Single and Combined Toxicity Effects of Zinc Oxide Nanoparticles: Uptake and Accumulation in Marine Microalgae, Toxicity Mechanisms, and Their Fate in the Marine Environment

Recently, there has been rapid growth in the production of zinc oxide nanoparticles (ZnO-NPs) due to their applications in household and cosmetic products. Over the last decade, considerable research was conducted to reveal the effect of ZnO-NPs on microalgae, which form the base of the aquatic food chain. This review discusses the fate and behavior of ZnO-NPs in the marine environment. Predominately, the toxicity mechanism of ZnO-NPs on marine microalgae could be attributed to three sources: the release of Zn2+ ions; the interaction between ZnO-NPs and algae cells; and the generation of reactive oxygen species (ROS). Most toxicity studies were carried out using single ZnO-NPs under conditions not often observed in natural ecosystems; however, organisms including microalgae are more likely exposed to ZnO-NPs mixed with other types of pollutants. This review highlights the importance of increasing the assessment studies of combined pollutants. Lastly, knowledge, research, gaps, and opportunities for further research in this field are presented