The Toxic Effects of Cu and CuO Nanoparticles on Euplotes aediculatus

The single-celled eukaryote Euplotes aediculatus was chosen to test and compare the toxic effects of Cu and CuO nanoparticles (NPs). The antioxidant enzymatic activity, morphological changes, and functional groups on the membrane were determined using spectrophotometry, microscopy, and Fourier transform infrared spectroscopy after NPs treatment. The toxicity of the NPs to cells was dose-dependent, and the 24 h-LC₅₀ values of the CuNPs and CuONPs were 0.46 µg/L and 1.24 × 10³ µg/L, respectively. These NPs increased the activities of superoxide dismutase, glutathione peroxidase, and catalase and destroyed the cell structure; moreover, the CuNPs were more toxic than the CuONPs. In addition to the higher enzymatic activity, CuNPs also caused nucleoli disappearance, chromatin condensation, and mitochondrial and pellicle damage. The oxidization of the functional groups of the membrane (PO₂ − , C–O–C, and δ(COH) of carbohydrates) also confirmed the severe damage caused by CuNPs. Our study showed that oxidative stress and organelle destruction played important roles in the toxic effects of these NPs on this protozoan. Compared with other aquatic organisms, E. aediculatus can be considered a potential indicator at the preliminary stage of environmental pollution.