Manufactured nanoparticles in the aquatic environment-biochemical responses on freshwater organisms: A critical overview

Developmental toxicity induced by Cu(OH)2 nanopesticide in zebrafish embryos

The current study evaluates the adverse effects of Cu(OH)₂ nanopesticide (CNPE) on the early life stages of zebrafish (Danio rerio). The developmental toxicity was determined using different parameters such as mortality (including LC₅₀ ), hatching, heart rates, malformations, and alteration of the gene expressions. Zebrafish embryos (4 hpf-hours postfertilization) were exposed to 1.0, 2.0, 4.0, 8.0, and 16.0 mg/l CNPE doses until 96 hpf. The 96 hours LC₅₀ was recorded at 6.258 mg/l. Seventy-two hpf total malformation index values for 2.0, 4.0, and 8.0 mg/l CNPE doses were 4.3, 7.2 and 7.9, respectively. 1.0 mg/l CNPE is not toxic for the zebrafish embryos/larvae. 2.0 to 8.0 CNPE doses caused some abnormalities in embryos/larvae morphology, including lack of body parts, tail deformities, chorda deformity, bubbled head, scoliosis, lordosis, weak or non-pigmentation, decreased heart rate and larva length. 16.0 mg/l CNPE caused mortality in 72 hpf. The expression levels of seven immune system-related genes (il-1β, il-8, cebp, tlr4, hsp70, NF-kB, and mtf-1) were examined. The transcription level of il-1β, il-8, tlr4, hsp70, and NF-kB genes significantly increased in the CNPE exposure groups. While the expression of the mtf-1 gene considerably decreased, the cebp gene expression level did not change in the 4.0 and 8.0 mg/l CNPE doses. In conclusion, CNPE could induce developmental toxicity with malformations in embryos/larvae and alter the gene expression.

Impacts of zinc oxide nano and bulk particles on redox-enzymes of the Punica granatum callus

The structure and function of cellular membranes were sustained by redox-enzymes. We studied the interaction between the oxidative stress caused by excessive accumulation of ZnO-nanoparticles (ZnO-NPs) in plants and the role of redox-enzymes that can alleviate this stress. The crude callus extract from pomegranate, which was treated with 0, 10, and 150 µg mL-1 ZnO-NPs or bulk particles (ZnO-BPs), was applied to study the activity and kinetics of redox-enzymes. The elevated ZnO-NPs, enhanced the lipoxygenase and polyphenol oxidase activity, while the ZnO-BPs did not modify them. The activities of superoxide dismutase, catalase, and phenylalanine ammonia-lyase were induced under ZnO-NPs or BPs treatments, whilst the opposite trend of peroxidase was observed. Ascorbate peroxidase activity increased under ZnO-NPs treatments but decreased under ZnO-BPs. The kinetics activity of enzymes showed changes under different levels of NPs and BPs. Additionally, NPs or BPs treatments reduced the uptake of copper, iron, magnesium, but increased zinc accumulation in callus tissues. Meanwhile, these treatments enhanced the accumulation of manganese ions but did not affect the accumulation of potassium and phosphorous in ZnO-NPs or BPs-stressed calli. Collectively, these results gave a quantitative evaluation of the competition of zinc and other minerals on the carriers, and in addition, they provided a basis for how to control ZnO-NPs or BPs toxicity via redox-enzymes.

Microalgal ecotoxicity of nanoparticles: An updated review

Nowadays, nanotechnology and its related industries are becoming a rapidly explosive industry that offers many benefits to human life. However, along with the increased production and use of nanoparticles (NPs), their presence in the environment creates a high risk of increasing toxic effects on aquatic organisms. Therefore, a large number of studies focusing on the toxicity of these NPs to the aquatic organisms are carried out which used algal species as a common biological model. In this review, the influences of the physio-chemical properties of NPs and the response mechanisms of the algae on the toxicity of the NPs were discussed focusing on the "assay" studies. Besides, the specific algal toxicities of each type of NPs along with the NP-induced changes in algal cells of these NPs are also assessed. Almost all commonly-used NPs exhibit algal toxicity. Although the algae have similarities in the symptoms under NP exposure, the sensitivity and variability of each algae species to the inherent properties of each NPs are quite different. They depend strongly on the concentration, size, characteristics of NPs, and biochemical nature of algae. Through the assessment, the review identifies several gaps that need to be further studied to make an explicit understanding. The findings in the majority of studies are mostly in laboratory conditions and there are still uncertainties and contradictory/inconsistent results about the behavioral effects of NPs under field conditions. Besides, there remains unsureness about NP-uptake pathways of microalgae. Finally, the toxicity mechanisms of NPs need to be thoughtfully understood which is essential in risk assessment.

Effects of environmental factors on the growth and microcystin production of Microcystis aeruginosa under TiO2 nanoparticles stress

Due to the growing use and release of nanomaterials, their toxic impacts on aquatic ecosystems have drawn widespread attention in recent years. In this study, we exposed Microcystis aeruginosa to 5 mg/L titanium dioxide nanoparticles (nTiO₂) under different culture conditions (pH 6, 7, 8, 9; 20 °C, 25 °C, 30 °C). The results showed that algae had the worst growth status with lowest biomass, lowest photosynthetic activity and highest reactive oxygen species (ROS) generation under 5 mg/L nTiO₂ at pH 6 and 20 °C. Images by scanning electron microscopy (SEM) revealed that nTiO₂ hindered light absorption by algal cells by wrapping the algal surface, which led to obvious cell surface deformation at pH 6 or 20 °C. In addition, microcystin-LR (MC-LR) production increased as temperature or pH decreased when exposed to nTiO₂ at 5 mg/L, demonstrating that falling pH or temperature enhanced the adverse effects toward algal cells under nTiO₂ stress and the potential risk of algae to the environment.

Developments in the Application of Nanomaterials for Water Treatment and Their Impact on the Environment

Nanotechnology is an uppermost priority area of research in several nations presently because of its enormous capability and financial impact. One of the most promising environmental utilizations of nanotechnology has been in water treatment and remediation where various nanomaterials can purify water by means of several mechanisms inclusive of the adsorption of dyes, heavy metals, and other pollutants, inactivation and removal of pathogens, and conversion of harmful materials into less harmful compounds. To achieve this, nanomaterials have been generated in several shapes, integrated to form different composites and functionalized with active components. Additionally, the nanomaterials have been added to membranes that can assist to improve the water treatment efficiency. In this paper, we have discussed the advantages of nanomaterials in applications such as adsorbents (removal of dyes, heavy metals, pharmaceuticals, and organic contaminants from water), membrane materials, catalytic utilization, and microbial decontamination. We discuss the different carbon-based nanomaterials (carbon nanotubes, graphene, graphene oxide, fullerenes, etc.), and metal and metal-oxide based nanomaterials (zinc-oxide, titanium dioxide, nano zerovalent iron, etc.) for the water treatment application. It can be noted that the nanomaterials have the ability for improving the environmental remediation system. The examination of different studies confirmed that out of the various nanomaterials, graphene and its derivatives (e.g., reduced graphene oxide, graphene oxide, graphene-based metals, and graphene-based metal oxides) with huge surface area and increased purity, outstanding environmental compatibility and selectivity, display high absorption capability as they trap electrons, avoiding their recombination. Additionally, we discussed the negative impacts of nanomaterials such as membrane damage and cell damage to the living beings in the aqueous environment. Acknowledgment of the possible benefits and inadvertent hazards of nanomaterials to the environment is important for pursuing their future advancement.

