, and adsorption of ENPs when released in aquatic systems, should be included, and assay protocols must be standardized. Such data could be used to model ENP genotoxicity processes in open environmental systems.

Comparative study on toxicity of ZnO and TiO2 nanoparticles on Artemia salina: effect of pre-UV-A and visible light irradiation

This study evaluated the toxicity potential of ZnO and TiO2 nanoparticles under pre-UV-A irradiation and visible light condition on Artemia salina. The nanoparticle suspension was prepared in seawater medium and exposed under pre-UV-A (0.23 mW/cm2) and visible light (0.18 mW/cm2) conditions. The aggregation profiles of both nanoparticles (NPs) and dissolution of ZnO NPs under both irradiation conditions at various kinetic intervals (1, 24, 48 h) were studied. The 48-h LC50 values were found to be 27.62 and 71.63 mg/L for ZnO NPs and 117 and 120.9 mg/L for TiO2 NPs under pre-UV-A and visible light conditions. ZnO NPs were found to be more toxic to A. salina as compared to TiO2 NPs. The enhanced toxicity was observed under pre-UV-A-irradiated ZnO NPs, signifying its phototoxicity. Accumulation of ZnO and TiO2 NPs into A. salina depends on the concentration of particles and type irradiations. Elimination of accumulated nanoparticles was also evident under both irradiation conditions. Other than ZnO NPs, the dissolved Zn2+ also had a significant effect on toxicity and accumulation in A. salina. Increased catalase (CAT) activity in A. salina indicates the generation of oxidative stress due to NP interaction. Thus, this study provides an understanding of the toxicity of photoreactive ZnO and TiO2 NPs as related to the effects of pre-UV-A and visible light irradiation.

Behavior and Potential Impacts of Metal-Based Engineered Nanoparticles in Aquatic Environments

The specific properties of metal-based nanoparticles (NPs) have not only led to rapidly increasing applications in various industrial and commercial products, but also caused environmental concerns due to the inevitable release of NPs and their unpredictable biological/ecological impacts. This review discusses the environmental behavior of metal-based NPs with an in-depth analysis of the mechanisms and kinetics. The focus is on knowledge gaps in the interaction of NPs with aquatic organisms, which can influence the fate, transport and toxicity of NPs in the aquatic environment. Aggregation transforms NPs into micrometer-sized clusters in the aqueous environment, whereas dissolution also alters the size distribution and surface reactivity of metal-based NPs. A unique toxicity mechanism of metal-based NPs is related to the generation of reactive oxygen species (ROS) and the subsequent ROS-induced oxidative stress. Furthermore, aggregation, dissolution and ROS generation could influence each other and also be influenced by many factors, including the sizes, shapes and surface charge of NPs, as well as the pH, ionic strength, natural organic matter and experimental conditions. Bioaccumulation of NPs in single organism species, such as aquatic plants, zooplankton, fish and benthos, is summarized and compared. Moreover, the trophic transfer and/or biomagnification of metal-based NPs in an aquatic ecosystem are discussed. In addition, genetic effects could result from direct or indirect interactions between DNA and NPs. Finally, several challenges facing us are put forward in the review.

Environmental release of engineered nanomaterials from commercial tiles under standardized abrasion conditions

The study presented here focuses on commercial antibacterial tiles whose emissivity of (nano) particles due to abrasion has yet barely been investigated. The tiles have been characterized regarding their surface properties and composition throughout their chain-of-use, i.e. from their state of commercialization until the experimental end-of-service life. In contrast to plane standard tiles, their surfaces form hilly surfaces. In the depressions, titanium dioxide is found at the surface, thus theoretically protected by the hilly areas against abrasion on the tile's surface. Furthermore, a deposition technique has been put in place by producers allowing for coating the before mentioned commercial tiles with titanium dioxide, thus being similar to those commercially available. It consists in depositing titanium dioxide on the surface, latter one allowing fixing the first. This development allows for better understanding the future options for product formulation and thus improvement with respect to particle release. The tests reveal the aerosolization from commercial antibacterial tiles of micronic and submicronic particles in the inhalable region or particles that can subjected to be released in the environment (<10μm). The aersolization of the particles from the coated tiles was found to be significantly higher compared to the non coated tiles.

