Cytotoxicity of single and binary mixtures of copper and silica nanoparticles exposed to Nitzschia closterium f. minutissima.

A large number of nanoparticles are produced and enter the aquatic environment, where they interact with each other, posing a potential threat to aquatic organisms. The toxicity of two types of nanoparticles (nCu and nSiO₂) on Nitzschia closterium f. minutissima (N. closterium f. minutissima) was investigated in this study by examining changes in microalgal cell density, instantaneous fluorescence rate (Ft), and a range of antioxidant parameters in the cells. It was found that both nCu and nSiO₂ showed time- and concentration-dependent toxic effects on N. closterium f. minutissima. nSiO₂ could promote microalgae growth at low concentrations by providing Si, an essential element for the synthesis of siliceous shells. As the exposure time increased, both the growth and photosynthetic efficiency of the microalgae were inhibited. Nanoparticles also produced oxidative stress and caused lipid peroxidation in the microalgae. In the meantime, SOD and CAT activity were altered to protect cells from oxidative damage. Inverted biomicroscopy images showed that the microalgae enhanced their cell size to adapt to the environmental stress as exposed to 1 mg/L nCu. Scanning electron microscope (SEM) images showed that 10 mg/L nSiO₂ could adsorb nCu and reduce the toxic effect of nCu on the microalgae, while 30 mg/L nSiO₂ caused mechanical damage to microalgal cells and accelerated the internalization of nanoparticles and Cu²⁺ in the cells.