Transcriptome alterations and genotoxic influences in zebrafish larvae after exposure to dissolved aluminum and aluminum oxide nanoparticles

Manufactured nanoparticles (NPs) can potentially cause negative effects on molecular (proteins and nucleic acids), subcellular, cellular, tissue, organ, and organism due to their unusual physicochemical characteristics. Ionizable NPs in water (e.g., Al₂O₃-NPs) may create toxic effects on aquatic animals. The present research determined the influences of Al₂O₃-NPs and appropriate concentrations of ionizing Al(III) using water-soluble AlCl₃ in zebrafish larvae (72 h post-fertilization, Danio rerio) by analyzing transcriptional alterations of stress-associated genes (rad51, p53, mt2) with quantitative real-time PCR (qRT-PCR). In addition, genotoxic effects of Al(III) and Al₂O₃-NPs were evaluated. The lethal concentrations that cause death of 50% (LC₅₀) of zebrafish larvae when exposed to 0-50 mg/l Al(III) and 0-500 mg/l Al₂O₃-NPs were 3.26 ± 0.38 and 130.19 ± 5.59 mg/l, respectively, for 96 h. A concentration-dependent increase was observed in the genotoxicity in cells of larvae exposed to Al(III) and Al₂O₃-NPs for 96 h. DNA damage was more severe in larvae exposed to Al(III) (41.0% tail) than that of Al₂O₃-NPs (21.8% tail). A complex induction of stress-associated genes was observed in fish and this induction was not directly related to the concentrations of Al(III) and Al₂O₃-NPs, although a significant induction was detected in mt2 gene of larvae exposed to Al(III) and Al₂O₃-NPs relative to control group. The induction levels of mt2 were 4.13 ± 0.1 and 2.13 ± 0.1-fold change (mean ± S.E.M.) in larvae at 15 mg/l of Al(III) and 100 mg/l of Al₂O₃-NP concentrations, respectively.

Revisiting the cytotoxicity of quantum dots: an in-depth overview

Recently, medical research has been shifting its focus to nanomedicine and nanotherapeutics in the pursuit of drug development research. Quantum dots (QDs) are a critical class of nanomaterials due to their unique properties, which include optical, electronic, and engineered biocompatibility in physiological environments. These properties have made QDs an attractive biomedical resource such that they have found application as both in vitro labeling and in vivo theranostic (therapy-diagnostic) agents. Considerable research has been conducted exploring the suitability of QDs in theranostic applications, but the cytotoxicity of QDs remains an obstacle. Several types of QDs have been investigated over the past decades, which may be suitable for use in biomedical applications if the barrier of cytotoxicity can be resolved. This review attempts to report and analyze the cytotoxicity of the major QDs along with relevant related aspects.

Physiological, structural and ultrastructural impacts of silver nanoparticles on the seagrass Cymodocea nodosa

Silver nanoparticles (AgNPs) are an emerging contaminant, currently considered to be a significant potential risk to the coastal environment. To further test potential risk, and to determine effect concentrations and sensitive response parameters, toxic effects of environmentally relevant AgNP concentrations on the seagrass Cymodocea nodosa were evaluated. Alterations of the cytoskeleton, endoplasmic reticulum, ultrastructure, photosystem II function, oxidative stress markers, cell viability, and leaf, rhizome and root elongation in C. nodosa exposed to AgNP concentrations (0.0002-0.2 mg L^-1) under laboratory conditions for 8 days were examined. An increase in H₂O₂ level, indicating oxidative stress, occurred after the 4th day even at 0.0002 mg L^-1. Increased antioxidant enzyme activity, potentially contributing to H₂O₂ level decline at the end of the experiment, and reduced protein content were also observed. Actin filaments started to diminish on the 6th day at 0.02 mg L^-1; microtubule, endoplasmic reticulum, chloroplast and mitochondrion disturbance appeared after 8 days at 0.02 mg L^-1, while toxic effects were generally more acute at 0.2 mg L^-1. A dose-dependent leaf elongation inhibition was also observed; as for juvenile leaves, toxicity index increased from 2.8 to 40.7% with concentration. Hydrogen peroxide (H₂O₂) overproduction and actin filament disruption appeared to be the most sensitive response parameters, and thus could be utilized as early warning indicators of risk to seagrass meadows. A risk quotient of 1.33 was calculated, confirming previous findings, that AgNPs may pose a significant risk to the coastal environment.

Effects of titanium dioxide nanoparticles on leaf cell structure and viability, and leaf elongation in the seagrass Halophila stipulacea

The ecotoxicity of titanium dioxide nanoparticles (TiO₂ NPs) is of increasing concern due to their extensive use in a variety of applications. This study aims to achieve a better understanding of TiO₂ NP ecotoxicity by assessing for the first time their effects on seagrasses. Changes in leaf cell structure and viability, and leaf elongation in Halophila stipulacea exposed under laboratory conditions to environmentally relevant TiO₂ NP concentrations (0.0015-1.5 mg L^-1) for 8 days were assessed. Actin filament (AF) disturbance firstly occurred in differentiating cells at 0.0015 mg L^-1 on the 8th day, while in meristematic cells at 0.15 mg L^-1 on the 6th day, both deteriorating concentration- and time-dependently. Endoplasmic reticulum (ER) appeared aggregated firstly at 0.015 mg L^-1 on the 8th day and earlier at the highest concentrations, while microtubules and cell ultrastructure appeared unaffected. Dead cells mainly occurred in older leaves; dead tooth, margin and intercostal epidermal cells exceeded 5% at 0.15-1.5 mg L^-1. A significant leaf elongation inhibition occurred at 0.015-1.5 mg L^-1 in older leaves and at 1.5 mg L^-1 in young apical leaves. AF, ER and leaf elongation impairment in H. stipulacea, being susceptible response parameters, could be used as early warning markers. A risk quotient >1 was calculated, indicating that TiO₂ NPs may pose a significant risk to the environment. The data presented underline the need for additional TiO₂ NP-seagrasses toxicity information, and could be utilized for the protection of the coastal environment.

Nanoparticles: An Experimental Study of Zinc Nanoparticles Toxicity on Marine Crustaceans. General Overview on the Health Implications in Humans

The presence of products containing nanoparticles or nanofibers is rapidly growing. Nanotechnology involves a wide spectrum of industrial fields. There is a lack of information regarding the toxicity of these nanoparticles in aqueous media. The potential acute toxicity of ZnO NPs using two marine crustacean species: the copepod Tigriopus fulvus and the amphypod Corophium insidiosum was evaluated. Acute tests were conducted on adults of T. Fulvus nauplii and C. insidiosum. Both test species were exposed for 96 h to 5 increasing concentrations of ZnO NPs and ZnSO4H2O, and the endpoint was mortality. Statistical analysis revealed that the mean LC50 values of both ZnO NPs and ZnSO4H2O (ZnO NPs: F = 59.42; P < 0.0015; ZnSO4H2O: F = 25.57; P < 0.0015) were significantly lower for Tigriopus fulvus than for Corophium insidiosum. This result confirms that the toxic effect could be mainly attributed to the Zn ions, confirming that the dissolution processes play a crucial role in the toxicity of the ZnO NPs.

Biological effects and bioaccumulation of gold in gilthead seabream (Sparus aurata) - Nano versus ionic form

The question of whether gold (Au) is more toxic as nanoparticles or in its ionic form remains unclear and controversial. The present work aimed to clarify the effects of 96 h exposure to 4, 80 and 1600 μg·L^-1 of 7 nm gold nanoparticles (AuNPs) - (citrate coated (cAuNPs) or polyvinylpyrrolidone coated (PVP-AuNPs)) - and ionic Au (iAu) on gilthead seabream (Sparus aurata). Effects at different levels of biological organization (behaviour, neurotransmission, biotransformation, oxidative stress/damage and genotoxicity) were assessed. cAuNPs induced oxidative stress and damage (lipid peroxidation increase), even at 4 μg·L^-1, and reduced the ability of S. aurata to swim against a water flow at 1600 μg·L^-1. Exposure to cAuNPs induced more adverse effects than exposure to PVP-AuNPs. All tested concentrations of Au (nano or ionic form) induced DNA breaks and cytogenetic damage in erythrocytes of S. aurata. Generally, iAu induced significantly more effects in fish than the nano form, probably associated with the significantly higher accumulation in the fish tissues. No fish mortality was observed following exposure to AuNPs, but mortality was observed in the group exposed to 1600 μg·L^-1 of iAu.

