Safety assessment and gastrointestinal retention of orally administered cerium oxide nanoparticles in rats.

Cerium oxide nanoparticles (CeO2 NPs, NM-212) are well-known for their catalytic properties and antioxidant potential, and have many applications in various industries, drug delivery, and cosmetic formulations. CeO2 NPs exhibit strong antimicrobial activity and can be used to efficiently remove pathogens from different environments. However, knowledge of the toxicological evaluation of CeO2 NPs is too limited to support their safe use. In this study, CeO2 NPs were orally administered to Sprague Dawley rats for 13 weeks at the doses of 0, 10, 100, and 1000 mg/kg bw/day, followed by a four week recovery period. The hematology values for the absolute and relative reticulocyte counts in male rats treated with 1000 mg/kg bw/day CeO2 NPs were lower than those in control rats. The clinical chemistry values for sodium and chloride in the treated male rat groups (100 and 1000 mg/kg/day) and total protein and calcium in the treated female rat groups (100 mg/kg/day) were higher than those in the control groups. However, these changes were not consistent in both sexes, and no abnormalities were found in the corresponding pathological findings. The results showed no adverse effects on any of the parameters assessed. CeO2 NPs accumulated in the jejunum, colon, and stomach wall of rats administered 1000 mg/kg CeO2 NPs for 90 days. However, these changes were not abnormal in the corresponding histopathological and immunohistochemical examinations. Therefore, 1000 mg/kg bw/day may be considered the "no observed adverse effect level" of CeO2 NPs (NM-212) in male and female SD rats under the present experimental conditions.

Genotoxic hazard assessment of cerium oxide and magnesium oxide nanoparticles in Drosophila.

The use of metal oxide nanoparticles (NPs) is steadily spreading, leading to increased environmental exposures to many organisms, including humans. To improve our knowledge of this potential hazard, we have evaluated the genotoxic risk of cerium oxide (CeO2NPs) and magnesium oxide (MgONPs) nanoparticle exposures using Drosophila as an in vivo assay model. In this study, two well-known assays, such as the wing somatic mutation and recombination test (wing-spot assay) and the single-cell gel electrophoresis test (comet assay) were used. As a novelty, and for the first time, changes in the expression levels of a wide panel of DNA repair genes were also evaluated. Our results indicate that none of the concentrations of CeO2NPs increased the total spot frequency in the wing-spot assay, while induction was observed at the highest dose of MgONPs. Regarding the comet assay, both tested NPs were unable to induce single DNA strand breaks or oxidative damage in DNA bases. Nevertheless, exposure to CeO2NPs induced significant increases in the expression levels of the Mlh1 and Brca2 genes, which are involved in the double-strand break repair pathway, together with a decrease in the expression levels of the MCPH1 and Rad51D genes. Regarding the effects of MgONPs exposure, the expression levels of the Ercc1, Brca2, Rad1, mu2, and stg genes were significantly increased, while Mlh1 and MCPH1 genes were decreased. Our results show the usefulness of our approach in detecting mild genotoxic effects by evaluating changes in the expression of a panel of genes involved in DNA repair pathways.

Genotoxic assessment of cerium and magnesium nanoparticles and their ionic forms in Eisenia hortensis coelomocytes by alkaline comet assay.

The present study aimed to evaluate the genotoxic potential of cerium oxide (CeO2 ), magnesium oxide (MgO) nanoparticles and their ionic forms by alkaline comet assay. Eisenia hortensis were exposed to different series of concentrations (25, 50, 100, 200, and 400 µg/ml) of chemicals for 48 h to find LC50 . The LC50 for MgO and CeO2 NPs were 70 and 80 µg/ml. Whereas, the LC50 for their ionic forms were 50 and 70 µg/ml. To assess the potential DNA damage caused by the chosen chemicals, E. hortensis was further exposed for 48 h to the following concentrations, based on their respective LC50s : LC50/2 , LC50 , and 2xLC50 . Comet scores demonstrated the significant increase (p < 0.05) in DNA damage at all concentrations, both for NPs and ionic forms in a concentration-dependent manner. Findings of the present study revealed the genotoxic effects of CeO2 NPs, MgO NPs and their ionic forms on E. hortensis. RESEARCH HIGHLIGHTS: Genotoxic assessment of CeO2 and MgO NPs and their ionic forms was conducted. Characterization of NPs through electron microscopy and alkaline comet assay was performed on E. Hortensis. Highest DNA damage of CeO2 and MgO NPs was observed on earthworm.

