Review of titanium dioxide nanoparticle phototoxicity: Developing a phototoxicity ratio to correct the endpoint values of toxicity tests

Building species trait-specific nano-QSARs: Model stacking, navigating model uncertainties and limitations, and the effect of dataset size

A strong need exists for broadly applicable nano-QSARs, capable of predicting toxicological outcomes towards untested species and nanomaterials, under different environmental conditions. Existing nano-QSARs are generally limited to only a few species but the inclusion of species characteristics into models can aid in making them applicable to multiple species, even when toxicity data is not available for biological species. Species traits were used to create classification- and regression machine learning models to predict acute toxicity towards aquatic species for metallic nanomaterials. Afterwards, the individual classification- and regression models were stacked into a meta-model to improve performance. Additionally, the uncertainty and limitations of the models were assessed in detail (beyond the OECD principles) and it was investigated whether models would benefit from the addition of more data. Results showed a significant improvement in model performance following model stacking. Investigation of model uncertainties and limitations highlighted the discrepancy between the applicability domain and accuracy of predictions. Data points outside of the assessed chemical space did not have higher likelihoods of generating inadequate predictions or vice versa. It is therefore concluded that the applicability domain does not give complete insight into the uncertainty of predictions and instead the generation of prediction intervals can help in this regard. Furthermore, results indicated that an increase of the dataset size did not improve model performance. This implies that larger dataset sizes may not necessarily improve model performance while in turn also meaning that large datasets are not necessarily required for prediction of acute toxicity with nano-QSARs.

Past, present, and possible future policies on plastic use in the United States, particularly microplastics and nanoplastics: A review

As the levels of plastic use in global society have increased, it has become crucial to regulate plastics of all sizes including both microplastics (MPs) and nanoplastics (NPs). Here, the published literature on the current laws passed by the US Congress and regulations developed by various federal agencies such as the US Environmental Protection Agency and the US Food and Drug Administration (FDA) that could be used to regulate MPs and NPs have been reviewed and analyzed. Statutes such as the Clean Water Act, the Safe Drinking Water Act, the Toxic Substances Control Act (TSCA), the Resource Conservation and Recovery Act, and the Clean Air Act can all be used to address plastic pollution. These statutes have not been invoked for MP and NP waste in water or air. The Federal Food, Drug, and Cosmetic Act provides guidance on how the FDA should evaluate plastics use in food, food packaging, cosmetics, drug packaging, and medical devices. The FDA has recommended that acceptable levels of ingestible contaminant from recycled plastic are less than 1.5 µg/person/day, which is 476 000 times less than the possible ingested daily dose. Plastic regulation is present at the state level. States have banned plastic bags, and several cities have banned plastic straws. California is the only state beginning to focus on monitoring MPs in drinking water. The future of MP regulation in the USA should use TSCA to test the safety of plastics. The other statutes need to include MPs in their definitions. For the FDA, MPs should be redefined as contaminants-allowing tolerances to be set for MPs in food and beverages. Through minor changes in how MPs are classified, it is possible to begin to use the current statutes to understand and begin to minimize the possible effects of MPs on human health and the environment. Integr Environ Assess Manag 2023;19:474-488. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Influence of TiO2 nanocomposite UV filter surface chemistry and their interactions with organic UV filters on uptake and toxicity toward cultured fish gill cells

Aquatic environments have been found to be contaminated with a variety of inorganic and organic UV filters. This includes novel nano-sized titanium dioxide (TiO₂) composite particles, which have been increasingly developed and incorporated into commercial sunscreens in recent years. So far, relatively little is known about the effects of this novel class of UV filters on aquatic life. Therefore, this study aimed to determine and compare the toxicity of three such nanoparticulate TiO₂ UV filters with different surface coatings, namely Eusolex® T-Avo (SiO₂-coated), T-Lite™ SF (Al(OH)₃/PDMS-coated), and Eusolex® T-S (Al₂O₃/stearic acid-coated) either alone, or in the presence of selected organic UV filters (octinoxate, avobenzone, octocrylene), toward fish using RTgill-W1 cell cultures as an in vitro experimental model. Besides standard exposure protocols, alternative approaches (i.e., exposure to water accommodated fractions (WAFs), hanging-drop exposure) were explored to account for nanoparticle (NP)-specific fate in the medium and obtain additional/complementary information on their toxicity in different conditions. The AlamarBlue, CFDA-AM and Neutral Red Retention (NR) assays were used to measure effects on different cellular endpoints. Transmission electron microscopy (TEM) was used to examine NP uptake. Our results showed that none of the TiO₂ NP UV filters were cytotoxic at the concentrations tested (0.1-10 µg/mL; 24 h) but there were differences in their uptake by the cells. Thus, only the hydrophilic T-AVO was detected inside cells, but the hydrophobic T-Lite SF and T-S were not. In addition, our results show that the presence of NPs (or the used dispersant) tended to decrease organic UV filter toxicity. The level of combination effect depended on both NP-type (surface chemistry) and concentration, suggesting that the reduced toxicity resulted from reduced availability of the organic UV filters due to their adsorption to the NP surface. Thus, mixtures of TiO₂ NP UV filters and organic UV filters may have a different toxicological profile compared to the single substances, but probably do not pose an increased hazard.

