Bioaccumulation of ionic titanium and titanium dioxide nanoparticles in zebrafish eleutheroembryos

Phytotoxicity of binary nanoparticles and humic acid on Lactuca sativa L

Nanoplastics and metal oxide nanoparticles are serious threats that inevitably enter the environment. Their similar particle properties likely lead to interaction and thus cause more unpredictable ecotoxicity to organisms. In this study, it was found that polystyrene nanoplastics (PS NPs) aggravate the toxic effect of iron oxide nanoparticles (Fe2O3 NPs) on Lactuca sativa L. by inducing severe oxidative stress and root deformation, and the expansion of damaged cells from the xylem to the epidermis was observed using confocal laser scanning. Exposure to PS NPs + Fe2O3 NPs correspondingly elevated iron accumulation in the roots and leaves by 1.39 and 1.17 times compared to the amount observed with Fe2O3 NPs individually. Examination of the physicochemical properties, iron ion release, and molecular interactions of the NPs indicated that PS NPs interact with Fe2O3 NPs to form heteroaggregates and facilitate leaching of iron ions, which resulted in aggravating the toxic effect. These were alleviated by the addition of humic acid (HA), which dispersed the heteroaggregates and reduced the release of iron ions. The findings in the present study provide new perspectives for the ecotoxicological risk of binary nano-pollution in the natural environment.

Environmental and human health risk assessment of mixture of Covid-19 treating pharmaceutical drugs in environmental waters

This study identified ecological and human health risks exposure of COVID-19 pharmaceuticals and their metabolites in environmental waters. Environmental concentrations in aquatic species were predicted using surface water concentrations of pharmaceutical compounds. Predicted No-Effect Concentrations (PNEC) in aquatic organisms (green algae, daphnia, and fish) was estimated using EC₅₀/LC₅₀ values of pharmaceutical compounds taken from USEPA ECOSAR database. PNEC for human health risks was calculated using the acceptable daily intake values of drugs. Ecological PNEC revealed comparatively high values in algae (Chronic toxicity PNEC values, high to low: ribavirin (2.65 × 10⁵ μg/L) to ritonavir (2.3 × 10^-1 μg/L)) than daphnia and fish. Risk quotient (RQ) analysis revealed that algae (Avg. = 2.81 × 10⁴) appeared to be the most sensitive species to pharmaceutical drugs followed by daphnia (Avg.: 1.28 × 10⁴) and fish (Avg.: 1.028 × 10³). Amongst the COVID-19 metabolites, lopinavir metabolites posed major risk to aquatic species. Ritonavir (RQ = 6.55) is the major drug responsible for human health risk through consumption of food (in the form fish) grown in pharmaceutically contaminated waters. Mixture toxicity analysis of drugs revealed that algae are the most vulnerable species amongst the three trophic levels. Maximum allowable concentration level for mixture of pharmaceuticals was found to be 0.53 mg/L.

Titanium dioxide nanoparticle affects motor behavior, neurodevelopment and axonal growth in zebrafish (Danio rerio) larvae

More attention has been recently paid to the ecotoxicity of titanium dioxide nanoparticles (nano-TiO₂) owing to its common use in many fields. Although previous studies have shown that nano-TiO₂ is neurotoxic, the mechanism is still largely unknown. In the present study, zebrafish embryos were exposed to 0.01, 0.1, and 1.0 mg/L nano-TiO₂ and 1.0 mg/L micro-TiO₂ for up to 6 days post-fertilization (dpf). Exposure to 1.0 mg/L nano-TiO₂ significantly decreased the body length and weight of zebrafish larvae; however, the hatching and mortality rate of zebrafish embryos did not change. Behavioral tests showed that nano-TiO₂ exposure significantly reduced the swimming speed and clockwise rotation times of the larvae. The results revealed that nano-TiO₂ treatment adversely affected motor neuron axon length in Tg (hb9-GFP) zebrafish and decreased central nervous system (CNS) neurogenesis in Tg (HuC-GFP) zebrafish. Additionally, real-time polymerase chain reaction analysis demonstrated that genes associated with neurogenesis (nrd and elavl3) and axonal growth (α1-tubulin, mbp, and gap43) were significantly affected by nano-TiO₂ exposure. In conclusion, our study demonstrated that early-life stage exposure of zebrafish to nano-TiO₂ causes adverse neural outcomes through the inhibition of neurodevelopment and motor neuron axonal growth.

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.

Uptake, translocation, size characterization and localization of cerium oxide nanoparticles in radish (Raphanus sativus L.)