Assessment of pulmonary toxicity of potential antioxidant drug PEGylated nanoceria after intratracheal instillation in rats.

Cerium oxide (CeO2 ) nanoparticles have unique redox properties and exert excellent antioxidant effects in the biological environment. In recent years, many researchers have focused on the CeO2 nanoparticles as an effective antioxidant drug in the prevention and treatment of various diseases. However, the toxicity of CeO2 nanoparticles in vivo remains controversial and still needs intensive research. Therefore, the objective of this study is to investigate the pulmonary and systemic toxicity in rats after 14 days of exposure to the PEGylated CeO2 nanoparticles (abbreviated as CNPs; exposure dose of 2, 10, or 20 mg/kg) through a single intratracheal instillation (IT). We assessed the indicators of lung injury and the pathological damage degree of lung tissue. The bronchoalveolar lavage fluid (BALF) analysis and lung histopathology revealed the occurrence of slight pulmonary inflammation in the 20-mg/kg experimental group rats. However, the inflammation factors in the lung tissue of every group rats did not significantly increase, and the levels of superoxide dismutase (SOD) and glutathione (GSH) in lung tissue homogenate rose considerably in the experimental groups. Collectively, these results indicated that pulmonary exposure by the high dose of CNPs could induce mild pulmonary inflammation but did not cause severe systemic toxicity. Moreover, we speculate that the mechanism of pulmonary toxicity of CNPs in rats was due to the autophagic death of healthy lung epithelial cells mediated by endoplasmic reticulum stress. Our results implicate that CNPs can be safely used as an antioxidant drug for the oxidative stress pulmonary diseases.

In vitro and in vivo assessment of the genotoxic effects of ceric ammonium nitrate and 1,3-propane sultone.

A variety of methods have been developed for accurate and systematic evaluation of chemical genotoxicity. Ceric ammonium nitrate (CAN) and 1,3-propane sultone (1,3-PS) have been extensively applied in industrial fields. Although 1,3-PS, but not CAN, has been reported as a potent carcinogen, systematic assessment of the genotoxic properties of these chemicals has not been conducted. The purpose of this study was to establish a decision tree for evaluating genotoxicity based on the good laboratory practices (GLP) system using 1,3-PS and CAN as test chemicals. In vitro studies were performed including the bacterial reverse mutation assay, chromosomal aberration assay, and micronucleus assay. We conducted in vivo studies using a combined micronucleus and alkaline comet (MN-CMT) assay and the Pig-a gene mutation assay, which is a promising method for detecting gene mutations in vivo. CAN showed negative responses in all in vitro genotoxicity assays and the in vivo combined MN-CMT assay. Meanwhile, 1,3-PS had positive results in all in vitro and in vivo genotoxicity assays. In this study, we confirmed the genotoxicity of 1,3-PS and CAN using both in vitro and in vivo assays. We propose a decision tree for evaluating chemical-induced genotoxicity.

Safety assessment of cerium oxide nanoparticles: combined repeated-dose toxicity with reproductive/developmental toxicity screening and biodistribution in rats.

