Correlation of α/γ-Fe2O3 nanoparticles with the toxicity of particulate matter originating from subway tunnels in Seoul stations, Korea

According to the increasing concern about particulate matter (PM) pollution at subway systems, particularly its potentially severe effects on human health, this study investigated the constituents, characteristics, and toxicity of PM collected at underground subway stations in Seoul, Korea. It was found that α/γ-Fe₂O₃ NPs, which are considered as thermal products derived from the brake-wheel-rail interface, were the main components of PM (57.6% and 48% of PM₁₀ and PM_2.5, respectively). In addition, hydrothermally synthesized α/γ-Fe₂O₃ NPs, proposing to possess similar properties to those of Fe₂O₃ contained in PM, were used to investigate the correlation of these oxides with PM toxicity. In particular, the synthesized γ-Fe₂O₃ NPs induced a negligibly toxic, while the synthesized α-Fe₂O₃ NPs and PM showed remarkably toxic effects on HeLa cells and zebrafish embryos, specifically in reducing cell proliferation to 85% and 72% survival, causing high apoptosis of 29.8% and 29.3%, and inhibiting the development of embryos up to 60% and 8% after prolonged exposure, respectively. It is considered that α-Fe₂O₃ NPs were primarily responsible for the harmful effects of PM, resulting in significant damage to DNA due to their capacity of producing high reactive oxygen species (ROS) and, thus, deleterious effects on the human body.