Comparative toxicity assessment of individual, binary and ternary mixtures of SiO2, Fe3O4, and ZnO nanoparticles in freshwater microalgae, Scenedesmus obliquus: Exploring the role of dissolved ions

Metal oxide nanoparticles (NPs) are considered among the most prevalent engineered nanomaterials. To have a deeper understanding of the mode of action of multiple metal oxide nanoparticles in mixtures, we have used a unicellular freshwater microalga Scenedesmus obliquus as a model organism. The toxicity of silicon dioxide (SiO2), iron oxide (Fe3O4), and zinc oxide (ZnO) NPs was studied individually as well as in their binary (SiO2 + Fe3O4, Fe3O4 + ZnO, and ZnO + SiO2) and ternary (SiO2 + Fe3O4 + ZnO) combinations. The effects of metal ions from ZnO and Fe3O4 were investigated as well. The results observed from the study, showed that a significant amount of toxicity was contributed by the dissolved ions in the mixtures of the nanoparticles. Decreases in the cell viability, ROS generation, lipid peroxidation, antioxidant enzyme activity, and photosynthetic efficiency were analyzed. Among all the individual particles, ZnO NPs showed the maximum effects and increased the toxicities of the binary mixtures. The binary and ternary mixtures of the NPs clearly showed increased toxic effects in comparison with the individual entities. However, the ternary combination had lesser toxic effects than the binary combination of Fe3O4 + ZnO. The decline in cell viability and photosynthetic efficiency were strongly correlated with various oxidative stress biomarkers emphasizing the crucial role of reactive oxygen species in inducing the toxic effects. The findings from this study highlight the importance of evaluating the combinatorial effects of various metal oxide NPs as part of a comprehensive ecotoxicity assessment in freshwater microalgae.

Automated summary

This study investigated the toxicity of metal oxide nanoparticles (NPs) in mixtures using a freshwater microalga as a model organism. The results showed that dissolved ions in the nanoparticles mixtures contributed significantly to the toxicity. The binary and ternary mixtures of NPs exhibited higher toxic effects compared to individual entities. These findings highlight the importance of evaluating the combinatorial effects of metal oxide NPs.