Toxicity of mixtures of zinc oxide and graphene oxide nanoparticles to aquatic organisms of different trophic level: particles outperform dissolved ions

Joint Toxicity and Interaction of Carbon-Based Nanomaterials with Co-Existing Pollutants in Aquatic Environments: A Review

This review paper focuses on the joint toxicity and interaction of carbon-based nanomaterials (CNMs) with co-existing pollutants in aquatic environments. It explores the potential harmful effects of chemical mixtures with CNMs on aquatic organisms, emphasizing the importance of scientific modeling to predict mixed toxic effects. The study involved a systematic literature review to gather information on the joint toxicity and interaction between CNMs and various co-contaminants in aquatic settings. A total of 53 publications were chosen and analyzed, categorizing the studies based on the tested CNMs, types of co-contaminants, and the used species. Common test models included fish and microalgae, with zebrafish being the most studied species. The review underscores the necessity of conducting mixture toxicity testing to assess whether the combined effects of CNMs and co-existing pollutants are additive, synergistic, or antagonistic. The development of in silico models based on the solid foundation of research data represents the best opportunity for joint toxicity prediction, eliminating the need for a great quantity of experimental studies.

Single and combined effects of titanium (TiO2) and zinc (ZnO) oxide nanoparticles in the rainbow trout gill cell line RTgill-W1

Understanding the environmental impact of nanoparticle (NP) mixtures is essential to accurately assess the risk they represent for aquatic ecosystems. However, although the toxicity of individual NPs has been extensively studied, information regarding the toxicity of combined NPs is still comparatively rather scarce. Hence, this research aimed to investigate the individual and combined toxicity mechanisms of two widely consumed nanoparticles, zinc oxide (ZnO NPs) and titanium dioxide (TiO2 NPs), using an in vitro model, the RTgill-W1 rainbow trout gill epithelial cell line. Sublethal concentrations of ZnO NPs (0.1 µg mL-1) and TiO2 (30 µg mL-1) and a lethal concentration of ZnO NPs causing 10% mortality (EC10, 3 µg mL-1) were selected based on cytotoxicity assays. Cells were then exposed to the NPs at the selected concentrations alone and to their combination. Cytotoxicity assays, oxidative stress markers, and targeted gene expression analyses were employed to assess the NP cellular toxicity mechanisms and their effects on the gill cells. The cytotoxicity of the mixture was identical to the one of ZnO NPs alone. Enzymatic and gene expression (nrf2, gpx, sod) analyses suggest that none of the tested conditions induced a strong redox imbalance. Metal detoxification mechanisms (mtb) and zinc transportation (znt1) were affected only in cells exposed to ZnO NPs, while tight junction proteins (zo1 and cldn1), and apoptosis protein p53 were overexpressed only in cells exposed to the mixture. Osmoregulation (Na + /K + ATPase gene expression) was not affected by the tested conditions. The overall results suggest that the toxic effects of ZnO and TiO2 NPs in the mixture were significantly enhanced and could result in the disruption of the gill epithelium integrity. This study provides new insights into the combined effects of commonly used nanoparticles, emphasizing the importance of further investigating how their toxicity may be influenced in mixtures.

The impact of nTiO2 and GO (graphene oxide), and their combinations, on freshwater Chlorella sp.: a comparative study in lake water and BG-11 media

Titanium dioxide nanoparticles (nTiO2) and graphene oxide (GO) are extensively used nanomaterials in various products and applications. Freshwater ecosystems are a crucial sink for these pollutants, posing severe threats to aquatic organisms. Although multiple studies have investigated the pristine toxicity of nTiO2 and GO in freshwater organisms, the combined toxicity of these materials remains unexplored. Interaction media is a crucial factor in evaluating toxicity nanomaterial toxicity towards algae. In this study, we have investigated the comparative effect of sterilized and filtered freshwater and BG-11 medium on the pristine and combined toxicity of nTiO2 and GO on freshwater algae Chlorella sp. Results indicated that the combination of nTiO2 and GO showed more toxicity when compared to their respective pristine forms. This could be due to the additive effect exhibited by nTiO2 and GO on Chlorella sp. The enhanced growth inhibition for the combined toxicity was in the order of 1 mg L-1 nTiO2 + 1 mg L-1 GO > 1 mg L-1 nTiO2 + 0.1 mg L-1 GO > 0.1 mg L-1 nTiO2 + 1 mg L-1 GO > 0.1 mg L-1 nTiO2 + 0.1 mg L-1 GO. All test groups that interacted in BG-11 media exhibited less toxicity when compared to corresponding groups in the lake water medium. This could be attributed to the cushioning effect of BG-11 medium, providing supplementary nutrition to the algal cells. This signifies that the environmentally relevant conditions could be more detrimental than the laboratory conditions. This study elucidates valuable insights into the potential detrimental effects associated with the combination of nTiO2 and GO on freshwater algae. Furthermore, we have evaluated the growth inhibition, oxidative stress, and photosynthetic activity of Chlorella sp. in both environmentally relevant interaction medium and well-defined culture medium.

Biomedical application of TiO2NPs can cause arterial thrombotic risks through triggering procoagulant activity, activation and aggregation of platelets

BACKGROUND

Titanium dioxide nanoparticles (TiO2NPs) are widely used in medical application. However, the relevant health risk has not been completely assessed, the potential of inducing arterial thrombosis (AT) in particular.

METHODS

Alterations in platelet function and susceptibility to arterial thrombosis induced by TiO2NPs were examined using peripheral blood samples from healthy adult males and an in vivo mouse model, respectively.

RESULTS

Here, using human platelets (hPLTs) freshly isolated from health volunteers, we demonstrated TiO2NP treatment triggered the procoagulant activity of hPLTs through phosphatidylserine exposure and microvesicles generation. In addition, TiO2NP treatment increased the levels of glycoprotein IIb/IIIa and P-selectin leading to aggregation and activation of hPLTs, which were exacerbated by providing physiology-mimicking conditions, including introduction of thrombin, collagen, and high shear stress. Interestingly, intracellular calcium levels in hPLTs were increased upon TiO2NP treatment, which were crucial in TiO2NP-induced hPLT procoagulant activity, activation and aggregation. Moreover, using mice in vivo models, we further confirmed that TiO2NP treatment a reduction in mouse platelet (mPLT) counts, disrupted blood flow, and exacerbated carotid arterial thrombosis with enhanced deposition of mPLT.

CONCLUSIONS

Together, our study provides evidence for an ignored health risk caused by TiO2NPs, specifically TiO2NP treatment augments procoagulant activity, activation and aggregation of PLTs via calcium-dependent mechanism and thus increases the risk of AT.

Immunomodulatory effects of single and combined exposure to ZnO and TiO2 nanoparticles on rainbow trout challenged with Aeromonas salmonicida achromogenes

The increasing release of engineered nanoparticles (ENPs) in aquatic ecosystems stresses the need for stringent investigations of nanoparticle mixture toxicity towards aquatic organisms. Here, the individual and combined immunotoxicity of two of the most consumed ENPs, the ZnO and the TiO2 ones, was investigated on rainbow trout juveniles (Oncorhynchus mykiss). Fish were exposed to environmentally realistic concentrations (21 and 210 µg L-1 for the ZnO and 210 µg L-1 for the TiO2) for 28 days, and then challenged with the pathogenic bacterium, Aeromonas salmonicida achromogenes. Antioxidant and innate immune markers were assessed before and after the bacterial infection. None of the experimental conditions affected the basal activity of the studied innate immune markers and the redox balance. However, following the bacterial infection, the expression of genes coding for pro and anti-inflammatory cytokines (il1β and il10), as well as innate immune compounds (mpo) were significantly reduced in fish exposed to the mixture. Conversely, exposure to ZnO NPs alone seemed to stimulate the immune response by enhancing the expression of the IgM and c3 genes for instance. Overall, our results suggest that even though the tested ENPs at their environmental concentration do not strongly affect basal immune functions, their mixture may alter the development of the immune response when the organism is exposed to a pathogen by interfering with the inflammatory response.