Titanium dioxide nanoparticles as a risk factor for the health of Neotropical tadpoles: a case study of Dendropsophus minutus (Anura: Hylidae)

The production and use of titanium dioxide (TiO₂) nanoparticles are increasing worldwide. The release of this substance into the environment can induce toxic effects in aquatic invertebrates and vertebrates, although the exact nature of its impacts on Neotropical amphibians is still poorly understood. In this context, the present study evaluated the toxicity of TiO₂ nanoparticles and their counterpart-dissolved titanium dioxide (TiO₂)-in the tadpoles of Dendropsophus minutus. The biometric parameters, DNA damage, and behavioral changes were verified in tadpoles exposed to three different concentrations (0.1 mg·L^-1, 1.0 mg·L^-1, and 10 mg·L^-1) of TiO₂ nanoparticles and dissolved TiO₂ for 7 days. We verified significant DNA damage in the D. minutus tadpoles exposed to both forms of Ti, in comparison with the control group. We also identified a reduction in total size, body length, and width, and the height of the musculature of the tail of the tadpoles exposed to all concentrations of both substances in comparison with the control. In the behavioral test, the tadpoles exposed to nanoparticles and dissolved TiO₂ presented reduced mobility and a tendency to be less aggregated than normal. Here, the simultaneous use of multiple biomarkers was fundamental for the reliable assessment of the adverse effects of nanomaterials on anuran amphibians and the establishment of a systematic approach to the biomonitoring of aquatic ecosystems. The present study expands our understanding of the genotoxic, morphological, and behavioral effects of TiO₂ nanoparticles and dissolved TiO₂ on anuran amphibians, and contributes to the establishment of further research for the more systematic assessment of the environmental risk of nanomaterials.

Retinal cytotoxicity of silica and titanium dioxide nanoparticles

The retina plays a key role in human vision. It is composed of cells that are essential for vision signal generation. Thus far, conventional medications have been ineffective for treating retinal diseases because of the intrinsic blood-retinal barrier. Nanoparticles (NPs) are promising effective platforms for ocular drug delivery. However, nanotoxicity in the retinal tissue has not received much attention. This study used R28 cells (a retinal precursor cell line that originated from rats) to investigate the safety of two commonly used types of NPs: silica nanoparticles (SiO2NPs, 100 nm) and titanium dioxide nanoparticles (TiO2NPs, 100 nm). Cellular viability and reactive oxygen species generation were measured after 24, 48, and 72 h of exposure to each NP. Cellular autophagy and the mTOR pathways were evaluated. The retinal toxicity of the NPs was investigated in vivo in rat models. Both types of NPs were found to induce significant dose-dependent toxicity on the R28 cells. A significant elevation of reactive oxygen species generation was also observed. Increased autophagy and decreased mTOR phosphorylation were observed after SiO2NPs and TiO2NPs exposure. The diffuse apoptosis of the retinal cellular layers was detected after intravitreal injection.

The toxicology properties of modified hydrothermal nanotitania extraction

INTRODUCTION

The nanoparticle has become a part of world industry. This substance has been proven as potentially beneficial for its usage as a catalyst and semi-conductor due to its high surface area and the effects of the quantum size effect. It exhibits potential characteristics and would be applied in a wider scope of usage compared to bulk particles because the smaller the size of the particles, the more room for the extent of their usage. Nano titanium dioxide application as semi-conductors together with a catalyst is highly attributed to its high photochemical stability and ability to be produced at a low-cost. The consequence of this - exposure of nano titanium dioxide particles to humans - raises concerns regarding health and safety. Therefore, this research action works designed to offer a thorough analysis of toxicology impacts produced by our own synthesis modified hydrothermal in vitro experiments.

MATERIAL AND METHODS

Our nanotitania extraction with 0.05% silver was tested for its toxicity against L929 mouse cells. The cytotoxicity effect of nanotitania extract was evaluated by MTT assay. Cell viability (% CV) was calculated using a formula.

RESULTS

There are non-cytotoxicity activity of 0.05% nanotitania at concentrations 1.5, 3.1, 6.3, 12.5, and 25 mg/ml on L929 cell lines except at concentration 50 and 100 mg/ml. The result was related to the optical density reading.

CONCLUSIONS

There is no cytotoxic effect of nanotitania extraction with 0.05% silver in the growth inhibition test with L929 mouse with the exception of the 100 mg/ml extract.

