Lactational exposure to polystyrene nanoplastics is associated with dose-related ovarian alterations in rat offspring

Polystyrene nanoplastics (PS-NPs) are an emerging class of environmental contaminants with increasing concern regarding their potential effects on reproductive development. This study examined whether maternal lactational exposure to PS-NPs is associated with alterations in ovarian growth, structure, and function in female rat offspring. The dams were administered PS-NPs at doses of 0, 0.1, 1, or 10 mg/kg/day exclusively during the 21-day lactation period. Female offspring were evaluated on postnatal days 30 (PD30) and 60 (PD60). Macroscopic assessments indicated dose-related reductions in body weight, ovarian weight, and ovarian length at both postnatal stages in females. Qualitative fluorescence microscopy using rhodamine-labeled PS-NPs revealed dose-related fluorescent signals within the follicular and stromal compartments of the ovary at PD30 and PD60, supporting particle localization in ovarian tissue. Histological and morphometric analyses revealed a reduction in pre-antral follicle numbers at PD30, progressive thinning of the granulosa layer, and a decreased parenchyma-to-stroma ratio, particularly in high-dose offspring. Biochemical analyses indicated oxidative imbalance, characterized by an elevated total oxidant status (TOS) and oxidative stress index (OSI) at PD30, along with a reduced total antioxidant capacity (TAC) and higher oxidative indices at PD60. Endocrine evaluation at PD60 showed dose-related decreases in circulating estradiol and progesterone levels. Immunohistochemical analysis demonstrated increased P53 immunoreactivity and reduced BCL-2 expression, consistent with apoptosis-related signaling in ovarian tissue. Collectively, these findings suggest that lactational exposure to PS-NPs is associated with dose-related ovarian alterations accompanied by oxidative imbalance, endocrine disruption, particle localization, and apoptosis-associated responses, highlighting lactation as a potentially sensitive postnatal exposure window.