Cerium oxide nanoparticles (CeO2 NPs) are widely used in various commercial applications because of their characteristic properties. People can be easily exposed to CeO2 NPs in real life, but the safety assessment of CeO2 NPs has not been fully investigated. Therefore, in this study, we conducted a combined repeated-dose and reproductive/developmental toxicity screening study (OECD testing guideline 422) to investigate the potential hazards on human health, including reproductive/developmental functions, after repeated daily CeO2 NPs oral gavage administration to both males and females. In addition, tissues from parental animals and their pups were collected to analyze the internal accumulation of cerium. CeO2 NPs were orally administered to Sprague-Dawley rats at doses of 0, 100, 300 and 1000 mg/kg during their pre-mating, mating, gestation and early lactation periods. In the general systemic and reproductive/developmental examinations, no marked toxicities were observed in any in-life and terminal observation parameters in this study. In the biodistribution analysis, cerium was not detected in either parental or pup tissues (blood, liver, lungs and kidneys). Repeated oral exposure of CeO2 NPs did not induce marked toxicities affecting general systemic and reproductive/developmental functions up to the dose level of 1000 mg/kg and the CeO2 NPs were not systemically absorbed in parental animals or their pups. This result could be used in risk assessment for humans, and additional toxicity studies with CeO2 NPs will be necessary considering various physicochemical properties and exposure probabilities of these nanoparticles.

In vitro genotoxicity assessment and comparison of cerium (IV) oxide micro- and nanoparticles.

Cerium (IV) oxide (CeO2), which is used as a biomaterial, has wide application in areas such as the biomedical, glass polishing, electronic, automotive, and pharmacology industries. Comparing with the literature, in this study, the genotoxic effects of cerium (IV) oxide microparticles (COMPs) and cerium (IV) oxide nanoparticles (CONPs) were investigated for the first time in human peripheral blood cultures at concentrations of 0.78, 1.56, 3.125, 6.25, 12.5, 25, and 50 ppm for 72 h under in vitro conditions. Particle sizes of COMPs and CONPs were determined using scanning electron microscopic analysis. Micronucleus and chromosome aberration tests were used to determine the genotoxicity of COMPs and CONPs. The average particle sizes of COMPs and CONPs were approximately 148.25 and 25.30 nm, respectively. It was determined that CeO2 particles in both micro and nano sizes were toxic at all concentrations compared to the negative control group (distilled water). Importantly, COMPs and CONPs were genotoxic even at the lowest concentration (0.78 ppm). Comparing particle sizes, the data indicated that COMPs were more toxic than CONPs. The results suggest that genotoxicity of COMPs and CONPs may be a function of applied concentrations and particle sizes.

A Multiparametric Approach to Cerium Oxide Nanoparticle Toxicity Assessment in Non-Biting Midges.

Cerium oxide nanoparticles (CeO2 NPs) are included in the Organisation for Economic Co-operation and Development (OECD) priority list of engineered nanomaterials for assessment of their environmental impact. The present study was carried out to assess the CeO2 NP toxicity to the freshwater midge Chironomus riparius larvae at concentrations of 2.5, 25, 250, and 2500 mg of CeO2 NP/kg of sediment. Experiments were designed to assess the prolonged exposure of midges to CeO2 NPs while adhering to OECD test guideline 218. The following parameters were investigated: CeO2 NP uptake by larvae, oxidative stress parameters, in vivo genotoxic effects, and life trait parameters. Inductively coupled plasma-mass spectrometry analysis showed a significant positive correlation between the concentration of CeO2 NPs in the sediment and its uptake by the larvae. No significant mortality was observed in C. riparius, and oxidative stress was not detected. The only significantly induced sublethal effect was genotoxicity, which began to manifest at a lowest-observed-effect concentration of 25 mg kg-1 of sediment and progressively increased at higher concentrations. Our results indicate that exposure to CeO2 NP-contaminated freshwater sediments does not pose a risk to chironomids at environmentally realistic concentrations. However, the significant accumulation of CeO2 NPs by chironomid larvae may pose a risk through trophic transfer to organisms further up the food chain. Environ Toxicol Chem 2019;39:131-140. © 2019 SETAC.

In vitro assessment of CeO2 nanoparticles effects on intestinal microvilli morphology.