Multigenerational plasticity of Daphnia magna under thermal stress across ten generations

The effects of increasing temperature owing to thermal discharge and global warming on zooplanktons such as Daphnia magna are a growing concern. The purpose of this study was to evaluate the effects of elevated temperature (25 °C) on oxidative stress responses, growth, and reproduction of D. magna across 10 generations. The number of offspring per female at 21 d was significantly increased and the rate of adult somatic growth (5-21 d) was decreased in the F0 generation at 25 °C compared with those at the reference temperature 20 °C. However, the F3 generation showed the lowest number of offspring and the highest adult somatic growth rate and oxidative stress responses (5 d) at 25 °C. Moreover, all life-history traits seemed to recover to the levels of the control group from the F6 generation at 20 °C. These findings suggest that D. magna under continuous thermal stress exhibits non-adaptive responses in the early generations (F0-F3) and changes to adaptive responses in the later generations (F6-F9). However, the underlying epigenetic mechanism should be identified in the future.

Chemical and Colloidal Dynamics of MnO2 Nanosheets in Biological Media Relevant for Nanosafety Assessment

Many layered crystal phases can be exfoliated or assembled into ultrathin 2D nanosheets with novel properties not achievable by particulate or fibrous nanoforms. Among these 2D materials are manganese dioxide (MnO2 ) nanosheets, which have applications in batteries, catalysts, and biomedical probes. A novel feature of MnO2 is its sensitivity to chemical reduction leading to dissolution and Mn2+ release. Biodissolution is critical for nanosafety assessment of 2D materials, but the timing and location of MnO2 biodissolution in environmental or occupational exposure scenarios are poorly understood. This work investigates the chemical and colloidal dynamics of MnO2 nanosheets in biological media for environmental and human health risk assessment. MnO2 nanosheets are insoluble in most aqueous phases, but react with strong and weak reducing agents in biological fluid environments. In vitro, reductive dissolution can be slow enough in cell culture media for MnO2 internalization by cells in the form of intact nanosheets, which localize in vacuoles, react to deplete intracellular glutathione, and induce cytotoxicity that is likely mediated by intracellular Mn2+ release. The results are used to classify MnO2 nanosheets within a new hazard screening framework for 2D materials, and the implications of MnO2 transformations for nanotoxicity testing and nanosafety assessment are discussed.

Effects of gold nanoparticles in gilthead seabream-A proteomic approach

Despite the widespread use of nanoparticles (NPs), there are still major gaps of knowledge regarding the impact of nanomaterials in the environment and aquatic animals. The present work aimed to study the effects of 7 and 40 nm gold nanoparticles (AuNPs) - citrate and polyvinylpyrrolidone (PVP) coated - on the liver proteome of the estuarine/marine fish gilthead seabream (Sparus aurata). After 96 h, exposure to AuNP elicited alterations on the abundance of 26 proteins, when compared to the control group. AuNPs differentially affected several metabolic pathways in S. aurata liver cells. Among the affected proteins were those related to cytoskeleton and cell structure, gluconeogenesis, amino acids metabolism and several processes related to protein activity (protein synthesis, catabolism, folding and transport). The increased abundance of proteins associated with energy metabolism (ATP synthase subunit beta), stress response (94 kDa glucose-regulated protein) and cytoskeleton structure (actins and tubulins) may represent the first signs of cellular oxidative stress induced by AuNPs. Although higher gold accumulation was found in the liver of S. aurata exposed to 7 nm PVP-AuNPs, the 7 nm cAuNPs were more bioactive, inducing more effects in liver proteome. Gold accumulated more in the spleen than in the other assessed tissues of S. aurata exposed to AuNPs, highlighting its potential role on the elimination of these NPs.

Elucidating Toxicodynamic Differences at the Molecular Scale between ZnO Nanoparticles and ZnCl2 in Enchytraeus crypticus via Nontargeted Metabolomics

Much effort has been devoted to clarifying the comparative toxicity of ZnO nanoparticles (NPs) and Zn ions; however, little is known about their toxicodynamic processes at the metabolic level. Here, we investigated the acute (2d) and chronic (7d) effects to a soil species, Enchytraeus crypticus, of two sublethal doses of ZnO-NPs and ZnCl₂ (10 and 30 mg/L Zn) using ultrahigh performance liquid chromatography-quadrupole-time-of-flight/mass spectrometry-based metabolomics. The metabolomics analysis identified 99, 128, 121, and 183 significantly changed metabolites (SCMs) in E. crypticus exposed to ZnO-NPs for 2d, ZnCl₂ for 2d, ZnO-NPs for 7d, and ZnCl₂ for 7d, respectively, suggesting that ZnCl₂ induced stronger metabolic reprogramming than ZnO-NPs, and a longer exposure time caused greater metabolite changes. Among the SCMs, 67 were shared by ZnO-NPs and ZnCl₂ after 2d and 84 after 7d. These metabolites were mainly related to oxidative stress and antioxidant defense, membrane disturbance, and energy expenditure. The targeted analysis on physiological and biochemical responses further proved the metabolic observations. Nevertheless, 32 (33%) and 37 (31%) SCMs were found only in ZnO-NP treatments after 2 and 7d, respectively, suggesting that the toxicity of ZnO-NPs cannot be solely attributed to the released Zn ions. Metabolic pathway analysis revealed significant perturbations of galactose metabolism, amino sugar and nucleotide sugar metabolism, and glycerophospholipid metabolism in all test groups. Based on involvement frequency, glucose-1-phosphate, glycerol 3-phosphate, and phosphorylcholine could serve as universal biomarkers for exposure to different Zn forms. Four pathways perturbed by ZnO-NPs were nanospecific upon acute exposure and three upon chronic exposure. Our findings demonstrated that metabolomics is an effective tool for understanding the molecular toxicity mechanism and highlighted that time-series measurements are essential for discovering and comparing modes of action of metal ions and NPs.

Effect of ageing of bare and coated nanoparticles of zinc oxide applied to soil on the Zn behaviour and toxicity to fish cells due to transfer from soil to water bodies

This study evaluated the influence of ageing of ZnO nanoparticles (NPs) applied to soil on the potential availability and chemical speciation of Zn, and also of their toxicity to aquatic organisms due to transfer of contaminants from soil to water. To this end, soil samples were spiked with two types of bare nanoparticles: b1ZnO NPs (rod- and elongated-shaped) and b2ZnO NPs (near-spherical shaped) and ZnO NPs coated with (3-aminopropyl)triethoxysilane (cZnO NPs) within the 0-800 mg Zn kg^-1 soil dose range, and were left to age for 0, 30, 60 and 90 days. The available concentration and speciation of Zn in soil were determined by the DGT (diffusive gradients in thin films) technique and sequential extraction procedures, respectively. The toxicity of the aqueous extracts from the ZnO NP-treated soils was assessed in vitro in established fish cell lines (RTG-2). The highest distribution percentages of the applied Zn occurred in the organically complexed (OC), followed by the exchangeable (EXC) fraction, for all NP types, applied doses and incubation times. The toxicity of NPs depended on their intrinsic properties: b1ZnO NPs affected the membrane function, reductase enzyme activity and, to a lesser extent, reactive oxygen species (ROS) levels of fish cells, whereas b2ZnO NPs and cZnO NPs affected mainly ROS generation. Ageing increased Zn soil availability, but toxicity to fish cells showed no trend over time. The particle dissolution of ZnO NPs did not explain the observed toxicity, hence a nanoparticles-specific effect should be assumed. The findings of this study seem to indicate that the transfer of ZnO NP from contaminated soils to aquatic ecosystems should be addressed.

