An insight into the mechanisms of nanoceria toxicity in aquatic photosynthetic organisms

Environmentally degradable carbon dots for inhibiting P. globosa growth and reducing hemolytic toxin

Red tides not only destroy marine ecosystems but also pose a great threat to human health. The traditional anti-red tide materials are difficult to degrade effectively in the natural environment and there may be risks of environmental leakage and secondary pollution. Furthermore, they cannot reduce the toxicity of toxins released by algae. It is very important to prepare degradable materials that can effectively control red tide and reduce their toxins in the future. Herein, degradable CDs (De-CDs) with biocompatibility and non-toxicity is successfully prepared using the one-step electrolytic method. De-CDs can effectively inhibit P. globosa (algae associated with red tide) growth. More importantly, the De-CDs not only can attenuate the toxicity of toxins released by P. globosa, but also can be degraded under visible-light irradiation in the seawater and avoids environmental leakage. The successful preparation of De-CDs provides a new idea for degradable materials with anti-red tide algae in the future.

Harnessing cerium-based biomaterials for the treatment of bone diseases

Bone, an actively metabolic organ, undergoes constant remodeling throughout life. Disturbances in the bone microenvironment can be responsible for pathologically bone diseases such as periodontitis, osteoarthritis, rheumatoid arthritis and osteoporosis. Conventional bone tissue biomaterials are not adequately adapted to complex bone microenvironment. Therefore, there is an urgent clinical need to find an effective strategy to improve the status quo. In recent years, nanotechnology has caused a revolution in biomedicine. Cerium(III, IV) oxide, as an important member of metal oxide nanomaterials, has dual redox properties through reversible binding with oxygen atoms, which continuously cycle between Ce(III) and Ce(IV). Due to its special physicochemical properties, cerium(III, IV) oxide has received widespread attention as a versatile nanomaterial, especially in bone diseases. This review describes the characteristics of bone microenvironment. The enzyme-like properties and biosafety of cerium(III, IV) oxide are also emphasized. Meanwhile, we summarizes controllable synthesis of cerium(III, IV) oxide with different nanostructural morphologies. Following resolution of synthetic principles of cerium(III, IV) oxide, a variety of tailored cerium-based biomaterials have been widely developed, including bioactive glasses, scaffolds, nanomembranes, coatings, and nanocomposites. Furthermore, we highlight the latest advances in cerium-based biomaterials for inflammatory and metabolic bone diseases and bone-related tumors. Tailored cerium-based biomaterials have already demonstrated their value in disease prevention, diagnosis (imaging and biosensors) and treatment. Therefore, it is important to assist in bone disease management by clarifying tailored properties of cerium(III, IV) oxide in order to promote the use of cerium-based biomaterials in the future clinical setting. STATEMENT OF SIGNIFICANCE: In this review, we focused on the promising of cerium-based biomaterials for bone diseases. We reviewed the key role of bone microenvironment in bone diseases and the main biological activities of cerium(III, IV) oxide. By setting different synthesis conditions, cerium(III, IV) oxide nanostructures with different morphologies can be controlled. Meanwhile, tailored cerium-based biomaterials can serve as a versatile toolbox (e.g., bioactive glasses, scaffolds, nanofibrous membranes, coatings, and nanocomposites). Then, the latest research advances based on cerium-based biomaterials for the treatment of bone diseases were also highlighted. Most importantly, we analyzed the perspectives and challenges of cerium-based biomaterials. In future perspectives, this insight has given rise to a cascade of cerium-based biomaterial strategies, including disease prevention, diagnosis (imaging and biosensors) and treatment.

Understanding boron toxicity in aquatic plants (Salvinia natans and Lemna minor) in the presence and absence of EDTA

Even though boron is a widely used element in various industries and a contributor to water pollution worldwide, few studies have examined the toxicity of boron in aquatic plants. EDTA is used to maintain aquatic plants cultures, however it is possible to modify the toxicity of metals. The objective of this study is to assess the toxicity of boron in aquatic plants and explore the impact of EDTA presence on the resulting toxic responses. Floating watermoss Salvinia natans and duckweed Lemna minor were exposed to concentrations ranging from 5 to 100 mg/L for 7 days and 1 to 60 mg/L for 3 days, respectively. Growth and photosynthetic activity parameters were investigated in the presence and absence of EDTA. Growth inhibitions in both aquatic plants were observed in a concentration-dependent manner, irrespective of the presence or absence of EDTA. For instance, based on the specific growth rate (leaves coverage), EC10 values for S. natans were calculated as 12.7 (9.9-15.3) mg/L and 8.0 (5.8-10.3) mg/L with and without EDTA, respectively. In the case of L. minor, EC10 values were calculated as 1.3 (0.8-1.89) mg/L and 2.0 (0.4-4.3) mg/L with EDTA without EDTA, respectively. Significant effects were also observed on the photosynthetic capacity, however there was no change in the increase of boron concentration. Generally, negligible effects of EDTA to the toxicity of boron were observed in the present study. By comparing toxicity results based on the presence and absence of EDTA, which is an essential element in the test medium, the results of this study are expected to be utilized for the ecological risk assessment of boron in aquatic ecosystems.

Effects of different concentrations and particle sizes of microplastics on the full life history of freshwater Chlorella

Microplastics (MPs) as pollutants can have adverse effects on aquatic ecosystems; however, their effects on the full life history of microalgae need to be further explored and thoroughly examined. In this study, we investigated influence of polystyrene (PS) plastics with different concentrations (10/50/100 mg/L) and particle sizes (0.1/0.5/1 μm) on the full life history of Chlorella; their potential environmental risks were also analyzed. The results showed that PS(0.1um) had the strongest inhibitory effect on Chlorella growth (Max(inhibition) 68.42%), PS(0.5/1um) can not only promote (Max(promotion) 55.48% and 55.05%) but also prolong cell growth; PS has various effects on photosynthetic efficiency of Chlorella. PS(0.1um) can significantly promote Fv/Fm, inhibit RC/ABS, F0/Fv, DIo/RC, and both inhibit and promote rETRmax, but effect of PS(0.5/1μm) is generally consistent with that of control group; PS affects the morphological structure and interaction of Chlorella significantly, and can squeeze and aggregate cells. Zeta potential fluctuated greatly in the initial stage of experiment, and was stable as Relative conductivity in the later stage. About 65.5% of PS(0.1um) can enter cell, which has potential risk of entering the food chain; Statistics on long and short-term impacts showed significant differences in growth and photosynthesis efficiencies, as well as in interactions; the potential environmental risk index (PERI) indicates that class II (slightly polluted) has the highest percentage (64.72%), and that the concentration and composition of MPs are important influences on potential environmental risk. Overall, the long-term impacts of PS were diverse, but Chlorella also showed good resilience. Meanwhile, we found that most of the previous short-term studies may be one-sided and incomplete, the real impacts of MPs may be overestimated. Our research could provide scientific support for assessing the risks posed by MPs.

Evaluation of Apical and Molecular Effects of Algae Pseudokirchneriella subcapitata to Cerium Oxide Nanoparticles

Cerium oxide engineered nanoparticles (nCeO₂) are widely used in various applications and are, also, increasingly being detected in different environmental matrixes. However, their impacts on the aquatic environment remain poorly quantified. Hence, there is a need to investigate their effects on non-target aquatic organisms. Here, we evaluated the cytotoxic and genotoxic effects of <25 nm uncoated-nCeO₂ on algae Pseudokirchneriella subcapitata. Apical (growth and chlorophyll a (Chl a) content) and genotoxic effects were investigated at 62.5-1000 µg/L after 72 and 168 h. Results demonstrated that nCeO₂ induced significant growth inhibition after 72 h and promotion post 96-168 h. Conversely, nCeO₂ induced enhanced Chl a content post 72 h, but no significant changes were observed between nCeO₂-exposed and control samples after 168 h. Hence, the results indicate P. subcapitata photosynthetic system recovery ability to nCeO₂ effects under chronic-exposure conditions. RAPD-PCR profiles showed the appearance and/or disappearance of normal bands relative to controls; indicative of DNA damage and/or DNA mutation. Unlike cell recovery observed post 96 h, DNA damage persisted over 168 h. Thus, sub-lethal nCeO₂-induced toxicological effects may pose a more serious threat to algae than at present anticipated.

