The effect of nano-scale Zn-doped TiO2 and pure TiO2 particles on Hydra magnipapillata

A systematic review on toxicity assessment of persistent emerging pollutants (EPs) and associated microplastics (MPs) in the environment using the Hydra animal model

Emerging pollutants (EPs) are causative for teratogenic and reproductive effects. EPs are detected in all the environmental matrices at higher levels. A suitable model for aquatic toxicity assessment is Hydra, because of morphological, behavioral, reproductive (sexual and asexual), and biochemical changes. Many researchers have used Hydra for toxicity assessment of organic chemicals (BPA), heavy metals, pharmaceuticals, nanomaterials and microplastics. Various Hydra species were used for environmental toxicity studies; however H. magnipapillata was predominantly used due to the availability of its genome and proteome sequences. Teratogenic and reproductive changes in Hydra are species specific. Teratogenic effects were studied using sterozoom dissecting microscope, acridine orange (AO) and 4',6-diamidino-2-phenylindole (DPAI) staining. Reactive oxygen species (ROS) generation by EPs had been understood by the Dichlorodihydrofluorescein Diacetate (DCFDA) staining and comet assay. Multiple advanced techniques would aid to understand the effects at molecular level, such as real-time PCR, rapid amplification of cDNA end- PCR. EPs modulated the major antioxidant enzyme levels, therefore, defense mechanism was affected by the higher generation of reactive oxygen species. Genome sequencing helps to know the mode of action of pollutants, role of enzymes in detoxification, defense genes and stress responsive genes. Molecular techniques were used to obtain the information for evolutionary changes of genes and modulation of gene expression by EPs.

Toxicological effects of Ag2O and Ag2CO3 doped TiO2 nanoparticles and pure TiO2 particles on zebrafish (Danio rerio)

In this study, the toxic effects of silver oxide and silver carbonate doped TiO₂ nanoparticles (Ag₂O-TiO₂ NPs and Ag₂CO₃-TiO₂NPs), TiO₂ nanoparticles (TiO₂ NPs), and bulk TiO₂ on gene expression, lipid peroxidation, genotoxicity, and histological alterations in zebrafish (Danio rerio) was assessed. The physicochemical properties of the synthesized nanoparticles were evaluated by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), diffuse reflectance spectroscopy (DRS), dynamic light scattering (DLS), and Zeta potential analyses. TiO₂NPs after doping with Ag showed shift to higher wavelengths and decrease of band gap energy. Also, remarkable reduction in the size of Ag-doped TiO₂NPs in comparison with the TiO₂ NPs was observed. According to our results, acute toxicity increased in the order of bulk TiO₂ < TiO₂ NPs < Ag₂O-TiO₂NPs < Ag₂CO₃-TiO₂NPs, respectively. Results of sub-lethal experiments after 30 days of exposure, showed higher expression of Gpx, Hsp70, Ucp-2, and Bax genes, and lower expression of Bcl-2 gene in Ag-doped TiO₂NPs than pure TiO₂ particles (TiO₂ NPs and bulk TiO₂) treatments (p < 0.05). However, the mRNA levels of SOD and CAT genes were significantly higher in pure TiO₂ particles than doped TiO₂NPs (p < 0.05). Moreover, levels of malondialdehyde, abnormalities of peripheral blood cells and severity of histological lesions in liver, gill, intestine and kidney tissues were more evident in Ag-dopedTiO₂ NPs than pure TiO₂ particles. It can be concluded that Ag doping of TiO₂ NPs significantly increased their toxicity and resulted in more histological lesions, apoptosis and oxidative stress than pure TiO₂ particles in adult zebrafish.

Activated carbon from pyrolysed sugarcane bagasse: Silver nanoparticle modification and ecotoxicity assessment

Activated carbon from pyrolysed sugarcane bagasse (ACPB) presented pore size ranges from 1.0 to 3.5nm, and surface area between 1200 and 1400m(2)g(-1) that is higher than commonly observed to commercial activated carbon. The ACPB material was successfully loaded with of silver nanoparticles with diameter around 35nm (0.81wt.%). X-ray photoelectron spectroscopy (XPS) analyses showed that the material surface contains metallic/Ag(0) (93.60wt.%) and ionic/Ag(+) states (6.40wt.%). The adsorption capacity of organic model molecules (i.e. methylene blue and phenol) was very efficient to ACPB and ACPB loaded with silver nanoparticles (ACPB-AgNP), indicating that the material modification with silver nanoparticles has not altered its adsorption capacity. ACPB-AgNP inhibited bacteria growth (Escherichia coli), it is a promising advantage for the use of these materials in wastewater treatment and water purification processes. However, ACPB-AgNP showed environmental risks, with toxic effect to the aquatic organism Hydra attenuata (i.e. LC50 value of 1.94mgL(-1)), and it suppressed root development of Lycopersicum esculentum plant (tomato). Finally, this work draw attention for the environmental implications of activated carbon materials modified with silver nanoparticles.