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.

TiO2 nanoparticles for the remediation of eutrophic shallow freshwater systems: Efficiency and impacts on aquatic biota under a microcosm experiment

The application of nanomaterials (NMs) in the remediation of eutrophic waters, particularly in the control of internal loading of nutrients, has been started, but limited investigations evaluated the effectiveness of these new treatment approaches and of their potential impacts on species from shallow freshwater lakes. The present work investigated, under a microcosm experiment, the application of a TiO2 nanomaterial both for reducing nutrient (mainly phosphorus and nitrogen forms) desorption and release from sediments (preventive treatment-PT) and for eliminating algal blooms (remediation treatment-RT). Furthermore, we also intended to assess the potential impacts of nano-TiO2 application on key freshwater species. The results showed the effectiveness of nano-TiO2 in controlling the release of phosphates from surface sediment and the subsequent reduction of total phosphorus in the water column. A reduction in total nitrogen was also observed. Such changes in nutrient dynamics contributed to a progressive inhibition of development of algae after the application of the NM in PT microcosms. Concerning the ability of nano-TiO2 to interact with algal cells, this interaction has likely occurred, mainly in RT, enhancing the formation of aggregates and their rapid settlement, thus reducing the algal bloom. Both treatments caused deleterious effects on freshwater species. In PT, Daphnia magna and Lemna minor showed a significant inhibition of several endpoints. Conversely, no inhibitory effect on the growth of Chironomus riparius was recorded. In opposite, C. riparius was the most affected species in RT microcosms. Such difference was probably caused by the formation of larger TiO2-algae aggregates in RT, under a high algal density, that rapidly settled in the sediment, becoming less available for pelagic species. In summary, despite the effectiveness of both treatments in controlling internal nutrient loading and in the mitigating algal bloom episodes, their negative effects on biota have to be seriously taken into account.

Ecotoxicity Effects of Nanomaterials on Aquatic Organisms

The increasing production and use of engineered nanomaterials raise concerns about inadvertent exposure and the potential for adverse effects on the aquatic environment. The aim of this chapter is focused on studies of nanotoxicity in different models of aquatic organisms and their impact. Moreover, the chapter provides an overview of nanoparticles, their applications, and the potential nanoparticle-induced toxicity in aquatic organisms. The topics discussed in this chapter are the physicochemical characteristic of nanomaterials (size, aggregation, morphology, surface charge, reactivity, dissolution, etc.) and their influence on toxicity. Further, the text discusses the direct effect of nanomaterials on development stage (embryonic and adult) in aquatic organisms, the mechanism of action as well as the toxicity data of nanomaterials in different species.f action as well as the toxicity data of nanomaterials in different species.

A critical evaluation of the fish early-life stage toxicity test for engineered nanomaterials: experimental modifications and recommendations

There are concerns that regulatory toxicity tests are not fit for purpose for engineered nanomaterials (ENMs) or need modifications. The aim of the current study was to evaluate the OECD 210 fish, early-life stage toxicity test for use with TiO2 ENMs, Ag ENMs, and MWCNT. Both TiO2 ENMS (≤160 mg l(-1)) and MWCNT (≤10 mg l(-1)) showed limited acute toxicity, whilst Ag ENMs were acutely toxic to zebrafish, though less so than AgNO3 (6-day LC50 values of 58.6 and 5.0 µg l(-1), respectively). Evidence of delayed hatching, decreased body length and increased muscle width in the tail was seen in fish exposed to Ag ENMs. Oedema (swollen yolk sacs) was also seen in fish from both Ag treatments with, for example, mean yolk sac volumes of 17, 35 and 39 µm(3) for the control, 100 µg l(-1) Ag ENMs and 5 µg l(-1) AgNO3 treatments, respectively. Among the problems with the standard test guidelines was the inability to maintain the test solutions within ±20 % of nominal concentrations. Pronounced settling of the ENMs in some beakers also made it clear the fish were not being exposed to nominal concentrations. To overcome this, the exposure apparatus was modified with the addition of an exposure chamber that ensured mixing without damaging the delicate embryos/larvae. This allowed more homogeneous ENM exposures, signified by improved measured concentrations in the beakers (up to 85.7 and 88.1 % of the nominal concentrations from 10 mg l(-1) TiO2 and 50 µg l(-1) Ag ENM exposures, respectively) and reduced variance between measurements compared to the original method. The recommendations include: that the test is conducted using exposure chambers, the use of quantitative measurements for assessing hatching and morphometrics, and where there is increased sensitivity of larvae over embryos to conduct a shorter, larvae-only toxicity test with the ENMs.