Photoactive titanium dioxide nanoparticles modify heterotrophic microbial functioning

Nanoparticulate titanium dioxide (nTiO₂) is frequently applied, raising concerns about potential side effects on the environment. While various studies have assessed structural effects in aquatic model ecosystems, its impact on ecosystem functions provided by microbial communities (biofilms) is not well understood. This is all the more the case when considering additional stressors, such as UV irradiation - a factor known to amplify nTiO₂-induced toxicity. Using pairwise comparisons, we assessed the impact of UV (UV-A = 1.6 W/m²; UV-B = 0.7 W/m²) at 0, 20 or 2000 μg nTiO₂/L on two ecosystem functions provided by leaf-associated biofilms: while leaf litter conditioning, important for detritivorous invertebrate nutrition, seems unaffected, microbial leaf decomposition was stimulated (up to 25%) by UV, with effect sizes being higher in the presence of nTiO₂. Although stoichiometric and microbial analyses did not allow for uncovering the underlying mechanism, it seems plausible that the combination of a shift in biofilm community composition and activity together with photodegradation as well as the formation of reactive oxygen species triggered changes in leaf litter decomposition. The present study implies that the multiple functions a microbial community performs are not equally sensitive. Consequently, relying on one of the many functions realized by the same microbial community may be misleading for environmental management.

Titanium Dioxide Induces Apoptosis under UVA Irradiation via the Generation of Lysosomal Membrane Permeabilization-Dependent Reactive Oxygen Species in HaCat Cells

Titanium dioxide nanoparticles (TiO₂ NPs) have wide commercial applications, owing to their small size; however, the biosafety of TiO₂ NPs should be evaluated further. In this study, we aimed to investigate the cytotoxicity of TiO₂ NPs in the presence and absence of ultraviolet A (UVA) irradiation in human keratinocyte HaCaT cells. TiO₂ NPs did not significantly affect cell viability in the absence of UVA irradiation. Nonetheless, UVA-irradiated TiO₂ NPs induced caspase-dependent apoptosis of HaCaT cells. Exposure of HaCaT cells to TiO₂ NPs and UVA resulted in reactive oxygen species (ROS) generation and lysosomal membrane permeabilization (LMP); both effects were not observed in the absence of UVA irradiation. An analysis of the relationship between LMP and ROS, using CA-074 as a cathepsin inhibitor or NAC as an antioxidant, showed that LMP stimulates ROS generation under these conditions. These results imply that LMP-dependent oxidative stress plays a critical role in the UVA phototoxicity of TiO₂ NPs in HaCaT cells.

Review of aquatic toxicity of pharmaceuticals and personal care products to algae

Pharmaceuticals and Personal Care Products (PPCPs) have been frequently detected in the environment around the world. Algae play a significant role in aquatic ecosystem, thus the influence on algae may affect the life of higher trophic organisms. This review provides a state-of-the-art overview of current research on the toxicity of PPCPs to algae. Nanoparticles, contained in personal care products, also have been considered as the ingredients of PPCPs. PPCPs could cause unexpected effects on algae and their communities. Chlorophyta and diatoms are more accessible and sensitive to PPCPs. Multiple algal endpoints should be considered to provide a complete evaluation on PPCPs toxicity. The toxicity of organic ingredients in PPCPs could be predicted through quantitative structure-activity relationship model, whereas the toxicity of nanoparticles could be predicted with limitations. Light irradiation can change the toxicity through affecting algae and PPCPs. pH and natural organic matter can affect the toxicity through changing the existence of PPCPs. For joint and tertiary toxicity, experiments could be conducted to reveal the toxic mechanism. For multiple compound mixture toxicity, concentration addition and independent addition models are preferred. However, there has no empirical models to study nanoparticle-contained mixture toxicity. Algae-based remediation is an emerging technology to prevent the release of PPCPs from water treatment plants. Although many individual algal species are identified for removing a few compounds from PPCPs, algal-bacterial photobioreactor is a preferable alternative, with higher chances for industrial applications.

Effects of copper in Daphnia are modulated by nanosized titanium dioxide and natural organic matter: what is the impact of aging duration?

During its aquatic life cycle, nanosized titanium dioxide (nTiO₂) may interact with natural organic matter (NOM) ultimately altering the ecotoxicity of co-occurring chemical stressors such as heavy metals (e.g. copper (Cu)). In this context, the following hypotheses were tested: (1) aging of nTiO₂ along with Cu reduces Cu toxicity, (2) nTiO₂ agglomerates have a lower potential to reduce Cu toxicity and (3) aging of nTiO₂ in presence of NOM reduces Cu toxicity further. A multifactorial test design crossing three nTiO₂ levels (0.0, 0.6 and 3.0 mg/L) with two levels of NOM (0 versus 8 mg total organic carbon (TOC)/L) and seven nominal Cu concentrations (ranging from 0 to 1536 μg/L) aged in ASTM medium for 0, 1, 3 and 6 days was realised, while two aging scenarios were applied (type 1: nTiO₂ jointly aged with Cu; type 2: Cu added after nTiO₂ aging). Subsequently, Cu toxicity was assessed using the immobility of Daphnia magna after 48 h of exposure as response variable. The experiments revealed that neither aging duration nor the extent of agglomeration (type 1 vs. type 2 aging) has a substantial impact on Cu induced toxicity. Moreover, it was confirmed that the presence of NOM substantially reduced Cu induced toxicity, independent of the aging scenario and duration. More importantly, the data suggest the ingestion of Cu loaded nTiO₂ as additional exposure pathway contributing to Cu toxicity. In conclusion, it seems unlikely that nTiO₂ concentrations currently detected in or predicted for aquatic ecosystems, which are at least one order of magnitude below the concentration tested here, influence Cu toxicity meaningfully.