An innovative strategy to control Microcystis growth using tea polyphenols sustained-release particles: preparation, characterization, and inhibition mechanism

Allelochemicals have been shown to inhibit cyanobacterial blooms for several years. In view of the disadvantages of "direct-added" mode, natural and pollution-free tea polyphenolic allelochemicals with good inhibitory effect on cyanobacteria were selected to prepare sustained-release particles by microcapsule technology. Results showed that the encapsulation efficiency of tea polyphenols sustained-release particles (TPSPs) was 50.6% and the particle size ranged from 700 to 970 nm, which reached the nanoscale under optimum preparation condition. Physical and chemical properties of TPSPs were characterized to prove that tea polyphenols were well encapsulated and the particles had good thermal stability. The optimal dosage of TPSPs was determined to be 0.3 g/L, at which the inhibition rate on Microcystis aeruginosa in logarithmic growth period could be maintained above 95%. Simultaneous decrease in algal density and chlorophyll-a content indicated that the photosynthesis of algal cells was affected leading to cell death. Significant changes of antioxidant enzyme activities suggested that Microcystis aeruginosa's antioxidant systems had been disrupted. Furthermore, TPSPs increased the concentration of O^2- which led to lipid peroxidation of cell membrane and a subsequent increase in malondialdehyde (MDA) content. Meanwhile, the protein content, nucleic acid content, and electrical conductivity in culture medium rose significantly indicating the cell membrane was irreversibly damaged. This work can provide a basis for the utilization of environmentally friendly algal suppressants.

CeO2 nanoparticles improve prooxidant/antioxidant balance, life quality and survival of old male rats

Due to its unique redox chemistry, nanoceria is considered as potent free radical scavenger and antioxidant. However, their protective capacity in aging organisms remains controversial. To detect the anti-aging effects associated with the redox activity of 2 and 10 nm nano-CeO2, different test systems were used, including in vitro analysis, in situ assay of mitochondria function and in vivo studies of suitable nano-CeO₂ on aging of male Wistar rats from 22 months-old to the end of life. The 2 nm nanoparticles exhibited not only antioxidant (^·OH scavenging; chemiluminescence assay; decomposition of H₂O₂, phosphatidylcholine autooxidation) but also prooxidant properties (reduced glutathione and reduced nicotinamide adenine dinucleotide phosphate oxidation) as well as affected mitochondria whereas in most test systems 10 nm nano-CeO₂ showed less activity or was inert. Prolonged use of the more redox active 2 nm nano-CeO₂ (0.25-0.3 mg/kg/day) in vivo with drinking water resulted in improvement in physiological parameters and normalization of the prooxidant/antioxidant balance in liver and blood of aging animals. Survival analysis using Kaplan-Meier curve and Gehan tests with Yates' correction showed that by the time the prooxidant-antioxidant balance was assessed (32 months), survival rates exceeded the control values most considerably. The apparent median survival for the control rats was 900 days, and for the experimental rats-960 days. In general, the data obtained indicate the ability of extra-small 2 nm nano-CeO2 to improve quality of life and increase the survival rate of an aging organism.

Effects of microplastics of different sizes on the Chlorella vulgaris - Ganoderma lucidum co-pellets formation processes

The effects of different sized MPs on the formation process of algal-fungal co-pellets were studied. The results show that a maximum biomass recovery of 70.96% and a minimum F_v/F_m ratio of 0.463 reached with 5.000 μm-microplastics. Chlorella vulgaris cells and microplastics adhered evenly to the mycelia of Ganoderma lucidum. The contact angle decreased 24.02% and 34.68% with addition of 0.065 μm and 0.500 μm microplastics, respectively, compared to the control group, while the lowest crystallinity index (7.05%) was obtained with 0.065 μm-microplastics addition. Moreover, 5.000 μm microplastics promoted the extracellular polymeric substances (EPS) secretion, with the soluble polysaccharide content increasing by 40.50% and the soluble protein content increasing by 23.25% compared with the single algal-fungal system, while bound polysaccharides increased by 113.26% and bound proteins increased by 29.48%. The 5.000 μm microplastics also significantly promoted enzyme activity in the co-pellets. These results provide a theoretical basis for algal recovery in microplastic-containing water.

Toxicity mechanism of cerium oxide nanoparticles on cyanobacteria Microcystis aeruginosa and their ecological risks

The extensive application of cerium oxide nanoparticles (CeO₂ NPs), a type of rare earth nanomaterial, led to pollution into aquatic environments. Cyanobacteria, a significant component of freshwater ecosystems, can interact with CeO₂ NPs. However, little attention has been paid as to whether CeO₂ NPs will have adverse effects on cyanobacteria. In the present study, Microcystis aeruginosa (FACHB-942) was exposed to different concentrations (0, 1, 10, and 50 mg/L) of CeO₂ NPs. Results showed 50 mg/L CeO₂ NPs inhibited algal growth (11.48% ± 5.76%), suppressed photosynthesis and induced the generation of reactive oxygen species (ROS) after 72 h exposure. The toxicity mechanism is the adsorption of CeO₂ NPs on cell surface, the ROS formation and the intracellular Ce. Additionally, the intracellular microcystins (MCs) content was significantly induced (11.84% ± 1.47%) by 50 mg/L CeO₂ NPs, while no significance was found in 1 and 10 mg/L CeO₂ NP treatments. Results indicated high concentrations of CeO₂ NPs could be toxic to algae through the adverse effects on algal growth and photosynthesis. Moreover, the promoted MCs production could also pose a threat to freshwater ecosystems due to the possible release into the environment.

The Combined Effect of ZnO and CeO2 Nanoparticles on Pisum sativum L.: A Photosynthesis and Nutrients Uptake Study

Cerium oxide nanoparticles (CeO2 NPs) and zinc oxide nanoparticles (ZnO NPs) are emerging pollutants that are likely to occur in the contemporary environment. So far, their combined effects on terrestrial plants have not been thoroughly investigated. Obviously, this subject is a challenge for modern ecotoxicology. In this study, Pisum sativum L. plants were exposed to either CeO2 NPs or ZnO NPs alone, or mixtures of these nano-oxides (at two concentrations: 100 and 200 mg/L). The plants were cultivated in hydroponic system for twelve days. The combined effect of NPs was proved by 1D ANOVA augmented by Tukey's post hoc test at p = 0.95. It affected all major plant growth and photosynthesis parameters. Additionally, HR-CS AAS and ICP-OES were used to determine concentrations of Cu, Mn, Fe, Mg, Ca, K, Zn, and Ce in roots and shoots. Treatment of the pea plants with the NPs, either alone or in combination affected the homeostasis of these metals in the plants. CeO2 NPs stimulated the photosynthesis rate, while ZnO NPs prompted stomatal and biochemical limitations. In the mixed ZnO and CeO2 treatments, the latter effects were decreased by CeO2 NPs. These results indicate that free radicals scavenging properties of CeO2 NPs mitigate the toxicity symptoms induced in the plants by ZnO NPs.

Cerium, gadolinium, lanthanum, and neodymium effects in simplified acid mine discharges to Raphidocelis subcapitata, Lepidium sativum, and Vicia faba

The alteration of rare earth elements (REEs) biogeochemical cycles has increased the potential effects related to their environmental exposure in a one-health perspective. Cerium (Ce), gadolinium (Gd), lanthanum (La), and neodymium (Nd) are frequently related to technological applications and their environmental concentrations are already in the μg/kg - mg/kg (i.e., or L) range depending on the considered matrices. The effect of Ce, Gd, La, and Nd was investigated in a simulated AMD (0.01-10.22 mg/L) at pH 4 and 6 considering a battery of photosynthetic organisms (Raphidocelis subcapitata, Lepidium sativum, and Vicia faba) according to a multiple-endpoint approach (growth inhibition, germination index, and mutagenicity). According to modelled chemical speciation, the considered elements were mostly in the trivalent free form (86-88%) at pH 4. Gd, La, and Nd exerted the most relevant toxic effect at pH 4. The pH 6 scenario evidenced a reduction in REEs toxicity level. Mutagenicity was detected only at pH 4 by Gd (up to 3-fold compared to negative controls), La and Nd, while Ce did not show any adverse effect. Toxic effects due to Ce, Gd, La, and Nd can be reduced by controlling the pH, but several gaps of knowledge still remain about their uptake and trophic transfer, and long-term effects on targeted species.

