Nanomaterials are widely believed to induce toxic effects on organisms by evoking oxidative stress. We evaluated the toxic effects of nanomaterials on the cardiac and behavioral changes in Daphnia magna under varying exposure conditions. Titanium dioxide nanoparticles (TiO₂ NPs), silver nanoparticles (AgNPs), and silver nitrate (AgNO₃) were selected for the acute toxicity tests. The adverse effects of the substances on the neonates including heart rate, swimming speed, and oxidative stress were measured. The heart rate level decreased as the concentration of both NPs and silver ions (Ag⁺) increased. The average swimming speed was measured to be approximately 15 mm/min for the control group. The swimming speed generally increased with a longer exposure to both NPs although it reached a plateau at the lowest concentration of AgNPs. A similar but less clear trend was observed for Ag⁺. For all substances, the overall swimming speed exhibited no correlation or weak negative correlations with the exposure concentration. The oxidative stress levels increased after exposure compared with the control group. We conclude that aquatic nanotoxicity tests should consider multilevel physicochemical, physiological, and behavioral parameters for the official guidelines to quantify more robust adverse outcomes.

The increasingly widespread use of engineered nanoparticles in medical, industrial, and food applications has raised concerns regarding their potential toxicity to humans and the environment. Silicon dioxide nanoparticles (SiO₂ NPs), which have relatively low direct toxicity, have been increasingly applied in both consumer products and biomedical applications, leading to significantly higher exposure for humans and the environment. We carried out a toxicity assessment of SiO₂ NPs using the common water flea D. magna by focusing on physiological and behavioral indicators such as heart rate, swimming performance, and growth. Exposure to SiO₂ NPs did not produce acute or chronic toxicity at limited concentrations (<100 μg/mL), but did have statistically significant negative effects on heart rate, swimming distance, and body size. The use of fluorescein isothiocyanate in a silica matrix allowed the tracing and visualization of clear SiO₂ NP accumulation in D. magna, which was confirmed by ICP-MS. Although exposure to SiO₂ NPs seemed to affect cardiac and swimming performance, such end-point experiments may be insufficient to fully understand the toxicity of these nanoparticles. However, the physiological and behavioral changes shown here suggest potential adverse effects on the aquatic environment by substances previously considered nontoxic.

Once metal-based engineered nanoparticles (NPs) are released into the aquatic environment, they are expected to interact with other existing co-contaminants, which may alter the bioavailability and toxicity of the individual chemicals. A knowledge gap exists as to how the interaction of NPs with other co-contaminants occurs. In this study, we selected zinc oxide (ZnO) NPs among various NPs, with silver (Ag) ion existing as a contaminant in the aquatic environment by Ag NPs widely used. A novel modeling strategy was demonstrated enabling quantitative and predictive evaluation of the aqueous mixture nanotoxicity. Individual and binary mixture toxicity tests of ZnO NPs and silver (as AgNO₃) on Daphnia magna were conducted and compared to determine whether the presence of Ag ions affects the toxicity of ZnO NPs. Binary mixture toxicity was evaluated based on the concentration addition (CA) and independent action models. The CA dose-ratio dependent model was found to be the model of best fit for describing the pattern of mixture toxicity. The MIX I and MIX III suspensions (higher ratios of ZnO NPs to AgNO₃) showed a synergism, whereas the MIX II suspension (lower ratio of ZnO NPs to AgNO₃) showed an antagonism. The synergistic mixture toxicity at higher ratios of ZnO NPs to AgNO₃ was caused by either the physiological or metabolic disturbance induced by the excessive ionic Zn or increased transport and accumulation in D. magna via the formation of complex of ionic Ag with ZnO NPs. Therefore, the toxicity level contributed via their aggregation and physicochemical properties and the dissolved ions played a crucial role in the mixture toxicities of the NPs.

Nanomaterials are widely believed to induce toxic effects on organisms by evoking oxidative stress. In this study, we evaluated the toxic effects of nanomaterials on cardiac and behavioral changes in Daphnia magna under varying exposure conditions. Titanium dioxide nanoparticles (TiO₂ NPs), silver nanoparticles (AgNPs), and silver nitrate (AgNO₃) were selected for the acute toxicity tests. The adverse effects of the substances on the neonates including heart rate, swimming speed, and oxidative stress, were measured. The heart rate level decreased as the concentration of NPs and silver ions (Ag⁺) increased. The average swimming speed was measured to be approximately 15 mm/min for the control group. The swimming speed generally increased for longer exposure to both NPs, although it reached a plateau at the lowest concentration of AgNPs. A similar but less clear trend was observed for Ag⁺. For all substances, the overall swimming speed exhibited no correlation or weak negative correlations with the exposure concentration. The oxidative stress levels increased after exposure compared to the control group. We conclude that aquatic nanotoxicity tests should consider multilevel physicochemical, physiological, and behavioral parameters for the official guidelines to quantify more robust adverse outcomes.