Nanoparticle stability in lake water shaped by natural organic matter properties and presence of particulate matter

Tritiated stainless steel (nano)particle release following a nuclear dismantling incident scenario: Significant exposure of freshwater ecosystem benthic zone

Nuclear facilities continue to be developed to help meet global energy demands while reducing fossil fuel use. However, an incident during the dismantling of these facilities could accidentally release tritiated particles (e.g. stainless steel) into the environment. Herein, we investigated the environmental dosimetry, fate, and impact of tritiated stainless steel (nano)particles (1 mg.L-1 particles and 1 MBq.L-1 tritium) using indoor freshwater aquatic mesocosms to mimic a pond ecosystem. The tritium (bio)distribution and particle fate and (bio)transformation were monitored in the different environmental compartments over 4 weeks using beta counting and chemical analysis. Impacts on picoplanktonic and picobenthic communities, and the benthic freshwater snail, Anisus vortex, were assessed as indicators of environmental health. Following contamination, some tritium (∼16%) desorbed into the water column while the particles rapidly settled onto the sediment. After 4 weeks, the particles and the majority of the tritium (>80%) had accumulated in the sediment, indicating a high exposure of the benthic ecological niche. Indeed, the benthic grazers presented significant behavioral changes despite low steel uptake (<0.01%). These results provide knowledge on the potential environmental impacts of incidental tritiated (nano)particles, which will allow for improved hazard and risk management.

Removal efficiency and adsorption mechanisms of CeO2 nanoparticles onto granular activated carbon used in drinking water treatment plants

The presence of NPs in drinking water resources raises a global concern on their potential risk for human health, and whether or not drinking water treatment plants are able to effectively remove NPs to prevent their ingestion by humans. In this study, we investigate the efficiency of granular activated carbon (GAC), commonly used in conventional municipal water treatment processes, for the removal of CeO₂ NPs. In ultrapure water, NPs are found to have a good affinity for GAC and results indicate an increase in the adsorption capacity from 0.62 ± 0.10 to 5.05 ± 0.51 mg/g, and removal efficiency from 35 % ± 4 to 54 % ± 5 with increasing NPs concentration. Kinetic studies reveal that intraparticle diffusion is not the only rate controlling step indicating that mass transfer effect is also playing a role. Adsorption mechanisms are mainly controlled by the electrostatic attractions between the positively charged NPs and negatively charged GAC. Although electrostatic conditions in Lake Geneva water are less favorable for NPs adsorption, the adsorption capacity and removal efficiency are higher than in ultrapure water with values raising from 0.41 ± 0.17 to 7.13 ± 1.13 mg/g and 26 % ± 8 to 75 % ± 11, respectively. Furthermore, the external mass transfer process onto GAC surface is more important than for ultrapure water. NPs adsorption mechanism is explained by the presence of divalent cations and natural organic matter (NOM) which promote the formation of CeO₂ NPs-NOM-divalent cation heteroaggregates increasing both adsorption and removal efficiency by cation bridging.

Novelty Cosmetic Filters Based on Nanomaterials Composed of Titanium Dioxide Nanoparticles

The following work describes the synthesis of new physical filters based on TiO₂/SiO₂ and TiO₂/Ag nanostructures. Titanium dioxide nanoparticles (TiO₂ NPs) were applied as control material and a popular physical UV filter. The advantage of using materials on the nanometer scale is the elimination of the skin whitening effect that occurs when using photoprotective cosmetics containing titanium dioxide on a macro scale. In addition, the silica coating makes the material less harmful, and the silver coating enriches the material with antibacterial properties. Nanoparticles and nanostructures have been characterized by Energy Dispersive X-Ray Analysis (EDX), the Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), and Fourier-Transform Infrared Spectroscopy (FT-IR) methods. Due to the use of physical filters in anti-radiation protection cosmetics, water-in-oil (W/O) emulsion has been prepared. All cosmetic formulations have been tested for stability. The sun protection research with the Sun Protection Diagnostic SP37 was carried out. These studies made it possible to determine the natural sun protection time and to compare the synthesized materials. Furthermore, one of the most important parameters when describing this type of cosmetic is water resistance, which has also been measured. The results show that the new type of material of TiO₂/Ag used as a new physical filter in emulsion W/O shows the best sun protection compared with other obtained nanomaterials. It is most likely due to the improved optical properties of the combination of noble metals, for example, silver with TiO₂.