Some nanoparticles (NPs) have been shown to disrupt intestinal microvilli morphology in vitro, an alteration that could potentially affect nutrient absorption and barrier properties. This study aimed at evaluating the potential effect of CeO2 NPs (4-8 nm, citrate stabilized) on Caco-2 microvilli morphology. In addition to the standard Caco-2 cell clone, the C2BBe1 clone was used, as it is considered to develop a more homogeneous cellular morphology. Semiautomated microvilli density quantification and a new cell scoring approach were used to evaluate scanning electron microscopy (SEM) images. The quantification method made use of the whole micrograph surface, avoiding the need to choose subareas for analysis, and increasing the representativeness of the results when compared to previous studies. The main advantage of the scoring system is that it informs on the intercellular variability within a cell preparation. Benzalkonium was used as a positive control inducing toxicity and morphological alterations on microvilli. After three-week differentiation, Caco-2 cells were exposed to 100 µg/mL of CeO2 NPs for 24 h. The integrity of the membrane was evaluated by transepithelial electrical resistance (TEER) and thereafter processed for its observation by SEM. Results showed that both the standard Caco-2 clone and the C2BBe1 clone present notable morphological heterogeneity. The two evaluation approaches were able to identify morphological effects caused by the positive control, but did not detect statistically significant morphological alterations after exposure to CeO2 NPs.

Effects of the chronic exposure to cerium dioxide nanoparticles in Oncorhynchus mykiss: Assessment of oxidative stress, neurotoxicity and histological alterations.

Cerium dioxide nanoparticles (CeO2-NPs) have a variety of uses, especially in the production of solar panels, oxygen pumps, gas sensors, computer chips and catalytic converters. Despite their worldwide use, the few published studies demonstrate that metallic nanoparticles, in general, are still not properly characterized in terms of their potencial ecotoxicological effects. CeO2-NPs, in particular, have demonstrated extreme antioxidant activity, but their in vivo toxicity is still unknown. This work intended to characterize the chronic toxicity (28 days) of three different ecologically relevant concentrations (0.1, 0.01, and 0.001 µg/L) of CeO2-NPs in the rainbow trout (Oncorhynchus mykiss), in terms of biomarkers of oxidative stress [activity of the enzymes glutathione S-transferases (GSTs) and catalase (CAT)] and neurotoxicity [activity of the enzyme acetylcholinesterase (AChE)], as well as histological alterations in liver and gills. In the hereby study, GSTs activity was increased in gills of fish exposed to the highest CeO2-NPs level. Moreover, a potential anti-oxidant response was also reported, with a significant increase of CAT activity observed in livers of the same fish. AChE, however, was not significantly altered in fish eyes. Individuals exposed to CeO2-NPs also presented marked changes in the gills (e.g. epithelial lifting, intercellular edema, lamellar hypertrophy and hyperplasia, secondary lamella fusion and aneurysms) and liver (e.g. hepatocyte vacuolization, pyknotic nucleus, enlargement of sinusoids and hyperemia). The semi-quantitative analysis (organs pathological index) also showed the establishment of a dose-effect relationship. Further studies about the ecotoxicological effects of the CeO2-NPs have yet to be conducted, considering their properties, as the aggregation chemistry and the ratio of its redox state, which may affect their availability to the organism and their toxicity in the environment and biota.

Assessment of the toxic effects of mixtures of three lanthanides (Ce, Gd, Lu) to aquatic biota.

Lanthanide (LNs) release into the environment is expected to greatly increase in the coming years due to a high demand for new technologies. However there is a gap in the ecological risk assessment of these metals because most of the ecotoxicological studies have been performed with only one element, although they are usually found in nature as a group. This research evaluated the effects of mixtures of three lanthanides, cerium (Ce), gadolinium (Gd), and lutetium (Lu), representative of the light, middle and heavy rare earth elements, respectively, on seven aquatic species (A. fischeri, R. subcapitata, C. vulgaris, B. calyciflorus, H. incongruens, D. magna and D. rerio). Lanthanide content decreased over time in all toxicity test media and it was observed that LN sedimentation starts at the beginning of the tests with a steep decline of the available LN amount. Potential toxic effects of LNs were observed only in five species of the seven studied, predominantly in the unicellular organism (A. fischeri) and in the organisms belonging to the lower trophic levels (R. subcapitata and B. calyciflorus). The multi-toxicity approach performed in this study showed synergistic effects in tests performed with the bacteria A. fischeri and the algae R. subcapitata, and antagonistic effects for the rotifer B. calyciflorus. Although predicting the response of aquatic organisms exposed to multi-elements is not an easy task and can be masked by potential interactions with other compounds or even by nutrient removal. The variation in toxic action among species observed in this study reveals that lanthanide interaction in toxicity mechanisms should not be discarded, and supports that further studies with LN mixtures are required to properly understand their toxic behaviour in nature ecosystems.