Alginate coating modifies the biological effects of cerium oxide nanoparticles to the freshwater bivalve Dreissena polymorpha

The adsorption of biomacromolecules is a fundamental process that can alter the behaviour and adverse effects of nanoparticles (NPs) in natural systems. While the interaction of NPs with natural molecules present in the environment has been described, their biological impacts are largely unknown. Therefore, this study aims to provide a first evidence of the influence of biomolecules sorption on the toxicity of cerium oxide nanoparticles (CeO₂NPs) towards the freshwater bivalve Dreissena polymorpha. To this aim, we compared naked CeO₂NPs and coated with alginate and chitosan, two polysaccharides abundant in aquatic environments. Mussels were exposed to the three CeO₂NPs (naked, chitosan- and alginate-coated) up to 14 days at 100 μg L^-1, which is a concentration higher than the environmental one predicted for this type of NP. A suite of biomarkers related to oxidative stress and energy metabolism was applied, and metabolomics was also carried out to identify metabolic pathways potentially targeted by CeO₂NPs. Results showed that the coating with chitosan reduced NP aggregation and increased the stability in water. Nonetheless, the Ce accumulation in mussels was similar in all treatments. As for biological effects, all three types of CeO₂NPs reduced significantly the level of reactive oxygen species and the activity of superoxide dismutase, glutathione peroxidase and glutathione-S-transferase. The effect was more pronounced in individuals exposed to CeO₂NPs coated with alginate, which also significantly induced the activity of the electron transport system. Metabolomics analysis of amino acid metabolism showed modulation only in mussels treated with CeO₂NPs coated with alginate. In this group, 25 metabolites belonging to nucleotides, lipids/sterols and organic osmolytes were also modulated, suggesting that the nanoparticles affect energetic metabolism and osmoregulation of mussels. This study highlights the key role of the interaction between nanoparticles and natural molecules as a driver of nanoparticle ecotoxicity.

Harmful effects of metal(loid) oxide nanoparticles

Abstract

The incorporation of nanomaterials (NMs), including metal(loid) oxide (MOx) nanoparticles (NPs), in the most diversified consumer products, has grown enormously in recent decades. Consequently, the contact between humans and these materials increased, as well as their presence in the environment. This fact has raised concerns and uncertainties about the possible risks of NMs to human health and the adverse effects on the environment. These concerns underline the need and importance of assessing its nanosecurity. The present review focuses on the main mechanisms underlying the MOx NPs toxicity, illustrated with different biological models: release of toxic ions, cellular uptake of NPs, oxidative stress, shading effect on photosynthetic microorganisms, physical restrain and damage of cell wall. Additionally, the biological models used to evaluate the potential hazardous of nanomaterials are briefly presented, with particular emphasis on the yeast Saccharomyces cerevisiae, as an alternative model in nanotoxicology. An overview containing recent scientific advances on cellular responses (toxic symptoms exhibited by yeasts) resulting from the interaction with MOx NPs (inhibition of cell proliferation, cell wall damage, alteration of function and morphology of organelles, presence of oxidative stress bio-indicators, gene expression changes, genotoxicity and cell dead) is critically presented. The elucidation of the toxic modes of action of MOx NPs in yeast cells can be very useful in providing additional clues about the impact of NPs on the physiology and metabolism of the eukaryotic cell. Current and future trends of MOx NPs toxicity, regarding their possible impacts on the environment and human health, are discussed.

Key points

• The potential hazardous effects of MOx NPs are critically reviewed.

• An overview of the main mechanisms associated with MOx NPs toxicity is presented.

• Scientific advances about yeast cell responses to MOx NPs are updated and discussed.

Single and Repeated Applications of Cerium Oxide Nanoparticles Differently Affect the Growth and Biomass Accumulation of Silene flos-cuculi L. (Caryophyllaceae)

Cerium oxide nanoparticles (nCeO2) have a wide variety of applications in industry. Models demonstrated that nCeO2 can reach environmental compartments. Studies regarding the relationships between plants and nCeO2 considered only crop species, whereas a relevant knowledge gap exists regarding wild plant species. Specimens of Silene flos-cuculi (Caryophyllaceae) were grown in greenhouse conditions in a substrate amended with a single dose (D1) and two and three doses (D2 and D3) of 20 mg kg-1 and 200 mg kg-1 nCeO2 suspensions, respectively. sp-ICP-MS and ICP-MS data demonstrated that nCeO2 was taken up by plant roots and translocated towards aerial plant fractions. Biometric variables showed that plants responded negatively to the treatments with a shortage in biomass of roots and stems. Although not at relevant concentrations, Ce was accumulated mainly in roots and plant leaves.

Effects of Ceria Nanoparticles and CeCl3 on Plant Growth, Biological and Physiological Parameters, and Nutritional Value of Soil Grown Common Bean (Phaseolus vulgaris)

The release of metal ions may play an important role in toxicity of metal-based nanoparticles. In this report, a life cycle study is carried out in a greenhouse, to compare the effects of ceria nanoparticles (NPs) and Ce³⁺ ions at 0, 50, 100, and 200 mg Ce kg^-1 on plant growth, biological and physiological parameters, and nutritional value of soil-grown common bean plants. Ceria NPs have a tendency to negatively affect photosynthesis, but the effect is not statistically significant. Ce³⁺ ionic treatments at 50, 100, and 200 mg Ce kg^-1 result in increases of 1.25-, 0.66-, and 1.20-fold in stomatal conductance, respectively, relative to control plants. Both ceria NPs and Ce³⁺ ions disturb the homeostasis of antioxidant defense system in the plants, but only 200 mg Ce kg^-1 ceria NPs significantly induce lipid peroxidation in the roots. Ceria NP treatments tend to reduced fresh weight and to increase mineral contents of the green pods, but have no effect on the organic nutrient contents. On the contrary, Ce³⁺ ion treatments modify the organic compositions and thus alter the nutritional quality and flavor of the green pods. These results suggest that the two Ce forms may have different mechanisms on common bean plants.

Biomonitoring of 45 inorganic elements measured in plasma from Spanish subjects: A cross-sectional study in Andalusian population

Heavy metals and other toxic elements are frequently detected in humans. Rare earth elements (REE) have arisen as a novel group of substances considered as emerging pollutants due to its dependence for high tech industry. We designed a study aimed to conduct the biomonitoring a total of 45 inorganic elements in the population of Andalusia (Spain). A total of 419 participants were recruited and their plasma samples analyzed. Concentration of elements, including elements in the ATSDR's priority pollutant list and REE were measured by ICP-MS in the blood plasma of participants. Arsenic, copper, lead, selenium, antimony, strontium, and bismuth were detected in ˃98% of subjects. Median values of arsenic, mercury and lead were 1.49, 1.46, and 5.86 ng/mL, respectively. These concentrations did not exceed reference values published by international agencies. We observed a positive correlation between age and plasma concentrations of arsenic, mercury, antimony and strontium. Sum of elements was lower in the group of subjects younger than 45 years old (P = 0.002). Positive correlations were observed between body mass index (BMI) and plasma concentrations of barium, cerium, osmium, tin, and ytterbium. 7 out of 26 REEs showed a percentage of detection ≥ 90%. Bismuth, yttrium, and cerium were quantified at the highest concentrations (median value = 7.7, 0.19, and 0.16 ng/mL, respectively). We found that plasma levels of 6 REEs were higher among males, and a positive correlation between REEs and age was detected. The present results suggest a potential interaction with the human physiology that deserves additional research. Given the high persistence of these elements in the environment, and the significant technological dependence on them, future studies are needed to elucidate the potential sources of exposure and possible adverse effects on health, especially in the most vulnerable populations.

Protection effect of cerium oxide nanoparticles against radiation-induced acute lung injuries in rats

INTRODUCTION

Radiation therapy is one of the most common tools for treating cancer. The aim is to deliver adequate doses of radiation to kill cancer cells and the most challenging part during this procedure is to protect normal cells from radiation. One strategy is to use a radioprotector to spare normal tissues from ionizing radiation effects. Researchers have pursued cerium oxide nanoparticles as a therapeutic agent, due to its diverse characteristics, which include antioxidant properties, making it a potential radioprotector.

MATERIALS AND METHODS

One hundred rats were divided into five groups of A) control group, intraperitoneal (IP) saline injection was done twice a week; B) bi-weekly IP injection of 14.5 nM (0.00001 mg/kg) CNP for two weeks; C) a single whole thorax radiation dose of 18 Gy; D) a single whole thorax radiation dose of 18 Gy + bi-weekly injection of 14.5 nM CNP for two weeks after radiation; E) bi-weekly IP injection of 14.5 nM CNP for two weeks prior to radiation + a single whole thorax radiation dose of 18 Gy. Thirty days after irradiation, 7 rats from each group were anesthetized and their lungs extracted for histopathological examination.

RESULTS

Statistical analyses revealed that CNP significantly decreased the incidence of tissue collapse and neutrophile aggregation in rats receiving CNP before radiation in comparison with the radiation group.

CONCLUSION

The results suggested the possibility of using CNP as a future radioprotector due to its ability to protect normal cells against radiation-induced damage.