Cytotoxicity inhibition of catechol's type molecules by grafting on TiO2 and Fe2O3 nanoparticles surface

The potential toxicity deriving from the interaction between chemicals and manufactured nanoparticles (NPs) represents an emerging threat to the environment and human health. Several studies have focused on the risks and (eco)toxicity of manufactured NPs as a consequence of their extensive use in recent years, however, there is still a limited understanding of the combined effects caused by manufactured NPs in the presence of other environmental contaminants. This is particularly relevant to aquatic environments, where many types of pollutants are inevitably released and can be involved in many kinds of reactions. In this context, the interaction between catecholate type ligands and two different nanomaterials, namely TiO₂ and Fe₂O₃ NPs, was investigated by performing cytotoxicity assays with the topminnow fish hepatoma cell line (PLHC-1) using: i) the original organic molecules, ii) pristine NPs alone, and iii) modified NPs obtained by grafting the ligands on the NPs surface. Cytotoxic effects were explored at three different levels, specifically on cellular metabolism, membrane integrity and lysosomal activity. The outcomes from these assays showed cytotoxicity only for the free catechol type ligands, while in general no significant decrease in cell viability was observed for pristine NPs, as well as for the modified NPs, regardless the initial cytotoxicity level of the organic ligands These results suggest that the binding of catechols on the NPs' surface inhibited their cytotoxicity, indicating that TiO₂ and Fe₂O₃ NPs may act as sorbents of these contaminants, thus reducing their possible detrimental effects.

Colloidal stability classification of TiO2 nanoparticles in artificial and in natural waters by cluster analysis and a global stability index: Influence of standard and natural colloidal particles

In the field of exposure-driven risk assessment of engineered nanoparticles (NPs), the highly complex interactions of NPs with natural components in surface waters are considered key factors to understand their fate and behavior in the environment. However, since experimental approaches aiming at imitating environmentally relevant conditions include many parameters and lead to a high number of outcomes, statistical tools can be extremely useful to support the results' interpretation. In this context, a multimethod approach was applied to investigate the colloidal behavior of TiO₂ NPs in both artificial waters and natural brackish water (from the Venice lagoon, Italy), in the presence of standard kaolinite and natural organic matter (NOM), or of the fine fraction of natural colloidal particles (NCPs) from the lagoon sediment. In detail, the experimental data obtained, i.e. hydrodynamic size, surface charge and sedimentation velocity values, were i) statistically treated by hierarchical clustering and ii) merged into a global stability index (I_G). The hierarchical clustering allowed to group the dispersions into three colloidal stability classes, where the main discriminant was the medium composition (i.e. ionic strength and presence of NOM), while the I_G allowed to establish a colloidal stability ranking of the dispersions within each class. Moreover, the comparison among the different dispersions suggested that kaolinite could be considered as a suitable surrogate for NCPs, to estimate the colloidal behavior and environmental fate of TiO₂ NPs in natural aqueous media.

The suitable biomass carbon source for improving nitrogen removal in surface flow constructed wetland system: Fresh vs. withered

Plant biomass can be used as a carbon source to enhance the nitrogen removal effect. Related researches mainly focused on withered biomass, while little on fresh biomass. In this study, batch experiments revealed that the carbon release rate (60.5 mg TOC g^-1) of fresh biomass was significantly higher than that of withered biomass (44.9 mg TOC g^-1), while the nitrogen release rate showed the opposite trend. Compared with withered biomass, fresh biomass could release more sugar and less refractory humic acid, which means higher bioavailability. After adding fresh biomass, TN removal rate increased from 18.65% to 51.59%. The TN removal in the wetland adding withered biomass increased from 13.59% to 42.25%. The biomass addition had a slight impact on the effluent sensory quality in the first two days. After adding fresh biomass and withered biomass, the relative abundance of denitrifying bacteria like Flavobacterium and Pseudomonas in the system significantly increased. In general, fresh biomass was more suitable as a denitrification carbon source for surface flow constructed wetlands.