Ecological risk assessment of cerium for tropical agroecosystems.

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC5 = 281.6 mg Ce kg-1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.

Interaction, transformation and toxicity assessment of particles and additives used in the semiconducting industry.

Chemical mechanical planarization (CMP) is a widely used technique for the manufacturing of integrated circuit chips in the semiconductor industry. The process generates large amounts of waste containing engineered particles, chemical additives, and chemo-mechanically removed compounds. The environmental and health effects associated with the release of CMP materials are largely unknown and have recently become of significant concern. Using a zebrafish embryo assay, we established toxicity profiles of individual CMP particle abrasives (SiO2 and CeO2), chemical additives (hydrogen peroxide, proline, glycine, nicotinic acid, and benzotriazole), as well as three model representative slurries and their resulting waste. These materials were characterized before and after use in a typical CMP process in order to assess changes that may affect their toxicological profile and alter their surface chemistry due to polishing. Toxicity outcome in zebrafish is discussed in relation with the physicochemical characteristics of the abrasive particles and with the type and concentration profile of the slurry components pre and post-polishing, as well as the interactions between particle abrasives and additives. This work provides toxicological information of realistic CMP slurries and their polishing waste, and can be used as a guideline to predict the impact of these materials in the environment.

Application of Bayesian networks for hazard ranking of nanomaterials to support human health risk assessment.

In this study, a Bayesian Network (BN) was developed for the prediction of the hazard potential and biological effects with the focus on metal- and metal-oxide nanomaterials to support human health risk assessment. The developed BN captures the (inter) relationships between the exposure route, the nanomaterials physicochemical properties and the ultimate biological effects in a holistic manner and was based on international expert consultation and the scientific literature (e.g., in vitro/in vivo data). The BN was validated with independent data extracted from published studies and the accuracy of the prediction of the nanomaterials hazard potential was 72% and for the biological effect 71%, respectively. The application of the BN is shown with scenario studies for TiO2, SiO2, Ag, CeO2, ZnO nanomaterials. It is demonstrated that the BN may be used by different stakeholders at several stages in the risk assessment to predict certain properties of a nanomaterials of which little information is available or to prioritize nanomaterials for further screening.

Assessment of the in vitro dermal irritation potential of cerium, silver, and titanium nanoparticles in a human skin equivalent model.

Metal nanoparticles can potentially contact human skin during their manufacture and use in commercial products. This study examined the potential of metal nanoparticles to elicit irritant contact dermatitis in a human skin equivalent model (HSEM) derived from keratinocytes. Ag (10-100 nm), TiO2 (22-214 nm), and CeO2 (15-40 nm) nanoparticles were studied. The Ag particles were either coated/shelled with silica or capped with citrate or polyvinylpyrrolidone and were in water. The TiO2 and CeO2 particles were suspended in media containing 10% fetal bovine serum. The particles (1 mg/ml) were applied to the epidermal surface of the HSEM. Positive (5% sodium dodecyl sulfate (SDS)) and negative controls (saline or media) were included. After 1-h exposure at 37 °C, the HSEM was washed with saline to remove the nanoparticles. Following a 42-h incubation (37 °C), HSEM viability was assessed using the MTT assay. A test substance is considered a dermal irritant if the HSEM viability is < 50%. The mean viability for the SDS-treated HSEM was 7.8%. The viabilities of the nanoparticle-treated HSEM were 91% or greater. The Ag, TiO2, and CeO2 nanoparticles examined were not dermal irritants under the conditions used in this study. The stratum corneum of the HSEM may limit penetration of metal nanoparticles to induce toxicity.