Effect of 10 different TiO2 and ZrO2 (nano)materials on the soil invertebrate Enchytraeus crypticus

Nearly 80% of all the nano-powders produced worldwide are metal oxides, and among these materials titanium dioxide (TiO2 ) is one of the most produced. Titanium dioxide's toxicity is estimated as low to soil organisms, but some studies have shown that TiO2 nanoparticles can cause oxidative stress. Additionally, it is known that TiO2 is activated by ultraviolet (UV) radiation, which can promote photocatalytic generation of reactive oxygen species, which is seldom taken into account in toxicity testing. In the present study, the authors investigated the effects of different TiO2 and zirconium materials on the soil oligochaete Enchytraeus crypticus, using exposure via soil, water, and soil:water extracts, and studied the effects combined with UV radiation. The results showed that zirconium dioxide (bulk and nano) was not toxic, whereas zirconium tetrachloride reduced enchytraeid reproduction in soil (50% effect concentration = 502 mg/kg). The TiO2 materials were also not toxic via soil exposure or under UV radiation. However, pre-exposure to TiO2 and UV radiation via aqueous media caused a lower reproductive output post-exposure in clean soil (20-50% less but only observed at the lowest concentration tested, 1 mg/L); that is, the effect of TiO2 in water was potentiated by the UV radiation and measurable as a decrease in reproduction in soil media.

An in vivo study on the photo-enhanced toxicities of S-doped TiO2 nanoparticles to zebrafish embryos (Danio rerio) in terms of malformation, mortality, rheotaxis dysfunction, and DNA damage

The role of light on the acute toxicities of S-doped and Sigma TiO2 nanoparticles in zebrafish was studied. Metrics included mortality for both, and rheotaxis dysfunction and DNA damage for S-doped only. It was found that the acute toxicity of S-TiO2 nanoparticles was enhanced by simulated sunlight (SSL) irradiation (96-h LC50 of 116.56 ppm) and exceeded that of Sigma TiO2, which was essentially non-toxic. Behavioral disorder, in terms of rheotaxis, was significantly increased by treatment with S-TiO2 nanoparticles under SSL irradiation. In order to further understand its toxicity mechanism, we investigated hair cells in neuromasts of the posterior lateral line (PLL) using DASPEI staining. Significant hair cell damage was observed in the treated larvae. The Comet assay was employed to investigate the DNA damage, which might be responsible for the loss of hair cells. Production of the superoxide anion ([Formula: see text]), a major ROS generated by TiO2 nanoparticles, was assayed and used to postulate causative factors to account for these damages. Oxidative effects were most severe in the liver, heart, intestine, pancreatic duct, and pancreatic islet - results consistent with our earlier findings in the investigation of embryonic malformation. TEM micrographs, used to further investigate the fate of S-TiO2 nanoparticles at the cellular level, suggested receptor-mediated autophagy and vacuolization. Our findings validate the benefit of using the transparent zebrafish embryo as an in vivo model for evaluating photo-induced nanotoxicity. These results highlight the importance of conducting a systematic risk assessment in connection with the use of doped TiO2 nanoparticles in aquatic ecosystems.

Toxicity assessment of TiO₂ nanoparticles in zebrafish embryos under different exposure conditions

The popularity of TiO2 nanoparticles (nano-TiO2) lies in their wide range of nanotechnological applications, together with low toxicity. Meanwhile, recent studies have shown that the photocatalytic properties of this material can result in alterations in their behavior in the environment, causing effects that have not yet been fully elucidated. The objective of this study was to evaluate the toxicity of two formulations of nano-TiO2 under different illumination conditions, using an experimental model coherent with the principle of the three Rs of alternative animal experimentation (reduction, refinement, and replacement). Embryos of the fish Danio rerio were exposed for 96h to different concentrations of nano-TiO2 in the form of anatase (TA) or an anatase/rutile mixture (TM), under either visible light or a combination of visible and ultraviolet light (UV). The acute toxicity and sublethal parameters evaluated included survival rates, malformation, hatching, equilibrium, and overall length of the larvae, together with biochemical biomarkers (specific activities of catalase (CAT), glutathione S-transferase (GST), and acid phosphatase (AP)). Both TA and TM caused accelerated hatching of the larvae. Under UV irradiation, there was greater mortality of the larvae of the groups exposed to TM, compared to those exposed to TA. Exposure to TM under UV irradiation altered the equilibrium of the larvae. Alterations in the activities of CAT and GST were indicative of oxidative stress, although no clear dose-response relationship was observed. The effects of nano-TiO2 appeared to depend on both the type of formulation and the illumination condition. The findings contribute to elucidation of the factors involved in the toxicity of these nanoparticles, as well as to the establishment of protocols for risk assessments of nanotechnology.