Assessment of impact of α-Fe2 O3 and γ-Fe2 O3 nanoparticles on phytoplankton species Selenastrum capricornutum and Nannochloropsis oculata

In this study, the impact of alpha-iron oxide (α-Fe₂ O₃ , 20-40 nm) and gamma iron oxide (γ-Fe₂ O₃ , 20-40 nm) nanoparticles (NPs) on phytoplankton species Selenastrum capricornutum and Nannochloropsis oculata was investigated Characterizations of the NPs were systematically carried out by TEM, dynamic light scattering, zeta potential, X-ray diffraction, SEM, and Fourier transformation infrared spectroscopy. Acute toxicity was tested between 0.2 and 50 mg/L for each NP for a period of 72 hours exposure. γ-Fe₂ O₃ NP inhibited development of N oculata at the rate of 54% in 0.2 mg/L group with a high mortality rate of up to 82%. α-Fe₂ O₃ NPs were less toxic that induced 97% mortality on N oculata at 10 mg/L suspensions. In contrast, α-Fe₂ O₃ NP inhibited growth of S capricornutum strongly (73%) in 0.2 mg/L group. γ-Fe₂ O₃ NPs showed similar growth inhibition (72%) on S capricornutum in 10 mg/L suspensions. Despite the differential effects, the results indicated acute toxicity of α-Fe₂ O₃ and γ-Fe₂ O₃ NPs on N oculata and S capricornutum.

Potential Hazard of Lanthanides and Lanthanide-Based Nanoparticles to Aquatic Ecosystems: Data Gaps, Challenges and Future Research Needs Derived from Bibliometric Analysis

Lanthanides (Ln), applied mostly in the form of nanoparticles (NPs), are critical to emerging high-tech and green energy industries due to their distinct physicochemical properties. The resulting anthropogenic input of Ln and Ln-based NPs into aquatic environment might create a problem of emerging contaminants. Thus, information on the biological effects of Ln and Ln-based NPs is urgently needed for relevant environmental risk assessment. In this mini-review, we made a bibliometric survey on existing scientific literature with the main aim of identifying the most important data gaps on Ln and Ln-based nanoparticles' toxicity to aquatic biota. We report that the most studied Ln for ecotoxicity are Ce and Ln, whereas practically no information was found for Nd, Tb, Tm, and Yb. We also discuss the challenges of the research on Ln ecotoxicity, such as relevance of nominal versus bioavailable concentrations of Ln, and point out future research needs (long-term toxicity to aquatic biota and toxic effects of Ln to bottom-dwelling species).

Natural molecule coatings modify the fate of cerium dioxide nanoparticles in water and their ecotoxicity to Daphnia magna

The ongoing development of nanotechnology has raised concerns regarding the potential risk of nanoparticles (NPs) to the environment, particularly aquatic ecosystems. A relevant aspect that drives NP toxicity is represented by the abiotic and biotic processes occurring in natural matrices that modify NP properties, ultimately affecting their interactions with biological targets. Therefore, the objective of this study was to perform an ecotoxicological evaluation of CeO₂NPs with different surface modifications representative of NP bio-interactions with molecules naturally occurring in the water environment, to identify the role of biomolecule coatings on nanoceria toxicity to aquatic organisms. Ad hoc synthesis of CeO₂NPs with different coating agents, such as Alginate and Chitosan, was performed. The ecotoxicity of the coated CeO₂NPs was assessed on the marine bacteria Aliivibrio fischeri, through the Microtox® assay, and with the freshwater crustacean Daphnia magna. Daphnids at the age of 8 days were exposed for 48 h, and several toxicity endpoints were evaluated, from the molecular level to the entire organism. Specifically, we applied a suite of biomarkers of oxidative stress and neurotoxicity and assessed the effects on behaviour through the evaluation of swimming performance. The different coatings affected the hydrodynamic behaviour and colloidal stability of the CeO₂NPs in exposure media. In tap water, NPs coated with Chitosan derivative were more stable, while the coating with Alginate enhanced the aggregation and sedimentation rate. The coatings also significantly influenced the toxic effects of CeO₂NPs. Specifically, in D. magna the CeO₂NPs coated with Alginate triggered oxidative stress, while behavioural assays showed that CeO₂NPs coated with Chitosan induced hyperactivity. Our findings emphasize the role of environmental modification in determining the NP effects on aquatic organisms.

Cerium oxide nanoparticles: properties, biosynthesis and biomedical application

Cerium oxide nanoparticles have revolutionized the biomedical field and is still in very fast pace of development. Hence, this work elaborates the physicochemical properties, biosynthesis, and biomedical applications of cerium oxide nanoparticles.

Toxicity of superparamagnetic iron oxide nanoparticles to the microalga Chlamydomonas reinhardtii

Superparamagnetic iron oxide nanoparticles (SPION) have been widely studied for different biomedical and environmental applications. In this study we evaluated the toxicity and potential alterations of relevant physiological parameters caused to the microalga Chlamydomonas reinhardtii (C. reinhardtii) upon exposure to SPION. The results showed dose-dependent toxicity. A mechanistic study combining flow cytometry and physiological endpoints showed a toxic response consisting of a decrease in metabolic activity, increased oxidative stress and alterations in the mitochondrial membrane potential. Additionally, and due to the light absorption of SPION suspensions, we observed a significant shading effect, causing a marked decrease in photosynthetic activity. In this work, we demonstrated for the first time, the internalization of SPION by endocytosis in C. reinhardtii. These results demonstrated that SPION pose a potential risk for the environment if not managed properly.

Microscale and molecular analyses of river biofilm communities treated with microgram levels of cerium oxide nanoparticles indicate limited but significant effects

Cerium oxide (CeO₂) nanoparticles are used as in-fuel catalysts and in manufacturing processes, creating a potential for release to aquatic environments. Exposures at 1 and 10 μg/L CeO₂-nanoparticles were made to assess effects during the development of river biofilm communities. Scanning transmission x-ray microscopy (STXM) indicated extensive sorption of nanoparticles to the community and co-localization with lipid moieties. Following 8 weeks of development, polycarbonate coupons were removed from the reactors and used for molecular analyses, denaturing gradient gel electrophoresis analysis (DGGE-16S rRNA) and 16S rRNA amplicon sequencing. Microscopic imaging of the biofilm communities (bacterial, photosynthetic biomass, exopolymer composition, thickness, protozoan numbers), as well as carbon substrate utilization fingerprinting was performed. There was a trend toward reduced photosynthetic biomass, but no significant effects of CeO₂ exposure were found on photosynthetic and bacterial biomass or biofilm thickness. Sole carbon source utilization analyses indicated increased utilization of 10 carbon sources in the carbohydrate, carboxylic acid and amino acids categories related to CeO₂ exposures; however, predominantly, no significant effects (p < 0.05) were detected. Measures of microbial diversity, lectin binding affinities of exopolymeric substances and results of DGGE analyses, indicated significant changes to community composition (p < 0.05) with CeO₂ exposure. Increased binding of the lectin Canavalia ensiformis was observed, consistent with changes in bacterial-associated polymers. Whereas, no significant changes were observed in binding to residues associated with algal and cyanobacterial exopolymers. 16S rRNA amplicon sequencing of community DNA indicated changes in diversity and shifts in community composition; however, these did not trend with increasing CeO₂ exposure. Counting of protozoans in the biofilm communities indicated no significant effects on this trophic level. Thus, based on biomass and functional measures, CeO₂ nanoparticles did not appear to have significant effects; however, there was evidence of selection pressure resulting in significant changes in microbial community composition.

Quantitative assessment of photosynthetic activity of Chlorella (Class Trebouxiophyceae) adsorbed onto soil by using fluorescence imaging

In the present study, we evaluate our previously developed non-destructive soil algal toxicity method using species from a different class of algae; Class Trebouxiophyceae (Chlorella vulgaris and Chlorella sorokiniana), and directly measure the photosynthetic activity of these species adsorbed onto the soil as a new toxicity endpoint. This study shows that non-destructive soil algal toxicity method is applicable to non-specific test species, including those of Class Trebouxiophyceae as well as Class Chlorophyceae (Chlorococcum infusionum and Chlamydomonas reinhardtii). Furthermore, by performing photosynthesis image analysis, we verify that it is possible to measure the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soils without the need to extract algal cells from the soil. We propose that the non-destructive soil algal toxicity method represents a novel technique for 1) evaluating pollutants in soil using non-specific algae and 2) conveniently and rapidly assessing the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soil as a new toxicity endpoint.