A critical review on fate, behavior, and ecotoxicological impact of zinc oxide nanoparticles on algae

The rapid inclusion of zinc oxide nanoparticles (ZnO NPs) in nanotechnology-based products over the last decade has generated a new threat in the apprehension of the environment. The massive use of zinc nanosized products will certainly be disposed of and be released, eventually entering the aquatic ecosystem, posing severe environmental hazards. Moreover, nanosized ZnO particles owing the larger surface area per volume exhibit different chemical interactions within the aquatic ecosystem. They undergo diverse potential transformations because of their unique physiochemical properties and the feature of receiving medium. Therefore, assessment of their impact is critical not only for scavenging the present situation but also for preventing unintended environmental hazards. Algae being a primary producer of the aquatic ecosystem help assess the risk of massive NPs usage in environmental health. Because of their nutritional needs and position at the base of aquatic food webs, algal indicators exhibit relatively unique information concerning ecosystem conditions. Moreover, algae are presently the most vital part of the circular economy. Hence, it is imperative to understand the physiologic, metabolic, and morphologic changes brought by the ZnO NPs to the algal cells along with the development of the mechanism imparting toxicity mechanism. We also need to develop an appropriate scientific strategy in the innovation process to restrain the exposure of NPs at safer levels. This review provides the details of ZnO NP interaction with algae. Moreover, their impact, mechanism, and factors affecting toxicity to the algae are discussed.

Environmental and Health Impacts of Graphene and Other Two-Dimensional Materials: A Graphene Flagship Perspective

Two-dimensional (2D) materials have attracted tremendous interest ever since the isolation of atomically thin sheets of graphene in 2004 due to the specific and versatile properties of these materials. However, the increasing production and use of 2D materials necessitate a thorough evaluation of the potential impact on human health and the environment. Furthermore, harmonized test protocols are needed with which to assess the safety of 2D materials. The Graphene Flagship project (2013-2023), funded by the European Commission, addressed the identification of the possible hazard of graphene-based materials as well as emerging 2D materials including transition metal dichalcogenides, hexagonal boron nitride, and others. Additionally, so-called green chemistry approaches were explored to achieve the goal of a safe and sustainable production and use of this fascinating family of nanomaterials. The present review provides a compact survey of the findings and the lessons learned in the Graphene Flagship.

Single and mixture toxicity of cadmium and copper to swim bladder in early life stages of Japanese medaka (Oryzias latipes)

Toxicity observed in aquatic ecosystems often cannot be explained by the action of a single pollutant. Likewise, evaluation standards formulated by a single effect cannot truly reflect the environmental quality requirements. The study of mixtures is needed to provide environmental relevance and knowledge of combined toxicity. In this study, the embryos of Japanese medaka (Oryzias latipes) were treated with individual and binary mixture of copper (Cu) and cadmium (Cd) until 12 days post-fertilization (dpf). Hatching, mortality, development, histology and gene expression were assessed. Our results showed that the highest concentration mixture of Cd (10 mg/L) and Cu (1 mg/L) affected survival, hatching time and hatching success. Occurrence of uninflated swim bladder was the highest (value) with exposure to 10 mg/L Cd. Swim bladder was commonly over-inflated in a mixture (0.1 mg/L Cd + 1.0 mg/L Cu) exposure. Individuals exposed to the mixture (0.1 Cd + 1.0 Cu mg/L) showed up to a 7.69% increase in swim bladder area compared to the control group. The mixtures containing 0.1 or 10 mg/L Cd, each with 1.0 mg/L Cu resulted in significantly increased of Pbx1b expression, higher than any Cd or Cu alone (p < 0.01). In the co-exposure group (0.1/10 Cd + 1.0 Cu mg/L), Pbx1b expression was found at 12 dpf but not 7 dpf in controls. Higher concentrations of Cd may progressively reduce Pbx1b expression, potentially explaining why 75% of individuals in the 10 mg/L Cd group failed to inflate their swim bladders. Additionally, the swim bladder proved to be a valuable bio-indicator for biological evaluation.

Ecotoxicological effects of zinc oxide nanoparticles (ZnO-NPs) on aquatic organisms: Current research and emerging trends

The rapid advancement of nanotechnology has contributed to the development of several products that are being released to the consumer market without careful analysis of their potential impact on the environment. Zinc oxide nanoparticles (ZnO-NPs) are used in several fields and are applied in consumer products, technological innovations, and biomedicine. In this sense, this study aims to compile existing knowledge regarding the effects of ZnO-NPs on non-target organisms, with the goal of ensuring the safety of human health and the environment. To achieve this objective, a systematic review of the available data on the toxicity of these nanomaterials to freshwater and marine/estuarine aquatic organisms was carried out. The findings indicate that freshwater invertebrates are the most commonly used organisms in ecotoxicological tests. The environmental sensitivity of the studied species was categorized as follows: invertebrates > bacteria > algae > vertebrates. Among the most sensitive species at each trophic level in freshwater and marine/estuarine environments are Daphnia magna and Paracentrotus lividus; Escherichia coli and Vibrio fischeri; Scenedesmus obliquus and Isochrysis galbana; and Danio rerio and Rutilus caspicus. The primary mechanisms responsible for the toxicity of ZnO-NPs involve the release of Zn2+ ions and the generation of reactive oxygen species (ROS). Thus, the biosynthesis of ZnO-NPs has been presented as a less toxic form of production, although it requires further investigation. Therefore, the synthesis of the information presented in this review can help to decide which organisms and which exposure concentrations are suitable for estimating the toxicity of nanomaterials in aquatic ecosystems. It is expected that this information will serve as a foundation for future research aimed at reducing the reliance on animals in ecotoxicological testing, aligning with the goal of promoting the sustainable advancement of nanotechnology.

Life-cycle risk assessment of graphene-enabled textiles in fire protection gear

A nanomaterial life-cycle risk assessment (Nano LCRA) of a graphene-enabled textile used in the construction of heat and fire-resistant personal protective equipment (PPE) was conducted to develop, analyze, and prioritize potential occupational, health and environmental risks. The analysis identifies potential receptors and exposure pathways at each product life-cycle stage and makes a qualitative evaluation of the potential significance of each scenario. A literature review, quality evaluation, and database were developed as part of the LCRA to identify potential hazards associated with graphene-based materials (GBMs) throughout the product life-cycle. Generally, risks identified from graphene-enabled textiles were low. Of the developed exposure scenarios, occupational inhalation exposures during raw material and product manufacturing ranked highest. The analysis identifies the key potential human and environmental hazards and exposures of the products across the product life-cycle of graphene enabled textiles. Priority research gaps to reduce uncertainty include evaluating long-term, low dose graphene exposures typical of the workplace, as well as the potential release and hazard characterization of graphene-acrylic nanocomposites.

Effect of long-term exposure of mixture of ZnO and CuO nanoparticles on Scenedesmus obliquus

The present study investigated the possible toxic effect of ZnO and CuO nanoparticles (NPs) on freshwater microalgae, Scenedesmus obliquus at environmentally- relevant nanoparticle concentration (1 mg/L) and high concentration (10 mg/L) in BG-11 medium under white light LED-illumination over 35 days. The effect of time on the stability of media, nanoparticles, and their relation to toxicity to algae was also studied. The transmission electron microscopy indicated structural damage to algae due to the presence of a mixture of nanoparticles (at 10 mg/L). FTIR (Fourier Transform infrared) analysis of a sample containing a mixture of nanoparticles showed an addition of bonds and a difference in the peak location and its intensity values. The inhibition time for biomass was observed between 14 days and 21 days at 10 mg/L NPs. At 1 mg/L, the order of toxicity of NPs to algae was found to be: CuO NPs (highest toxicity) > ZnO NPs>ZnO + CuO NPs (least toxicity). During exposure of algae cells to a mixture of NPs at 10 mg/L NP concentration, a smaller value of metal deposition was observed than that during exposure to individual NPs. Antagonistic toxic effects of two NPs on dry cell weight of algae was observed at both concentration levels. Future work is needed to understand the steps involved in toxicity due to mixture of NPs to algae so that environmental exposures of algae to NPs can be managed and minimized.