Genotoxic and cytotoxic effects of ZnO nanoparticles for Dunaliella tertiolecta and comparison with SiO2 and TiO2 effects at population growth inhibition levels

The increasing use of oxide nanoparticles (NPs) in commercial products has intensified the potential release into the aquatic environment where algae represent the basis of the trophic chain. NP effects upon algae population growth were indeed already reported in literature, but the concurrent effects at cellular and genomic levels are still largely unexplored. Our work investigates the genotoxic (by COMET assay) and cytotoxic effects (by qualitative ROS production and cell viability) of ZnO nanoparticles toward marine microalgae Dunaliella tertiolecta. A comparison at defined population growth inhibition levels (i.e. 50% Effect Concentration, EC50, and No Observed Effect Concentration, NOEC) with SiO2 and TiO2 genotoxic effects and previously investigated cytotoxic effects (Manzo et al., 2015) was performed in order to elucidate the possible diverse mechanisms leading to algae growth inhibition. After 72h exposure, ZnO particles act firstly at the level of cell division inhibition (EC50: 2mg Zn/L) while the genotoxic action is evident only starting from 5mg Zn/L. This outcome could be ascribable mainly to the release of toxic ions from the aggregate of ZnO particle in the proximity of cell membrane. In the main, at EC50 and NOEC values for ZnO NPs showed the lowest cytotoxic and genotoxic effect with respect to TiO2 and SiO2. Based on Mutagenic Index (MI) the rank of toxicity is actually: TiO2>SiO2>ZnO with TiO2 and SiO2 that showed similar MI values at both NOEC and EC50 concentrations. The results presented herein suggest that up to TiO2 NOEC (7.5mg/L), the algae DNA repair mechanism is efficient and the DNA damage does not result in an evident algae population growth inhibition. A similar trend for SiO2, although at lower effect level with respect to TiO2, is observable. The comparison among all the tested nanomaterial toxicity patterns highlighted that the algae population growth inhibition occurred through pathways specific for each NP also related to their different physicochemical behaviors in seawater.

Co-exposure of ZnO nanoparticles and UV radiation to Daphnia magna and Danio rerio: Combined effects rather than protection

The application of nanoparticles (NPs) in consumer products has been increasing over the past few years. Their release into the environment is likely to happen at any stage of production or during the use of products containing NPs. Zinc oxide NPs (ZnO-NP) are among the most-used NPs on the market due to its intrinsic properties, such as ultraviolet (UV) absorption. The aim of the present study was to assess the combined effects of ZnO-NP and UV radiation on 2 freshwater species: Daphnia magna and Danio rerio. The initial hypothesis was that the presence of ZnO-NP in the aquatic media would decrease the damaging effects of UV radiation for both species. The endpoints assessed for D. magna were immobilization, feeding inhibition, and reproduction output. For D. rerio, egg development was studied during 96 h and mortality, hatching delay, and abnormal development were the endpoints recorded. Combined exposures were designed based on the single toxicity of both stressors and analyzed based on the independent action concept and exploring possible deviations for synergism/antagonism, dose level, and dose ratio. Combined exposures with D. magna induced synergism on reproduction, decreasing the number of neonates produced more than expected based on both stressors' individual toxicity. Single exposures of D. rerio embryos to both stressors induced negative effects. The combined exposures caused a dose-ratio deviation pattern on mortality and hatching, with a synergism observed when ZnO-NP was the dominant stressor, changing to antagonism when UV radiation dominated the combined exposure. Regarding the results attained, studying ZnO toxicity under laboratory conditions may underestimate the risks when considering the potential interaction on effects when combined with UV radiation.