Influence of different types of nanomaterials on their bioaccumulation in a paddy microcosm: a comparison of TiO2 nanoparticles and nanotubes

We investigated the environmental fate and bioaccumulation of TiO2 nanomaterials in a simplified paddy microcosm over a period of 17 days. Two types of TiO2 nanomaterials, nanoparticles (TiO2-NP) and nanotubes (TiO2-NT), were synthesized to have a negative surface charge. Ti concentrations in the environmental media (water, soil), crops (quillworts, water dropworts), and some lower and higher trophic organisms (biofilms, algae, plant-parasitic nematodes, white butterfly larva, mud snail, ricefish) were quantified after exposure periods of 0, 7, and 17 days. The titanium levels of the two nanomaterials were the highest in biofilms during the exposure periods. Bioaccumulation factors indicated that TiO2-NP and TiO2-NT were largely transferred from a prey (e.g., biofilm, water dropwort) to its consumer (e.g., nematodes, mud snail). Considering the potential entries of such TiO2 nanomaterials in organisms, their bioaccumulation throughout the food chain should be regarded with great concern in terms of the overall health of the ecosystem.

Toxaphene affects the levels of mRNA transcripts that encode antioxidant enzymes in Hydra

We evaluated toxaphene-induced acute toxicity in Hydra magnipapillata. The median lethal concentrations of the animals (LC(50)) were determined to be 34.5 mg/L, 25.0 mg/L and 12.0 mg/L after exposure to toxaphene for 24 h, 48 h and 72 h, respectively. Morphological responses of hydra polyps to a range of toxaphene concentrations suggested that toxaphene negatively affects the nervous system of H. magnipapillata. We used real-time quantitative PCR of RNA extracted from polyps exposed to two concentrations of toxaphene (0.3 mg/L and 3 mg/L) for 24 h to evaluate the differential regulation of levels of transcripts that encode six antioxidant enzymes (CAT, G6PD, GPx, GR, GST and SOD), two proteins involved in detoxification and molecular stress responses (CYP1A and UB), and two proteins involved in neurotransmission and nerve cell differentiation (AChE and Hym-355). Of the genes involved in antioxidant responses, the most striking changes were observed for transcripts that encode GPx, G6PD, SOD, CAT and GST, with no evident change in levels of transcripts encoding GR. Levels of UB and CYP1A transcripts increased in a dose-dependent manner following exposure to toxaphene. Given that toxaphene-induced neurotoxicity was not reflected in the level of AChE transcripts and only slight accumulation of Hym-355 transcript was observed only at the higher of the two doses of toxaphene tested, there remains a need to identify transcriptional biomarkers for toxaphene-mediated neurotoxicity in H. magnipapillata. Transcripts that respond to toxaphene exposure could be valuable biomarkers for stress levels in H. magnipapillata and may be useful for monitoring the pollution of aquatic environments.

Advances in carcinogenic metal toxicity and potential molecular markers

Metal compounds such as arsenic, cadmium, chromium, cobalt, lead, mercury, and nickel are classified as carcinogens affecting human health through occupational and environmental exposure. However, the underlying mechanisms involved in tumor formation are not well clarified. Interference of metal homeostasis may result in oxidative stress which represents an imbalance between production of free radicals and the system's ability to readily detoxify reactive intermediates. This event consequently causes DNA damage, lipid peroxidation, protein modification, and possibly symptomatic effects for various diseases including cancer. This review discusses predominant modes of action and numerous molecular markers. Attention is paid to metal-induced generation of free radicals, the phenomenon of oxidative stress, damage to DNA, lipid, and proteins, responsive signal transduction pathways with major roles in cell growth and development, and roles of antioxidant enzymatic and DNA repair systems. Interaction of non-enzymatic antioxidants (carotenoids, flavonoids, glutathione, selenium, vitamin C, vitamin E, and others) with cellular oxidative stress markers (catalase, glutathione peroxidase, and superoxide dismutase) as well as certain regulatory factors, including AP-1, NF-κB, Ref-1, and p53 is also reviewed. Dysregulation of protective pathways, including cellular antioxidant network against free radicals as well as DNA repair deficiency is related to oncogenic stimulation. These observations provide evidence that emerging oxidative stress-responsive regulatory factors and DNA repair proteins are putative predictive factors for tumor initiation and progression.