Due to their unique physical and chemical properties, the production and use of cerium oxide nanoparticles (CeO₂ NPs) in different areas, especially in automotive industry, is rapidly increasing, causing their presence in the environment. Released CeO₂ NPs can undergo different transformations and interact with the soil and hence with plants, providing a potential pathway for human exposure and leading to serious concerns about their impact on the ecosystem and human organism. This study investigates the uptake, bioaccumulation, possible translocation and localization of CeO₂ NPs in a model plant (Raphanus sativus L.), whose edible part is in direct contact with the soil where contamination is more likely to happen. The stability of CeO₂ NPs in plant growth medium as well as after applying a standard enzymatic digestion procedure was tested by single particle ICP-MS (SP-ICP-MS) showing that CeO₂ NPs can remain intact after enzymatic digestion; however, an agglomeration process was observed in the growth medium already after one day of cultivation. An enzymatic digestion method was next used in order to extract intact nanoparticles from the tissues of plants cultivated from the stage of seeds, followed by size characterization by SP-ICP-MS. The results obtained by SP-ICP-MS showed a narrower size distribution in the case of roots suggesting preferential uptake of smaller nanoparticles which led to the conclusion that plants do not take up the CeO₂ NPs agglomerates present in the medium. However, nanoparticles at higher diameters were observed after analysis of leaves plus stems. Additionally, a small degree of dissolution was observed in the case of roots. Finally, after CeO₂ NPs treatment of adult plants, the spatial distribution of intact CeO₂ NPs in the radish roots was studied by laser ablation ICP-MS (LA-ICP-MS) and the ability of NPs to enter and be accumulated in root tissues was confirmed.

Morphometric characteristics and time to hatch as efficacious indicators for potential nanotoxicity assay in zebrafish

Although the effects of nano-sized titania (nTiO₂ ) on hatching events (change in hatching time and total hatching) in zebrafish have been reported, additional consequences of nTiO₂ exposure (i.e., the effects of nTiO₂ -induced changes in hatching events and morphometric parameters on embryo-larvae development and survivability) have not been reported. To address this knowledge gap, embryos 4 h postfertilization were exposed to nTiO₂ (0, 0.01, 10, and 1000 μg/mL) for 220 h. Hatching rate (58, 82, and 106 h postexposure [hpe]), survival rate (8 times from 34 to 202 hpe), and 21 morphometric characteristics (8 times from 34 to 202 hpe) were recorded. Total hatching (rate at 106 hpe) was significantly and positively correlated to survival rate, but there was no direct association between nTiO₂ -induced change in hatching time (hatching rate at 58 and 82 hpe) and survival rate. At 58, 82, and 106 hpe, morphometric characteristics were significantly correlated to hatching rate, suggesting that the nTiO₂ -induced change in hatching time can affect larval development. The morphometric characteristics that were associated with change in hatching time were also significantly correlated to survival rate, suggesting an indirect significant influence of the nTiO₂ -induced change in hatching time on survivability. These results show a significant influence of nTiO₂ -induced change in hatching events on zebrafish embryo-larvae development and survivability. They also show that morphometric maldevelopments can predict later-in-life consequences (survivability) of an embryonic exposure to nTiO₂ . This suggests that zebrafish can be sensitive biological predictors of nTiO₂ acute toxicity. Environ Toxicol Chem 2018;37:3063-3076. © 2018 SETAC.

An assessment of applicability of existing approaches to predicting the bioaccumulation of conventional substances in nanomaterials

The experimental determination of bioaccumulation is challenging, and a number of approaches have been developed for its prediction. It is important to assess the applicability of these predictive approaches to nanomaterials (NMs), which have been shown to bioaccumulate. The octanol/water partition coefficient (K_OW ) may not be applicable to some NMs that are not found in either the octanol or water phases but rather are found at the interface. Thus the K_OW values obtained for certain NMs are shown not to correlate well with the experimentally determined bioaccumulation. Implementation of quantitative structure-activity relationships (QSARs) for NMs is also challenging because the bioaccumulation of NMs depends on nano-specific properties such as shape, size, and surface area. Thus there is a need to develop new QSAR models based on these new nanodescriptors; current efforts appear to focus on digital processing of NM images as well as the conversion of surface chemistry parameters into adsorption indices. Water solubility can be used as a screening tool for the exclusion of NMs with short half-lives. Adaptation of fugacity/aquivalence models, which include physicochemical properties, may give some insights into the bioaccumulation potential of NMs, especially with the addition of a biota component. The use of kinetic models, including physiologically based pharmacokinetic models, appears to be the most suitable approach for predicting bioaccumulation of NMs. Furthermore, because bioaccumulation of NMs depends on a number of biotic and abiotic factors, it is important to take these factors into account when one is modeling bioaccumulation and interpreting bioaccumulation results. Environ Toxicol Chem 2018;37:2972-2988. © 2018 SETAC.