Effects of humic acid and ionic strength on TiO₂ nanoparticles sublethal toxicity to zebrafish

The stability and bioavailability of titanium dioxide nanoparticles (TiO2 NPs) suspension could be modified by the physicochemical properties of solution. In the present study, the effect of humic acid (HA) and ionic strength (by adding NaCl) on aggregation and sedimentation of TiO2 NPs suspension were investigated. Accordingly, the sublethal toxicity of TiO2 NPs suspensions with different HA and NaCl concentrations toward zebrafish (Danio rerio) was evaluated by monitoring the changes of superoxide dismutase, catalase, malonaldehyde and glutathione in gill, liver and intestine. The results showed that the aggregations formation and hydrodynamic diameter of TiO2 NPs in suspensions are not essential characteristics to decide toxicity. The varied oxidative stress responses detected in gill, liver and intestine derived from different toxicity mechanisms of TiO2 NPs. Nevertheless, the oxidative stress could be suppressed by the adding of HA and/or the increase of ionic strength, which can decrease the bioavailability of TiO2 NPs in water. The study suggests that the environmental factors, such as HA and ionic strength, are important for the fate (aggregation and sedimentation) and toxicity of nanomaterials in aquatic environment.

Quantification of titanium from TiO2 particles in biological tissue

This study presents the development of a strategy for the quantification of titanium from titanium dioxide polydisperse particles (TiO2) in dry biological tissue. Calf liver was chosen as laboratory testing material. The challenge was to (i) obtain a complete mineralization of the solid material (biological tissue and TiO2) and (ii) ensure the accuracy of the determined concentrations with a sufficient sensitivity. Mineralization was performed using a mixture of concentrated nitric and hydrofluoric acids. Atomic mass spectrometry associated with light-scattering technique was used to control the physical state (dissolved and particle forms) of titanium and reliably estimate the total titanium concentration in calf liver. The monitoring of (46)Ti and (49)Ti, operating in helium collision/reaction cell mode, and using external calibration with internal standard addition, allowed the quantification of Ti while removing isobaric interferences. The limit of detection and quantification were 0.7 and 2.3μg (Ti)g(-1) (tissue) respectively. The mean analytical recovery over the whole procedure was (103±6)% in a range of concentrations from LOD to 200μg(Ti)g(-1) (tissue).

Combination effects of nano-TiO2 and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on biotransformation gene expression in the liver of European sea bass Dicentrarchus labrax

The aim of present study was to investigate the influence of titanium dioxide nanoparticles (nano-TiO2, Aeroxide® P25) on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dependent biotransformation gene expression in liver of juvenile European sea bass Dicentrarchus labrax. An in vivo 7day waterborne exposure was performed with nano-TiO2 (1mg/L) and 2,3,7,8-TCDD (46pg/L), singly and in combination. The mRNA expression of aryl hydrocarbon receptor repressor (Ahrr), estrogen receptor (erβ2), ABC transport proteins as Abcb1, Abcc1-c2-g2, cytochrome P450 (cyp1a), glutathione-s-transferase (gsta), glutathione reductase (gr) and engulfment and motility (ELMO) domain-containing protein 2 (elmod2) was investigated. Ahrr, erβ2, abcc1 and abcg2 resulted down-regulated with respect to controls in all experimental groups. Co-exposure to nano-TiO2 and 2,3,7,8-TCDD caused a further significant down regulation of ahrr, erβ2, Abcb1 and Abcc2 compared to single chemical exposure (nano-TiO2 or 2,3,7,8-TCDD alone). No effects were observed for 2,3,7,8-TCDD and nano-TiO2 alone in abcb1 gene, while abcc2 was down-regulated by nano-TiO2 alone. Cyp1a, gst and elmod2 genes were up-regulated by 2,3,7,8-TCDD and to a similar extent after co-exposure. Overall the results indicate that nano-TiO2 is unlikely to interfere with 2,3,7,8-TCDD-dependent biotransformation gene expression in the liver of European sea bass, although the effects of co-exposure observed in ABC transport mRNAs might suggest an impact on xenobiotic metabolite disposition and transport in European sea bass liver.