Adsorption of titanium dioxide nanoparticles onto zebrafish eggs affects colonizing microbiota

Teleost fish embryos are protected by two acellular membranes against particulate pollutants that are present in the water column. These membranes provide an effective barrier preventing particle uptake. In this study, we tested the hypothesis that the adsorption of antimicrobial titanium dioxide nanoparticles onto zebrafish eggs nevertheless harms the developing embryo by disturbing early microbial colonization. Zebrafish eggs were exposed during their first day of development to 2, 5 and 10 mg TiO2 L-1 (NM-105). Additionally, eggs were exposed to gold nanorods to assess the effectiveness of the eggs' membranes in preventing particle uptake, localizing these particles by way of two-photon microscopy. This confirmed that particles accumulate onto zebrafish eggs, without any detectable amounts of particles crossing the protective membranes. By way of particle-induced X-ray emission analysis, we inferred that the titanium dioxide particles could cover 25-45 % of the zebrafish egg surface, where the concentrations of sorbed titanium correlated positively with concentrations of potassium and correlated negatively with concentrations of silicon. A combination of imaging and culture-based microbial identification techniques revealed that the adsorbed particles exerted antimicrobial effects, but resulted in an overall increase of microbial abundance, without any change in heterotrophic microbial activity, as inferred based on carbon substrate utilization. This effect persisted upon hatching, since larvae from particle-exposed eggs still comprised higher microbial abundance than larvae that hatched from control eggs. Notably, pathogenic aeromonads tolerated the antimicrobial properties of the nanoparticles. Overall, our results show that the adsorption of suspended antimicrobial nanoparticles on aquatic eggs can have cascading effects across different life stages of oviparous animals. Our study furthermore suggests that aggregation dynamics may occur that could facilitate the dispersal of pathogenic bacteria through aquatic ecosystems.

Acute waterborne and chronic sediment toxicity of silver and titanium dioxide nanomaterials towards the oligochaete, Lumbriculus variegatus

The use of silver (Ag) and titanium dioxide (TiO₂) nanomaterials (NMs) in industrial processes and consumer products has experienced considerable growth since the late 20th century. Throughout their lifecycle, both Ag NM and TiO₂NM are released into the environment, with benthic systems anticipated to be the final sink. Their potential toxicity towards benthic species is therefore of major concern. This study investigated the toxicity of silver (Ag; NM-300 K) and titanium dioxide (TiO₂; NM-104) NMs to the freshwater oligochaete, Lumbriculus variegatus in acute (0-96-h) waterborne and chronic (28-d) sediment studies. Toxicity was investigated via assessment of mortality, behaviour, and antioxidant enzyme activity. The 96-h LC₅₀ for Ag NMs in water was 0.51 mg/l (95% CI, 0.45-0.56), with L. variegatus displaying inhibited predation-avoidance behaviour compared to controls (6.66 ± 10%) successful response at 24-h), as well as significant increases (p < 0.05) in catalase (CAT) activity at sub-lethal concentrations at 24-h. Behavioural improvement and the return of antioxidant enzymes to control levels was observed after 48 and 72-h. AgNO₃ exposure proved more toxic than Ag NM (96-h LC₅₀ = 0.034 mg/l, 95% CI, 0.031-0.037) but resulted in no changes to antioxidant enzymes following sub-lethal exposure. Furthermore, Ag dissolution from Ag NM (~2-4%) could not account for the full extent of toxicity observed, suggesting a nano-specific effect. Increased environmental relevance via the inclusion of Suwannee River Humic Acid (SRHA, 5 mg/l) alleviated sub-lethal Ag NM toxicity despite a comparable 96-h LC₅₀ (0.54 mg/l, 95% CI, 0.51-0.57). Significant effects of Ag NMs in formulated sediments (mortality, biomass) were only recorded according to OECD 225 at the highest test concentration (1333 mg/kg) for Ag NM indicating a potential attenuating effect of sediments towards toxicity. No toxicity was observed for TiO₂ NM in aquatic or sediment exposures up to concentrations of 2000 mg/l and 1333 mg/kg, respectively.