Effect of titanium dioxide nanoparticles on the bioavailability and neurotoxicity of cypermethrin in zebrafish larvae

In aquatic environment, the presence of nanoparticles (NPs) has been reported to modify the bioavailability and toxicity of the organic toxicants. Nevertheless, the combined toxicity of NPs and the pesticides that were used world-widely still remains unclear. Cypermethrin (CYP), a synthetic pyrethroid insecticide, is commonly used for controlling agricultural and indoor pests. Therefore, the effects of titanium dioxide NPs (nTiO₂) on CYP bioconcentration and its effects on the neuronal development in zebrafish were investigated in our study. Zebrafish embryos (2- hour-post-fertilization, hpf) were exposed to CYP (0, 0.4, 2 and 10 μg/L) alone or co-exposed with nTiO₂ (1 mg/L) until 120-hpf. nTiO₂ is taken up by zebrafish larvae and also it can adsorb CYP. The zebrafish body burdens of CYP was observed and CYP uptake was increased by nTiO₂, indicating that the nTiO₂ could accelerate the bioaccumulation of CYP in larvae. Co-exposure of nTiO₂ and CYP induced the generation of reactive oxygen species. Exposure to CYP alone significantly decreased the mRNA expression of genes, including glial fibrillary acidic protein (gfap), α1-tubulin, myelin basic protein (mbp) and growth associated protein (gap-43). Besides, reductions of serotonin, dopamine and GABA concentrations were observed in zebrafish and the larval locomotion was significantly decreased in response to the lower level of the neurotransmitters. Moreover, co-exposure of nTiO₂ and CYP caused further significantly decreased in the locomotion activity, and enhanced the down-regulation of the mRNA expression of specific genes and the neurotransmitters levels. The results demonstrated that nTiO₂ increased CYP accumulation and enhanced CYP-induced developmental neurotoxicity in zebrafish.

Montmorillonite clay alters toxicity of silver nanoparticles in zebrafish (Danio rerio) eleutheroembryo

An exponential development in the use of silver nanoparticles (AgNPs) in consumer products has accelerated their release in aquatic environment. As the AgNPs enters into the aquatic systems, their fate may change due to interactions with abiotic (e.g. clay particles) or biotic factors. The abundantly present clay particles are expected to more prone for interaction with nanoparticles in aquatic systems. In the present study, it is demonstrated that AgNPs interacts with clay particles and forms heteroagglomerates. Furthermore, an impact on toxicity potential of AgNPs after interactions with clay particles was assessed by using zebrafish eleutheroembryos (72 h post hatching) as an in vivo model. The mortality rate of zebrafish eleutheroembryos was higher in case of exposure to AgNPs-clay complexes (pH 4.0 and 7.0) as compared to bare AgNPs. In addition, at earlier time points, the eleutheroembryos expressed higher levels of morphological changes in tail, yolk and pericardia, but the edema in yolk sac was followed by cell death. It can be concluded from the observations made in the present study that the inorganic colloids in the aquatic matrices can alter the fate and toxicity potential of nanoparticles.

High bioconcentration of titanium dioxide nanoparticles in Daphnia magna determined by kinetic approach

The environmental risk assessments of titanium dioxide nanoparticles (TiO2 NPs) have drawn wide attention and one of the required critical information is the bioconcentration potentials of these nanoparticles in aquatic organisms. In the present study, the bioconcentration of six commercially available TiO2 NPs with different sizes and surface properties were quantified in a freshwater cladoceran Daphnia magna using kinetic modeling approach. We first calculated the uptake rate constant (ku) and depuration rate constant (ke) of TiO2 NPs and then employed a first-order kinetic model to predict the bioconcentration factors (BCF) at different TiO2 NPs concentrations. Both the ku and ke of TiO2 NPs were significantly affected by the exposure concentration and the nanoparticle property. The predicted BCF values in D. magna of six TiO2 NPs ranged from 2.40×10(5)L/kg to 1.52×10(6)L/kg, and had no clear correlation with the exposure concentration. Large nominal size resulted in a lower BCF of TiO2 NPs at lower exposure concentration. Higher hydrophobicity and Al(OH)3 coating also resulted in a higher BCF. All the six TiO2 NPs in this study were therefore considered very bioaccumulative. More attention should be paid to bioconcentration in the environmental risk assessments of TiO2 NPs, and the physicochemical properties of TiO2 NPs should be taken into account.

Titanium dioxide nanoparticles enhance mortality of fish exposed to bacterial pathogens

Nano-TiO2 is immunotoxic to fish and reduces the bactericidal function of fish neutrophils. Here, fathead minnows (Pimephales promelas) were exposed to low and high environmentally relevant concentration of nano-TiO2 (2 ng g(-1) and 10 μg g(-1) body weight, respectively), and were challenged with common fish bacterial pathogens, Aeromonas hydrophila or Edwardsiella ictaluri. Pre-exposure to nano-TiO2 significantly increased fish mortality during bacterial challenge. Nano-TiO2 concentrated in the kidney and spleen. Phagocytosis assay demonstrated that nano-TiO2 has the ability to diminish neutrophil phagocytosis of A. hydrophila. Fish injected with TiO2 nanoparticles displayed significant histopathology when compared to control fish. The interplay between nanoparticle exposure, immune system, histopathology, and infectious disease pathogenesis in any animal model has not been described before. By modulating fish immune responses and interfering with resistance to bacterial pathogens, manufactured nano-TiO2 has the potential to affect fish survival in a disease outbreak.