However, the toxicity of ZnO nanoparticles is not directly related to their entering into the cell, rather their intimate contact onto the cell causes changes in the microenvironment in the vicinity of the organism-particle contact area to either increase metal solubilization or to generate ROS, that may ultimately damage cell membrane
Moreover, the toxicity of ZnO nanoparticles is not only affected by the light via ROS production, but may also happen in the dark although its mechanism is not yet defined
the mechanism of toxicity is still only partially understood