How does aquatic macrophyte Salvinia auriculata respond to nanoceria upon an increased CO2 source? A Fourier transform-infrared photoacoustic spectroscopy and chlorophyll a fluorescence study

With the continued increase of technological uses of cerium oxide nanoparticles (CeO₂ NPs or nanoceria) and their unregulated disposal, the accumulation of nanoceria in the environment is inevitable. Concomitantly, atmospheric carbon dioxide (CO₂) levels continue to rise, increasing the concentrations of bicarbonate ions in aquatic ecosystems. This study investigates the influence of CeO₂ NPs (from 0 to 100 μgL^-1) in the presence and absence of an elevated bicarbonate (HCO₃^-) ion concentration (1 mM), on vibrational biochemical parameters and photosystem II (PSII) activity in leaf discs of Salvinia auriculata. Fourier transform-infrared photoacoustic spectroscopy (FTIR-PAS) was capable of diagnostic use to understand biochemical and metabolic changes in leaves submitted to the CeO₂ NPs and also detected interactive responses between CeO₂ NPs and HCO₃^- exposure at the tissue level. The results showed that the higher CeO₂ NPs levels in the presence of HCO₃^- increased the non-photochemical quenching (NPQ) and coefficient of photochemical quenching in dark (qP_d) compared to the absence of HCO₃. Moreover, the presence of HCO₃^- significantly decreased the NPQ at all levels of CeO₂ NPs demonstrating that HCO₃^- exposure may change the non-radiative process involved in the operation of the photosynthetic apparatus. Overall, the results of this study are useful for providing baseline information on the interactive effects of CeO₂ NPs and elevated HCO₃^- ion concentration on photosynthetic systems.

Chronic exposure of the freshwater alga Pseudokirchneriella subcapitata to five oxide nanoparticles: Hazard assessment and cytotoxicity mechanisms

The increasing use of nanoparticles (NPs) unavoidably enhances their unintended introduction into the aquatic systems, raising concerns about their nanosafety. This work aims to assess the toxicity of five oxide NPs (Al₂O₃, Mn₃O₄, In₂O₃, SiO₂ and SnO₂) using the freshwater alga Pseudokirchneriella subcapitata as a primary producer of ecological relevance. These NPs, in OECD medium, were poorly soluble and unstable (displayed low zeta potential values and presented the tendency to agglomerate). Using the algal growth inhibition assay and taking into account the respective 72 h-EC₅₀ values, it was possible to categorize the NPs as: toxic (Al₂O₃ and SnO₂); harmful (Mn₃O₄ and SiO₂) and non-toxic/non-classified (In₂O₃). The toxic effects were mainly due to the NPs, except for SnO₂ which toxicity can mainly be attributed to the Sn ions leached from the NPs. A mechanistic study was undertaken using different physiological endpoints (cell membrane integrity, metabolic activity, photosynthetic efficiency and intracellular ROS accumulation). It was observed that Al₂O_3, Mn₃O₄ and SiO₂ induced an algistatic effect (growth inhibition without loss of membrane integrity) most likely as a consequence of the cumulative effect of adverse outcomes: i) reduction of the photosynthetic efficiency of the photosystem II (Ф_PSII); ii) intracellular ROS accumulation and iii) loss of metabolic activity. SnO₂ NPs also provoked an algistatic effect probably as a consequence of the reduction of Ф_PSII since no modification of intracellular ROS levels and metabolic activity were observed. Altogether, the results here presented allowed to categorize the toxicity of the five NPs and shed light on the mechanisms behind NPs toxicity in the green alga P. subcapitata.

Use of Cyanobacterial Luminescent Bioreporters to Report on the Environmental Impact of Metallic Nanoparticles

Due to their ecological relevance, low cost, and easy maintenance, cyanobacteria have been used for bioreporter development. In this study, a battery of cyanobacterial bioreporters has been used to assess the ecotoxicity of four highly used metallic nanoparticles (NPs). The toxicity of these NPs was tested using the bioreporter Nostoc CPB4337 (Anabaena CPB4337). As oxidative stress is a primary toxic mechanism of metallic NPs, cyanobacterial reactive oxygen species (ROS)-detecting bioreporters were used. Metallic NPs release metal ions, which contribute to their toxic effect and the formation of ROS, so a metal-detecting bioreporter was also used to detect the bioavailable metals. The results confirm that ROS production by NPs was due to the NPs per se and not by released free-ions, which in fact were almost undetectable. Although the metal-detecting bioreporter could not detect the dissolved metal ions, it was able to detect the metallic NPs themselves, indicating that this bioreporter may be useful to detect them in the environment. ROS production varied depending on the growth medium or environmental matrices conditions and on the NP type. This work demonstrated the different levels of ROS production by metallic NPs and the importance of nanotoxicology studies in real matrices.

Toxicity mechanisms of ZnO UV-filters used in sunscreens toward the model cyanobacteria Synechococcus elongatus PCC 7942

Zinc oxide (ZnO) nanoparticles are commonly used in sunscreens for their UV-filtering properties. Their growing use can lead to their release into ecosystems, raising question about their toxicity. Effects of these engineered nanomaterials (ENMs) on cyanobacteria, which are important primary producers involved in many biogeochemical cycles, are unknown. In this study, we investigated by several complementary approaches the toxicological effects of two marketed ZnO-ENMs (coated and uncoated) on the model cyanobacteria Synechococcus elongatus PCC 7942. It was shown that despite the rapid adsorption of ENMs on cell surface, toxicity is mainly due to labile Zn released by ENMs. Zn dissipates cell membrane potential necessary for both photosynthesis and respiration, and induces oxidative stress leading to lipid peroxidation and DNA damages. It leads to global downregulation of photosystems, oxidative phosphorylation, and transcription/translation machineries. This also translates into significant decrease of intracellular ATP content and cell growth inhibition. However, there is no major loss of pigments and even rather an increase in exposed cells compared to controls. A proposed way to reduce the environmental impact of Zn would be the improvement of the coating stability to prevent solubility of ZnO-ENMs.

Synthesis and biomedical applications of nanoceria, a redox active nanoparticle

Background

Nanoceria has recently received much attention, because of its widespread biomedical applications, including antibacterial, antioxidant and anticancer activity, drug/gene delivery systems, anti-diabetic property, and tissue engineering.

Main body

Nanoceria exhibits excellent antibacterial activity against both Gram-positive and Gram-negative bacteria via the generation of reactive oxygen species (ROS). In healthy cells, it acts as an antioxidant by scavenging ROS (at physiological pH). Thus, it protects them, while in cancer cells (under low pH environment) it acts as pro-oxidant by generating ROS and kills them. Nanoceria has also been effectively used as a carrier for targeted drug and gene delivery in vitro and in vivo models. Besides, nanoceria can also act as an antidiabetic agent and confer protection towards diabetes-associated organ pathophysiology via decreasing the ROS level in diabetic subjects. Nanoceria also possesses excellent potential in the field of tissue engineering. In this review, firstly, we have discussed the different methods used for the synthesis of nanoceria as these are very important to control the size, shape and Ce³⁺/Ce⁴⁺ ratio of the particles upon which the physical, chemical, and biological properties depend. Secondly, we have extensively reviewed the different biomedical applications of nanoceria with probable mechanisms based on the literature reports.

Conclusion

The outcome of this review will improve the understanding about the different synthetic procedures and biomedical applications of nanoceria, which should, in turn, lead to the design of novel clinical interventions associated with various health disorders.

Graphical abstract

Changes in soil properties after remediation influence the performance and survival of soil algae and earthworm

Previous research on soil remediation focused on soil properties and not on its effects on soil ecosystems. The present study investigated the adverse effects of soil physicochemical changes due to remediation on the biological indicators Chlorococcum infusionum and Chlamydomonas reinhardtii (algae) and Eisenia andrei (earthworm). Soil physicochemical properties, concentrations of total, bioavailable, and water-soluble heavy metals in soil were measured before and after remediation. Changes in soil pH, electrical conductivity, total nitrogen, and total phosphorous immediately after soil remediation were the primary causes of the biomass and photosynthetic activity inhibition observed in C. infusionum and C. reinhardtii, and the survival, normality, and burrowing behavior decrease observed in E. andrei in remediated soils showing dramatic changes in those properties. These findings suggest that remediated soils need some time to recover before restoring their functions, although heavy metals are no longer contaminating the soil.