Ecotoxicity of a mixture of nanoparticles on algal species Scendesmus obliquus in OECD growth media, wastewater, and pond water

The possible impact of ZnO and CuO nanoparticles (NPs) (individually and in binary mixture) was investigated using the freshwater microalgae, Scenedesmus obliquus. The present study shows the effect of nanoparticles on algae in OECD growth media, wastewater, and pond water during a 96-h toxicity test. At 0.1 mg/L concentration of the mixture of NPs, the reduction in the chlorophyll a content was 13.61 ± 1.34% (OECD media), 28.83 ± 1.85% (wastewater), and 31.81 ± 2.23% (pond water). Values of reduction in biomass were observed to be 42.13 ± 1.38, 39.96 ± 1.03, and 33.10 ± 1.29% for OECD media, wastewater, and pond water, respectively. The highest increase in lipid values was observed in the case of pond water (6.3 ± 1.31%). A significant increase in the value of EPS-generated protein was observed in the wastewater sample. EPS-generated carbohydrate values were increased in OECD media but decreased in the wastewater matrix. The transmission electron microscope images showed structural damage to algae cells due to the exposure to a mixture of nanoparticles at higher concentrations. Fourier transform infrared analysis showed an addition of bonds and differences in the peak and its intensity during exposure to high concentrations of NPs. Overall, this study gives fundamental insights into the interaction and toxicity of a mixture of NPs to algal species in different water matrices.

Using Machine Learning to Predict Adverse Effects of Metallic Nanomaterials to Various Aquatic Organisms

The wide production and use of metallic nanomaterials (MNMs) leads to increased emissions into the aquatic environments and induces high potential risks. Experimentally evaluating the (eco)toxicity of MNMs is time-consuming and expensive due to the multiple environmental factors, the complexity of material properties, and the species diversity. Machine learning (ML) models provide an option to deal with heterogeneous data sets and complex relationships. The present study established an in silico model based on a machine learning properties-environmental conditions-multi species-toxicity prediction model (ML-PEMST) that can be applied to predict the toxicity of different MNMs toward multiple aquatic species. Feature importance and interaction analysis based on the random forest method indicated that exposure duration, illumination, primary size, and hydrodynamic diameter were the main factors affecting the ecotoxicity of MNMs to a variety of aquatic organisms. Illumination was demonstrated to have the most interaction with the other features. Moreover, incorporating additional detailed information on the ecological traits of the test species will allow us to further optimize and improve the predictive performance of the model. This study provides a new approach for ecotoxicity predictions for organisms in the aquatic environment and will help us to further explore exposure pathways and the risk assessment of MNMs.

Comparative toxicity assessment of individual, binary and ternary mixtures of SiO2, Fe3O4, and ZnO nanoparticles in freshwater microalgae, Scenedesmus obliquus: Exploring the role of dissolved ions

Metal oxide nanoparticles (NPs) are considered among the most prevalent engineered nanomaterials. To have a deeper understanding of the mode of action of multiple metal oxide nanoparticles in mixtures, we have used a unicellular freshwater microalga Scenedesmus obliquus as a model organism. The toxicity of silicon dioxide (SiO2), iron oxide (Fe3O4), and zinc oxide (ZnO) NPs was studied individually as well as in their binary (SiO2 + Fe3O4, Fe3O4 + ZnO, and ZnO + SiO2) and ternary (SiO2 + Fe3O4 + ZnO) combinations. The effects of metal ions from ZnO and Fe3O4 were investigated as well. The results observed from the study, showed that a significant amount of toxicity was contributed by the dissolved ions in the mixtures of the nanoparticles. Decreases in the cell viability, ROS generation, lipid peroxidation, antioxidant enzyme activity, and photosynthetic efficiency were analyzed. Among all the individual particles, ZnO NPs showed the maximum effects and increased the toxicities of the binary mixtures. The binary and ternary mixtures of the NPs clearly showed increased toxic effects in comparison with the individual entities. However, the ternary combination had lesser toxic effects than the binary combination of Fe3O4 + ZnO. The decline in cell viability and photosynthetic efficiency were strongly correlated with various oxidative stress biomarkers emphasizing the crucial role of reactive oxygen species in inducing the toxic effects. The findings from this study highlight the importance of evaluating the combinatorial effects of various metal oxide NPs as part of a comprehensive ecotoxicity assessment in freshwater microalgae.

Assessment of Genotoxicity of Zinc Oxide Nanoparticles Using Mosquito as Test Model

The widespread applications of ZnO NPs in the different areas of science, technology, medicine, agriculture, and commercial products have led to increased chances of their release into the environment. This created a growing public concern about the toxicological and environmental effects of the nanoparticles. The impact of these NPs on the genetic materials of living organisms is documented in some cultured cells and plants, but there are only a few studies regarding this aspect in animals. In view of this, the present work regarding the assessment of the genotoxicity of zinc oxide nanoparticles using the mosquito Culex quinquefaciatus has been taken up. Statistically significant chromosomal aberrations over the control are recorded after the exposure of the fourth instar larvae to a dose of less than LD20 for 24 h. In order to select this dose, LD20 of ZnO NPs for the mosquito is determined by Probit analysis. Lacto-aceto-orcein stained chromosomal preparations are made from gonads of adult treated and control mosquitoes. Both structural aberrations, such as chromosomal breaks, fragments, translocations, and terminal fusions, resulting in the formation of rings and clumped chromosomes, and numerical ones, including hypo- and hyper-aneuploidy at metaphases, bridges, and laggards at the anaphase stage are observed. The percentage frequency of abnormalities in the shape of sperm heads is also found to be statistically significant over the controls. Besides this, zinc oxide nanoparticles are also found to affect the reproductive potential and embryo development as egg rafts obtained from the genetic crosses of ZnO nanoparticle-treated virgin females and normal males are small in size with a far smaller number of eggs per raft. The percentage frequencies of dominant lethal mutations indicated by the frequency of unhatched eggs are also statistically significant (p < 0.05) over the control. The induction of abnormalities in all of the three short-term assays studied during the present piece of work indicates the genotoxic potential of ZnO NPs, which cannot be labeled absolutely safe, and this study pinpoints the need to develop strategies for the protection of the environment and living organisms thriving in it.

Nano-based smart formulations: A potential solution to the hazardous effects of pesticide on the environment

Inefficient usage, overdose, and post-application losses of conventional pesticides have resulted in severe ecological and environmental issues, such as pesticide resistance, environmental contamination, and soil degradation. Advances in nano-based smart formulations are promising novel methods to decrease the hazardous impacts of pesticide on the environment. In light of the lack of a systematic and critical summary of these aspects, this work has been structured to critically assess the roles and specific mechanisms of smart nanoformulations (NFs) in mitigating the adverse impacts of pesticide on the environment, along with an evaluation of their final environmental fate, safety, and application prospects. Our study provides a novel perspective for a better understanding of the potential functions of smart NFs in reducing environmental pollution. Additionally, this study offers meaningful information for the safe and effective use of these nanoproducts in field applications in the near future.

Toxicokinetics and Particle Number-Based Trophic Transfer of a Metallic Nanoparticle Mixture in a Terrestrial Food Chain

Herein, we investigated to which extent metallic nanoparticles (MNPs) affect the trophic transfer of other coexisting MNPs from lettuce to terrestrial snails and the associated tissue-specific distribution using toxicokinetic (TK) modeling and single-particle inductively coupled plasma mass spectrometry. During a period of 22 days, snails were fed with lettuce leaves that were root exposed to AgNO3 (0.05 mg/L), AgNPs (0.75 mg/L), TiO2NPs (200 mg/L), and a mixture of AgNPs and TiO2NPs (equivalent doses as for single NPs). The uptake rate constants (ku) were 0.08 and 0.11 kg leaves/kg snail/d for Ag and 1.63 and 1.79 kg leaves/kg snail/d for Ti in snails fed with NPs single- and mixture-exposed lettuce, respectively. The elimination rate constants (ke) of Ag in snails exposed to single AgNPs and mixed AgNPs were comparable to the corresponding ku, while the ke for Ti were lower than the corresponding ku. As a result, single TiO2NP treatments as well as exposure to mixtures containing TiO2NPs induced significant biomagnification from lettuce to snails with kinetic trophic transfer factors (TTFk) of 7.99 and 6.46. The TTFk of Ag in the single AgNPs treatment (1.15 kg leaves/kg snail) was significantly greater than the TTFk in the mixture treatment (0.85 kg leaves/kg snail), while the fraction of Ag remaining in the body of snails after AgNPs exposure (36%) was lower than the Ag fraction remaining after mixture exposure (50%). These results indicated that the presence of TiO2NPs inhibited the trophic transfer of AgNPs from lettuce to snails but enhanced the retention of AgNPs in snails. Biomagnification of AgNPs from lettuce to snails was observed in an AgNPs single treatment using AgNPs number as the dose metric, which was reflected by the particle number-based TTFs of AgNPs in snails (1.67, i.e., higher than 1). The size distribution of AgNPs was shifted across the lettuce-snail food chain. By making use of particle-specific measurements and fitting TK processes, this research provides important implications for potential risks associated with the trophic transfer of MNP mixtures.