Fate and removal efficiency of polystyrene nanoplastics in a pilot drinking water treatment plant

Occurrence of microplastics and nanoplastics in aquatic systems, as well as in water compartments used to produce drinking water have become a major concern due to their impact on the environment and public health. Nanoplastics in particular, in regard to their fate and removal efficiency in drinking water treatment plants (DWTP), which ensure water quality and supply drinking water for human consumption have been, by far, rarely investigated. This study investigates the removal efficiency of polystyrene (PS) nanoplastics in a conventional water treatment plant providing drinking water for 500'000 consumers. For that purpose, a pilot-scale DWTP, located within the main treatment plant station, reproducing at a reduced scale the different processes and conditions of the main treatment plant is used. The results show that filtration process through sand and granular activated carbon (GAC) filters in the absence of coagulation achieves an overall nanoplastic removal of 88.1%. The removal efficiency of filtration processes is mainly attributed to physical retention and adsorption mechanisms. On the other hand, it is found that coagulation process greatly improves the removal efficiency of nanoplastics with a global removal efficiency equal to 99.4%. The effective removal efficiency of sand filtration increases considerably from 54.3% to 99.2% in the presence of coagulant, indicating that most of PS nanoplastics are removed during sand filtration process. The higher removal efficiency with the addition of coagulant is related to nanoplastics surface charge reduction and aggregation thus significantly increasing their retention in the filter media.

Toxic Effects and Mechanisms of Silver and Zinc Oxide Nanoparticles on Zebrafish Embryos in Aquatic Ecosystems

The global application of engineered nanomaterials and nanoparticles (ENPs) in commercial products, industry, and medical fields has raised some concerns about their safety. These nanoparticles may gain access into rivers and marine environments through industrial or household wastewater discharge and thereby affect the ecosystem. In this study, we investigated the effects of silver nanoparticles (AgNPs) and zinc oxide nanoparticles (ZnONPs) on zebrafish embryos in aquatic environments. We aimed to characterize the AgNP and ZnONP aggregates in natural waters, such as lakes, reservoirs, and rivers, and to determine whether they are toxic to developing zebrafish embryos. Different toxic effects and mechanisms were investigated by measuring the survival rate, hatching rate, body length, reactive oxidative stress (ROS) level, apoptosis, and autophagy. Spiking AgNPs or ZnONPs into natural water samples led to significant acute toxicity to zebrafish embryos, whereas the level of acute toxicity was relatively low when compared to Milli-Q (MQ) water, indicating the interaction and transformation of AgNPs or ZnONPs with complex components in a water environment that led to reduced toxicity. ZnONPs, but not AgNPs, triggered a significant delay of embryo hatching. Zebrafish embryos exposed to filtered natural water spiked with AgNPs or ZnONPs exhibited increased ROS levels, apoptosis, and lysosomal activity, an indicator of autophagy. Since autophagy is considered as an early indicator of ENP interactions with cells and has been recognized as an important mechanism of ENP-induced toxicity, developing a transgenic zebrafish system to detect ENP-induced autophagy may be an ideal strategy for predicting possible ecotoxicity that can be applied in the future for the risk assessment of ENPs.

Immunosafe(r)-by-design nanoparticles: Molecular targets and cell signaling pathways in a next-generation model proxy for humans

Nanotechnology research covers a wide field of studies pointing to design and shape complex matter in a scale between 1 and 100nm, with unique size-depending properties and applications. The value and potential of engineered nanoparticles in human diagnostics and therapies essentially relay on their safety and biocompatibility. Entering a cell, in fact, these particles take complex interactions with the surrounding biological environment, dramatically changing their own identity. The formation of a custom-made protein corona is the first signal of their interplay with the cell defensive mechanisms, and a major issue in their application in medicine. Preliminary in-depth studies in model organisms have been developed to assess immunological safety and competence in facing the host immune system and its defensive response. New affordable animal models are emerging in pilot nano-response and safety studies. Sea urchins, benthic marine Echinoderms, have a wide and very efficient immune system working with innate defense mechanisms and are widely used in immune studies. Nano-safety studies have been showing that the sea urchin Paracentrotus lividus displays an excellent sensing system and high defensive capability, joined to the availability of easily accessible immune cells. As in mammals, nanoparticle recognition and interaction activate specific signaling pathways, metabolic rewiring and homeostasis maintenance. In this chapter, we point to the value of planning new research and developing nano-immune studies using an easy nonmammalian next-generation model, able to unravel new specific response mechanisms to nanoparticles.