Assessment of DNA damage and oxidative stress in juvenile Channa punctatus (Bloch) after exposure to multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) have many applications in industry and used as additives in polymers, catalysts, anodes in lithium-battery and drug delivery. There is little information about MWCNTs' (210 nm) genotoxic potential on juvenile freshwater fish Channa punctatus. Therefore, in this study, we have determined the toxic effects of MWCNTs on freshwater fish C. punctatus by assessing toxicological endpoints such as oxidative stress, mutagenicity, and genotoxicity after acute MWCNTs exposure for 5 days. MWCNTs LC₅₀ -96 hours value for C. punctatus was 21.8 mg/L and on this basis three different MWCNTs concentrations were selected, that is, sub-lethal I, II, and III, for 5-days exposure trials with C. punctatus. The level of lipid peroxidation increased in the gills and kidney of exposed fish at sub-lethal concentrations II and III. Contrastingly, glutathione decreased more in the gills than in the kidney. The activity of catalase enzymes decreased more in the gills than in the kidney at sublethal concentrations I and II. Glutathione S-transferase decreased in gill tissue but increased in kidney tissue following sub-lethal III exposure. Moreover, the level of glutathione reductase decreased in both tissues. In addition, MWCNTs genotoxicity was confirmed by DNA damage in lymphocytes, gills, kidney cells, and production of micronuclei (MNi) in red blood cells of freshwater fish following sub-lethal I, II, and III exposures. In conclusion, this study revealed that application of micronucleus and comet assays for in vivo laboratory studies using freshwater fish for screening the genotoxic potential of MWCNTs.

The toxicity of non-aged and aged coated silver nanoparticles to the freshwater shrimp Paratya australiensis

Nanoparticles (NPs) transform in the environment which result in alterations to their physicochemical properties. However, the effects of aging on the toxicity of NPs to aquatic organisms remain to be determined. Further the reports that have been published present contradictory results. The aim of this study was to examine the stability of differently coated silver nanoparticles (AgNPs) in media and the influence of aging of these NP on potential toxicity to freshwater shrimp Paratya australiensis. Coating-dependent changes in the stability of AgNP were observed with aging. Curcumin (C) coated AgNPs were stable, while tyrosine (T) coated AgNPs and epigallocatechin gallate (E) coated AgNPs aggregated in the P. australiensis medium. Increased lipid peroxidation and catalase activity was noted in P. australiensis exposed to AgNPs, suggesting oxidative stress was associated with NP exposure. The enhanced oxidative stress initiated by aged C-AgNPs suggests that aging of these NPs produced different toxicological responses. In summary, data suggest that coating-dependent alterations in NPs, together with aging affect both persistence and subsequent toxicity of NPs to freshwater organisms. Thus, the coating-dependent fate and toxicity of AgNPs together with the effect of their aging need to be considered in assessing the environmental risk of AgNPs to aquatic organisms.

The Toxicity of Nanoparticles to Organisms in Freshwater

Nanotechnology is a rapidly growing industry yielding many benefits to society. However, aquatic environments are at risk as increasing amounts of nanoparticles (NPs) are contaminating waterbodies causing adverse effects on aquatic organisms. In this review, the impacts of environmental exposure to NPs, the influence of the physicochemical characteristics of NPs and the surrounding environment on toxicity and mechanisms of toxicity together with NP bioaccumulation and trophic transfer are assessed with a focus on their impacts on bacteria, algae and daphnids. We identify several gaps which need urgent attention in order to make sound decisions to protect the environment. These include uncertainty in both estimated and measured environmental concentrations of NPs for reliable risk assessment and for regulating the NP industry. In addition toxicity tests and risk assessment methodologies specific to NPs are still at the research and development stage. Also conflicting and inconsistent results on physicochemical characteristics and the fate and transport of NPs in the environment suggest the need for further research. Finally, improved understanding of the mechanisms of NP toxicity is crucial in risk assessment of NPs, since conventional toxicity tests may not reflect the risks associated with NPs. Behavioural effects may be more sensitive and would be efficient in certain situations compared with conventional toxicity tests due to low NP concentrations in field conditions. However, the development of such tests is still lacking, and further research is recommended.

Polymeric and inorganic nanoscopical antimicrobial fillers in dentistry

Failure of dental treatments is mainly due to the biofilm accumulated on the dental materials. Many investigations have been conducted on the advancements of antimicrobial dental materials. Polymeric and inorganic nanoscopical agents are capable of inhibiting microorganism proliferation. Applying them as fillers in dental materials can achieve enhanced microbicidal ability. The present review provides a broad overview on the state-of-the-art research in the field of antimicrobial fillers which have been adopted for incorporation into dental materials over the last 5 years. The antibacterial agents and applications are described, with the aim of providing information for future investigations. STATEMENT OF SIGNIFICANCE: Microbial infection is the primary cause of dental treatment failure. The present review provides an overview on the state-of-art in the field of antimicrobial nanoscopical or polymeric fillers that have been applied in dental materials. Trends in the biotechnological development of these antimicrobial fillers over the last 5 years are reviewed to provide a backdrop for further advancement in this field of research.

A sub-individual multilevel approach for an integrative assessment of CuO nanoparticle effects on Corbicula fluminea

Because they are widely used, copper oxide nanoparticles (CuO NPs) are likely to enter the aquatic environment and then reach the sediment. We have examined the effect of CuO NPs in the freshwater endobenthic bivalve Corbicula fluminea. Some previous studies have investigated effects at biochemical and physiological levels, but molecular endpoints are still poorly studied despite they are sensitive in early detection of NPs effect. In the present study, we have investigated short-term effects (96 h) of CuO NP (12, 30 nm; 0, 20 and 100 μg/L) using molecular endpoints as well as more conventional biochemical and physiological markers. The expression of antioxidant (CuZnSOD, MnSOD, Cat, Se-GPx, Trxr) and antitoxic (GST-Pi, HSP70, MT, Pgp, MRP1) related genes was measured at the mRNA level while antioxidant (SOD, TAC) and antitoxic (GST, ACP) defenses, energetic reserves and metabolism (ETS, Tri, LDH), and cellular damages (LPO) were assessed using a biochemical approach. The filtration rate measured at 96 h provided information at the physiological scale. Gene expression and filtration rate were responsive to CuO NPs but the effects differed according to the NP size. The results suggest that defense mechanisms may have been set up following 30 nm-NP exposure. The response to 12 nm-NP was lower but still showed that exposure to 12 nm-NP led to activation of cellular elimination mechanisms. The lowering of the filtration rate may have protected the organisms from the contamination. However, this raised the question of further repercussions on organism biology. Together, the results (i) indicate that CuO NP may exert effects at different levels even after a short-term exposure and (ii) point out the precocity of molecular response.

Effects of titanium dioxide nanoparticles on Microcystis aeruginosa and microcystins production and release

Due to growing production and use, release of nanoparticles (NPs) into the aquatic environment may pose a hazard to ecosystem. In this study, Microcystis aeruginosa was exposed to different concentrations (0.1, 1, 10, 50, 100 mg/L) of titanium dioxide (TiO₂) NPs to assess their impact on algae. Meanwhile, the production and release of microcystins (MCs) was determined. Results showed that TiO₂ NPs significantly decreased the maximal photochemical efficiency of photosystem II, and thus inhibited the photosynthetic activity of M. aeruginosa. They also increased the content of reactive oxygen species (ROS) and malondialdehyde (MDA), indicating their oxidative damage on algae. Besides, TiO₂ NPs at high concentrations (50 and 100 mg/L) aggregated on the algal surface and block the light, herein inhibited algae growth (16.03%±2.50% and 54.13%±0.93%) but induced the production (25.02%±1.23% and 114.43%±2.96%) and release (20.96%±13.30% and 12.10%±8.80%) of MCs. These results indicated that high concentrations of TiO2 NPs increased MCs concentration in water system, which may be harmful to aquatic ecosystem.

