Toxicities of three metal oxide nanoparticles to a marine microalga: Impacts on the motility and potential affecting mechanisms

With the fast growth of the production and application of engineered nanomaterials (ENMs), nanoparticles (NPs) that escape into the environment have drawn increasing attention due to their ecotoxicological impacts. Motile microalgae are a type of primary producer in most ecosystems; however, the impacts of NPs on the motility of microalgae have not been studied yet. So the toxic impacts of three common metal oxide NPs (nTiO₂, nZnO, and nFe₂O₃) on swimming speed and locomotion mode of a marine microalgae, Platymonas subcordiformis, were investigated in this study. Our results demonstrated that both the velocity and linearity (LIN) of swimming were significantly decreased after the exposure of P. subcordiformis to the tested NPs. In addition, the obtained data indicate that NPs may suppress the motility of P. subcordiformis by constraining the energy available for swimming, as indicated by the significantly lower amounts of intracellular ATP and photosynthetic pigments and the lower activities of enzymes catalyzing glycolysis. Incubation of P. subcordiformis with the tested NPs generally resulted in the overproduction of reactive oxygen species (ROS), aggravation of lipid peroxidation, and induction of antioxidant enzyme activities, suggesting that imposing oxidative stress, which may impair the structural basis for swimming (i.e. the membrane of flagella), could be another reason for the observed motility suppression. Moreover, NP exposure led to significant reductions in the cell viability of P. subcordiformis, which may be due to the disruption of the energy supply (i.e., photosynthesis) and ROS-induced cellular damage. Our results indicate that waterborne NPs may pose a great threat to motile microalgae and subsequently to the health and stability of the marine ecosystem.