Emerging investigator series: metal nanoparticles in freshwater: transformation, bioavailability and effects on invertebrates

MNPs may undergo different environmental transformations in aquatic systems, consequently changing their mobility, bioavailability and toxicity to freshwater invertebrates.

Novel multimethod approach for the determination of the colloidal stability of nanomaterials in complex environmental mixtures using a global stability index: TiO2 as case study

A systematic study on the colloidal behavior of uncoated and polyvinylpyrrolidone (PVP) coated TiO₂ engineered nanomaterials (ENMs) in simulated aqueous media is herein reported, in which conditions representative for natural waters (pH, presence of divalent electrolytes (i.e. Ca²⁺/Mg²⁺ and SO₄^2-), of natural organic matter (NOM) and of suspended particulate matter (SPM)) were systematically varied. The colloidal stability of the different dispersions was investigated by means of Dynamic and Electrophoretic Light Scattering (DLS and ELS) and Centrifugal Separation Analysis (CSA), and a global stability index based on these three techniques was developed. The index allows to quantitatively classify the nano-based dispersions according to their colloidal stability affected by the different parameters studied. This multimethod approach clearly identifies inorganic SPM followed by divalent electrolytes as the main natural components destabilizing TiO₂ ENMs upon entering in simulated natural waters, while it highlights a moderate stabilization induced by NOM, depending mainly on pH. Moreover, the PVP coating was found to attenuate the influence of these parameters on the colloidal stability. The obtained results show how the global stability index developed is influenced by the complexity of the system, suggesting the importance of combining the information gathered from all the techniques employed to better elucidate the fate and behavior of ENMs in natural surface waters.

Formation and evolution of the nanoparticle environmental corona: The case of Au and humic acid

Studying the behaviour of nanomaterials after their release into natural water is essential to understand the risk associated to their environmental exposure. In particular, the interaction and adsorption of dissolved organic matter onto nanoparticles strongly influence the behaviour and fate of nanomaterials in natural water systems. We herein study the interaction of Au and Ag nanoparticles and humic acids, the principal component of natural dissolved organic matter. Physicochemical characterization results showed the formation of an organic matter corona, consisting of two layers: a "hard" one, firmly bound to the nanoparticle surface, and a "soft" one, in dynamic equilibrium and, consequently, highly dependent on the media organic matter concentration. The extent of the electro-steric stabilization of the so called environmental corona depends on the size of the supramolecular association of humic acid (which depends on its hydrophilic and lipophilic moieties), the nanoparticle size, the total concentration of organic matter in the media, and the ratio between them. Interestingly, environmental coronas can eventually prevent Ca²⁺ and Mg²⁺ induced aggregation at concentrations range present in most of the freshwater bodies. The humic coating formed on top of the Au or control Ag nanoparticles presented a similar profile, but the corrodibility of Ag led to a more natural detachment of the corona. These results were further confirmed by exposing the nanoparticles to a model of natural water and standard mud (LUFA 2.2 dispersion). In the latter case, after several days, nanoparticle sedimentation was observed, which was attributed to interactions with macro organic and inorganic matter (fraction larger than particulate matter).

