Toxicity of Copper Oxide Nanoparticles to Chlorella Pyrenoidosa As Affected By Dissolved Organic Matter.

Abstract: This work investigated toxicity of CuO nanoparticles (NPs) to freshwater alga (Chlorella pyrenoidosa) in the presence of fulvic acid (FA). CuO NPs could inhibit the growth of algae, with a 72 h median effective concentration (EC₅₀) at 45.6 mg L^-1. FA significantly enhanced the toxicity of CuO NPs and the EC₅₀ value decreased to 10.3 mg L^-1. The enhanced toxicity by FA was attributed to the increased Cu²⁺ release and CuO suspension stability. Algal morphology was observed by Transmission Electron Microscope (TEM). Compared with the control, the cells treated by CuO ENPs have a thicker extracellular polymer layer which played an important role in NP uptake. By adding the endocytosis inhibitors, we found that intracellular Cu content decreased by 26%, suggesting that endocytosis is one of the ways of NPs uptake. Endocytosis of CuO NPs by algal cells was also confirmed by TEM observations. In addition, after CuO NP exposure, algal cell plasmolysis, photosynthesis chloroplast lamella rupture, and nuclear membrane damage were found. CuO NPs dispersed in cytoplasm, nuclei, chloroplast lamella in the form of a single or aggregates with a few particles. Moreover, the accumulation of additional reactive oxygen radicals (ROS) caused oxidative stress, which resulted in membrane lipid peroxidation and mitochondrial depolarization, finally algal cells apoptosis.