Chronic exposure to polystyrene microplastics at environmentally relevant concentration induced growth retardation in Macrobrachium rosenbergii via multi-pathway toxicity: Oxidative stress, microbial dysbiosis, and biodistribution

This study investigated the toxic mechanisms of environmentally relevant concentrations (1 mg/L) of polystyrene microplastics (5 μm) on juvenile Macrobrachium rosenbergii, a freshwater species of economic importance, through a 42-d chronic exposure and a 14-d recovery experiment. The results showed that microplastics significantly inhibited growth, causing a 15.6% reduction in body length and a 29.6% decrease in body weight, and accumulated extensively in the gills, stomachs, intestines, and hemolymph (residue level: 4.777 mg/kg). Ultrastructural analysis revealed persistent mitochondrial swelling in gill filaments and shedding of intestinal villi, even during the recovery phase. Oxidative stress biomarkers (GSH-Px) and upregulated lipid metabolism genes (fas and acc) indicated metabolic dysregulation. Additionally, the gut microbiota exhibited significantly increased α-diversity, with an increased abundance of Proteobacteria (potential pathogens) and a reduction in Firmicutes (beneficial taxa), suggesting microecological imbalance. This study is the first to elucidate the multifaceted toxicity mechanisms of microplastics at environmentally relevant concentrations (1 mg/L), demonstrating that they suppress growth in M. rosenbergii through physical damage, oxidative stress, and microbiota disruption, thereby providing a scientific basis for pollution control in freshwater aquaculture.