Applicability of OECD TG 201, 202, 203 for the aquatic toxicity testing and assessment of 2D Graphene material nanoforms to meet regulatory needs

Tests using algae and/or cyanobacteria, invertebrates (crustaceans) and fish form the basic elements of an ecotoxicological assessment in a number of regulations, in particular for classification of a substance as hazardous or not to the aquatic environment according to the Globally Harmonised System of Classification and Labelling of Chemicals (GHS-CLP) (GHS, 2022) and the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals, EC, 2006). Standardised test guidelines (TGs) of the Organisation for Economic Co-operation and Development (OECD) are available to address the regulatory relevant endpoints of growth inhibition in algae and cyanobacteria (TG 201), acute toxicity to invertebrates (TG 202), and acute toxicity in fish (TG 203). Applying these existing OECD TGs for testing two dimensional (2D) graphene nanoforms may require more attention, additional considerations and/or adaptations of the protocols, because graphene materials are often problematic to test due to their unique attributes. In this review a critical analysis of all existing studies and approaches to testing used has been performed in order to comment on the current state of the science on testing and the overall ecotoxicity of 2D graphene materials. Focusing on the specific tests and available guidance's, a complete evaluation of aquatic toxicity testing for hazard classification of 2D graphene materials, as well as the use of alternative tests in an integrated approach to testing and assessment, has been made. This information is essential to ensure future assessments generate meaningful data that will fulfil regulatory requirements for the safe use of this "wonder" material.

Toxicity of Silver Nanoparticles in the Presence of Zinc Oxide Nanoparticles Differs for Acute and Chronic Exposures in Zebrafish

We assessed the acute toxicity effects (96 h) of silver nanoparticles (Ag NPs) and zinc oxide nanoparticles (ZnO NPs) and chronic (28 d) exposure to Ag NPs, including in combination with ZnO NPs. In the chronic studies, we further assessed the toxicokinetics and bioaccumulation of Ag and the resulting histopathological effects in the gill, intestine, and liver of zebrafish. Co-exposures with ZnO NPs reduced the toxicity of Ag NPs for acute (lethality) but enhanced the toxicity effects (tissue histopathology) for chronic exposures. The histological lesions for both NPs exposures in the gill included necrosis and fusion of lamellae, for the intestine necrosis and degeneration, and in the liver, mainly necrosis. The severity of the histological lesions induced by the Ag NPs was related to the amount of accumulated Ag in the zebrafish organs. The Ag accumulation in different organs was higher in the presence of ZnO NPs in the order of the gill > intestine > liver. Depuration kinetics illustrated the lowest half-life for Ag occurred in the gill and for the combined exposure of Ag with ZnO NPs. Our findings illustrate that in addition to tissue, time, and exposure concentration dependencies, the Ag NPs toxicity can also be influenced by the co-exposure to other NPs (here ZnO NPs), emphasizing the need for more combination exposure effects studies for NPs to more fully understand their potential environmental health risks.

Review and Prospects on the Ecotoxicity of Mixtures of Nanoparticles and Hybrid Nanomaterials

The rapid development of nanomaterials (NMs) and the emergence of new multicomponent NMs will inevitably lead to simultaneous exposure of organisms to multiple engineered nanoparticles (ENPs) at varying exposure levels. Understanding the joint impacts of multiple ENPs and predicting the toxicity of mixtures of ENPs are therefore evidently of importance. We reviewed the toxicity of mixtures of ENPs to a variety of different species, covering algae, bacteria, daphnia, fish, fungi, insects, and plants. Most studies used the independent-action (IA)-based model to assess the type of joint effects. Using co-occurrence networks, it was revealed that 53% of the cases with specific joint response showed antagonistic, 25% synergistic, and 22% additive effects. The combination of nCuO and nZnO exhibited the strongest interactions in each type of joint interaction. Compared with other species, plants exposed to multiple ENPs were more likely to experience antagonistic effects. The main factors influencing the joint response type of the mixtures were (1) the chemical composition of individual components in mixtures, (2) the stability of suspensions of mixed ENPs, (3) the type and trophic level of the individual organisms tested, (4) the biological level of organization (population, communities, ecosystems), (5) the exposure concentrations and time, (6) the endpoint of toxicity, and (7) the abiotic field conditions (e.g., pH, ionic strength, natural organic matter). This knowledge is critical in developing efficient strategies for the assessment of the hazards induced by combined exposure to multiple ENPs in complex environments. In addition, this knowledge of the joint effects of multiple ENPs assists in the effective prediction of hybrid NMs.

Application of α-Fe2O3 nanoparticles in controlling antibiotic resistance gene transport and interception in porous media

Metal oxide nanoparticles (MONPs) with a large specific surface area are expected to bind with antibiotic resistance genes (ARGs), thereby controlling ARGs' contamination by reducing their concentration and mobilization. Here, adsorption experiments were carried out and it was found that α-Fe₂O₃ NPs could chemically bind with ARGs (tetM-carrying plasmids) in water with an adsorption rate of 0.04 min^-1 and an adsorption capacity of 7.88 g/kg. Mixing α-Fe₂O₃ NPs into quartz sand column markedly increased the interceptive removal of ARGs from inflow water. The interception rate of 1.0 μg/mL ARGs in ultrapure water (25 mL, 5 pore volumes) through the sand column (plexiglass, length 8 cm, internal diameter 1.4 cm) with 1 g/kg α-Fe₂O₃ NPs was 1.73 times of that through the pure sand column; the interception rate overall increased with increasing addition of α-Fe₂O₃ NPs, reaching 68.8% with 20 g/kg α-Fe₂O₃ NPs. Coexisting Na⁺ (20 mM), Ca²⁺ (20 mM), and acidic condition (pH 4.0) could further increase the interception rate of ARGs by 1 g/kg α-Fe₂O₃ NPs from 21.1% to 86.2%, 90.7%, and 96.2%, respectively. The presence of PO₄^3- and humic acid at environmentally relevant concentrations would not significantly affect the interception of ARGs. In the treatment groups with PO₄^3- and humic acid, the removal rate decreased by only 1.8% and 0.1%, respectively. In addition, the interceptive removal of ARGs by α-Fe₂O₃ NPs-incorporated sand column was even better in actual surface water samples (87.2%) than that in the ultrapure water (21.1%). The findings provide a promising approach to treat ARGs-polluted water.

Alone and combined toxicity of ZnO nanoparticles and graphene quantum dots on microalgae Gymnodinium

Investigation of ZnO nanoparticles (nano-ZnO) and graphene quantum dots (GQDs) toxicology on dinoflagellate Gymnodinium helps to understand the effects of different surface characteristic nanoparticles on marine algae. The growth and biological responses of the algae exposed to 1, 10, 20 mg L^-1 nano-ZnO and GQDs in f/2 media were explored. Nano-ZnO showed slight effects on algal cells growth, while the growth inhibition rates of Gymnodinium increased as GQDs concentration increasing. Both nanoparticle treatments induced accumulation of reactive oxygen species and activated intracellular antioxidant defensive system, including SOD and ATPase, which were related to the two nanoparticles concentration. Under combined exposure of nano-ZnO and GQDs, the inhibitory effects decreased compared to the single GQDs and showed antagonistic effect. The addition of nano-ZnO could decrease the toxicity of GQDs due to aggregation and sedimentation interaction between nanoparticles. The morphologic change of the cells observed by SEM proved that nanoparticles adsorbed onto the cell surfaces and caused the cell shrinkage.

