The toxic effect of two types of nanoparticles on Pseudourostyla cristata

AgNPs and TiO₂NPs are the most common nanomaterials in industrial production and our daily life. Here, we used the single-cell protozoan ciliate Pseudourostyla cristata as the test organism to study AgNPs and TiO₂NPs against their acute toxic effect on P. cristata by using the probability unit method, AO-PI double fluorescent staining, Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), and enzyme activity assay. The results showed that the 24h-LC₅₀ of AgNPs and TiO₂NPs against P. cristata was 1.21 × 10^-5 mg/L and 138.75 mg/L, respectively. The 24h-EC₅₀ were 3.55 × 10^-6 mg/L and 88.85 mg/L. This indicates that the acute toxicity of AgNPs on P. cristata is stronger than TiO₂NPs. AO-PI double fluorescent staining and TEM showed that TiO₂NPs, but not AgNPs, caused damage to the cell membrane. However, the high-oxidation of AgNPs and TiO₂NPs on the constituents of the cell membrane component (amide I, -COO-, ν_a (PO^2-), δ (C-OH) of the polysaccharide, etc.) was both detected by ATR-FTIR. Besides, AgNPs and TiO₂NPs initially increased the activity of the cell superoxide dismutase (SOD) and then reduced it while the activity of the catalase (CAT) continued to increase. The above results indicate that the acute toxicity of AgNPs to P. cristata is much stronger than that of TiO₂NPs, but TiO₂NPs is more resistant to the structure and composition of cell membranes, suggesting that other mechanisms of toxicity are present. P. cristata is sensitive to the toxicity of AgNPs and TiO₂NPs, so it can be used as a model organism to predict the environmental risk of nanomaterials in the early stage.