Toxicological aspects of photocatalytic degradation of selected xenobiotics with nano-sized Mn-doped TiO2

The toxic effects of two selected xenobiotics, bisphenol A (BPA) and atrazine (ATZ), were evaluated after photocatalytic degradation using nano-sized, Mn-doped TiO2. Undoped and Mn-doped TiO2 nanoparticles were synthesized. The samples were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), UV-vis-diffuse reflectance spectra (DRS), X-ray fluorescence spectroscopy (XRF), and BET surface area. The photocatalytic efficiency of the undoped and Mn-doped TiO2 was evaluated for BPA and ATZ. The toxicity of the synthesized photocatalysts and photocatalytic by-products of BPA and ATZ was determined using frog embryos and tadpoles, zebrafish embryos, and bioluminescent bacteria. Possible toxic effects were also evaluated using selected enzyme biomarkers. The results showed that Mn-doped TiO2 nanoparticles did not cause significant lethality in Xenopus laevis embryos and tadpoles, but nonfiltered samples caused lethality in zebrafish. Furthermore, Mn-doping of TiO2 increased the photocatalytic degradation capability of nanoparticles, and it successfully degraded BPA and AZT, but degradation of AZT caused an increase of the lethal effects on both tadpoles and fish embryos. Degradation of BPA caused a significant reduction of lethal effects, especially after 2-4h of degradation. However, biochemical assays showed that both Mn-doped TiO2 and the degradation by-products caused a significant change of selected biomarkers on X. laevis tadpoles; thus, the ecological risks of Mn-doped TiO2 should be considered due to nanomaterial applications and for spilled nanoparticles in an aquatic ecosystem. Also, the risk of nanoparticles should be considered using indicator reference biochemical markers to verify the environmental health impacts.

Genotoxicity of metal oxide nanomaterials: review of recent data and discussion of possible mechanisms

Nanotechnology has rapidly entered into human society, revolutionized many areas, including technology, medicine and cosmetics. This progress is due to the many valuable and unique properties that nanomaterials possess. In turn, these properties might become an issue of concern when considering potentially uncontrolled release to the environment. The rapid development of new nanomaterials thus raises questions about their impact on the environment and human health. This review focuses on the potential of nanomaterials to cause genotoxicity and summarizes recent genotoxicity studies on metal oxide/silica nanomaterials. Though the number of genotoxicity studies on metal oxide/silica nanomaterials is still limited, this endpoint has recently received more attention for nanomaterials, and the number of related publications has increased. An analysis of these peer reviewed publications over nearly two decades shows that the test most employed to evaluate the genotoxicity of these nanomaterials is the comet assay, followed by micronucleus, Ames and chromosome aberration tests. Based on the data studied, we concluded that in the majority of the publications analysed in this review, the metal oxide (or silica) nanoparticles of the same core chemical composition did not show different genotoxicity study calls (i.e. positive or negative) in the same test, although some results are inconsistent and need to be confirmed by additional experiments. Where the results are conflicting, it may be due to the following reasons: (1) variation in size of the nanoparticles; (2) variations in size distribution; (3) various purities of nanomaterials; (4) variation in surface areas for nanomaterials with the same average size; (5) differences in coatings; (6) differences in crystal structures of the same types of nanomaterials; (7) differences in size of aggregates in solution/media; (8) differences in assays; (9) different concentrations of nanomaterials in assay tests. Indeed, due to the observed inconsistencies in the recent literature and the lack of adherence to appropriate, standardized test methods, reliable genotoxicity assessment of nanomaterials is still challenging.

