Effects of polyvinyl chloride microplastics with different particle sizes on growth, physiology, and intestinal microbiota of Macrobrachium rosenbergii

Background: This study addresses a critical knowledge gap regarding the long-term, multi-size-dependent toxic effects of polyvinyl chloride microplastics (PVC-MPs) on economically important freshwater aquaculture species, specifically the giant freshwater prawn (Macrobrachium rosenbergii). Given the severe microplastic pollution in intensive aquaculture regions like China's Pearl River Delta, understanding these impacts is vital for ecological risk assessment and sustainable aquaculture. Methods: Post-larval M. rosenbergii were exposed to environmentally relevant concentrations (1 mg/L) of fluorescent PVC-MPs of three particle sizes (30, 60, 90 μm) for 28 days, followed by a 14-day recovery period in clean water. A comprehensive analysis was conducted, including assessments of growth and survival, microplastic accumulation, tissue ultrastructure and apoptosis, gene expression related to antioxidant defense, immunity, and growth, and intestinal microbiota composition. Results: Exposure to PVC-MPs significantly inhibited growth and reduced survival, with the 90 μm particles showing the strongest effect. MPs accumulated in gills and intestines within one day and entered the circulatory system. They caused significant ultrastructural damage and increased apoptosis in gills, intestines, and hepatopancreas. Molecular responses showed an initial upregulation followed by suppression of antioxidant and immune-related genes after long-term exposure. Gut microbiota analysis revealed dysbiosis, characterized by decreased Firmicutes and increased Proteobacteria. Recovery experiments indicated particle-size-dependent clearance: large (90 μm) MPs were completely eliminated within 14 days, while smaller particles (30, 60 μm) persisted in tissues. Conclusion: PVC-MPs impair M. rosenbergii growth through physical damage, oxidative stress, immune suppression, and gut microbiota dysbiosis, with toxicity and clearance efficiency being particle-size-dependent. These findings provide insights into the ecological risks of microplastics in aquaculture.