The exploration of chronic combined toxic mechanisms of environmental PFOA and polyethylene micro/nanoplastics on adult zebrafish (Danio rerio), using aquatic microcosm systems.

Understanding the extent of environmental damage caused by plastic particles and emerging pollutants in aquaculture, particularly within recirculating aquaculture systems (RAS) that rely on advanced water treatment technologies, is constrained by insufficient knowledge regarding the chronic combined toxicity of these contaminants on representative fish species under real environmental conditions. This study investigates the combined toxic effects of polyethylene microplastics (PE-MPs), polyethylene nanoplastics (PE-NPs), and perfluorooctanoic acid (PFOA) on adult zebrafish at environmentally relevant concentrations in aquatic microcosm systems (AMS) simulating RAS exposure scenarios. The combined exposure to PE-MPs, PE-NPs, and PFOA exhibited time-dependent toxicity patterns: synergistic effects on zebrafish gills and liver after 7 days, followed by antagonistic interactions after 28 days of chronic exposure. MPs induced higher intestinal toxicity than NPs through mechanical damage and lipid peroxidation mechanisms. Both individual and combined exposures caused structural alterations in zebrafish intestines, with MPs provoking more severe villi atrophy and goblet cell reduction compared to NPs, while co-exposure exacerbated these pathological changes. Notably, PFOA triggered acetylcholine upregulation in intestinal and hepatic tissues, revealing stronger neurotoxic impacts than those observed in gill systems. Additionally, the co-exposure to MPs + PFOA and NPs + PFOA led to an increased abundance of Fusobacterium in zebrafish intestines, thereby enhancing their susceptibility to pathogenic infections. These findings highlight the complex temporal dynamics and tissue-specific risks of microplastic-PFOA interactions in closed aquaculture environments, providing critical insights for optimizing RAS water management strategies against emerging contaminant mixtures.