Magnetic iron oxide nanoparticles: An emerging threat for the environment and human health

Magnetic iron oxide nanoparticles (Fe_xO_y NPs, mainly Fe₃O₄ and γ-Fe₂O₃) are nanomaterials ubiquitously present in aquatic, terrestrial, and atmospheric environments, with a high prevalence and complex sources. Over the past decade, numerous reports have emerged on the presence of exogenous particles in human body, facilitated by the rapid development of separation and detection methods. The health risk associated with magnetic Fe_xO_y NP have garnered escalating attention due to their presence in human blood and brain tissues, especially for their potential association with neurodegenerative diseases like Alzheimer's disease. In this paper, we provide a comprehensive overview of sources, analysis methods, environmental impacts, and health risks of magnetic Fe_xO_y NP. Currently, most researches are primarily based on engineered Fe_xO_y NP, while reports about magnetic Fe_xO_y NP existing in real-world environments are still limited, especially for their occurrence levels in various environmental matrices, environmental transformation behavior, and biotoxic effects. Our study reviews this emerging pollutant, providing insights to address current research deficiencies and chart the course for future studies.