Finding Nano: Challenges Involved in Monitoring the Presence and Fate of Engineered Titanium Dioxide Nanoparticles in Aquatic Environments

In recent years, titanium dioxide (TiO2) has increasingly been used as an inorganic ultraviolet (UV) filter for sun protection. However, nano-TiO2 may also pose risks to the health of humans and the environment. Thus, to adequately assess its potential adverse effects, a comprehensive understanding of the behaviour and fate of TiO2 in different environments is crucial. Advances in analytical and modelling methods continue to improve researchers’ ability to quantify and determine the state of nano-TiO2 in various environments. However, due to the complexity of environmental and nanoparticle factors and their interplay, this remains a challenging and poorly resolved feat. This paper aims to provide a focused summary of key particle and environmental characteristics that influence the behaviour and fate of sunscreen-derived TiO2 in swimming pool water and natural aquatic environments and to review the current state-of-the-art of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) approaches to detect and characterise TiO2 nanoparticles in aqueous media. Furthermore, it critically analyses the capability of existing fate and transport models to predict environmental TiO2 levels. Four particle and environmental key factors that govern the fate and behaviour of TiO2 in aqueous environments are identified. A comparison of SP-ICP-MS studies reveals that it remains challenging to detect and characterise engineered TiO2 nanoparticles in various matrices and highlights the need for the development of new SP-ICP-MS pre-treatment and analysis approaches. This review shows that modelling studies are an essential addition to experimental studies, but they still lack in spatial and temporal resolution and mostly exclude surface transformation processes. Finally, this study identifies the use of Bayesian Network-based models as an underexplored but promising modelling tool to overcome data uncertainties and incorporates interconnected variables.

Release and fate of nanoparticulate TiO2 UV filters from sunscreen: Effects of particle coating and formulation type

Nanoparticulate mineral UV filters, such as titanium dioxide (TiO₂) nanocomposites, are being increasingly used in sunscreens as an alternative to organic UV filters. However, there is still a lack of understanding regarding their fate and behavior in aquatic environments and potential environmental impacts after being released from a bather's skin during recreational activities. In this work, we assessed the release, fate, and transformation of two commercial nanocomposite TiO₂ UV filters, one hydrophobic and one hydrophilic, in ultrapure water and simulated fresh- and seawater. The hydrophobic TiO₂ nanocomposite, T-SA, was coated with a primary Al₂O₃ photopassivation layer and a secondary stearic acid layer, while the hydrophilic TiO₂ nanocomposite, T-SiO₂, was coated with a single SiO₂ photopassivation layer. The influence of the sunscreen formulation was examined by dispersing the TiO₂ nanocomposites in their typical continuous phase (i.e., oil for T-SA and water for T-SiO₂) before introduction into the aqueous system. After 48 h of aqueous aging and 48 h of settling, 88-99% of the hydrophobic T-SA remained floating on top of the water column in all aqueous systems. On the other hand, 100% of the hydrophilic T-SiO₂ settled out of the water column in the fresh- and seawaters. With respect to the photopassivation coatings, no loss of the T-SA Al₂O₃ layer was detected after aqueous aging, but 99-100% dissolution of the SiO₂ layer on the T-SiO₂ nanocomposite was observed after 48 h in the fresh- and seawaters. This dissolution left behind T-SiO₂ by-products exhibiting a photocatalytic activity similar to that of bare rutile TiO₂. Overall, the results demonstrated that the TiO₂ surface coating and sunscreen formulation type drive environmental behavior and fate and that loss of the passivation layer can result in potentially harmful, photoactive by-products. These insights will help guide regulations and assist manufacturers in developing more environmentally safe sunscreens.

Gold nanoparticles coated with polyvinylpyrrolidone and sea urchin extracellular molecules induce transient immune activation

We report that the immunogenicity of colloidal gold nanoparticles coated with polyvinylpyrrolidone (PVP-AuNPs) in a model organism, the sea urchin Paracentrotus lividus, can function as a proxy for humans for in vitro immunological studies. To profile the immune recognition and interaction from exposure to PVP-AuNPs (1 and 10 μg mL^-1), we applied an extensive nano-scale approach, including particle physicochemical characterisation involving immunology, cellular biology, and metabolomics. The interaction between PVP-AuNPs and soluble proteins of the sea urchin physiological coelomic fluid (blood equivalent) results in the formation of a protein "corona" surrounding the NPs from three major proteins that influence the hydrodynamic size and colloidal stability of the particle. At the lower concentration of PVP-AuNPs, the P. lividus phagocytes show a broad metabolic plasticity based on the biosynthesis of metabolites mediating inflammation and phagocytosis. At the higher concentration of PVP-AuNPs, phagocytes activate an immunological response involving Toll-like receptor 4 (TLR4) signalling pathway at 24 hours of exposure. These results emphasise that exposure to PVP-AuNPs drives inflammatory signalling by the phagocytes and the resolution at both the low and high concentrations of the PVP-AuNPs and provides more details regarding the immunogenicity of these NPs.