Damage assessment for soybean cultivated in soil with either CeO2 or ZnO manufactured nanomaterials.

With increasing use, manufactured nanomaterials (MNMs) may enter soils and impact agriculture. Herein, soybean (Glycine max) was grown in soil amended with either nano-CeO2 (0.1, 0.5, or 1.0gkg-1 soil) or nano-ZnO (0.05, 0.1, or 0.5gkg-1 soil). Leaf chlorosis, necrosis, and photosystem II (PSII) quantum efficiency were monitored during plant growth. Seed protein and protein carbonyl, plus leaf chlorophyll, reactive oxygen species (ROS), lipid peroxidation, and genotoxicity were measured for plants at harvest. Neither PSII quantum efficiency, seed protein, nor protein carbonyl indicated negative MNM effects. However, increased ROS, lipid peroxidation, and visible damage, along with decreased total chlorophyll concentrations, were observed for soybean leaves in the nano-CeO2 treatments. These effects correlated to aboveground leaf, pod, and stem production, and to root nodule N2 fixation potential. Soybeans grown in soil amended with nano-ZnO maintained growth, yield, and N2 fixation potential similarly to the controls, without increased leaf ROS or lipid peroxidation. Leaf damage was observed for the nano-ZnO treatments, and genotoxicity appeared for the highest nano-ZnO treatment, but only for one plant. Total chlorophyll concentrations decreased with increasing leaf Zn concentration, which was attributable to zinc complexes-not nano-ZnO-in the leaves. Overall, nano-ZnO and nano-CeO2 amended to soils differentially triggered aboveground soybean leaf stress and damage. However, the consequences of leaf stress and damage to N2 fixation, plant growth, and yield were only observed for nano-CeO2.

Assessment of the toxic potential of engineered metal oxide nanomaterials using an acellular model: citrated rat blood plasma.

Citrated Sprague-Dawley rat blood plasma was used as a biologically relevant exposure medium to assess the acellular toxic potential of two metal oxide engineered nanomaterials (ENMs), zinc oxide (nZnO), and cerium oxide (nCeO2). Plasma was incubated at 37 °C for up to 48 h with ENM concentrations ranging between 0 and 200 mg/L. The degree of ENM-induced oxidation was assessed by assaying for reactive oxygen species (ROS) levels using dichlorofluorescein (DCF), pH, ferric reducing ability of plasma (FRAP), lipase activity, malondialdehyde (MDA), and protein carbonyls (PC). Whereas previous in vitro studies showed linear-positive correlations between ENM concentration and oxidative damage, our results suggested that low concentrations were generally pro-oxidant and higher concentrations appeared antioxidant or protective, as indicated by DCF fluorescence trends. nZnO and nCeO2 also affected pH in a manner dependent on concentration and elemental composition; higher nZnO concentrations maintained a more alkaline pH, while nCeO2 tended to decrease pH. No other biomarkers of oxidative damage (FRAP, MDA, PC, lipase activity) showed changes at any ENM concentration or time-point tested. Differential dissolution of the two ENMs was also observed, where as much as ∼31.3% of nZnO was instantaneously dissolved to Zn2+ and only negligible nCeO2 was degraded. The results suggest that the direct oxidative potential of nZnO and nCeO2 in citrated rat blood plasma is low, and that a physiological or immune response is needed to generate appreciable damage biomarkers. The data also highlight the need for careful consideration when selecting a model for assessing ENM toxicity.

Integrated assessment of ceria nanoparticle impacts on the freshwater bivalve Dreissena polymorpha.