Co-exposure of zinc oxide nanoparticles and multi-layer graphenes in blackfish (Capoeta fusca): evaluation of lethal, behavioural, and histopathological effects

Zinc oxide nanoparticles (ZnO NPs) and multi-layer graphenes (MLGs) are widely used, and due to the lack of appropriate wastewater treatment may end up in the aquatic environment, with unknown consequences to biota. The main purpose of this study was to assess the acute toxicity, histopathological and behavioural changes caused by the exposure of ZnO NPs and MLGs, alone and combined, to the blackfish Capoeta fusca. The estimated mean 96 h-LC₅₀ for ZnO NPs was 4.9 mg L^-1 and 68.4 mg L^-1 for MLGs. In combination, MLGs increased the acute toxicity of the ZnO NPs. The effects of the different NPs on the gills included hyperplasia, aneurisms, and fusion of the lamellae. In the intestine, exposure to the NPs resulted in an increase in the number and swelling of goblet cells and tissue degeneration. Loss of balance, restlessness, erratic and abnormal swimming patterns were the most common behavioural changes seen in the ZnO NPs' exposed blackfish. In contrast with the acute toxicity findings, MLGs decreased the histopathological and behavioural effects of the ZnO NPs on both gills and intestinal tissues as well as fish behaviour. Our experimental results illustrated insights into the simultaneous exposure assessment of metal-based NPs and carbon nanomaterials, although further research is needed on the interactions exposure of these substances to interpreting the toxicological effects of metal-based nanomaterials seen in exposed organisms.

Individual and Binary Mixture Toxicity of Five Nanoparticles in Marine Microalga Heterosigma akashiwo

The investigation of the combined toxic action of different types of nanoparticles (NPs) and their interaction between each other and with aquatic organisms is an important problem of modern ecotoxicology. In this study, we assessed the individual and mixture toxicities of cadmium and zinc sulfides (CdS and ZnS), titanium dioxide (TiO₂), and two types of mesoporous silicon dioxide (with no inclusions (SMB3) and with metal inclusions (SMB24)) by a microalga growth inhibition bioassay. The counting and size measurement of microalga cells and NPs were performed by flow cytometry. The biochemical endpoints were measured by a UV-VIS microplate spectrophotometer. The highest toxicity was observed for SMB24 (EC50, 3.6 mg/L) and CdS (EC50, 21.3 mg/L). A combined toxicity bioassay demonstrated that TiO₂ and the SMB3 NPs had a synergistic toxic effect in combinations with all the tested samples except SMB24, probably caused by a “Trojan horse effect”. Sample SMB24 had antagonistic toxic action with CdS and ZnS, which was probably caused by metal ion scavenging.

Effects of natural organic matter on the joint toxicity and accumulation of Cu nanoparticles and ZnO nanoparticles in Daphnia magna

Various modern products have metallic nanoparticles (MNPs) embedded to enhance products performance. Technological advances enable nowadays even multiple hybrid nanoparticles. Consequently, the future co-release of multiple MNPs will inevitably result in the presence of MNP mixtures in the environment. An important question is if the responses of mixtures of MNPs can be dealt with in a similar way as with the responses of biota to mixtures of metal salts. Moreover, natural organic matter (NOM) is an important parameter affecting the behavior and effect of MNPs. Herein, we determined the joint toxicity and accumulation of copper nanoparticles (CuNPs) and zinc oxide nanoparticles (ZnONPs) in Daphnia magna in the absence and presence of Suwannee River natural organic matter (SR-NOM), compared to the joint toxicity and accumulation of corresponding metal salts. The results of toxicity testing showed that the joint toxicity of CuNPs + ZnONPs was greater than the single toxicity of CuNPs or ZnONPs. The joint toxic action of CuNPs + ZnONPs was additive or more-than-additive for D. magna. A similar pattern was found in the toxicity of the mixtures of Cu- and Zn-salts from the literature data. The presence of SR-NOM had no significant impact on the joint toxicity of CuNPs + ZnONPs. The calculated component-specific contribution to overall toxicity indicated that SR-NOM increased the relative contribution of dissolved ions released from the MNPs to the toxicity of the binary mixtures at high-effect concentrations of individual MNPs. Moreover, dissolved Zn-ions released from the ZnONPs were found to dominate the joint toxicity of CuNPs + ZnONPs in the presence of SR-NOM. Furthermore, the results of the accumulation experiment displayed that the presence of SR-NOM significantly enhanced the accumulation of either CuNPs or ZnONPs in D. magna exposed to the MNP mixtures.

Aquatic Toxicity Effects and Risk Assessment of 'Form Specific' Product-Released Engineered Nanomaterials

The study investigated the toxicity effects of 'form specific' engineered nanomaterials (ENMs) and ions released from nano-enabled products (NEPs), namely sunscreens, sanitisers, body creams and socks on Pseudokirchneriella subcapitata, Spirodela polyrhiza, and Daphnia magna. Additionally, risk estimation emanating from the exposures was undertaken. The ENMs and the ions released from the products both contributed to the effects to varying extents, with neither being a uniform principal toxicity agent across the exposures; however, the effects were either synergistic or antagonistic. D. magna and S. polyrhiza were the most sensitive and least sensitive test organisms, respectively. The most toxic effects were from ENMs and ions released from sanitisers and sunscreens, whereas body creams and sock counterparts caused negligible effects. The internalisation of the ENMs from the sunscreens could not be established; only adsorption on the biota was evident. It was established that ENMs and ions released from products pose no imminent risk to ecosystems; instead, small to significant adverse effects are expected in the worst-case exposure scenario. The study demonstrates that while ENMs from products may not be considered to pose an imminent risk, increasing nanotechnology commercialization may increase their environmental exposure and risk potential; therefore, priority exposure cases need to be examined.

Effect of ZnO nanoparticles on Zn, Cu, and Pb dissolution in a green bioretention system for urban stormwater remediation

Stormwater runoff from urban and suburban areas can carry hazardous pollutants directly into aquatic ecosystems. These pollutants, such as metals, nutrients, aromatic hydrocarbons, pesticides, and pharmaceuticals, are very toxic to aquatic organisms. Recently, significant amounts of zinc oxide engineered nanoparticles (ZnO-NPs) have been detected in urban stormwater and its bioretention systems. This raises concerns about a potential increase of stormwater toxicity and reduced performance of the treatment infrastructures. To tackle these issues, we developed a simple, low-cost bioretention system to remediate stormwater and retain ZnO-NPs. This system retained up to 73% Zn, 66% Cu, and >99% Pb. However, the removal efficiency for Pb was lower after adding ZnO-NPs to the system, possibly due to the remobilization of Pb phosphates. The effect of ZnO-NPs on stormwater toxicity and metal accumulation in wetland plants was also evaluated.

Behavior of engineered nanoparticles in aquatic environmental samples: Current status and challenges

The increasing use of engineered nanoparticles (ENPs) in consumer products has led to their increased presence in natural water systems. Here, we present a critical overview of the studies that analyzed the fate and transport behavior of ENPs using real environmental samples. We focused on cerium dioxide, titanium dioxide, silver, carbon nanotubes, and zinc oxide, the widely used ENPs in consumer products. Under field scale settings, the transformation rates of ENPs and subsequently their physicochemical properties (e.g., toxicity and bioavailability) are primarily influenced by the modes of interactions among ENPs and natural organic matter. Other typical parameters include factors related to water chemistry, hydrodynamics, and surface and electronic properties of ENPs. Overall, future nanomanufacturing processes should fully consider the health, safety, and environmental impacts without compromising the functionality of consumer products.

Graphene nanoplatelets and reduced graphene oxide elevate the microalgal cytotoxicity of nano-zirconium oxide

Novel products often have a multitude of nanomaterials embedded; likewise within many products graphite-based products are decorated with nano-zirconium oxide (nZrO₂) because graphene is an ultrahigh conductive material whereas nZrO₂ is for instance fire-retardant. As a consequence, the pristine/isolated nanoparticle has unique beneficial properties but it is no longer the only compound that needs to be considered in risk assessment. Data on joint toxicological implications are particularly important for the hazard assessment of multicomponent nanomaterials. Here, we investigated the mechanisms underlying the cytotoxicity induced by the co-occurrence of nZrO₂ and two graphene nanomaterials including graphene nanoplatelets (GNPs) and reduced graphene oxide (RGO) to the freshwater algae Chlorella pyrenoidosa. Exposure to GNPs and/or RGO induced enhanced cytotoxicity of nZrO₂ to the algae. Intracellular oxidative stress and cellular membrane functional changes in C. pyrenoidosa were the reason for the enhancement of toxicity induced by the binary mixtures of GNPs/RGO and nZrO₂. Furthermore, mitochondria-generated ROS played a major role in regulating the treatment-induced cellular response in the algae. Observations of cellular superficial- and ultra-structures indicated that the binary mixtures provoked oxidative damage to the algal cells. RGO increased the cytotoxicity and the extent of cellular oxidative stress to a higher extent than GNPs. These findings provide new insights that are of use in the risk assessment of mixtures of graphene-based carbon nanomaterials and other ENPs, and fit the new ideas on product testing that respects the combination effects.