In light-sensitive drug delivery system nanoparticles mediate oxidative stress

In light-sensitive drug delivery systems, more and more nanoparticles were applied to load various drug molecules. However, few studies focused on their biomedical effects such as the regulation of heme oxygenase-1 (HO-1) expression and reactive oxygen species (ROS) generation which could influence cellular redox reaction. In the present article, through review of literature, analysis of high-throughput sequencing database, the mechanisms of drug delivery based on organic (poly-lactic-co-glycolic acid (PLGA) and polyethylene glycol (PEG)) and inorganic (Au, ZnO, SiO₂ and TiO₂) nanoparticles were introduced briefly. Besides, it was also expounded that nuclear factor-erythroid 2 (NF-E2)-related factor 2/BTB domain and CNC homolog 1 (Nrf2/Bach1) might be involved in the regulation of HO-1 and the quantum effect of photon altered ROS generation. The exogenous nanoparticles certainly have various biomedical effects that even affect the pathogenesis of some diseases like atopic dermatitis. Thus, biomedical effect of nanoparticles depends on HO-1/ROS needs further research.

Materials Science Challenges in Skin UV Protection: A Review

UV radiation is one of the critical environmental stress factors for human skin, which can trigger various problems such as pruritus, burning, erythema, premature skin aging and skin cancer. Hence, UV protection has become an indispensable daily routine and the use of topical sunscreen products is rapidly increasing. However, there are emerging concerns over the efficiency and safety of existing chemical and physical UV filters used in consumer products. Furthermore, there is no universally approved method for assessing sun protection efficiency regardless of the immediate end user need to develop safer sunscreen products that afford broad-spectrum photoprotection. It is evident that the current organic and inorganic UV filters have significant unfavorable impacts on human, environmental, and marine safety. Therefore, effective alternative UV filters should be established. This article comprehensively reviews the properties, safety, health and ecological concerns of various UV filters including TiO₂ and ZnO nanoparticles as well as the limitations of the testing protocols and guidelines provided by major regulatory bodies. The photoreactivity of UV filters used in sunscreen remains a major challenge, and it is crucial to develop new sunscreen ingredients, which not only protect the consumer, but also the environment.

TiO2 Nanomaterials Non-Controlled Contamination Could Be Hazardous for Normal Cells Located in the Field of Radiotherapy

Among nanomaterials (NMs), titanium dioxide (TiO₂) is one of the most manufactured NMs and can be found in many consumers' products such as skin care products, textiles and food (as E171 additive). Moreover, due to its most attractive property, a photoactivation upon non-ionizing UVA radiation, TiO₂ NMs is widely used as a decontaminating agent. Uncontrolled contaminations by TiO₂ NMs during their production (professional exposure) or by using products (consumer exposure) are rather frequent. So far, TiO₂ NMs cytotoxicity is still a matter of controversy depending on biological models, types of TiO₂ NMs, suspension preparation and biological endpoints. TiO₂ NMs photoactivation has been widely described for UV light radiation exposure, it could lead to reactive oxygen species production, known to be both cyto- and genotoxic on human cells. After higher photon energy exposition, such as X-rays used for radiotherapy and for medical imaging, TiO₂ NMs photoactivation still occurs. Importantly, the question of its hazard in the case of body contamination of persons receiving radiotherapy was never addressed, knowing that healthy tissues surrounding the tumor are indeed exposed. The present work focuses on the analysis of human normal bronchiolar cell response after co-exposition TiO₂ NMs (with different coatings) and ionizing radiation. Our results show a clear synergistic effect, in terms of cell viability, cell death and oxidative stress, between TiO₂ NMS and radiation.

Mechanisms of (photo)toxicity of TiO2 nanomaterials (NM103, NM104, NM105): using high-throughput gene expression in Enchytraeus crypticus

Titanium dioxide (TiO2) based nanomaterials (NMs) are among the most produced NMs worldwide. When irradiated with light, particularly UV, TiO2 is photoactive, a property that is explored for several purposes. There are an increasing number of reports on the negative effects of photoactivated TiO2 on non-target organisms. We have here studied the effect of a suite of reference type TiO2 NMs (i.e. NM103, NM104, and NM105 and compared these to the bulk) with and without UV radiation to the oligochaete Enchytraeus crypticus. High-throughput gene expression was used to assess the molecular mechanisms, while also anchoring it to the known effects at the organism level (i.e., reproduction). Results showed that the photoactivity of TiO2 (UV exposed) played a major role in enhancing TiO2 toxicity, activating the transcription of oxidative stress, lysosome damage and apoptosis mechanisms. For non-UV activated TiO2, where toxicity at the organism level (reproduction) was lower, results showed potential for long-term effects (i.e., mutagenic and epigenetic). NM specific mechanisms were identified: NM103 affected transcription and translation, NM104_UV negatively affected the reproductive system/organs, and NM105_UV activated superoxide anion response. Results provided mechanistic information on UV-related phototoxicity of TiO2 materials and evidence for the potential long-term effects.