Impact of copper oxide nanoparticles (CuO NPs) exposure on embryo development and expression of genes related to the innate immune system of zebrafish (Danio rerio)

CuO NPs are nanomaterials with catalytic activity and unique thermo-physical properties used in different fields such as sensors, catalysts, surfactants, batteries, antimicrobials and solar energy transformations. Because of its wide field of use, these nanoparticles accumulate in the aquatic environment and thus lead to toxic effects on aquatic organisms. The toxicological findings about CuO NPs are controversial and these effects of CuO NPs on aquatic organisms have not been elucidated in detail. Therefore, the aim of this study was to investigate the toxic effect of CuO NPs on zebrafish embryos using different parameters including molecular and morphologic. For this purpose, zebrafish embryos at 4 h after post fertilization (hpf) were exposed to different concentrations of CuO NPs (0.5, 1, 1.5 mg/L) until 96 hpf. Mortality, hatching, heartbeat, malformation rates were examined during the exposure period. In addition, Raman spectroscopy was used to determine whether CuO NPs entered into the tissues of zebrafish larvae or not. Moreover, the alterations in the expression of genes related to the antioxidant system and innate immune system were examined in the embryos exposed to CuO NPs during 96 h. The results showed that CuO NPs was not able to enter into the zebrafish embryos/larvae tissues but caused an increased the mortality rate, a delayed hatching, and a decreased heartbeat rate. Moreover, CuO NPs caused several types of abnormalities such as head and tail malformations, vertebral deformities, yolk sac edema, and pericardial edema. RT-PCR results showed that the transcription of mtf-1, hsp70, nfkb and il-1β, tlr-4, tlr-22, trf, cebp was changed by the application of CuO NPs. In conclusion, short-term exposure to CuO NPs has toxic effects on the development of zebrafish embryos.

Behavior, remediation effect and toxicity of nanomaterials in water environments

In recent years, nanotechnology has been developing continuously. Due to their advantageous huge specific surface areas, microinterface characteristics, remediation ability and potential environmental risks, nanomaterials have become a hot topic in the field of environmental research. With the mass production and use of nanomaterials, they will inevitably be discharged or leaked into the water environment. In this paper, we will describe some typical nanomaterials, such as nanoscale zero valent iron (nZVI), graphene nanomaterials (GNMs), TiO₂ nanoparticles (NPs), ZnO NPs, Fe₃O₄ NPs, carbon nanotubes (CNTs), Ag NPs, and other nanomaterials in water environments, focusing on the positive and negative effects of some nanomaterials in water environments. The remediation function and the impact of nanomaterials in water environments, including behavior of nanomaterials and their toxicity to aquatic organisms will be discussed. This will be of great significance for our subsequent research on nanomaterials.

A holistic study on potential toxic effects of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) on zebrafish (Danio rerio) embryos/larvae

Multi-walled carbon nanotubes (MWCNTs) have widespread use in industrial and consumer products and great potential in biomedical applications. This leads to inevitably their release into the environment and the formation of their toxic effects on organisms. These effects can change depending on their physicochemical characteristics. Therefore, the toxicological findings of MWCNTs are inconsistent. Their toxicities related to surface modification have not been elucidated in a holistic manner. Hence, this study was conducted to clarify their potential toxic effects on zebrafish embryos/larvae in a comprehensive approach using morphologic, biochemical and molecular parameters. Zebrafish embryos were exposed to 5, 10, 20 mg/L doses of MWCNTs-COOH at 4 h after fertilization and grown until 96 hpf. Physiological findings demonstrated that they induced a concentration-dependent increase in the mortality rate, delayed hatching and decrease in the heartbeat rate. Moreover, it caused abnormalities including yolk sac edema, pericardial edema, head, tail malformations, and vertebral deformities. These effects may be due to the alterations in antioxidant and immune system related gene expressions after their entry into zebrafish embryo/larvae. The entry was confirmed from the evaluation of Raman spectra collected from the head, yolk sac, and tail of control and the nanotube treated groups. The gene expression analysis indicated the changes in the expression of oxidative stress (mtf-1, hsp70, and nfkb) and innate immune system (il-1β, tlr-4, tlr-22, trf, and cebp) related genes, especially an increased in the expression of the hsp70 and il-1β. These findings proved the developmental toxicities of MWCNTs-COOH on the zebrafish embryos/larvae.

Quantitative Proteomic Analysis to Understand the Mechanisms of Zinc Oxide Nanoparticle Toxicity to Daphnia pulex (Crustacea: Daphniidae): Comparing with Bulk Zinc Oxide and Zinc Salt

The widespread use of zinc oxide nanoparticles (ZnO NPs) has resulted in their release to the environment. There has been concern about the ecotoxicity of ZnO NPs, but little is known about their toxic mechanisms. In the present study, we conducted acute toxicity tests to show that ZnO NPs are more toxic to the freshwater crustacean Daphnia pulex compared to bulk ZnO or ZnSO₄·7H₂O. To provide an integrated and quantitative insights into the toxicity of ZnO NPs, we conducted isobaric tags for relative and absolute quantitation (iTRAQ) proteomic analysis, which detected 262, 331, and 360 differentially expressed proteins (DEPs) in D. pulex exposed to ZnO NPs, bulk ZnO, and ZnSO₄·7H₂O, respectively. Among the DEPs, 224 were shared among the three treatments. These proteins were related to energy metabolism, oxidative stress, and endoplasmic reticulum stress. The three forms of Zn all caused D. pulex to downregulate Chitinase expression, disrupt Ca²⁺ homeostasis, and reduce expression of digestive enzymes. Nevertheless, 29 proteins were expressed only in the ZnO NP treatment. In particular, histone (H3) and ribosomal proteins (L13) were obviously influenced under ZnO NP treatment. However, increased expression levels of h3 and l13 genes were not induced only in ZnO NP treatment, they were sensitive to Zn ions under the same exposure concentration. These results indicate that the three zinc substances have a similar mode of action and that released zinc ions are the main contributor to ZnO NP toxicity to D. pulex under a low concentration. Further investigation is needed to clarify whether a small proportion of DEPs or higher bioavailability cause ZnO NPs to be more toxic compared to bulk ZnO or ionic zinc.

Investigation of toxic effects of amorphous SiO2 nanoparticles on motility and oxidative stress markers in rainbow trout sperm cells

In this study, we investigated the effects of SiO₂ nanoparticles (SiO₂-NPs) (1, 10, 25, 50, and 100 mg/L) for 24 h in vitro on the motility parameters and oxidative stress markers such as total glutathione (TGSH), catalase (CAT), and malondialdehyde (MDA) of rainbow trout, Oncorhynchus mykiss sperm cells. Therefore, SiO₂-NPs were synthesized with sol-gel reaction from tetraethoxy orthosilicate (TEOS). The prepared nanoparticle structures were characterized for chemical structure, morphology and thermal behavior employing Fourier transform infrared spectroscopy, X-ray spectroscopy, scanning electron micrograph, and thermal analysis (DTA/TGA/DSC) techniques. After exposure, there was statistically significant (p < 0.05) decreases in velocities of sperm cells. CAT activity significantly (p < 0.05) decreased by 9.6% in sperm cell treated with 100 mg/L. In addition, MDA level significantly increased by 70.4% and 77.5% in sperm cell treated with 50 and 100 mg/L SiO₂-NPs, respectively (p < 0.05). These results showed that SiO₂-NPs may have toxic effect on rainbow trout sperm cells in 50 mg/L and more.