Toxicity of a Binary Mixture of TiO2 and Imidacloprid Applied to Chlorella vulgaris

Nanoparticles have applications in various fields such as manufacturing and materials synthesis, the environment, electronics, energy harvesting, and medicine. Besides many applications of nanoparticles, further research is required for toxic environmental effect investigation. The toxic effect of titanium dioxide nanoparticles on the physiology of the green alga Chlorella vulgaris was studied with a widely used pesticide, imidacloprid (IMD). Chlorella vulgaris was exposed for 120 h in Bold's basal medium to different toxic compounds, such as (i) a high concentration of TiO₂ nanoparticles, 150-2000 mg/L, usually optimised in the photocatalytic degradation of wastewater, (ii) an extremely toxic pesticide for the aquatic environment, imidacloprid, in concentrations ranging from 5 to 40 mg/L, (iii) TiO₂ nanoparticles combined with imidacloprid, usually used in a photocatalytic system. The results show that the TiO₂ nanoparticles and IMD inhibited Chlorella vulgaris cell growth and decreased the biovolume by approximately 80% when 2 g/L TiO₂ was used, meaning that the cells devised a mechanism to cope with a potentially stressful situation; 120 h of Chlorella vulgaris exposure to 40 mg/L of IMD resulted in a 16% decreased cell diameter and a 41% decrease in cell volume relative to the control sample, associated with the toxic effect of pesticides on the cells. Our study confirms the toxicity of nanoparticles through algal growth inhibition with an effective concentration (EC50) value measured after 72 h of 388.14 mg/L for TiO₂ and 13 mg/L for IMD in a single-toxic system. The EC50 of TiO₂ slowly decreased from 258.42 to 311.11 mg/L when IMD from 5 to 20 mg/L was added to the binary-toxic system. The concentration of TiO₂ in the binary-toxic system did not change the EC50 for IMD, and its value was 0.019 g/L. The photodegradation process of imidacloprid (range of 5-40 mg/L) was also investigated in the algal medium incubated with 150-600 mg/L of titanium dioxide.

Mechanism of nanotoxicity in Chlorella vulgaris exposed to zinc and iron oxide

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Growth kinetics of C. vulgaris is influenced by NPs exposure.

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NPs exposure influence proline, carotenoid, activity of SOD, CAT and LDH.

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NPs exposure disintegrate cellular membrane.

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Zinc and iron oxide NPs are more toxic to C. vulgaris compared to bulk counterpart.

Usage of nanoparticle in various products has increased tremendously in the recent past. Toxicity of these nanoparticles can have a huge impact on aquatic ecosystem. Algae are the ideal organism of the aquatic ecosystem to understand the toxicity impact of nanoparticles. The present study focuses on the toxicity evaluation of zinc oxide (ZnO) and iron oxide (Fe₂O₃) nanoparticles towards freshwater microalgae, Chlorella vulgaris. The dose dependent growth retardation in Chlorella vulgaris is observed under ZnO and Fe₂O₃ nanoparticles and nanoform attributed more toxicity than their bulk counterparts. The IC₅₀ values of ZnO and Fe₂O₃ nanoparticles was reported at 0.258 mg L⁻¹ and 12.99 mg L^-1 whereas, for the bulk-form, it was 1.255 mgL^-1 and 17.88 mg L⁻¹, respectively. The significant decline in chlorophyll content and increase in proline content, activity of superoxide dismutase and catalase, indicated the stressful physiological state of microalgae. An increased lactate dehydrogenase level in treated samples suggested membrane disintegration by ZnO and Fe₂O₃ nanoparticles. Compound microscopy, scanning electron microscopy and transmission electron microscopy confirm cell entrapment, deposition of nanoparticles on the cell surface and disintegration of algal cell wall. Higher toxicity of nanoform in comparison to bulk chemistry is a point of concern.

Bioaccumulation and toxicokinetics of zinc oxide nanoparticles (ZnO NPs) co-exposed with graphene nanosheets (GNs) in the blackfish (Capoeta fusca)

In this study, we investigated the bioaccumulation and toxicokinetics of zinc oxide nanoparticles (ZnO NPs) alone and in the presence of graphene nanosheets (GNs) in the blackfish (Capoeta fusca). Blackfish were exposed via water to two ZnO NPs concentrations alone or as a combination with GNs and uptake of Zn into the gills, intestine, liver, and kidney was assessed at 7, 14 and 28 d. Zn elimination from these tissues was then assessed after a further 7, 14 and 28 d in clean water for both ZnO NPs concentrations and combined ZnO NPs/GN exposures. In the body tissues analyzed of exposed fish, the highest amounts of Zn occurred in the intestine and the lowest amount in the liver. Zn levels in blackfish after 28 d of exposure were higher in all treatment groups compared to those on 7 d (p < 0.05). For both ZnO NPs exposure concentrations, the highest amount of Zn was eliminated from the intestine, followed by the gills. Furthermore, elimination kinetics for both ZnO NPs concentrations alone and in combination with GNs showed that the shortest half-life for Zn is occurring in the intestine. Moreover, uptake rates of Zn in fish exposed to ZnO NPs + GNs followed the same pattern observed for the ZnO NP, with intestine and gills having the highest levels followed by kidney and liver. Thus, we show accumulation and elimination of Zn from ZnO NPs in blackfish depends on the tissue, exposure concentration and duration, and is dependent on the presence of GNs.

Status Quo in Data Availability and Predictive Models of Nano-Mixture Toxicity

Co-exposure of nanomaterials and chemicals can cause mixture toxicity effects to living organisms. Predictive models might help to reduce the intensive laboratory experiments required for determining the toxicity of the mixtures. Previously, concentration addition (CA), independent action (IA), and quantitative structure–activity relationship (QSAR)-based models were successfully applied to mixtures of organic chemicals. However, there were few studies concerning predictive models for toxicity of nano-mixtures before June 2020. Previous reviews provided comprehensive knowledge of computational models and mechanisms for chemical mixture toxicity. There is a gap in the reviewing of datasets and predictive models, which might cause obstacles in the toxicity assessment of nano-mixtures by using in silico approach. In this review, we collected 183 studies of nano-mixture toxicity and curated data to investigate the current data and model availability and gap and to derive research challenges to facilitate further experimental studies for data gap filling and the development of predictive models.

Combined Toxicity of TiO2 Nanospherical Particles and TiO2 Nanotubes to Two Microalgae with Different Morphology

The joint activity of multiple engineered nanoparticles (ENPs) has attracted much attention in recent years. Many previous studies have focused on the combined toxicity of different ENPs with nanostructures of the same dimension. However, the mixture toxicity of multiple ENPs with different dimensions is much less understood. Herein, we investigated the toxicity of the binary mixture of TiO₂ nanospherical particles (NPs) and TiO₂ nanotubes (NTs) to two freshwater algae with different morphology, namely, Scenedesmus obliquus and Chlorella pyrenoidosa. The physicochemical properties, dispersion stability, and the generation of reactive oxygen species (ROS) were determined in the single and binary systems. Classical approaches to assessing mixture toxicity were applied to evaluate and predict the toxicity of the binary mixtures. The results show that the combined toxicity of TiO₂ NPs and NTs to S. obliquus was between the single toxicity of TiO₂ NTs and NPs, while the combined toxicity to C. pyrenoidosa was higher than their single toxicity. Moreover, the toxicity of the binary mixtures to C. pyrenoidosa was higher than that to S. obliquus. A toxic unit assessment showed that the effects of TiO₂ NPs and NTs were additive to the algae. The combined toxicity to S. obliquus and C. pyrenoidosa can be effectively predicted by the concentration addition model and the independent action model, respectively. The mechanism of the toxicity caused by the binary mixtures of TiO₂ NPs and NTs may be associated with the dispersion stability of the nanoparticles in aquatic media and the ROS-induced oxidative stress effects. Our results may offer a new insight into evaluating and predicting the combined toxicological effects of ENPs with different dimensions and of probing the mechanisms involved in their joint toxicity.