An environmentally relevant concentration of titanium dioxide (TiO2) nanoparticles induces morphological changes in the mouthparts of Chironomus tentans

The present study was carried out in order to assess the influence of environmentally relevant concentrations of TiO₂ nanoparticles (E171 human food grade) toxicity on the freshwater midge Chironomus tentans. Tested concentrations were 125, 250, 500, 1000, 2000 and 4000 mg of E171 TiO₂ per 1 kg of sediment, for the experiment aiming at life trait toxicity observation; and 2.5, 25 and 250 mg of E171 TiO₂ per 1 kg of sediment for the experiment aiming at mouthpart deformity observation. The experimental design was constructed for the sediment dwelling chironomid larvae according to OECD guidelines. For the first time, a geometric morphometric approach was used to assess the deformities in chironomid larvae as sublethal implications of nanoparticle exposure. The present study showed a concentration-response relationship between the TiO₂ concentration in the substrate and the TiO₂ intake. The mortality and emergence ratio was affected at concentrations >1000 mg/kg. Geometric Morphometrics revealed the tendency of the mentum teeth to narrow and elongate and the mandibles to widen, as well as the loss of the first inner tooth, with a TiO₂ concentration rise. The variability of morphological changes observed in the mouthparts indicates that C. tentans could be used as a bioindicator in nano-TiO₂ monitoring.

JAK/STAT and TGF-ß activation as potential adverse outcome pathway of TiO2NPs phototoxicity in Caenorhabditis elegans

Titanium dioxide nanoparticles (TiO₂NPs) are widely used nanoparticles, whose catalytic activity is mainly due to photoactivation. In this study, the toxicity of TiO₂NPs was investigated on the nematode Caenorhabditis elegans, with and without UV activation. Comparative analyses across the four treatments revealed that UV-activated TiO₂NPs led to significant reproductive toxicity through oxidative stress. To understand the underlying molecular mechanism, transcriptomics and metabolomics analyses were conducted, followed by whole-genome network-based pathway analyses. Differential expression analysis from microarray data revealed only 4 DEGs by exposure to TiO₂NPs alone, compared to 3,625 and 3,286 DEGs by UV alone and UV-activated TiO₂NPs, respectively. Pathway analyses suggested the possible involvement of the JAK/STAT and TGF-ß pathways in the phototoxicity of TiO₂NPs, which correlated with the observation of increased gene expression of those pathways. Comparative analysis of C. elegans response across UV activation and TiO₂NPs exposure was performed using loss-of-function mutants of genes in these pathways. Results indicated that the JAK/STAT pathway was specific to TiO₂NPs, whereas the TGF-ß pathway was specific to UV. Interestingly, crosstalk between these pathways was confirmed by further mutant analysis. We consider that these findings will contribute to understand the molecular mechanisms of toxicity of TiO₂NPs in the natural environment.

Negligible cytotoxicity induced by different titanium dioxide nanoparticles in fish cell lines

Titanium dioxide nanoparticles (TiO₂-NPs) have a wide number of applications in cosmetic, solar and paint industries due to their photocatalyst and ultraviolet blocking properties. The continuous increase in the production of TiO₂-NPs enhances the risk for this manufactured nanomaterial to enter water bodies through treated effluents or agricultural amendments. TiO₂-NPs have shown very low toxicity in a number of aquatic organisms. However, there are no conclusive data about their deleterious effects and on their possible mechanisms of toxic action. At this level, in vitro cell culture systems are a useful tool to gain insight about processes underlying the toxicity of a wide variety of substances, including nanomaterials. Differences in the physiology of different taxa make advisable the use of cells coming from the taxon of interest, but collecting data from a variety of cellular types allows a better understanding of the studied processes. Taking all this into account, the aim of the present study was to assess the toxicity of three types of TiO₂-NP, rutile hydrophobic (NM-103), rutile hydrophilic (NM-104) and rutile-anatase (NM-105), obtained from the EU Joint Research Centre (JRC) repository, using various fish cell lines (RTG-2, PLHC-1, RTH-149, RTL-W1) and rainbow trout primary hepatocytes. For comparative purposes, the effect of different dispersion protocols, end-point assays and extended exposure time was studied in a fish cell line (RTG-2) and in the rat hepatoma cell line (H4IIE). TiO₂-NPs dispersions showed a variable degree of aggregation in cell culture media. Disruption of mitochondrial metabolic activity, plasma membrane integrity and lysosome function was not detected in any cell line after exposure to TiO₂-NPs at any time and concentration ranges tested. These results are indicative of a low toxicity of the TiO₂-NPs tested and show the usefulness of fish cells maintained in vitro as high throughput screening methods that can facilitate further testing in the framework of integrated testing strategies.

Assessment of Crystal Morphology on Uptake, Particle Dissolution, and Toxicity of Nanoscale Titanium Dioxide on Artemia salina

Knowledge of nanomaterial toxicity is critical to avoid adverse effects on human and environment health. In this study, the influences of crystal morphology on physico-chemical and toxic properties of nanoscale TiO2 (n-TiO2) were investigated. Artemia salina were exposed to anatase, rutile and mixture polymorphs of n-TiO2 in seawater. Short-term (24 h) and long-term (96 h) exposures were conducted in 1, 10 and 100 mg/L suspensions of n-TiO2 in the presence and absence of food. Anatase form had highest accumulation followed by mixture and rutile. Presence of food greatly reduced accumulation. n-TiO2 dissolution was not significant in seawater (p<0.05) nor was influenced from crystal structure. Highest toxic effects occurred in 96h exposure in the order of anatase > mixture > rutile. Mortality and oxidative stress levels increased with increasing n-TiO2 concentration and exposure time (p<0.05). Presence of food in the exposure medium alleviated the oxidative stress, indicating that deprivation from food could promote toxic effects of n-TiO2 under long-term exposure.

