Engineered and Weathered Polyethylene Terephthalate ( <scp>PET</scp> ) Microplastics and Nanoplastics Induce Form and Size‐Dependent Oxidative Stress, Oxidative <scp>DNA</scp> Damage, and Cytotoxicity in <scp>MCF</scp> ‐7 Cells

Microplastics are an emerging environmental contaminant of concern due to their extensive use, ubiquitous presence in the environment, and detection in humans, wildlife, and marine organisms. While overwhelming data suggest the toxicity of engineered (Pristine) micro/nanoplastics, the adverse effects of environmentally relevant weathered particles are still unclear. In this context, using cellular, molecular, and biochemical approaches, this study investigated adverse effects, such as cytotoxicity, oxidative stress, and oxidative DNA damage potential, following exposure of MCF-7 cells to non-weathered polyethylene terephthalate (PET) particles of varying morphologies and sizes (810 nm and 17 μm) as well as weathered microplastics. MTT assay for cell viability revealed dose-dependent toxicity of these particles toward MCF-7 cells. DCFH-DA assay revealed a significant increase in ROS production across all treatments relative to controls. Cytotoxicity and oxidative stress induced by micro- and nanoplastics were confirmed by increased expression of proapoptotic marker (BAX) and oxidative DNA damage marker gene OGG1, and decreased expression of anti-apoptotic marker (BCL-2). Moreover, western blot analysis showed a significant increase in the level of DNA double strand break marker protein H₂AX as well as decreased levels of antioxidant MnSOD, suggesting a mechanistic link between micro and nanoplastic-induced ROS and oxidative DNA damage-dependent cytotoxicity. In summary, the results of this study using multiple approaches provide new mechanistic insight into the micro- and nanoplastic-induced and oxidative stress-dependent cytotoxicity in MCF-7 cells. The novel and mechanistic findings of this study will have a significant impact on our understanding of the adverse effects of micro- and nanoplastics on human health.