The protective roles of TiO2 nanoparticles against UV-B toxicity in Daphnia magna

Emerging trends in nanoparticle toxicity and the significance of using Daphnia as a model organism

Nanoparticle production is on the rise due to its many uses in the burgeoning nanotechnology industry. Although nanoparticles have growing applications, there is great concern over their environmental impact due to their inevitable release into the environment. With uncertainty of environmental concentration and risk to aquatic organisms, the microcrustacean Daphnia spp. has emerged as an important freshwater model organism for risk assessment of nanoparticles because of its biological properties, including parthenogenetic reproduction; small size and short generation time; wide range of endpoints for ecotoxicological studies; known genome, useful for providing mechanistic information; and high sensitivity to environmental contaminants and other stressors. In this review, we (1) highlight the advantages of using Daphnia as an experimental model organism for nanotoxicity studies, (2) summarize the impacts of nanoparticle physicochemical characteristics on toxicity in relation to Daphnia, and (3) summarize the effects of nanoparticles (including nanoplastics) on Daphnia as well as mechanisms of toxicity, and (4) highlight research uncertainties and recommend future directions necessary to develop a deeper understanding of the fate and toxicity of nanoparticles and for the development of safer and more sustainable nanotechnology.

Effects of TiO2-NPs pretreatment on UV-B stress tolerance in Arabidopsis thaliana

As the ozone hole in the North and South poles continues to increase, the entire ecosystem will face an environmental crisis caused by enhanced UV-B radiation. Considering the function of TiO₂ and the application of nanomaterials in agriculture, the effect of TiO₂-NPs on UV-B stress tolerance in Arabidopsis was investigated. The phenotype of plants was determined, and the expression patterns of antioxidant systems and related genes were analyzed. Modification of the antioxidant system and changes in the flavonoid content of plants were observed by histochemical staining. The effects of TiO₂-NPs and UV-B on mitosis were observed at the cellular level, and the degree of DNA damage was analyzed by the detection of CPDs content. The effects of TiO₂-NPs and UV-B on SOD isozymes were detected by SOD isozyme Native-PAGE electrophoresis. A laser confocal microscope was used to explore the protective mechanism of TiO₂-NPs against UV-B radiation. Results showed that pretreatment of TiO₂-NPs significantly alleviated the stress of UV-B radiation on plants. TiO₂-NPs activated the antioxidant system of plants, improved the activity of antioxidant enzymes, and promoted the synthesis of flavonoids. Moreover, TiO₂-NPs could effectively shield UV-B radiation to prevent the depolymerization of microtubules in plant cells. 10 mg/L of TiO₂-NPs is a safe and effective application dose, which has no biological toxicity to plants. Our research results reported for the first time that pretreatment of TiO₂-NPs could effectively alleviate UV-B stress to plants, providing new ideas for the application of nanomaterials in agriculture.

Rethinking Nano-TiO2 Safety: Overview of Toxic Effects in Humans and Aquatic Animals

Titanium dioxide nanoparticles (nano-TiO₂ ) are widely used in consumer products, raising environmental and health concerns. An overview of the toxic effects of nano-TiO₂ on human and environmental health is provided. A meta-analysis is conducted to analyze the toxicity of nano-TiO₂ to the liver, circulatory system, and DNA in humans. To assess the environmental impacts of nano-TiO₂ , aquatic environments that receive high nano-TiO₂ inputs are focused on, and the toxicity of nano-TiO₂ to aquatic organisms is discussed with regard to the present and predicted environmental concentrations. Genotoxicity, damage to membranes, inflammation and oxidative stress emerge as the main mechanisms of nano-TiO₂ toxicity. Furthermore, nano-TiO₂ can bind with free radicals and signal molecules, and interfere with the biochemical reactions on plasmalemma. At the higher organizational level, nano-TiO₂ toxicity is manifested as the negative effects on fitness-related organismal traits including feeding, reproduction and immunity in aquatic organisms. Bibliometric analysis reveals two major research hot spots including the molecular mechanisms of toxicity of nano-TiO₂ and the combined effects of nano-TiO₂ and other environmental factors such as light and pH. The possible measures to reduce the harmful effects of nano-TiO₂ on humans and non-target organisms has emerged as an underexplored topic requiring further investigation.

Impact of wastewater-borne nanoparticles of silver and titanium dioxide on the swimming behaviour and biochemical markers of Daphnia magna: An integrated approach