Nanotitania Exposure Causes Alterations in Physiological, Nutritional and Stress Responses in Tomato (Solanum lycopersicum)

Titanium dioxide nanoparticles (nanotitania: TiO₂NPs) are used in a wide range of consumer products, paints, sunscreens, and cosmetics. The increased applications lead to the subsequent release of nanomaterials in environment that could affect the plant productivity. However, few studies have been performed to determine the overall effects of TiO₂NPs on edible crops. We treated tomato plants with 0.5, 1, 2, and 4 g/L TiO₂NPs in a hydroponic system for 2 weeks and examined physiological, biochemical, and molecular changes. The dual response was observed on growth and photosynthetic ability of plants depending on TiO₂NPs concentrations. Low concentrations (0.5-2 g/L) of TiO₂NPs boosted growth by approximately 50% and caused significant increase in photosynthetic parameters such as quantum yield, performance index, and total chlorophyll content as well as induced expression of PSI gene with respect to untreated plants. The high concentration (4 g/L) affected these parameters in negative manner. The catalase and peroxidase activities were also elevated in the exposed plants in a dose-dependent manner. Likewise, exposed plants exhibited increased expressions of glutathione synthase and glutathione S-transferase (nearly threefold increase in both roots and leaves), indicating a promising role of thiols in detoxification of TiO₂NPs in tomato. The elemental analysis of tissues performed at 0.5, 1, and 2 g/L TiO₂NPs indicates that TiO₂NPs transport significantly affected the distribution of essential elements (P, S, Mg, and Fe) in roots and leaves displaying about threefold increases in P and 25% decrease in Fe contents. This study presents the mechanistic basis for the differential responses of titanium nanoparticles in tomato, and calls for a cautious approach for the application of nanomaterials in agriculture. GRAPHICAL ABSTRACTMovement of nanotitania in plant tissues.

Attenuation of Microbial Stress Due to Nano-Ag and Nano-TiO2 Interactions under Dark Conditions

Engineered nanomaterials (ENMs) are incorporated into thousands of commercial products, and their release into environmental systems creates complex mixtures with unknown toxicological outcomes. To explore this scenario, we probe the chemical and toxicological interactions of nanosilver (n-Ag) and nanotitania (n-TiO₂) in Lake Michigan water, a natural aqueous medium, under dark conditions. We find that the presence of n-Ag induces a stress response in Escherichia coli, as indicated by a decrease in ATP production observed at low concentrations (in the μg L^-1 range), with levels that are environmentally relevant. However, when n-Ag and n-TiO₂ are present together in a mixture, n-TiO₂ attenuates the toxicity of n-Ag at and below 20 μg L^-1 by adsorbing Ag⁺_(aq). We observe, however, that toxic stress cannot be explained by dissolved silver concentrations alone and, therefore, must also depend on silver associated with the nanoscale fraction. Although the attenuating effect of n-TiO₂ on n-Ag's toxicity is limited, this study emphasizes the importance of probing the toxicity of ENM mixtures under environmental conditions to assess how chemical interactions between nanoparticles change the toxicological effects of single ENMs in unexpected ways.

Effects of human food grade titanium dioxide nanoparticle dietary exposure on Drosophila melanogaster survival, fecundity, pupation and expression of antioxidant genes

The fruitfly, Drosophila melanogaster was exposed to the human food grade of E171 titanium dioxide (TiO2). This is a special grade of TiO2 which is frequently omitted in nanotoxicology studies dealing with TiO2, yet it is the most relevant grade regarding oral exposure of humans. D. melanogaster larvae were exposed to 0.002 mg mL(-1), 0.02 mg mL(-1), 0.2 mg mL(-1), and 2 mg mL(-1) of TiO2 in feeding medium, and the survival, fecundity, pupation time, and expression of genes involved in oxidative stress response were monitored. TiO2 did not affect survival but significantly increased time to pupation (p < 0.001). Fecundity of D. melanogaster was unaffected by the treatment. Expression of the gene for catalase was markedly downregulated by the treatment, while the effect on the downregulation of superoxide dismutase 2 was less pronounced. After four days of dietary exposure TiO2 was present in a significant amount in larvae, but was not transferred to adults during metamorphosis. Two individuals with aberrant phenotype similar to previously described gold nanoparticles induced mutant phenotypes were detected in the group exposed to TiO2. In general, TiO2 showed little toxicity toward D. melanogaster at concentrations relevant to oral exposure of humans.