Tradeoff between risks through ingestion of nanoparticle contaminated water or fish: Human health perspective

This study proposed a framework (termed as "nanoHealthRisk" hereafter) for incorporating i) interaction of nanoparticles (NPs) with fishes, ii) availability of NPs to the human digestive system, and iii) estimation of health risk due to fish consumption and inadvertent ingestion of NP-contaminated surface water, for the first time as per the literature review. The framework was applied for estimating health risks due to hypothetical exposures of pristine ZnO, CuO, and TiO₂ NPs (without any surface functionalization) from fish tissues. Values of bio- concentration factors (BCF) of ZnO, CuO, and TiO₂ NPs in fish and model distributions of bio-assimilation factor of ZnO, CuO and TiO₂ NPs in the human digestive system were incorporated explicitly in the risk assessment of NPs for the first time. ZnO NP was observed to be transferred more to the human digestive system from aqueous matrix than the other two NPs. Maximum allowable values of NP posing no risk were found to be 0.115 mg/L, 0.152 mg/L, and 1.77 × 10⁷ mg/L for pristine ZnO, CuO and TiO₂ NP, respectively. At the environmental concentration range, exposures of studied NPs from aquatic environment under the assumptions used did not pose any health risk under the conditions studied in this study. More work is required to (1) Estimate bio-concentration factors of a mixture of NPs with other constituents in fish tissues, (2) Estimate dissolution of NP from fish tissue in human digestive media, (3) Generate new data to develop reference dose of NP for human health risk assessment, and (4) Study effect of NP fate in the water on health risk through fish consumption pathway. Until all above-mentioned aspects are not explicitly incorporated in the risk assessment framework, risk estimates do not represent the risk from environment completely. Thus, continuous monitoring of these NPs in the environment is required to protect health due to chronic exposure of small concentrations of NPs from an aqueous matrix.

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.

Graphene-Like Layers from Carbon Black: In Vivo Toxicity Assessment

Graphene-like (GL) layers, a new graphene-related material (GRM), possess peculiar chemical, colloidal, optical and transport properties. Considering the very recent promising application of GL layers in biomedical and bioelectronic fields, it is of utmost importance to investigate the toxicological profile of these nanomaterials. This study represents an important first report of a complete in vivo toxicity assessment of GL layers on embryonic zebrafish (Danio rerio). Our results show that GL layers do not lead to any perturbations in the different biological parameters evaluated, indicating their good biocompatibility on a vertebrate model. The new insight into the biosafety of GL layers will expand their applications in nanomedicine.

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.

Effects of nanomaterials on metal toxicity: Case study of graphene family on Cd

The risk of heavy metal cadmium (Cd) on aquatic organisms has drawn widespread attentions, but the effects of nanomaterials (e.g. graphene (G)) on Cd toxicity are rarely clarified. It was known that mixture of contaminants may exhibit more severe impact than the individual metal. Here, we conducted a study systematically on the effects of nanomaterials on the toxicity of Cd to Scenedesmus Obliquus (S. obliquus) with or without the presence of graphene family materials (GFMs) derived from G, such as graphene oxide (GO) and amine-modified graphene (GNH). Our results showed that the influence of GFMs on the acute toxicity of Cd to S. obliquus is in the order of GO > G > GNH based on their EC₅₀ of Cd-GFMs. The effects of GFMs on the cytotoxicity and oxidative damage of Cd to S. obliquus are varied with the concentrations of GFMs. The differences between the effects of GFMs on Cd toxicity may attribute to their different surface oxygen-containing functional groups contained in the nanomaterials. The adsorption capacity of nanomaterials on metal ions, their dispersibility in water and their interaction mode with organisms, may dominate main contributions to their effects on Cd toxicity. Our study aids to clarify the interference of nanoparticles on the ecotoxicity of metals, to avoid the misunderstanding of the potential risk of metals in the complicate water environments.

Review on Activated Carbons by Chemical Activation with FeCl3

This study reviews the most relevant results on the synthesis, characterization, and applications of activated carbons obtained by novel chemical activation with FeCl3. The text includes a description of the activation mechanism, which compromises three different stages: (1) intense de-polymerization of the carbon precursor (up to 300 °C), (2) devolatilization and formation of the inner porosity (between 300 and 700 °C), and (3) dehydrogenation of the fixed carbon structure (>700 °C). Among the different synthesis conditions, the activation temperature, and, to a lesser extent, the impregnation ratio (i.e., mass ratio of FeCl3 to carbon precursor), are the most relevant parameters controlling the final properties of the resulting activated carbons. The characteristics of the carbons in terms of porosity, surface chemistry, and magnetic properties are analyzed in detail. These carbons showed a well-developed porous texture mainly in the micropore size range, an acidic surface with an abundance of oxygen surface groups, and a superparamagnetic character due to the presence of well-distributed iron species. These properties convert these carbons into promising candidates for different applications. They are widely analyzed as adsorbents in aqueous phase applications due to their porosity, surface acidity, and ease of separation. The presence of stable and well-distributed iron species on the carbons’ surface makes them promising catalysts for different applications. Finally, the presence of iron compounds has been shown to improve the graphitization degree and conductivity of the carbons; these are consequently being analyzed in energy storage applications.

Acute toxic effects caused by the co-exposure of nanoparticles of ZnO and Cu in rainbow trout

The toxic effects produced by the co-exposure to low- and non-toxic concentrations of zinc oxide (ZnONPs) and copper nanoparticles (CuNPs) was assessed in rainbow trout following the OECD Test Guideline 203. Four groups of trouts were exposed for 96 h to a range of concentrations (0.0425-0.34 mg/L) of CuNPs (50 nm) in combination with a fixed non-toxic concentration (1.25 mg/L) of ZnONPs (25 nm) determined from an independent concentration-response study. One additional group was exposed to the highest concentration of CuNPs alone. Behaviour and mortality were observed during the experiment. After 96 h exposure, accumulated levels of Cu and Zn in the fish were measured by ICP-MS and ICP-OES, respectively. The induction of oxidative stress in liver and gills was evaluated by the glutathione-S-transferase (GST) activity and the reduced glutathione (GSH) / oxidized glutathione (GSSG) ratio. The ethoxyresorufin-O-deethylase (EROD) activity was also assessed. The results showed that CuNPs at the highest tested concentration do not cause acute toxicity, whereas exposure to all mixtures caused mortality, which was inversely proportional to the concentration of CuNPs (from 28% to 86% survival). Accumulated levels of Cu and Zn in the fish increased with the increasing concentrations of CuNPs, suggesting that the presence of CuNPs favours the entry of Zn. In general, the GST activity increased significantly in the gills of co-exposed groups, whereas the GSH/GSSG ratio was altered in the liver. The EROD activity was not modified. In conclusion, the co-exposure to these NPs potentiates their toxicity, observing an alteration of the GST activity and GSH/GSSG ratio in gill and liver, which was more pronounced at the lowest concentration of CuNPs. The lower toxic effect observed with the highest concentrations of CuNPs coincides with a greater internalization of Zn.