Due to their widespread use, silver (Ag) and titanium dioxide (TiO₂) nanoparticles (NPs) are commonly discharged into aquatic environments via wastewater treatment plants. The study was aimed to assess the effects of wastewater-borne AgNPs (NM-300 K; 15.5 ± 2.4 nm; 25-125 μg L^-1) and TiO₂NPs (NM-105; 23.1 ± 6.2 nm; 12.5-100 μg L^-1), from a laboratory-scale wastewater treatment plant, on Daphnia magna, at individual and subcellular level. For effect comparison, animals were also exposed to ASTM-dispersed NPs at the same nominal concentrations. The behaviour of D. magna was evaluated through monitoring of swimming height and allocation time for preferred zones after 0 h and 96 h of exposure. Biochemical markers of neurotransmission, anaerobic metabolism, biotransformation, and oxidative stress were subsequently determined. No 96-h EC₅₀ (immobilization ≤ 4 %) could be obtained with wastewater-borne NPs and ASTM-dispersed TiO₂NPs, whereas the ASTM-dispersed AgNPs resulted in an immobilization 96-h EC₅₀ of 113.8 μg L^-1. However, both wastewater-borne and ASTM-dispersed TiO₂NPs, at 12.5 μg L^-1, caused immediate (0 h) alterations on the swimming height. Allocation time analyses showed that animals exposed to ASTM-dispersed AgNPs spent more time on the surface and bottom at 0 h, and in the middle and bottom at 96 h. This pattern was not observed with ASTM-dispersed TiO₂NPs nor with wastewater-borne AgNPs and wastewater-borne TiO₂NPs. At the biochemical level, the more pronounced effects were observed with wastewater-borne AgNPs (e.g. induction of lactate dehydrogenase and glutathione S-transferase activities, and inhibition of catalase activity). This integrative approach showed that: (i) the behavioural and biochemical response-patterns were distinct in D. magna exposed to environmentally relevant concentrations of wastewater-borne and ASTM-dispersed NPs; (ii) the most pronounced effects on allocation time were induced by ASTM-dispersed AgNPs; and (iii) at the subcellular level, wastewater-borne AgNPs were more toxic than wastewater-borne TiO₂NPs. This study highlights the need for the assessment of the effects of wastewater-borne NPs under realistic exposure scenarios, since processes in wastewater treatment plants may influence their toxicity.

Effect of TiO2-ZnO-MgO Mixed Oxide on Microbial Growth and Toxicity against Artemia salina

Mixed oxide nanoparticles (MONs, TiO₂–ZnO–MgO) obtained by the sol-gel method were characterized by transmission electron microscopy, (TEM, HRTEM, and SAED) and thermogravimetric analysis (TGA/DTGA–DTA). Furthermore, the effect of MONs on microbial growth (growth profiling curve, lethal and sublethal effect) of Escherichia coli, Salmonella paratyphi, Staphylococcus aureus and Listeria monocytogenes, as well as the toxicity against Artemia salina by the lethal concentration test (LC₅₀) were evaluated. MONs exhibited a near-spherical in shape, polycrystalline structure and mean sizes from 17 to 23 nm. The thermal analysis revealed that the anatase phase of MONs is completed around 480–500 °C. The normal growth of all bacteria tested is affected by the MONs presence compared with the control group. MONs also exhibited a reduction on the plate count from 0.58 to 2.10 log CFU/mL with a sublethal cell injury from 17 to 98%. No significant toxicity within 24 h was observed on A. salina. A bacteriostatic effect of MONs on bacteria was evidenced, which was strongly influenced by the type of bacteria, as well as no toxic effects (LC₅₀ >1000 mg/L; TiO₂–ZnO (5%)–MgO (5%)) on A. salina were detected. This study demonstrates the potential of MONs for industrial applications.

Chronic impacts of TiO2 nanoparticles on Populus nigra L. leaf decomposition in freshwater ecosystem

Titanium dioxide (TiO₂) nanoparticles have been applied in diverse commercial products, which could lead to toxic effects on aquatic microbes and would inhibit some important ecosystem processes. The study aimed to investigate the chronic impacts of TiO₂ nanoparticles with different concentrations (5, 50, and 500 mg L^-1) on Populus nigra L. leaf decomposition in the freshwater ecosystem. After 50 d of decomposing, a significant decrease in decomposition rates was observed with higher concentrations of TiO₂ nanoparticles. During the period of litter decomposition, exposure of TiO₂ nanoparticles led to decreases in extracellular enzyme activities, which was caused by the reduction of microbial especially fungal biomass. In addition, the diversity and composition of the fungal community associated with litter decomposition were strongly affected by the concentrations of TiO₂ nanoparticles. The diversity and composition of the fungal community associated with litter decomposition was strongly affected. The abundance of Tricladium chaetocladium decreased with the increasing concentrations of TiO₂ nanoparticles, indicating the little contribution of the species to the litter decomposition. In conclusion, this study provided the evidence for the chronic exposure effects of TiO₂ nanoparticles on the litter decomposition and further the functions of freshwater ecosystems.

Comparative assessment of toxicity of ZnO and amine-functionalized ZnO nanorods toward Daphnia magna in acute and chronic multigenerational tests

Zinc oxide nanomaterials (ZnO NM) have been used in a large number of applications due to their interesting physicochemical properties. However, the increasing use of ZnO NM has led to concerns regarding their environmental impacts. In this study, the acute and chronic toxicity of ZnO nanorods (NR) bare (ZnONR) and amine-functionalized (ZnONR@AF) toward the freshwater microcrustacean Daphnia magna was evaluated. The ZnO NR were characterized by transmission electron microscopy (TEM), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and the zeta potential and hydrodynamic diameter (HD). The acute EC50_(48h) values for D. magna revealed that the ZnONR@AF were more toxic than the ZnONR. The generation of reactive oxygen species (ROS) was observed in both NM. Regarding the chronic toxicity, the ZnONR@AF were again found to be more toxic than the ZnONR toward D. magna. An effect on longevity was observed for ZnONR, while ZnONR@AF affected the reproduction, growth and longevity. In the multigenerational recovery test, we observed that maternal exposure can affect the offspring even when these organisms are not directly exposed to the ZnO NR.

Negatives and Positives: Contaminants and Other Stressors in Aquatic Ecosystems

Published research is reviewed to provide examples of both positive and negative interactions of contaminants and: climate change; habitat change; invasive and introduced species; and, eutrophication including harmful algal blooms. None of these stressor interactions results solely in negative effects. Research must shift from examining contaminants or other stressors in isolation to considering potential positive and negative effects of interactions, with the ultimate goal of providing the necessary information for the effective management of ecosystem services.