Size matters--The phototoxicity of TiO2 nanomaterials

Under solar radiation several titanium dioxide nanoparticles (nano-TiO2) are known to be phototoxic for daphnids. We investigated the influence of primary particle size (10, 25, and 220 nm) and ionic strength (IS) of the test medium on the acute phototoxicity of anatase TiO2 particles to Daphnia magna. The intermediate sized particles (25 nm) showed the highest phototoxicity followed by the 10 nm and 220 nm sized particles (median effective concentrations (EC50): 0.53, 1.28, 3.88 mg/L). Photoactivity was specified by differentiating free OH radicals (therephthalic acid method) and on the other hand surface adsorbed, as well as free OH, electron holes, and O2(-) (electron paramagnetic resonance spectroscopy, EPR). We show that the formation of free OH radicals increased with a decrease in primary particle size (terephthalic acid method), whereas the total measured ROS content was highest at an intermediate particle size of 25 nm, which consequently revealed the highest photoxicity. The photoactivities of the 10 and 220 nm particles as measured by EPR were comparable. We suggest that phototoxicity depends additionally on the particle-daphnia interaction area, which explains the higher photoxicity of the 10 nm particles compared to the 220 nm particles. Thus, phototoxicity is a function of the generation of different ROS and the particle-daphnia interaction area, both depending on particle size. Phototoxicity of the 10 nm and 25 nm sized nanoparticles decreased as IS of the test medium increased (EC50: 2.9 and 1.1 mg/L). In conformity with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory we suggest that the precipitation of nano-TiO2 was more pronounced in high than in low IS medium, causing a lower phototoxicity. In summary, primary particle size and IS of the medium were identified as factors influencing phototoxicity of anatase nano-TiO2 to D. magna.

Titanium Dioxide Nanoparticles Increase Superoxide Anion Production by Acting on NADPH Oxidase

Titanium dioxide (TiO₂) anatase nanoparticles (NPs) are metal oxide NPs commercialized for several uses of everyday life. However their toxicity has been poorly investigated. Cellular internalization of NPs has been shown to activate macrophages and neutrophils that contribute to superoxide anion production by the NADPH oxidase complex. Transmission electron micrososcopy images showed that the membrane fractions were close to the NPs while fluorescence indicated an interaction between NPs and cytosolic proteins. Using a cell-free system, we have investigated the influence of TiO₂ NPs on the behavior of the NADPH oxidase. In the absence of the classical activator molecules of the enzyme (arachidonic acid) but in the presence of TiO₂ NPs, no production of superoxide ions could be detected indicating that TiO₂ NPs were unable to activate by themselves the complex. However once the NADPH oxidase was activated (i.e., by arachidonic acid), the rate of superoxide anion production went up to 140% of its value without NPs, this effect being dependent on their concentration. In the presence of TiO₂ nanoparticles, the NADPH oxidase produces more superoxide ions, hence induces higher oxidative stress. This hyper-activation and the subsequent increase in ROS production by TiO₂ NPs could participate to the oxidative stress development.

Are sunscreens a new environmental risk associated with coastal tourism?

The world coastal-zone population and coastal tourism are expected to grow during this century. Associated with that, there will be an increase in the use of sunscreens and cosmetics with UV-filters in their formulation, which will make coastal regions worldwide susceptible to the impact of these cosmetics. Recent investigations indicate that organic and inorganic UV-filters, as well as many other components that are constituents of the sunscreens, reach the marine environment--directly as a consequence of water recreational activities and/or indirectly from wastewater treatment plants (WWTP) effluents. Toxicity of organic and inorganic UV filters has been demonstrated in aquatic organism. UV-filters inhibit growth in marine phytoplankton and tend to bioaccumulate in the food webs. These findings together with coastal tourism data records highlight the potential risk that the increasing use of these cosmetics would have in coastal marine areas. Nevertheless, future investigations into distribution, residence time, aging, partitioning and speciation of their main components and by-products in the water column, persistence, accumulation and toxicity in the trophic chain, are needed to understand the magnitude and real impact of these emerging pollutants in the marine system.

Hazard effects of nanoparticles in central nervous system: Searching for biocompatible nanomaterials for drug delivery

Nanostructured materials are widely used in many applications of industry and biomedical fields. Nanoparticles emerges as potential pharmacological carriers that can be applied in the regenerative medicine, diagnosis and drug delivery. Different types of nanoparticles exhibit ability to cross the brain blood barrier (BBB) and accumulate in several brain areas. Then, efforts have been done to develop safer nanocarrier systems to treat disorders of central nervous system (CNS). However, several in vitro and in vivo studies demonstrated that nanoparticles of different materials exhibit a wide range of neurotoxic effects inducing neuroinflammation and cognitive impairment. For this reason, polymeric nanoparticles arise as a promisor alternative due to their biocompatible and biodegradable properties. After an overview of CNS location and neurotoxic effects of translocated nanoparticles, this review addresses the use of polymeric nanoparticles to the treatment of neuroinfectious diseases, as acquired immunodeficiency syndrome (AIDS) and meningitis.