Nanoparticle TiO2 size and rutile content impact bioconcentration and biomagnification from algae to daphnia

Little information is available about effect of particle size and crystal structure of nTiO₂ on their trophic transfer. In this study, 5 nm anatase, 10 nm anatase, 100 nm anatase, 20 nm P25 (80% anatase and 20% rutile), and 25 nm rutile nTiO₂ were selected to investigate the effects of size and crystal structure on the toxicity, bioconcentration, and trophic transfer of nTiO₂ to algae and daphnia. In the exposed daphnids, metabolic pathways affected by nTiO₂ and nTiO₂-exposed algae (nTiO₂-algae) were also explored. The 96 h IC₅₀ values of algae and the 48 h LC₅₀ values of daphnia were 10.3, 18.9, 43.9, 33.6, 65.4 mg/L and 10.5, 13.2, 37.0, 28.4, 60.7 mg/L, respectively, after exposed to nTiO₂-5A, nTiO₂-10A, nTiO₂-100A, nTiO₂-P25, and nTiO₂-25R, respectively. The bioconcentration factors (BCFs) for 0.1, 1, and 10 mg/L nTiO₂ in daphnia ranged from 21,220 L/kg to 145,350 L/kg. The nTiO₂ biomagnification factors (BMFs) of daphnia fed with 1 and 10 mg/L nTiO₂-exposed algae were consistently greater than 1.0 (5.7-122). The results show that the acute toxicity, BCF, and BMF all decreased with increasing size or rutile content of nTiO₂. All types of nTiO₂ were largely accumulated in the daphnia gut and were not completely depurated within 24 h. At the molecular level, 22 Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways of daphnia were impacted by the nTiO₂ and nTiO₂-algae treatments, including glutathione metabolism, aminoacyl-tRNA biosynthesis, among others. Six and four KEGG metabolic pathways were significantly disturbed in daphnids exposed to nTiO₂ and nTiO₂-algae, respectively, indicating the presence of algae partially alleviated the negative impact of nTiO₂ on metabolism. These findings increase understanding of the impacts of physicochemical properties of nTiO₂ on the food chain from molecular scale to that of the whole organism, and provide new insight into the ecological effect of nanomaterials.

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

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

Moina macrocopa as a non-target aquatic organism for assessment of ecotoxicity of silver nanoparticles: Effect of size

The release of nanomaterials in water reservoirs is hazardous. Very few reports are available on the interaction of different sized nanoparticles with aquatic organisms and aquatic environment. In the present study, silver nanoparticles (AgNPs) having an average particle size of 20.80 ± 2.31 and 40.04 ± 4.72 nm were synthesized using polyvinylpyrrolidone and l-tyrosine. Ecotoxicological effects of AgNPs were evaluated on less explored crustacean species, Moina macrocopa. The 48 h lethal values (48 h LC₅₀) of 20 and 40 nm AgNPs were 0.11 ± 0.02 and 0.12 ± 0.03 mg/L, respectively. Further, a size dependent inhibition of AgNPs on acetyl cholinesterase and digestive enzymes (trypsin, amylase, β-galactosidase) was observed, while that of the antioxidant enzymes (catalase, superoxide dismutase, glutathione-S-transferase) and alkaline phosphatase were enhanced as compared to control group. These results strengthen the potential of enzymes as biomarker in environmental risk assessment of AgNPs. AgNPs accumulated in the gut of M. macrocopa which could not be completely eliminated, thereby resulting in an increased metal body burden. The accumulation of AgNPs of 20 nm was lower than that of 40 nm indicating the influence of size of nanoparticles on uptake and toxicity. AgNPs agglomerated in moderately hard water medium (MHWM) and this agglomeration influenced the exposure the organism thereto. The size of AgNPs influenced the toxicity to M. macrocopa through interplay between uptake, accumulation, aggregation, and excretion in the organism and environment.

Metal accumulation, biochemical and behavioral responses on the Mediterranean clams Ruditapes decussatus exposed to two photocatalyst nanocomposites (TiO2 NPs and AuTiO2NPs)

Nanoparticle decoration with noble metal represents a promising alternative to improve their photocatalytic and photovoltaic properties. However, toxicity can be influenced by such modification, as the bioavailability of these substances may be influenced. To understand how decoration influences the NP impacts in marine ecosystems, we exposed suspension-feeding clams, Ruditapes decussatus, to two photocatalyst nanocomposites, TiO₂ NPs and AuTiO₂ NPs, over 2 concentrations, 50 μg L^-1and 100 μg L^-1, in a laboratory experiment. Accumulation of Au and Ti in gills and digestive gland was noted in clams after exposure to TiO₂ NPs and AuTiO₂ NPs using inductively coupled plasma optic emission spectroscopy (ICP-OES). TiO₂ and AuTiO₂ NPs alter the behavior of the clams Ruditapes decussatus by reducing filtration and respiration rates. Furthermore, the highest concentration of TiO₂NPs induces an overproduction of H₂O₂ in gills and digestive gland and NO production only in gills. Superoxide dismutase (SOD), Catalase (CAT), Glutathione-S-transferase (GST) and acetylcholinesterase (AChE) activities were induced in gills and digestives gland in concentration and nanocomposite type dependent manner. Decorated form presented higher Malondialdehyde (MDA) levels in gills and digestive gland than the undecorated form, suggesting different mechanisms of action that may be mediated through oxidative stress. In conclusion, the considered parameters could represent reliable biomarkers for the assessment of NP toxicity on R. decussatus as biological biomonitoring model. In addition, based on the obtained results, nanoparticle decoration influences the toxicity of metal nanoparticles in marine organism.

Negative effect of copper nanoparticles on the conjugation frequency of conjugative catabolic plasmids

Due to their antimicrobial properties, copper nanoparticles (CuNPs) have been proposed to be used in agriculture for pest control. Pesticides removal is mainly done by microorganisms, whose genes usually are found in conjugative catabolic plasmids (CCP). The aim of this work was to evaluate if CuNPs at subinhibitory concentrations modify the conjugation frequency (CF) of two CCP (pJP4 and pADP1). CuNPs were characterized by scanning electron microscopy with an X-ray detector, dynamic light scattering and X-ray diffraction. Mating assays were done in LB broth supplemented with CuNPs (10, 20, 50 and 100 µg mL^-1) or equivalent concentrations of CuSO₄. Interestingly, we observed that in LB, Cu⁺² release from CuNPs is fast as evaluated by atomic absorption spectrophotometry. Donor and recipient strains were able to grow in all copper concentrations assayed, but CF of mating pairs was reduced to 10% in the presence of copper at 20 or 50 µg Cu mL^-1 compared to control. Thus, our results indicated that both copper forms, CuNPs or CuSO₄, negatively affected the transfer of catabolic plasmids by conjugation. Since dissemination of degradative genes by conjugation contribute to degradation of pesticides by microorganisms, this work improves our understanding of the risks of using copper in agriculture soils, which could affect the biodegradative potential of microbial communities.

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.

Physiological responses of Chlorella sorokiniana to copper nanoparticles

Copper (Cu) nanomaterials have been increasingly researched and produced for many different consumer products. They have high reactivity and bactericidal properties, making them important in antifouling paints, which are thus directly introduced into aquatic ecosystems. However, studies are scarce on the behavior of Cu nanoparticles (Cu-NPs) in natural aquatic systems and their interactions with primary producers such as microalgae. We investigated the effects of NPs on some physiological responses of the freshwater phytoplankton Chlorella sorokiniana. The cells were exposed to nominal concentrations ranging from 2.50 to 635.00 μg L^-1 Cu-NPs for 96 h under laboratory-controlled conditions. The cultures were monitored daily for population growth and maximum photosynthetic quantum yield. Total lipids, proteins, and carbohydrates were quantified at 72 h of Cu-NP exposure. The results showed a positive correlation between nominal Cu-NPs and Cu in the biomass (0.97 correlation coefficient) and that this was inversely proportional to total carbohydrates, with a -0.64 correlation coefficient. At the higher end of the Cu-NP concentrations tested, higher total proteins and reduced growth rates were obtained in comparison with controls; we suggest that metal-binding proteins/antioxidants and nonstructural proteins were preferentially produced under these conditions. Our results contribute to an understanding of the interaction between Cu-NPs and a cosmopolitan phytoplankton, C. sorokiniana, and we emphasize that the disposal and use of Cu-NPs requires monitoring because even at environmentally relevant concentrations, the composition of the algae was affected. Environ Toxicol Chem 2019;38:387-395. © 2018 SETAC.