Influence of titanium dioxide nanoparticles on 2,3,7,8-tetrachlorodibenzo-p-dioxin bioconcentration and toxicity in the marine fish European sea bass (Dicentrarchus labrax)

The present study investigated the influence of nano-TiO(2) (1 mg L(-1)) on 2,3,7,8-tetrachlorodibenzo-p-dioxin(2,3,7,8-TCDD) (46 pg L(-1)) bioconcentration and toxicity in the European sea bass (Dicentrarchus labrax) during 7 days in vivo exposure. A multimarkers approach was applied in different organs: detoxification in liver; innate immunity and pro-inflammatory response and adaptive immunity in gills and spleen; genotoxicity in peripheral erythrocytes and muscle. Bioconcentration of 2,3,7,8-TCDD in presence of nano-TiO2 was investigated in liver, skin and muscle as well as interaction between nano-TiO2 and organic pollutants in artificial sea water (ASW). Nano-TiO2 negatively influenced immune response induced by 2,3,7,8-TCDD in spleen but not in gills and reduced the DNA damage induced by 2,3,7,8-TCDD in erythrocytes. nano-TiO2 did not interfere with 2,3,7,8-TCDD detoxification and bioconcentration according to the observed no interaction of the nano-TiO2 with organic pollutants in ASW.

Genotoxicity, potential cytotoxicity and cell uptake of titanium dioxide nanoparticles in the marine fish Trachinotus carolinus (Linnaeus, 1766)

Nanoparticles have physicochemical characteristics that make them useful in areas such as science, technology, medicine and in products of everyday use. Recently the manufacture and variety of these products has grown rapidly, raising concerns about their impact on human health and the environment. Adverse effects of exposure to nanoparticles have been reported for both terrestrial and aquatic organisms, but the toxic effects of the substances on marine organisms remain poorly understood. The main aim of this study was to evaluate the genotoxicity of TiO2-NP in the marine fish Trachinotus carolinus, through cytogenotoxic methods. The fish received two different doses of 1.5 μg and 3.0 μg-TiO2-NP g(-1) by intraperitoneal injection. Blood samples were collected to analyze erythrocyte viability using the Trypan Blue exclusion test, comet assay (pH>13), micronucleus (MN) and other erythrocyte nuclear abnormalities (ENA) 24, 48 and 72 h after injection. The possible cell uptake of TiO2-NP in fish injected with the higher dose was investigated after 72 h using transmission electron microscopy (TEM). The results showed that TiO2-NP is genotoxic and potentially cytotoxic for this species, causing DNA damage, inducing the formation of MN and other ENA, and decreasing erythrocyte viability. TEM examination revealed that cell uptake of TiO2-NP was mainly in the kidney, liver, gills and to a lesser degree in muscle. To the extent of the authors' knowledge, this is the first in vivo study of genotoxicity and other effects of TiO2-NP in a marine fish.

Chronic TiO₂ nanoparticle exposure to a benthic organism, Hyalella azteca: impact of solar UV radiation and material surface coatings on toxicity

There is limited information on the chronic effects of nanomaterials to benthic organisms, as well as environmental mitigating factors that might influence this toxicity. The present study aimed to fill these data gaps by examining various growth endpoints (weight gain, instantaneous growth rate, and total protein content) for up to a 21 d sediment exposure of TiO2 nanoparticles (nano-TiO2) to a representative benthic species, Hyalella azteca. An uncoated standard, P25, and an Al(OH)3 coated nano-TiO2 used in commercial products were added to sediment at 20 mg/L or 100 mg/L Under test conditions, UV exposure alone was shown to be a greater cause of toxicity than even these high levels of nano-TiO2 exposure, indicating that different hazards need to be addressed in toxicity testing scenarios. In addition, this study showed the effectiveness of a surface coating on the decreased photoactivity of the material, as the addition of an Al(OH)3 coating showed a dramatic decrease in reactive oxygen species (ROS) production. However, this reduced photoactivity was found to be partially restored when the coating had been degraded, leading to the need for future toxicity tests which examine the implications of weathering events on particle surface coatings.

