THE SILENT BURDEN OF REAL‑WORLD PET MICROPLASTICS: REVEALING CELL‑TYPE‑SPECIFIC IMPAIRMENT IN RUMINANT MODELS

Ruminants are increasingly exposed to microplastic contamination through forage ingestion, particularly polyethylene terephthalate (PET), which is widely used in agricultural practices. Beyond their ubiquity as environmental pollutants, microplastics may act as carriers of endocrine disruptors, raising concerns for reproductive health. Although PET particles have been detected in human placenta, bovine follicular fluid, and semen, their effects on reproductive and accessory tissues remain poorly understood. To investigate how PET microplastics interact with highly vascularized organs, we assessed their impact on ovine term placenta (oTP) cells and bovine mammary epithelial cells (MAC-T). Virgin PET was mechanically processed by progressive milling and sieving to obtain environmentally relevant size fractions (<20 μm and 20–50 μm) and characterized for morphology, size distribution, and crystallinity. Cells were exposed for 24–48 hours to 1, 5, and 50 μg/mL PET microplastics, and cell viability was first assessed; subsequently, functional endpoints (migration, proliferation, apoptosis) and metabolic endpoints (oxidative‑stress response, mitochondrial activity) were evaluated. Size‑dependent effects dominated the cellular responses to PET microplastics, with the <20 μm fraction driving the strongest alterations. oTP cells showed marked susceptibility, with viability reduction already at 1 μg/mL, while MAC-T cells were affected only at higher doses. Placental cells exhibited a pronounced oxidative‑stress disequilibrium accompanied by mitochondrial functional impairment, indicating that ROS accumulation disrupts mitochondrial homeostasis and ultimately compromises migratory behaviour. Conversely, mammary epithelial cells showed a shift in the apoptosis– proliferation axis, characterized by decreased mitotic activity and enhanced cell death. At elevated doses, both models displayed clear physical interactions with PET particles, consistent with intensified cell–particle contact. This study is the first to employ PET particles generated through a degradation process that mimics environmental fragmentation rather than relying on commercial microplastics. By using PET fractions that more closely reflect those ingested by ruminants in contaminated forage, the observed effects gain greater ecological and biological relevance. Moreover, considering the chronic exposure of livestock to microplastic‑contaminated feed, these results highlight the need to investigate environmentally aged particles and to clarify long‑term impacts on reproductive and mammary tissue functionality. [1] Ragusa et al., Environ Int, 2021. [2] Dong et al., J Hazard Mater, 2026. [3] Shelver et al., Sci Total Environ, 2025.