Exposures in realistic environmental conditions are essential to properly assess the effects of emerging pollutants on ecosystems. While ceria nanoparticles (nCeO2) production and use are expanding quickly, ecotoxicity studies remain very scarce. In this study, we set up experimental systems reproducing a simplified ecosystem to assess the effects of a chronic exposure to citrate-coated nCeO2 (ci-CeO2) and bare nCeO2 (ba-CeO2) on the freshwater mussel Dreissena polymorpha using an integrated multibiomarker approach. The fate of nanoparticles was tightly monitored to properly characterize the exposure. Organisms were exposed for 3 weeks and sampled weekly for biomarker analysis. Mussel filter-feeding activity resulted in significant removal of nCeO2 from the water column. At the same time, bioaccumulation was low, reaching its maximum in the first week. Mussels bioaccumulated ci-CeO2 three times more than ba-CeO2, probably due to coating-related differences in their behavior in the water column and in organisms. Meanwhile, biomarker results were integrated and synthesized using linear discriminant analysis, highlighting that pi-glutathione-S-transferase (piGST) mRNA, catalase (CAT) activity and lysosomal system were the most impacted of the seven biomarkers singled out by the discriminant analysis. These biomarker responses indicated that mussels exposed to both forms of nCeO2 were stressed and differentiate from the controls. Moreover, they responded differently to ba-CeO2 and ci-CeO2 exposure. However, biomarkers used in the experimental conditions of this study did not indicate severe nCeO2 toxicity on mussels, as cellular damage biomarkers and mussel filtering activity were left unimpaired. However, further studies are needed to investigate if the slight perturbations observed could lead to populational impacts in the long term.

Assessment of the Phytotoxicity of Metal Oxide Nanoparticles on Two Crop Plants, Maize (Zea mays L.) and Rice (Oryza sativa L.).

In this study, the phytotoxicity of seven metal oxide nanoparticles(NPs)-titanium dioxide (nTiO2), silicon dioxide (nSiO2), cerium dioxide (nCeO2), magnetite (nFe3O4), aluminum oxide (nAl2O3), zinc oxide (nZnO) and copper oxide (nCuO)-was assessed on two agriculturally significant crop plants (maize and rice). The results showed that seed germination was not affected by any of the seven metal oxide NPs. However, at the concentration of 2000 mg·L(-1), the root elongation was significantly inhibited by nCuO (95.73% for maize and 97.28% for rice), nZnO (50.45% for maize and 66.75% for rice). On the contrary, minor phytotoxicity of nAl2O3 was only observed in maize, and no obvious toxic effects were found in the other four metal oxide NPs. By further study we found that the phytotoxic effects of nZnO, nAl2O3 and nCuO (25 to 2000 mg·L(-)¹) were concentration dependent, and were not caused by the corresponding Cu(2+), Zn(2+) and Al(3+) ions (0.11 mg·L(-)¹, 1.27 mg·L(-)¹ and 0.74 mg·L(-)¹, respectively). Furthermore, ZnO NPs (<50 nm) showed greater toxicity than ZnO microparticles(MPs)(<5 µm) to root elongation of both maize and rice. Overall, this study provided valuable information for the application of engineered NPs in agriculture and the assessment of the potential environmental risks.

The hazard assessment of nanostructured CeO2-based mixed oxides on the zebrafish Danio rerio under environmentally relevant UV-A exposure.

The effect of nanomaterials on biota under realistic environmental conditions is an important question. However, there is still a lack of knowledge on how different illumination conditions alter the toxicity of some photocatalytic nanomaterials. We have investigated how environmentally relevant UV-A exposure (intensity 8.50 ± 0.61 W/m(2), exposure dose 9.0J/cm(2)) affected the toxicity of cerium oxide (CeO2)-based nanostructured materials to the early-life stages of zebrafish Danio rerio. Pure cerium oxide (CeO2), copper-cerium (CuO-CeO2) (with a nominal 10, 15 and 20 mol.% CuO content), cerium-zirconium (CeO2-ZrO2) and nickel and cobalt (Ni-Co) deposited over CeO2-ZrO2 were tested. It was found that under both illumination regimes, none of the tested materials affected the normal development or induced mortality of zebrafish early-life stages up to 100mg/L. Only in the case of CuO-CeO2, the growth of larvae was decreased (96 h LOEC values for CuCe10, CuCe15 and CuCe20 were 50, 50 and 10mg/L, respectively). To conclude, CeO2-based nanostructured materials are not severely toxic to zebrafish and environmentally relevant UV-A exposure does not enhance their toxicity.