Aged polystyrene microplastics exacerbate cadmium-induced hepatotoxicity in zebrafish through gut-liver axis metabolic dysregulation

Microplastics (MPs) are ubiquitous environmental contaminants that can adsorb heavy metals, with aging enhancing adsorption capacity. This intensifies the threat posed to aquatic organisms and complicates liver toxicity. Herein, zebrafish were exposed to polystyrene (PS) or aged PS (APS) (200 μg/L) and cadmium (Cd) (10 μg/L) for 21 days, either singly or in combination, to investigate hepatotoxicity and underlying mechanisms, focusing on the gut-liver axis. Results indicated that co-exposure to APS and Cd caused more severe liver damage. Aging of PS significantly enhanced its ability to adsorb Cd, leading to greater Cd accumulation. Oxidative stress (ROS, SOD, MDA, and CAT levels increased by 1.73, 0.90, 1.08, and 0.89-fold, respectively), inflammation (TNF-α level increased by 1.30-fold), and lipid accumulation (TG and T-CHO contents increased by 0.83 and 1.48-fold, respectively) were exacerbated in the liver. The expression levels of the corresponding genes in the liver were also significantly up-regulated. Metabolomic analysis revealed that PS + Cd co-toxicity was associated with cellular senescence pathway, while APS + Cd co-exposure induced lipid accumulation via the sphingolipid, PPP, and protein digestion and absorption metabolisms. Furthermore, APS + Cd exposure significantly reduced the expression of ZO-1 , Occludin , and MUC2 , leading to gut barrier disruption and gut microbial composition changes in gut microbial composition, including increased Firmicutes and Paracoccus , along with decreased Fusobacteriota, which contributed to stronger synergistic toxicity via the gut-liver axis, interacting with metabolites such as tetradecanoic acid. This study facilitated valuable insights into the broader implications of PS contamination and its interaction with heavy metals. • MPs and Cd combined toxicity on zebrafish liver was analyzed via the gut-liver axis • APS+Cd exposure induced higher toxicity than single exposure • APS+Cd exposure altered APS structure, exacerbated tissue damage and Cd adsorption • APS+Cd exposure disrupted gut barrier and gut microbial structure • APS+Cd exposure induced significant lipid metabolism disorders and accumulation