Comparison of TiO2 nanoparticle and graphene-TiO2 nanoparticle composite phototoxicity to Daphnia magna and Oryzias latipes

With a dramatic rise in complexity, needs of nanotoxicology research go beyond simple forms of nanomaterials. This study compared the phototoxicity of nano-TiO2 and graphene-TiO2 nanocomposite (GNP). GNP was synthesized based on a hydrothermal method, which simultaneously performed the reduction of graphene oxide and nano-TiO2 loading. A series of acute toxicity tests of nano-TiO2, graphene and GNP was performed on two aquatic organisms, Daphnia magna and Oryzias latipes. Fast and substantial agglomeration and sedimentation of nanoparticles in test media and surface attachment of nano-TiO2 and GNP on D. magna surface was observed. Similar phototoxicity of nano-TiO2 and GNP for both species existed, though compared with nano-TiO2, GNP had a 2.3-fold increase in visible light photocatalytic ROS generation. In summary, this study demonstrated the significance of illumination spectrum, particle behavior, and species sensitivity on nanophototoxicity, and the needs for research on increasingly sophisticated functional materials.

Heteroaggregation of titanium dioxide nanoparticles with model natural colloids under environmentally relevant conditions

The heteroaggregation of engineered nanoparticles (ENPs) with natural colloids (NCs), which are ubiquitous in natural surface waters, is a crucial process affecting the environmental transport and fate of ENPs. Attachment efficiencies for heteroaggregation, α hetero, are required as input parameters in environmental fate models to predict ENP concentrations and contribute to ENP risk assessment. Here, we present a novel method for determining α hetero values by using a combination of laser diffraction measurements and aggregation modeling based on the Smoluchowski equation. Titanium dioxide nanoparticles (TiO2 NPs, 15 nm) were used to demonstrate this new approach together with larger silicon dioxide particles (SiO2, 0.5 μm) representing NCs. Heteroaggregation experiments were performed at different environmentally relevant solution conditions. At pH 5 the TiO2 NPs and the SiO2 particles are of opposite charge, resulting in α hetero values close to 1. At pH 8, where all particles are negatively charged, α hetero was strongly affected by the solution conditions, with α hetero ranging from <0.001 at low ionic strength to 1 at conditions with high NaCl or CaCl2 concentrations. The presence of humic acid stabilized the system against heteroaggregation.

Toxicity assessment of TiO₂ nanoparticles in zebrafish embryos under different exposure conditions

The popularity of TiO2 nanoparticles (nano-TiO2) lies in their wide range of nanotechnological applications, together with low toxicity. Meanwhile, recent studies have shown that the photocatalytic properties of this material can result in alterations in their behavior in the environment, causing effects that have not yet been fully elucidated. The objective of this study was to evaluate the toxicity of two formulations of nano-TiO2 under different illumination conditions, using an experimental model coherent with the principle of the three Rs of alternative animal experimentation (reduction, refinement, and replacement). Embryos of the fish Danio rerio were exposed for 96h to different concentrations of nano-TiO2 in the form of anatase (TA) or an anatase/rutile mixture (TM), under either visible light or a combination of visible and ultraviolet light (UV). The acute toxicity and sublethal parameters evaluated included survival rates, malformation, hatching, equilibrium, and overall length of the larvae, together with biochemical biomarkers (specific activities of catalase (CAT), glutathione S-transferase (GST), and acid phosphatase (AP)). Both TA and TM caused accelerated hatching of the larvae. Under UV irradiation, there was greater mortality of the larvae of the groups exposed to TM, compared to those exposed to TA. Exposure to TM under UV irradiation altered the equilibrium of the larvae. Alterations in the activities of CAT and GST were indicative of oxidative stress, although no clear dose-response relationship was observed. The effects of nano-TiO2 appeared to depend on both the type of formulation and the illumination condition. The findings contribute to elucidation of the factors involved in the toxicity of these nanoparticles, as well as to the establishment of protocols for risk assessments of nanotechnology.