Lability-specific enrichment of typical engineered metal (oxide) nanoparticles by surface-functionalized microbubbles from waters

Enrichment of metallic engineered nanoparticles (MENPs) from environmental waters is a prerequisite for their removal, reliable analyses, and environmental process interpretations. This work investigated the enrichment of typical MENPs with different degrees of lability using surface-functionalized microbbubles. During the process, the transformation/dissolution characteristics of MENPs were considered, and the impact of surfactant or coagulant dose, pH of MENP suspensions, and water matrix was systematically investigated. Results show that the colloidal gas aphrons (CGAs) were capable of enriching over 90.0% of ionic Ag(I) which ended up as AgBr and Ag₂CO₃ in floats when the pH of suspension was 6.0. The polyaluminum chloride-modified CGAs with positive surface charges were good at capturing the particulate ZnO-NPs (~84.8%) but failed to collect the ionic species. It should be noted that the total MENP enrichment efficiency closely related to the content proportions of different species. In the river water, both of the dissolved natural organic matter (fulvic acids) and the electrolytes might influence the enrichment process by affecting the species transformation of Ag-NPs and ZnO-NPs. For the stable TiO₂-NPs, 97.1% of the nanoparticles were captured by CGAs. FAs apparently reinforced the enrichment performance since the molecules acted as bridge and facilitated the attachment between TiO₂-NP and CGAs. This work contributes to establishing the robust microbubble-induced enrichment method considering the characteristics of MENP contaminants.

What occurs in colloidal gas aphron-induced separation of titanium dioxide nanoparticles? Particle fate analysis by tracking technologies

As an important method of enriching, separating and removing nanoparticles, colloidal gas aphrons (CGAs) need to be investigated for the fate and interfacial behaviors of particles during the process. It is beneficial to sufficiently interpreting the process performance and mechanisms. This study employed complementary tracking technologies to analyze the extensively-used engineered nanoparticles - TiO₂ nanoparticles (TiO₂-NPs) in effluent and floats of CGA process. Results denote that, at the optimum SDS relative dosage of 0.78 mg/mg TiO₂, the particle number concentration was largely reduced by 2-4 orders of magnitude based on nanoparticle tracking analysis (NTA) whilst approximately 84.0% of TiO_2-NPs were separated according to inductively coupled plasma-mass spectrometry (ICP-MS). NTA shows the change of overall particle dispersion status in the water phase while ICP-MS provides the Ti-related separation effect. Particularly, the particle size variation for the scenario of overdosing CGAs was clearly observed by NTA. Micro-Raman, dynamic laser scattering and small angle laser light scattering exhibited advantages in obtaining the configuration and morphology of flocs. The large flocs with open structure were apt to form and be favorably separated at the appropriate CGA dosage. However, overdosing CGAs weakened the capture capacity of bubbles and gave rise to small and dense aggregates. This work, for the first time, shows the change of nanoparticles in water and solid phases using the important and novel nanoparticle collection method - CGA technology. It also provides a reference to other flotation-related technologies for studying the nanoparticle fate and the process performance.

