Polystyrene Microplastics Disrupt Vertical Transmission of the Breast Milk Microbiome, Impairing Early‐Life Gut Colonization and Immune Development in Offspring

ABSTRACT Microplastics, as a class of emerging contaminants (ECs), have been found to accumulate in mammary tissue, and their potential transgenerational risks to offspring health have garnered widespread attention. Here, we investigated whether maternal microplastic exposure may alter the breast milk microbiome, thereby disrupting early intestinal microbiota colonization in offspring and affecting their immune development. Pregnant and lactating dams were exposed to two concentrations of polystyrene microplastics (PS‐MPs, 10 and 40 mg/L) via drinking water. Our results showed that maternal PS‐MPs exposure disrupted early gut microbiota colonization in offspring, manifested as imbalances in both maternal milk microbiota and offspring gut microbiota. Beneficial bacterial abundance decreased (e.g., Ligilactobacillus ), while potentially harmful bacteria increased (e.g., Escherichia‐Shigella ). Concurrently, offspring from the exposed group exhibited excessive weight gain and impaired immune development, characterized by significantly reduced serum interleukin‐6 (IL‐6) levels, decreased splenic T‐cell proportions, and compromised intestinal barrier integrity. Further analysis indicated that these outcomes were associated with alterations in milk microbiome structure and short‐chain fatty acids (SCFAs) concentrations. Collectively, this study reveals the potential for maternal exposure to PS‐MPs to impair offspring gut microbiota colonization and immune development by reshaping breast milk microbiota, suggesting the potential hazards of PS‐MPs to maternal and infant health.