Will the antimicrobial properties of ZnONPs turn it into a more suitable option than AgNPs for water filtration? Comparative study in the removal of fish pathogen, Aeromonas hydrophila from the culture of juvenile common carp (Cyprinus carpio)

The purpose of this study was to investigate the possibility of using zinc oxide nanoparticles (ZnONPs) instead of silver nanoparticles (AgNPs) for removing Aeromonas hydrophila from water used to culture Cyprinus carpio juvenile. Antibacterial materials as filter media were prepared by coating ZnONPs (two coating methods, referred as ZnA and ZnB) or AgNPs (referred as Ag) on the porous surfaces of zeolite beads. The characterization of coated samples was determined using FESEM, EDS, and GFAAS. The antibacterial activities of prepared samples were evaluated by the zone of inhibition test, tube test, and flow test. The diameter of inhibitory zones formed by ZnONP- and AgNP-coated zeolite beads was significantly higher than uncoated zeolite (control) (P < 0.05). Also, the tube test results revealed 100% killing of the bacterial cells after 24 h of contact to all coated materials. In the flow test (without fish), the antibacterial efficiency of filter columns that contained ZnA, ZnB, and Ag found to be 34.84, 23.77, and 100% after 96 h, respectively. The mortality rate of carp juveniles cultured in infected water treated with AgNP filters was significantly lower than those cultured in infected water or treated with ZnONPs filters (P < 0.05). The results indicated that although ZnONP filter media have somewhat antimicrobial properties (especially in vitro), their ability to complete removal of microorganisms from the water is not as high as AgNP filters. So, it still seems that zeolite coated with AgNPs has a higher potential for water disinfection in aquaculture.

Comparative toxicity evaluation of graphene oxide (GO) and zinc oxide (ZnO) nanoparticles on Drosophila melanogaster

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Synthesis and complete characterization of Green and Chemical Zinc Oxide nanoparticles and Graphene Oxide nanoparticles.

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Comparison of Graphene Oxide nanoparticles with Zinc oxide nanoparticles formed through both Green and Chemical route of synthesis.

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Comparative toxicity evaluation of these real world nanoparticles on Drosophila melanogaster using various assays.

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Observations revealed that different biological responses were caused in the flies due to these nanomaterials that proved their toxicity at different concentrations upon prolonged exposures.

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Cues to the prospect of these nanoparticles in the field of insect and pest management.

Engineered nanomaterials consisting of multiple nanoparticles (NPs) are finding their use in fields as wide and diverse as medicine, environment, cosmetics, energy and electronics. However, health and environmental impacts of these NPs need to be discerned individually to understand their true toxicity. Due to the promising application of upcoming material like GO-ZnO nanocomposite, the toxicity of ZnO and GO NPs was evaluated and compared individually in our study. This study compares the toxicity of Graphene Oxide (GO) NPs and Zinc Oxide (ZnO) NPs synthesized by Green method and Chemical method on Drosophila melanogaster. The GO, Chemical ZnO and Green ZnO NPs were synthesized and characterized using SEM, HR-TEM, FT-IR, UV–vis, EDX, XRD and DLS studies. NPs were comparatively analyzed for their cytotoxic and neurotoxic behaviors using different assays like MTT assay, mortality rate, larval crawling and climbing assay, total protein content analysis for evaluating the toxic potential of each of these NPs at different concentrations of use. Green ZnO were found to be least cytotoxic while Chemical ZnO caused the most cell damage. GO were found to have intermediary cytotoxicity. However, a different trend was observed with neurotoxicity wherein Green ZnO reportedly affected the neuromuscular coordination the most, while GO was found to have the least affect. This study provided insights into the different toxic effects caused by GO and ZnO NPs on Drosophila as well as comparative toxic effects of Chemical vs Green ZnO NPs.

Nonselective uptake of silver and gold nanoparticles by wheat

Metallic nanoparticles (NPs) show unique reactivity to crop plants, but the uptake mechanisms remain unclear. We quantitatively evaluated the phytoavailability of particles to wheat (Triticum aestivum L.) in hydroponics upon exposure to AgNPs (15 nm) or AuNPs (13 and 33 nm). Particles were physically separated from the released Ag ions by a dialysis membrane, under which particle-specific uptake of AgNPs could be discerned. Plants did not differentiate AgNPs and AuNPs during particle uptake, with uptake rate constants of 1.1 ± 0.1, 1.2 ± 0.3, and 1.2 ± 0.1 L kg^-1 h^-1 for AgNPs, AuNPs (13 nm), and AuNPs (33 nm), respectively. We found little effect of particle size (13 or 33 nm AuNPs) or core composition (Ag or Au) on particle bioavailability. Plants stimulated the subsequent uptake of Evans blue stain and showed cell damage in root tips. These results imply similar physiological processes involved in particle-specific uptake of AgNPs and AuNPs. The internalization of particles was further confirmed by single particle inductively coupled plasma mass spectrometry (spICP-MS) and transmission electron microscope-energy dispersive spectrometer (TEM-EDS) analysis. The work here builds the knowledge base for the nature of particle-specific uptake of different NP types by crop plants.

Toxic effect of different types of titanium dioxide nanoparticles on Ceriodaphnia dubia in a freshwater system

In the current study, the effect of different types of titanium dioxide (TiO₂) nanoparticles (NPs) (rutile, anatase, and mixture) was analyzed on Ceriodaphnia dubia in the presence of algae under distinct irradiation conditions such as visible and UV-A. The toxicity experiments were performed in sterile freshwater to mimic the chemical composition of the freshwater system. In addition, the oxidative stress biomarkers such as MDA, catalase, and GSH were analyzed to elucidate the stress induced by the NPs on daphnids. Individually, both rutile and anatase NPs induced similar mortality under both visible and UV-A irradiations at all the test concentrations except 600 and 1200 μM where rutile induced higher mortality under UV-A. Upon visible irradiation, the binary mixture exhibited a synergistic effect at their lower concentration and an additive effect at higher concentrations. In contrast, UV-A irradiation demonstrated the additive effect of mixture except for 1200 μM which elucidated antagonistic effect. Mathematical model confirmed the effects of the binary mixture. The surface interaction between the individual NPs in the form of aggregation played a pivotal role in the induction of specific effects exhibited by the binary mixture. Oxidative stress biomarkers were highly increased upon NPs exposure especially under visible irradiation. These observations elucidated that the irradiation and crystallinity effect of TiO₂ NPs were noted only on certain biomarkers and not on the mortality.

Ecotoxicological effects on Scenedesmus obliquus and Danio rerio Co-exposed to polystyrene nano-plastic particles and natural acidic organic polymer

The importance of attention to unravel the interaction of nano-plastic particles (NPs) with natural acidic organic polymer (NAOP) in freshwater environment should not be neglected. However, toxicological data available for the interaction between NPs and NAOP remain limited. Here, we investigate the toxicological effects of three model polystyrene (PS) NPs with different functional groups (unmodified, amino- and carboxyl-modified PS NPs) on two freshwater organisms of different trophic levels (Scenedesmus obliquus and Danio rerio) in the absence and presence of two classes of NAOP, namely fulvic acid and humic acid. The NAOP interaction with the NPs is shown to alter oxidative stress and disturb membrane function in S. obliquus cells to a certain extent. Combined oxidative stress responses to the NPs and NAOP in D. rerio as a function of their mixture levels showed inhibition, alleviation, and reinforce. Changes in cellular oxidative stress and membrane function depended on the concentration and types of both NPs and NAOP. Furthermore, the characterization parameters of the NPs were important for the explanation of the ecotoxicological mechanism of the NPs in the presence of NAOP. Our findings emphasized the critical role of NAOP in the fate and toxicity of plastic particles in freshwater environment.

Acute biotoxicity assessment of heavy metals in sewage sludge based on the glucose consumption of Escherichia coli

As a simple and feasible method for acute biotoxicity assessment, personal glucose meter (PGM) can be successfully applied in the early warning of environmental pollutants in sewage. In this paper, the acute biotoxicity of single and joint heavy metals in sewage and real sludge samples was systematically described based on the glucose metabolism of Escherichia coli (E. coli). Results indicated that the biotoxicity order of five single heavy metals in sewage was Hg2+ > As3+ > Cu2+ > Zn2+ > Cd2+. The joint heavy metals of Cu2+ + Zn2+, Cu2+ + Cd2+, and Cu2+ + Hg2+ produced synergistic effects, while Cu2+ + As3+ and Cd2+ + Zn2+ possessed antagonistic effects for the combined biotoxicity. In spiked sludge, Cd2+ and Zn2+ owned higher biotoxicity than Cu2+ and As3+. Notably, the electroplate factory and housing estate sludge respectively showed the highest and lowest inhibition rates as 57.4% and 17.7% under the real sludge biotoxicity assessment. These results demonstrated that PGM was a sensitive and portable method, which could be widely used for acute biotoxicity assessment of heavy metals in sewage sludge.

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.