Physiological homeostasis alteration and cellular structure damage of Chlorella vulgaris exposed to silver nanoparticles with various microstructural morphologies

The toxicity of silver nanoparticles (AgNPs) with a single morphology to aquatic organisms has been well demonstrated in the past decade, but few studies have been carried out to evaluate the differences in toxicity among AgNPs with various microstructural morphologies. In this work, C. vulgaris was used as the tested organism to examine the differences in toxic effects among AgNSs, AgNCs, and AgPLs at concentrations of 0.5, 1.0, 2.0, and 5.0 mg/L. The results showed that the cell density and chlorophyll a content of C. vulgaris decreased when the dose of AgNPs was increased, while the inhibiting effects that were caused by AgPLs were stronger than those that were caused by AgNCs and AgNSs. Under short-term exposure to AgPLs, the ROS content was significantly higher than those under exposure to AgNCs and AgNSs, while the MDA content fluctuated without obvious regularity. The dose of AgPLs affected the antioxidative enzyme activity and lipid peroxidation more obviously than those of AgNSs and AgNCs. The superoxide dismutase and catalase contents in the former case were distinctly higher than those in the latter cases. Consequently, the cell apoptosis rate under exposure to AgPLs reached 83%, which was higher than those under exposure to AgNSs (50%) and AgNCs (71%). This work shows that the level of toxicity to C. vulgaris was in the order of AgPLs > AgNCs > AgNSs. The obtained results demonstrate that the microstructural morphologies of AgNPs determined their potential toxicity.