Sea Urchin Extracellular Proteins Design a Complex Protein Corona on Titanium Dioxide Nanoparticle Surface Influencing Immune Cell Behavior

Extensive exploitation of titanium dioxide nanoparticles (TiO₂NPs) augments rapid release into the marine environment. When in contact with the body fluids of marine invertebrates, TiO₂NPs undergo a transformation and adhere various organic molecules that shape a complex protein corona prior to contacting cells and tissues. To elucidate the potential extracellular signals that may be involved in the particle recognition by immune cells of the sea urchin Paracentrotus lividus, we investigated the behavior of TiO₂NPs in contact with extracellular proteins in vitro. Our findings indicate that TiO₂NPs are able to interact with sea urchin proteins in both cell-free and cell-conditioned media. The two-dimensional proteome analysis of the protein corona bound to TiO₂NP revealed that negatively charged proteins bound preferentially to the particles. The main constituents shaping the sea urchin cell-conditioned TiO₂NP protein corona were proteins involved in cellular adhesion (Pl-toposome, Pl-galectin-8, Pl-nectin) and cytoskeletal organization (actin and tubulin). Immune cells (phagocytes) aggregated TiO₂NPs on the outer cell surface and within well-organized vesicles without eliciting harmful effects on the biological activities of the cells. Cells showed an active metabolism, no oxidative stress or caspase activation. These results provide a new level of understanding of the extracellular proteins involved in the immune-TiO₂NP recognition and interaction in vitro, confirming that primary immune cell cultures from P. lividus can be an optional model for swift and efficient immune-toxicological investigations.

Mixture toxicity effects and uptake of titanium dioxide (TiO2) nanoparticles and 3,3',4,4'-tetrachlorobiphenyl (PCB77) in juvenile brown trout following co-exposure via the diet

Titanium dioxide nanoparticles (n-TiO₂) are among the man-made nanomaterials that are predicted to be found at high concentrations in the aquatic environment. There, they likely co-exist with other chemical pollutants. Thus, n-TiO₂ and other chemical pollutants can be taken up together or accumulate independently from each other in prey organisms of fish. This can lead to dietary exposure of fish to n-TiO₂-chemical pollutant mixtures. In this study, we examine if simultaneous dietary exposure to n-TiO₂ and 3,3',4,4'-Tetrachlorobiphenyl (PCB77) -used as a model compound for persistent organic pollutants with dioxin-like properties- can influence the uptake and toxicological response elicited by the respective other substance. Juvenile brown trout (Salmo trutta) were fed custom-made food pellets containing n-TiO_2, PCB77 or n-TiO₂+PCB77 mixtures for 15 days. Ti and PCB77 concentrations in the liver were measured by ICP-MS and GC-MS, respectively. Besides, n-TiO₂ uptake was assessed using TEM. Combination effects on endpoints specific for PCB77 (i.e., cytochrome P450 1A (CYP1A) induction) and endpoints shared by both PCB77 and n-TiO₂ (i.e., oxidative stress-related parameters) were measured in intestine and liver using RT-qPCR and enzyme activity assays. The results show that genes encoding for proteins/enzymes essential for tight junction function (zo-1) and ROS elimination (sod-1) were significantly upregulated in the intestine of fish exposed to n-TiO₂ and PCB77 mixtures, but not in the single-substance treatments. Besides, n-TiO₂ had a potentiating effect on PCB77-induced CYP1A and glutathione reductase (GR) expression/enzyme activity in the liver. This study shows that simultaneous dietary exposure to nanomaterials and traditional environmental pollutants might result in effects that are larger than observed for the substances alone, but that understanding the mechanistic basis of such effects remains challenging.

Anions influence the extraction of rutile nanoparticles from synthetic and lake water

Due to their recent widespread use, nanoparticles (NPs) may contaminate water sources and pose a health risk. Thus, it is important to understand the fate of NPs in order to evaluate potential threats. Here we show that the presence of anions influences the stability of NPs in synthetic and lake water. Concentrations of 0.3 and 3 mM PO₄³⁻ exhibited stronger stabilizing effects on NPs than 30 mM. Moreover, chloride ions promoted the coagulation of TiO₂ NPs over a range of concentrations (0.3–30 mM elicited similar effects). On the other hand, phosphate was found to hinder the coagulation effect. These results are expected to contribute to novel water purification strategies for the efficient removal of NPs. Further experiments should focus on the mechanism of phosphate on the removal of NPs in the coagulation/flocculation/sedimentation (C/F/S) process.

Different kinds of anions may influence the dispersion stability of nanoparticles in the manner of inner-sphere complexation or outer-sphere complexation.