Recovery of Alexandrium tamarense under chronic exposure of TiO2 nanoparticles and possible mechanisms

Harmful algal blooms (HAB), heavily influenced by human activities, pose serious hazard to aquatic ecology and human health. In this study, we monitored the physiological responses and paralytic shellfish poisoning toxins (PSTs) of the toxin-producing HAB species Alexandrium tamarense under titanium dioxide nanoparticles (_nTiO₂) exposure in the concentration range of 2-320 mg L^-1 over a period of 13 days. The results showed the acute inhibition of _nTiO₂ on the algal growth, photosynthetic efficiency and esterase activity at all concentrations except 2 mg L^-1. Nonetheless, they recovered after 13 days _nTiO₂ exposure from 20 to 80 mg L^-1. The EC₅₀ value increased from 85.1 mg L^-1 in Day 4 to 140.9 mg L^-1 in Day 13. The physiological recovery after prolonged exposure may result from the elimination of excess reactive oxygen species (ROS), a combined outcome of increased _nTiO₂ aggregation and algal antioxidant defense mechanisms. This observation is supported by the immediately increased antioxidant enzyme activities, including the superoxide dismutase (SOD) and catalase (CAT) activities upon _nTiO₂ exposure. Moreover, the production of PSTs in A. tamarense significantly increased by 1.41-1.76 folds after chronic _nTiO₂ exposure at all tested concentrations (p < 0.05), which might also be an adaptive response for the microalgae to overcome the stresses. In particular, the proportions of highly-toxic PSTs analogues GTX2/3, STX and dcSTX were significantly increased upon _nTiO₂ exposure (p < 0.05). Hence, the chronic _nTiO₂ exposure might aggravate the ecological impact of HABs. Furthermore investigations on different HAB species, especially those toxin-producing ones, and detail physiological responses are obviously needed.

Algal toxicity of binary mixtures of zinc oxide nanoparticles and tetrabromobisphenol A: Roles of dissolved organic matters

The present study investigated the impacts of dissolved organic matters (DOM) on joint toxicity involved in zinc oxide nanoparticles (ZnO NPs) and tetrabromobisphenol A (TBBPA) at relevant low-exposure concentrations (<1 mg/L). It was found that ZnO NPs in single and combined systems exhibited severe inhibition effects on a freshwater microalgae Scenedesmus obliquus. However, the presence of DOM slightly alleviated the growth inhibition toxicity induced by the binary mixtures of ZnO NPs and TBBPA. Ultrastructure analysis revealed that ZnO NPs caused structural damage to cells, including plasmolysis, membrane destruction, and the disruption of thylakoid in the chloroplast, regardless of the presence of coexisting substances. Oxidative stress biomarker quantitative analysis and in situ observations indicated that the massive accumulation of reactive oxygen species in the binary mixtures of ZnO NPs and TBBPA caused severe oxidative damage, but the presence of DOM significantly mitigated the damage.

Uptake and effects of cerium(III) and cerium oxide nanoparticles to Chlamydomonas reinhardtii

Cerium (Ce) and cerium oxide nanoparticles (CeO₂ NP) are increasingly used in different applications. Upon their release into the aquatic environment, the exposure of aquatic organisms becomes likely. In this study, the uptake of CeO₂ NP and Ce³⁺ into the wild type and cell wall free mutant of Chlamydomonas reinhardtii was examined upon short term exposure. Separation of CeO₂ NP and Ce³⁺ not taken up or loosely bound to the cells was performed by washing algae with EDTA. Despite a concentration and time dependent increase of cellular Ce upon exposure to CeO₂ NP with the maximal calculated Ce concentration corresponding to 1.1 CeO₂ NP per cell, an internalization of CeO₂ NP with a mean size of 140 nm in C. reinhardtii was excluded. In contrast, dissolved Ce³⁺ (1 and 10 μM) was taken up both in the wild type and cell wall free mutant of C. reinhardtii, with a linear increase of cellular Ce within 1-2 h and maximal cellular Ce of 6.04 × 10^-4 mol L_cell^-1 (wild type) and 9.0 × 10^-5 mol L_cell^-1 (cell wall free mutant). Based on competition with Ca²⁺ for Ce³⁺ uptake, on the comparison of the wild type and the cell wall free mutant and on inhibition of photosynthetic yield, we suggest that no efficient uptake routes for Ce³⁺ are available in C. reinhardtii and that a fraction of the cellular Ce in the wild type strongly sorbs to the algal cell wall.

Exposure of engineered nanoparticles to Alexandrium tamarense (Dinophyceae): Healthy impacts of nanoparticles via toxin-producing dinoflagellate

Human activities can enhance the frequency, intensity and occurrence of harmful algal blooms (HABs). Engineered nanoparticles (ENPs), contained in many materials, will inevitably enter coastal waters and thus cause unpredictable impacts on aquatic organisms. However, knowledge of the influence of ENPs on HAB species is still lacking. In this study, we examined the effects of titanium dioxide nanoparticles (_nTiO₂), zinc oxide nanoparticles (_nZnO) and aluminum oxide nanoparticles (_nAl₂O₃) on physiological changes and paralytic shellfish poisoning toxins (PSTs) production of Alexandrium tamarense. We found a dose-dependent decrease in photosynthetic activity of A. tamarense under all three ENPs and a significant growth inhibition induced by _nZnO. The largest reactive oxygen species (ROS) production was induced by _nTiO₂, followed by _nZnO and _nAl₂O₃. Moreover, the PSTs production rate increased by 3.9-fold for _nTiO₂ (p<0.01) and 4.5-fold for _nAl₂O₃ (p<0.01) at a concentration of 200mgL^-1. The major component, C2 was transformed to its epimer C1 and the proportion of decarbamoyl toxins increased under 200mgL^-1 of _nZnO and _nAl₂O₃. In addition, the proportion of carbamate toxins increased upon exposure to 2mgL^-1 ENPs, while decreased upon exposure to 200mgL^-1 ENPs. The changes in PSTs production and composition might be an adaptive response for A. tamarense to overcome the stress of ENPs exposure. This work brings the first evidence that ENP would affect PSTs production and profiles.

Microplate freeze-dried cyanobacterial bioassay for fresh-waters environmental monitoring

Microorganisms have been very useful in environmental monitoring due to their constant sensing of the surrounding environment, their easy maintenance and low cost. Some freeze-dried toxicity kits based on naturally bioluminescent bacteria are commercially available and commonly used to assess the toxicity of environmental samples such as Microtox (Aliivibrio fischeri) or ToxScreen (Photobacterium leiognathi), however, due to the marine origin of these bacteria, they could not be the most appropriate for fresh-waters monitoring. Cyanobacteria are one of the most representative microorganisms of aquatic environments, and are well suited for detecting contaminants in aqueous samples. This study presents the development and application of the first freeze-dried cyanobacterial bioassay for fresh-water contaminants detection. The effects of different cell growth phases, cryoprotectant solutions, freezing protocols, rehydration solutions and incubation conditions methods were evaluated and the best combination of these parameters for freeze-drying was selected. The study includes detailed characterization of sensitivity towards reference pollutants, as well as, comparison with the standard assays. Moreover, long-term viability and sensitivity were evaluated after 3 years of storage. Freeze-dried cyanobacteria showed, in general, higher sensitivity than the standard assays and viability of the cells remained after 3 years of storage. Finally, the validation of the bioassay using a wastewater sample was also evaluated. Freeze-drying of cyanobacteria in 96-well plates presents a simple, fast and multi-assay method for environmental monitoring.

Potency of (doped) rare earth oxide particles and their constituent metals to inhibit algal growth and induce direct toxic effects

Use of rare earth elements (REEs) has increased rapidly in recent decades due to technological advances. It has been accompanied by recurring rare earth element anomalies in water bodies. In this work we (i) studied the effects of eight novel doped and one non-doped rare earth oxide (REO) particles (aimed to be used in solid oxide fuel cells and gas separation membranes) on algae, (ii) quantified the individual adverse effects of the elements that constitute the (doped) REO particles and (iii) attempted to find a discernible pattern to relate REO particle physicochemical characteristics to algal growth inhibitory properties. Green algae Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata) were used as a test species in two different formats: a standard OECD201 algal growth inhibition assay and the algal viability assay (a 'spot test') that avoids nutrient removal effects. In the 24h 'spot' test that demonstrated direct toxicity, algae were not viable at REE concentrations above 1mgmetal/L. 72-hour algal growth inhibition EC₅₀ values for four REE salts (Ce, Gd, La, Pr) were between 1.2 and 1.4mg/L, whereas the EC₅₀ for REO particles ranged from 1 to 98mg/L. The growth inhibition of REEs was presumably the result of nutrient sequestration from the algal growth medium. The adverse effects of REO particles were at least in part due to the entrapment of algae within particle agglomerates. Adverse effects due to the dissolution of constituent elements from (doped) REO particles and the size or specific surface area of particles were excluded, except for La₂NiO₄. However, the structure of the particles and/or the varying effects of oxide composition might have played a role in the observed effects. As the production rates of these REO particles are negligible compared to other forms of REEs, there is presumably no acute risk for aquatic unicellular algae.

