Distribution, environmental behavior, and ecotoxicity of different metal oxide nanoparticles in the aquatic environment

Metal oxide nanoparticles (MONPs) are inevitably released into environment during the life cycle. Transformation processes of MONPs such as aggregation, deposition, and dissolution in environment will dominate the occurrence forms. Occurrence forms of MONPs will influence their mobility, bioavailability, and toxicity. Transformation of MONPs under the impact of pH, ionic strength (IS), and natural organic matter (NOM) are summarized to thoroughly identify environmental behavior of MONPs. The effect of MONPs on physiological and biochemical properties of microalgae in freshwater systems are discussed, and the toxicity mechanisms of MONPs were analyzed. The relationship between transformed occurrence forms of MONPs and their ecotoxicity caused by the variation of water quality factors is emphasized. Noteworthily, the transformation pathway of MONPs under the influence of environmental factors is uncertain, which makes it difficult to predict their occurrence forms in surface waters. Therefore, it's crucial to consider the combined impact of these factors on MONPs behavior in natural aquatic environment. Overall, this review aims to enhance the comprehension of their environmental risks in aquatic settings and establish a scientific foundation for the sustainable progression of nanotechnology.