Mechanism of nanotoxicity in exposed to zinc and iron oxide.

Usage of nanoparticle in various products has increased tremendously in the recent past. Toxicity of these nanoparticles can have a huge impact on aquatic ecosystem. Algae are the ideal organism of the aquatic ecosystem to understand the toxicity impact of nanoparticles. The present study focuses on the toxicity evaluation of zinc oxide (ZnO) and iron oxide (FeO) nanoparticles towards freshwater microalgae, . The dose dependent growth retardation in is observed under ZnO and FeO nanoparticles and nanoform attributed more toxicity than their bulk counterparts. The IC values of ZnO and FeO nanoparticles was reported at 0.258 mg L and 12.99 mg L whereas, for the bulk-form, it was 1.255 mgL and 17.88 mg L, respectively. The significant decline in chlorophyll content and increase in proline content, activity of superoxide dismutase and catalase, indicated the stressful physiological state of microalgae. An increased lactate dehydrogenase level in treated samples suggested membrane disintegration by ZnO and FeO nanoparticles. Compound microscopy, scanning electron microscopy and transmission electron microscopy confirm cell entrapment, deposition of nanoparticles on the cell surface and disintegration of algal cell wall. Higher toxicity of nanoform in comparison to bulk chemistry is a point of concern.