Toxicity and mechanisms of action of titanium dioxide nanoparticles in living organisms

Titanium dioxide nanoparticles (TiO₂ NPs) are one of the most widely used nanomaterials in the consumer products, agriculture, and energy sectors. Their large demand and widespread applications will inevitably cause damage to organisms and ecosystems. A better understanding of TiO₂ NP toxicity in living organisms may promote risk assessment and safe use practices of these nanomaterials. This review summarizes the toxic effects of TiO₂ NPs on multiple taxa of microorganisms, algae, plants, invertebrates, and vertebrates. The mechanism of TiO₂ NP toxicity to organisms can be outlined in three aspects: The Reactive Oxygen Species (ROS) produced by TiO₂ NPs following the induction of electron-hole pairs; cell wall damage and lipid peroxidation of the cell membrane caused by NP-cell attachment by electrostatic force owing to the large surface area of TiO₂ NPs; and TiO₂ NP attachment to intracellular organelles and biological macromolecules following damage to the cell membranes.

Effects and bioaccumulation of gold nanoparticles in the gilthead seabream (Sparus aurata) - Single and combined exposures with gemfibrozil

Gold nanoparticles (AuNPs) are found in a wide range of applications and therefore expected to present increasing levels in the environment. There is however limited knowledge concerning the potential toxicity of AuNPs as well as their combined effects with other pollutants. Hence, the present study aimed to investigate the effects of AuNPs alone and combined with the pharmaceutical gemfibrozil (GEM) on different biological responses (behaviour, neurotransmission, biotransformation and oxidative stress) in one of the most consumed fish in southern Europe, the seabream Sparus aurata. Fish were exposed for 96 h to waterborne 40 nm AuNPs with two coatings - citrate and polyvinylpyrrolidone (PVP), alone or combined with GEM. Antioxidant defences were induced in liver and gills upon both AuNPs exposure. Decreased swimming performance (1600 μg.L^-1) and oxidative damage in gills (4 and 80 μg.L^-1) were observed following exposure to polyvinylpyrrolidone coated gold nanoparticles (PVP-AuNPs). Generally, accumulation of gold in fish tissues and deleterious effects in S. aurata were higher for PVP-AuNPs than for cAuNPs exposures. Although AuNPs and GEM combined effects in gills were generally low, in liver, they were higher than the predicted. The accumulation and effects of AuNPs showed to be dependent on the size, coating, surface charge and aggregation/agglomeration state of nanoparticles. Additionally, it was tissue' specific and dependent on the presence of other contaminants. Although, gold intake by humans is expected to not exceed the estimated tolerable daily intake, it is highly recommended to keep it on track due to the increasing use of AuNPs.

Effects of lomefloxacin on survival, growth and reproduction of Daphnia magna under simulated sunlight radiation

Lomefloxacin, an antibacterial agent with known photo-induced toxicity in clinical studies, is frequently detected in aquatic environments. Investigating the photo-induced toxicity of lomefloxacin in aquatic organisms is therefore of importance for assessing its ecological risks. In this study, the effects of lomefloxacin on survival, growth and reproduction of Daphnia magna under simulated sunlight radiation (SSR) were investigated, and the mechanism of action was revealed. Results indicated that SSR containing UV radiation increased the acute toxicity of lomefloxacin to Daphnia magna relative to white fluorescent light irradiation. Under SSR, 100 μM lomefloxacin significantly enhanced reactive oxygen species (ROS) generation and lipid peroxidation, and decreased activities of superoxide dismutase and catalase. The biochemical observations and apparent effects on the organism indicate that oxidative stress plays a central role in the acute photo-induced toxicity. Chronic toxicity results showed that SSR significantly affected growth and reproduction of Daphnia magna, whereas lomefloxacin reduced the damage of UV radiation in SSR through light shielding. This study provides insight into the mechanism of photo-induced toxicity and can support the risk assessment of chemicals in the aquatic environment by including the impacts of sunlight irradiation on toxicity.

Do the pristine physico-chemical properties of silver and gold nanoparticles influence uptake and molecular effects on Gammarus fossarum (Crustacea Amphipoda)?

The specific and unique properties of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs), make them of high interest for different scientific and industrial applications. Their increasing use will inevitably lead to their release in the environment and aquatic ecosystems where they may represent a threat to aquatic organisms. Being a widespread and important component of the aquatic macroinvertebrate assemblage, amphipods and more specifically Gammarus fossarum will certainly be exposed to AgNPs and AuNPs. For these reasons, G. fossarum was selected as model organism for this study. The aim of the present work was the evaluation of the influence of both size (20, 40 and 80 nm) and surface coating (citrate CIT, polyethylene glycol PEG) on the acute toxicity of AgNPs and AuNPs on G. fossarum. We investigated the effects of AgNPs and AuNPs on the uptake by G. fossarum, NP tissue distribution and the expression of stress related genes by the use of ICP-MS, NanoSIMS50, Cytoviva®, and Rt-qPCR, respectively. Ag and Au bioaccumulation revealed a significant surface-coating dependence, with CIT-AgNPs and CIT-AuNPs showing the higher bio-accumulation potential in G. fossarum as compared to PEG-NPs. Opposite to that, no size-dependent effects on the bioaccumulation potential was observed. SIMS imaging and CytoViva® revealed an influence of the type of metal on the tissue distribution after uptake, with AgNPs detected in the cuticle and the gills of G. fossarum, while AuNPs were detected in the gut area. Furthermore, AgNPs were found to up-regulate CuZnSOD gene expression while AuNPs led to its down-regulation. Modulation of SOD may indicate generation of reactive species of oxygen and a possible activation of antioxidant defence in order to prevent and defend the organism from oxidative stress. However, further investigations are still needed to better define the mechanisms underlying the observed AgNPs and AuNPs effects.

Salinity mediates the toxic effect of nano-TiO2 on the juvenile olive flounder Paralichthys olivaceus

Increased production of engineered nanoparticles has raised extensive concern about the potential toxic effects on marine organisms living in estuarine and coastal environments. Meanwhile, salinity is one of the key environmental factors that may influence the physiological activities in flatfish species inhabiting in those waters due to fluctuations caused by freshwater input or rainfall. In this study, we investigated the oxidative stress and histopathological alteration of the juvenile Paralichthys olivaceus exposed to nano-TiO₂ (1 and 10 mg L^-1) under salinities of 10 and 30 psu for 4 days. In the gills, Na⁺-K⁺-ATPase activity significantly deceased after 4 days 10 psu exposure without nano-TiO₂ compared with 1 day of acclimating the salinity from the normal salinity (30 psu) to 10 psu. Under this coastal salinity, low concentration (1 mg L^-1) of nano-TiO₂ exerted significant impacts. In the liver, the activities of superoxide dismutase, catalase, the levels of lipid peroxide and malondialdehyde increased with nano-TiO₂ exposed under 30 psu. Such increase indicated an oxidative stress response. The result of the integrated biomarker responses showed that P. olivaceus can be adversely affected by high salinity and high concentration of nano-TiO₂ for a short-term (4 days) exposure. The histological analysis revealed the accompanying severe damages for the gill filaments. Principal component analysis further showed that the oxidative stress was associated with the nano-TiO₂ effect at normal salinity. These findings indicated that nano-TiO₂ and normal salinity exert synergistic effects on juvenile P. olivaceus, and low salinity plays a protective role in its physiological state upon short-term exposure to nano-TiO₂. The mechanism of salinity mediating the toxic effects of NPs on estuarine fish should be further considered.

Environmental impacts of nanomaterials

Nanotechnology is currently one of the highest priority research fields in many countries due to its immense potentiality and economic impact. Nanotechnology involves the research, development, production, and processing of structures and materials on a nanometer scale in various fields of science, technology, health care, industries, and agriculture. As such, it has contributed to the gradual restructuring of many associated technologies. However, due to the uncertainties and irregularities in shape, size, and chemical compositions, the presence of certain nanomaterials may exert adverse impacts on the environment as well as human health. Concerns have thus been raised about the destiny, transport, and transformation of nanoparticles released into the environment. A critical evaluation of the current states of knowledge regarding the exposure and effects of nanomaterials on the environment and human health is discussed in this review. Recognition on the potential advantages and unintended dangers of nanomaterials to the environment and human health is critically important to pursue their development in the future.