CeO2 NPs, toxic or protective to phytoplankton? Charge of nanoparticles and cell wall as factors which cause changes in cell complexity

CeO₂ nanoparticles (CeO₂ NPs) are well-known for their catalytic properties and antioxidant potential. Recent uses in therapy are based on the Ce⁺³ ions released by CeO₂ NPs. Reactions involving redox cycles between Ce⁺³ and Ce⁺⁴ oxidation stage seem to promote scavenging of reactive oxygen species (ROS), thus protecting cells from oxygen damage. However, the internalization of CeO₂ NPs and release of Ce⁺³ could be responsible for a toxic effect on cells. The literature reports controversial results on the toxicity of CeO₂ NPs to phytoplankton. Therefore, we have tested the potential toxic effect of two CeO₂ NPs (with positive and negative zeta potential) and bulk CeO₂ (at 0.1, 1, 10, 100 and 200mg·L^-1) on three species of microalgae from different environments: marine diatom (Phaeodactylum tricornutum), marine chlorophyte (Nannochloris atomus) and freshwater chlorophyte (Chlamydomonas reinhardtii) over 72h in batch cultures. Responses measured in the microalgae population are: growth, chlorophyll a, cell size, cell complexity, percentage of ROS, and percentage of cell membrane damage. Positive zeta potential CeO₂ NPs provoked greater cell complexity (up to 78, 172 and 23 times more cell complexity than in controls found for C. reinhardtii, P. tricornutum and N. atomus respectively) than negative zeta potential CeO₂ NPs. The SSC signal detected by flow cytometry measured increases of particles entering cells, and this is related to cell viability and levels of intracellular ROS (correlation between SSC and percentage of ROS of 0.72 and 0.97 found for C. reinhardtii and P. tricornutum). When increased cellular complexity over controls is between 2 and 6 times greater, CeO₂ (in bulk or nanoparticulate form) seems to protect against ROS. When increased cellular complexity is from 7 to 23 times greater, CeO₂ does not provoke toxic responses; however, when increased cellular complexity over controls is very high, from 61 to 172 times, increased ROS production and toxic responses are found. Results show that two factors, the charge of CeO₂ NPs and cell wall structure, constitute the primary barrier to the possible accumulation of CeO₂ NPs within phytoplankton cytosol.

Synergic use of chemical and ecotoxicological tools for evaluating multi-contaminated soils amended with iron oxides-rich materials

Abandoned waste piles from ancient mining activities are potential hot spots for the pollution of the surrounding areas. A pot experiment was carried out to check the potential toxicity of the dumping material present in one of these scenarios, and several amendments were tested to attenuate the spread of the contamination events. The waste material had an acid pH and a large total concentration of As and Cu. A dose-response experiment was performed with this material following OCDE 208 test. A proportion 90:10 uncontaminated soil: dumping material (% w/w) was selected for the following experiment, in order to surpass the amount of dumping material that caused 50% reduction in plant growth. Pots were filled with the 90:10 mixture, planted with seeds of Brassica napus and amended with the following materials: three iron oxides of Bayoxide® E33 series, iron (II) sulphate in combination with de-inking paper sludge (Fe+PS), iron oxide-rich rolling mill scale (ROL) and iron oxide-rich cement waste (CEM). Amendment effectiveness evaluation was based on chemical and biological assays: extractable trace element concentration, soil enzymatic activities, inhibition of light emission of V. fischeri and Anabaena sp., B. napus L. fresh weight and screening test for emergence of B. napus L. seedlings. Amendments E33HCF and Fe+PS were the most effective in reducing extractable As and Zn concentration. B. napus weight and dehydrogenase and β-glucosidase activities were positively increased with the two above mentioned treatments but they triggered more toxic effects for V. fischeri luminescence. E33P treatment was the only in which the EC₅₀ was higher than in the control. Anabaena sp. was less sensitive than V. fischeri as its luminescence was not hampered by any treatment. Trace element concentration did not significantly affect the failure in seed emergence. E33HCF and Fe+PS could act as proper amendments as they decreased extractable As and Zn. Further, plant fresh weight, enzymatic activities and some of the bioassays identified the latter treatments as the best ones among those tested here to this type of multi-contaminated soil.

CeO2 nanoparticle fate in environmental conditions and toxicity on a freshwater predator species: a microcosm study

We studied the fate and toxicity of two types of CeO₂ NPs (bare or citrate-coated) in environmentally relevant conditions, using large indoor microcosms. Long-term exposure was carried out on a three-leveled freshwater trophic chain, comprising microbial communities as primary producers, chironomid larvae as primary consumers, and amphibian larvae as secondary consumers. Whereas coated NPs preferentially sedimented, bare NPs were mainly found in the water column. However, mass balance indicated low recovery (51.5%) for bare NPs, indicating possible NP loss, against 98.8% of recovery for coated NPs. NPs were rather chemically stable, with less than 4% of dissolution. Chironomid larvae ingested large amounts of NPs and were vectors of contamination for amphibian larvae. Although bioaccumulation in amphibian larvae was important (9.47 and 9.74 mg/kg for bare and coated NPs, respectively), no biomagnification occurred through the trophic chain. Finally, significant genotoxicity was observed in amphibian larvae, bare CeO₂ NPs being more toxic than citrate-coated NPs. ᅟ.

Calcium mediates the cellular response of Chlamydomonas reinhardtii to the emerging aquatic pollutant Triclosan

The present study was aimed at investigating the role of intracellular free calcium, [Ca²⁺]_c, in the early cellular response of the green alga Chlamydomonas reinhardtii to the emergent pollutant Triclosan (13.8μM; 24h of exposure). There is a growing concern about the persistence and toxicity of this antimicrobial in aquatic environments, where non-target organisms such as C. reinhardtii, a primary producer of ecological relevance, might be severely impacted. A mechanistic study was undertaken which combined flow cytometry protocols, physiological as well as gene expression analysis. As an early response, Triclosan strongly altered [Ca²⁺]_c homeostasis which could be prevented by prechelation with the intracellular calcium chelator BAPTA-AM. Triclosan induced ROS overproduction which ultimately leads to oxidative stress with loss of membrane integrity, membrane depolarization, photosynthesis inhibition and mitochondrial membrane depolarization; within this context, Triclosan also induced an increase in caspase 3/7 activity and altered the expression of metacaspase genes which are indicative of apoptosis. All these adverse outcomes were dependent on [Ca²⁺]_c. Interestingly, an interconnection between [Ca²⁺]_c alterations and increased ROS formation by Triclosan was found. Taken altogether these results shed light on the mechanisms behind Triclosan toxicity in the green alga Chlamydomonas reinhardtii and demonstrate the role of [Ca²⁺]_c in mediating the observed toxicity.

Cerium oxide nanoparticles: green synthesis and biological applications

CeO2 nanoparticles (NPs) have shown promising approaches as therapeutic agents in biology and medical sciences. The physicochemical properties of CeO2-NPs, such as size, agglomeration status in liquid, and surface charge, play important roles in the ultimate interactions of the NP with target cells. Recently, CeO2-NPs have been synthesized through several bio-directed methods applying natural and organic matrices as stabilizing agents in order to prepare biocompatible CeO2-NPs, thereby solving the challenges regarding safety, and providing the appropriate situation for their effective use in biomedicine. This review discusses the different green strategies for CeO2-NPs synthesis, their advantages and challenges that are to be overcome. In addition, this review focuses on recent progress in the potential application of CeO2-NPs in biological and medical fields. Exploiting biocompatible CeO2-NPs may improve outcomes profoundly with the promise of effective neurodegenerative therapy and multiple applications in nanobiotechnology.

Effect of fluoride on the cell viability, cell organelle potential, and photosynthetic capacity of freshwater and soil algae

Although fluoride occurs naturally in the environment, excessive amounts of fluoride in freshwater and terrestrial ecosystems can be harmful. We evaluated the toxicity of fluoride compounds on the growth, viability, and photosynthetic capacity of freshwater (Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata) and terrestrial (Chlorococcum infusionum) algae. To measure algal growth inhibition, a flow cytometric method was adopted (i.e., cell size, granularity, and auto-fluorescence measurements), and algal yield was calculated to assess cell viability. Rhodamine123 and fluorescein diacetate were used to evaluate mitochondrial membrane potential (MMA, ΔΨ_m) and cell permeability. Nine parameters related to the photosynthetic capacity of algae were also evaluated. The results indicated that high concentrations of fluoride compounds affected cell viability, cell organelle potential, and photosynthetic functions. The cell viability measurements of the three algal species decreased, but apoptosis was only observed in C. infusionum. The MMA (ΔΨ_m) of cells exposed to fluoride varied among species, and the cell permeability of the three species generally decreased. The decrease in the photosynthetic activity of algae may be attributable to the combination of fluoride ions (F^-) with magnesium ions (Mg²⁺) in chlorophyll. Our results therefore provide strong evidence for the potential risks of fluoride compounds to microflora and microfauna in freshwater and terrestrial ecosystems.

