Environmentally relevant polyethylene terephthalate (PET) microplastics induce functional and oxidative alterations...

Ruminants are among the livestock most at risk of microplastics (MPs) exposure due to the ingestion of contaminated forage, particularly with polyethylene terephthalate (PET). Yet, despite this high risk, the potential effects of microplastics on reproductive function in these species remain largely unknown. Here, we studied how environmentally relevant PET-MPs impact placental functionality and cellular responses in an in vitro sheep model. First, virgin PET was mechanically processed through progressive milling and sieving to obtain two fractions of 20-50 μm or <20 μm, which were characterised in size, distribution, and crystal structure; then ovine term placental cells were exposed to both sizes of PET-MPs for 24-48 h. MTT revealed that the smaller PET-MPs reduced cell viability even at low concentrations (1 μg/mL), whereas the larger fraction induced cytotoxicity only at 50 μg/mL. Placental cells diminished migratory capacity in the presence of smaller PET-MPs. Oxidative stress assessment further demonstrated a reduced ability to metabolize H₂O₂, along with a decrease in mitochondrial membrane potential, indicating compromised mitochondrial function; additionally, apoptosis was also slightly increased following exposure to the <20 μm PETs. Overall, our findings show that PET-MPs, particularly those below 20 μm, impair multiple functional and metabolic endpoints in ovine term placental cells, highlighting the risk to reproductive health in ruminants chronically exposed to microplastic-contaminated feed.