Biocompatible and Light-Penetrating Hydrogels for Water Decontamination

Solar light-activated photocatalyst nanoparticles (NPs) are promising environment-friendly low cost tools for water decontamination, but their dispersion in the environment must be minimized. Here, we propose the incorporation of TiO₂-NPs (also in combination with graphene platelets) into highly biocompatible hydrogels as a promising approach for the production of photoactive materials for water treatment. We also propose a convenient fluorescence-based method to investigate the hydrogel photocatalytic activity in real time with a conventional fluorimeter. Kinetics analysis of the degradation profile of a target fluorescent model pollutant demonstrates that fast degradation occurs in the matrix bulk. Fluorescence anisotropy proved that small pollutant molecules diffuse freely in the hydrogel. Rheological and scanning electron microscopy characterization showed that the TiO₂-NP incorporation does not significantly alter the hydrogel mechanical and morphological properties.

Nanoecotoxicity assessment of graphene oxide and its relationship with humic acid

The risk assessment of nanomaterials is essential for regulatory purposes and for sustainable nanotechnological development. Although the application of graphene oxide has been widely exploited, its environmental risk is not well understood because several environmental conditions can affect its behavior and toxicity. In the present study, the graphene oxide effect from aquatic ecosystems was assessed considering the interaction with humic acid on 9 organisms: Raphidocelis subcapitata (green algae), Lemna minor (aquatic plant), Lactuca sativa (lettuce), Daphnia magna (planktonic microcrustacean), Artemia salina (brine shrimp), Chironomus sancticaroli (Chironomidae), Hydra attenuata (freshwater polyp), and Caenorhabditis elegans and Panagrolaimus sp. (nematodes). The no-observed-effect concentration (NOEC) was calculated for each organism. The different criteria used to calculate NOEC values were transformed and plotted as a log-logistic function. The hypothetical 5 to 50% hazardous concentration values were, respectively, 0.023 (0.005-0.056) and 0.10 (0.031-0.31) mg L-1 for graphene oxide with and without humic acid, respectively. The safest scenario associated with the predicted no-effect concentration values for graphene oxide in the aquatic compartment were estimated as 20 to 100 μg L-1 (in the absence of humic acid) and 5 to 23 μg L-1 (in the presence of humic acid). Finally, the present approach contributed to the risk assessment of graphene oxide-based nanomaterials and the establishment of nano-regulations. Environ Toxicol Chem 2018;37:1998-2012. © 2018 SETAC.

Oxidative stress induced by titanium dioxide nanoparticles increases under seawater acidification in the thick shell mussel Mytilus coruscus

Biochemical responses of the mussel Mytilus coruscus exposed to different concentrations of titanium dioxide nanoparticles (nano-TiO₂) (0, 2.5, 10 mg L^-1) and two pH levels (pH 8.1 and pH 7.3) for 14 days. Mussel responses were also investigated after a 7 days recovery period (pH 8.1 and no nanoparticle). Exposure to nano-TiO₂ led changes in antioxidant indexes (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH)), biotransformation enzyme activity (GST) and malondialdehyde level (MDA) in gills and digestive glands. An increase in MDA level and a decrease in SOD and GSH activities were observed in gill of mussels exposed to 10 mg L^-1 nano-TiO₂. This effect was more severe in mussels kept at pH 7.3 as compared to pH 8.1. A different response was observed in the digestive gland as SOD, CAT and GSH levels increased in mussels exposed to nano-TiO₂. These contrasting results in digestive glands and gills were only evident at high concentration of nano-TiO₂ and low pH. A 7 days recovery period was not sufficient to fully restore SOD, GPx, GST, GSH and MDA levels to levels before exposure to nano-TiO₂ and low pH. Overall, our results confirmed that seawater acidification modulates effects of nanoparticles in mussels, and that gills are more sensitive to these stressors as compared with digestive glands.

Effects of ZnO nanoparticles in the Caspian roach (Rutilus rutilus caspicus)

Most studies investigating the toxicity of zinc oxide nanoparticles (ZnO NPs) focused on the effect of size, whereas exposure concentration and duration remained poorly understood. In this study, the effect of acute and sub-acute exposures of ZnO NPs on Zn compartmentalization and biomarkers' expression were investigated in Rutilus rutilus caspicus (Caspian roach) considering various exposure scenarios: i) the assessment of the concentration-response curves and median lethal concentration (LC₅₀); ii) the assessment of the effects of organisms exposed at LC₅₀ value and one tenth of LC₅₀ value of ZnO NPs suspensions for 4 d and 28 d, respectively; iii) the assessment of 14 d depuration period. The same concentrations of ZnSO₄ were investigated. The highest Zn accumulation was detected in gill after sub-acute exposure (4.8 mg/L; 28 d) followed by liver, kidney and muscle. In gill, liver and muscle, Zn from Zn NPs accumulated higher concentrations. Depuration (14 d) decreased Zn content in each organ, but no complete removal occurred except for muscle. Biomarkers' activity was significantly over expressed after treatments, but depuration brought back their values to background levels and most effects were related to acute concentrations (48 mg/L; 4 d) and in presence of ZnSO₄. Histopathological analyses showed that the exposure to ZnO NPs increased lesions in gill, liver and kidney, with a direct proportionality between alterations and Zn accumulated in the target organs. After depuration, lesions regressed for both ZnO NPs and ZnSO₄, but not in a complete way. These data could contribute to increase the knowledge about ZnO NPs risk assessment in aquatic vertebrates, suggesting that the size of ZnO NPs can influence biomarker and histopathological effects.

Metabolomic and oxidative effects of quantum dots-indolicidin on three generations of Daphnia magna

This study evaluated the effect of QDs functionalized with the antimicrobial peptide indolicidin on oxidative stress and metabolomics profiles of Daphnia magna across three generations (F0, F1, and F2). Exposing D. magna to sub-lethal concentrations of the complex QDs-indolicidin, a normal survival of daphnids was observed from F0 to F2, but a delay of first brood, fewer broods per female, a decrease of length of about 50% compared to control. In addition, QDs-indolicidin induced a significantly higher production of reactive oxygen species (ROS) gradually in each generation and an impairment of enzymes response to oxidative stress such as superoxide dismutase (SOD), catalase (CAT) and glutathione transferase (GST). Effects were confirmed by metabolomics profiles that pointed out a gradual decrease of metabolomics content over the three generations and a toxic effect of QDs-indolicidin likely related to the higher accumulation of ROS and decreased antioxidant capacity in F1 and F2 generations. Results highlighted the capability of metabolomics to reveal an early metabolic response to stress induced by environmental QDs-indolicidin complex.

Silver engineered nanoparticles in freshwater systems - Likely fate and behaviour through natural attenuation processes

Growth in the nanotechnology sector is likely introducing unnatural formations of materials on the nanoscale (10^-9m) to the environment. Disposal and degradation of products incorporating engineered nanomaterials (ENMs) are likely being released into natural aquatic systems un-intentionally primarily via waste water effluents. The fate and behaviour of metallic based nanoparticles (NPs) such as silver (Ag) in aquatic waters is complex with high levels of variability and uncertainty. In-situ physical, biological and chemical (natural attenuation) processes are likely to influence ENM fate and behaviour in freshwater systems. Surfaced functionalized particles may inhibit or limit environmental transformations which influence particle aggregation, mobility, dissolution and eco-toxic potential. This paper focuses on ENM characteristics and the influence of physical, chemical and biological processes occurring in aquatic systems that are likely to impact metallic ENMs fate. A focus on silver NPs (while for comparison, reporting about other metallic ENMs as appropriate) released to aquatic systems is discussed relating to their likely fate and behaviour in this dynamic and complex environment. This paper further highlights the need for specific risk assessment approaches for metallic ENMs and puts this into context with regard to informing environmental policy and potential NP influence on environmental/human health.