Inhibitory mechanism of phthalate esters on Karenia brevis

The occurrence of phthalate esters (PAEs), a class of widely used and environmentally prevalent chemicals, raises concern to environmental and human health globally. The PAEs have been demonstrated to inhibit algae growth, but the underlying mechanisms remain unclear. In this research, diethyl ortho-phthalate (DEP), diallyl phthalate (DAP), di-n-butyl ortho-phthalate (DBP), di-iso-butyl ortho-phthalate, and benzyl-n-butyl ortho-phthalate (BBP) were screened from 11 species of PAEs to study their inhibitory effects on Karenia brevis and determine their target sites on algae. With increasing the alkyl chains of these five PAEs, the values of EC50,96h decreased. The content of malondialdehyde increased with the continuous accumulation of reactive oxygen species (ROS) in the algae cells. Moreover, the superoxide dismutase and catalase contents were first activated and then inhibited. The ultrastructures of Karenia brevis cells were detected by transmission electron microscopy, and cells treated with PAEs exhibiting distorted shapes and large vacuoles. Thus, the algae were damaged by ROS accumulation, resulting in lipid oxidation and algal growth inhibition. The inhibitors of the electron transport chain showed that the sites of ROS production and accumulation in K. brevis cells under DEP and BBP were the mitochondria and chloroplast, respectively. Moreover, the target sites of DAP and DBP were both the chloroplast and mitochondria. These results are useful for controlling PAEs contamination in and revealing the fate of PAEs in aquatic ecosystem.

Recent advances (2010-2015) in studies of cerium oxide nanoparticles' health effects

Cerium oxide nanoparticles, widespread applied in our life, have attracted much concern for their human health effects. However, most of the works addressing cerium oxide nanoparticles toxicity have only used in vitro models or in vivo intratracheal instillation methods. The toxicity studies have varied results and not all are conclusive. The information about risk assessments derived from epidemiology studies is severely lacking. The knowledge of occupational safety and health (OSH) for exposed workers is very little. Thus this review focuses on recent advances in studies of toxicokinetics, antioxidant activity and toxicity. Additionally, aim to extend previous health effects assessments of cerium oxide nanoparticles, we summarize the epidemiology studies of engineered cerium oxide nanoparticles used as automotive diesel fuel additive, aerosol particulate matter in air pollution, other industrial ultrafine and nanoparticles (e.g., fumes particles generated in welding and flame cutting processes).

Long and short term impacts of CuO, Ag and CeO2 nanoparticles on anaerobic digestion of municipal waste activated sludge

In this study, long and short term inhibition impacts of Ag, CuO and CeO2 nanoparticles (NPs) on anaerobic digestion (AD) of waste activated sludge (WAS) were investigated. CuO NPs were detected as the most toxic NPs on AD. As the CuO NP concentration increased from 5 to 1000 mg per gTS, an increase in the inhibition of AD from 5.8 to 84.0% was observed. EC50 values of short and long term inhibitions were calculated as 224.2 mgCuO per gTS and 215.1 mgCuO per gTS, respectively. Ag and CeO2 NPs did not cause drastic impacts on AD as compared to CuO NPs. In the long term test, Ag NPs created 12.1% decrease and CeO2 NPs caused 9.2% increase in the methane production from WAS at the highest dosage. FISH imaging also revealed that the abundance of Archaea in raw WAS was similar in short and long term tests carried out with WAS containing Ag and CeO2 NPs. On the other hand, CuO NPs caused inhibition of Archaea in the long term test. Digestion kinetics of WAS containing Ag, CeO2, CuO NPs were also evaluated with Gompertz, Logistic, Transference and First Order models. The hydrolysis rate constant (kH) for each concentration of Ag and CeO2 NPs and the raw WAS was 0.027745 d(-1) while the kH of WAS containing high concentrations of CuO NPs was found to be 0.001610 d(-1).

Effect of PFOA/PFOS pre-exposure on the toxicity of the herbicides 2,4-D, Atrazine, Diuron and Paraquat to a model aquatic photosynthetic microorganism

Pre-exposure to the perfluorinated compounds (PFCs) perfluorooctano sulphonate (PFOS) or perfluorooctanoic acid (PFOA) on the toxicity of four herbicides of different types and modes of action towards the self-luminescent recombinant cyanobacterium Anabaena CPB4337 was evaluated. The rationale of the approach is that both PFOS and PFOA as surfactants are known to modify cell membrane properties and pre-exposure to them might alter herbicide toxicity towards the cyanobacterium. Anabaena CPB4337 was pre-exposed during 72h to PFOS or PFOA at a concentration below their no observed effect concentration (NOEC). After pre-exposure, cells were exposed to increasing concentrations of 2,4-D Atrazine, Diuron and Paraquat and the toxicity was compared to that of non-pre-exposed ones. The data clearly showed that PFCs pre-treatment significantly altered the toxicity of the tested herbicides. However the effects resulting from PFOA and PFOS pre-exposure were not homogeneous for all the herbicides. In general PFOA pre-exposure resulted in increased herbicide toxicity except for atrazine, while PFOS pre-exposure resulted in increased toxicity for paraquat and diuron, and reduced toxicity for atrazine with no significant effect on 2,4-D toxicity. The strongest modifying effect was found for paraquat whose toxicity doubled with PFOA pre-exposure. Further analysis of membrane properties by flow cytometry revealed that both PFOA and PFOS were able to modify membrane integrity and membrane potential of Anabaena CPB4337 at the concentrations used in the pre-exposure experiments. These results reveal relevant indirect effects of PFCs pollution with eco-toxicological implications.

Untangling the biological effects of cerium oxide nanoparticles: the role of surface valence states

Cerium oxide nanoparticles (nanoceria; CNPs) have been found to have both pro-oxidant and anti-oxidant effects on different cell systems or organisms. In order to untangle the mechanisms which underlie the biological activity of nanoceria, we have studied the effect of five different CNPs on a model relevant aquatic microorganism. Neither shape, concentration, synthesis method, surface charge (ζ-potential), nor nominal size had any influence in the observed biological activity. The main driver of toxicity was found to be the percentage of surface content of Ce(3+) sites: CNP1 (58%) and CNP5 (40%) were found to be toxic whereas CNP2 (28%), CNP3 (36%) and CNP4 (26%) were found to be non-toxic. The colloidal stability and redox chemistry of the most and least toxic CNPs, CNP1 and CNP2, respectively, were modified by incubation with iron and phosphate buffers. Blocking surface Ce(3+) sites of the most toxic CNP, CNP1, with phosphate treatment reverted toxicity and stimulated growth. Colloidal destabilization with Fe treatment only increased toxicity of CNP1. The results of this study are relevant in the understanding of the main drivers of biological activity of nanoceria and to define global descriptors of engineered nanoparticles (ENPs) bioactivity which may be useful in safer-by-design strategies of nanomaterials.

Effects of Nano-CeO₂ with Different Nanocrystal Morphologies on Cytotoxicity in HepG2 Cells

Cerium oxide nanoparticles (nano-CeO₂) have been reported to cause damage and apoptosis in human primary hepatocytes. Here, we compared the toxicity of three types of nano-CeO₂ with different nanocrystal morphologies (cube-, octahedron-, and rod-like crystals) in human hepatocellular carcinoma cells (HepG2). The cells were treated with the nano-CeO₂ at various concentrations (6.25, 12.5, 25, 50, 100 μg/mL). The crystal structure, size and morphology of nano-CeO₂ were investigated by X-ray diffractometry and transmission electron microscopy. The specific surface area was detected using the Brunauer, Emmet and Teller method. The cellular morphological and internal structure were observed by microscopy; apoptotic alterations were measured using flow cytometry; nuclear DNA, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) and glutathione (GSH) in HepG2 cells were measured using high content screening technology. The scavenging ability of hydroxyl free radicals and the redox properties of the nano-CeO₂ were measured by square-wave voltammetry and temperature-programmed-reduction methods. All three types of nano-CeO₂ entered the HepG2 cells, localized in the lysosome and cytoplasm, altered cellular shape, and caused cytotoxicity. The nano-CeO₂ with smaller specific surface areas induced more apoptosis, caused an increase in MMP, ROS and GSH, and lowered the cell’s ability to scavenge hydroxyl free radicals and antioxidants. In this work, our data demonstrated that compared with cube-like and octahedron-like nano-CeO₂, the rod-like nano-CeO₂ has lowest toxicity to HepG2 cells owing to its larger specific surface areas.