Impacts of polystyrene nanoplastics on zebrafish gut microbiota and mechanistic insights

Aquatic environments are frequently contaminated with nanoplastics (NPs) ranging from 1-100 nm generated by plastic aging, but their bio-enrichment and toxicological impacts remain poorly understood. This study investigates how chronic exposure to carboxylated polystyrene nanoplastics (PNPs) alters gut microbiota composition and function in zebrafish (Danio rerio). Adult zebrafish were exposed to 50 nm PNPs at concentrations of 0.1, 1.0, and 10 mg/L for 14 and 28 days, followed by gut microbiota analysis using 16S rRNA gene sequencing. PNP exposure altered gut microbiota composition, including an increase in Proteobacteria abundance and a decrease in Firmicutes, Bacteroidetes, and the inflammation-related genus Alistipes. Beneficial probiotics such as Faecalibacterium, Streptococcus, Bifidobacterium, and Lachnospira were diminished, while pathogenic bacteria proliferated. TEM imaging revealed the internalization of PNP particles within intestinal tissues resulted in vacuolation, suggesting potential epithelial damage. Co-occurrence network patterns of gut microbiota greatly decreased during treatment with NPs. The neutral community model showed that among PNP treatments, 0.1 mg/L led to a less predictable (stochastic assembly process). PNP exposure led to increased predicted microbial functions (via PICRUSt2) related to xenobiotic metabolism, infection pathways, and lipopolysaccharide (LPS) production, while RNA transport and N-glycan biosynthesis were decreased. However, pathways related to microbial antioxidants exhibited significant variation across different PNP levels. These results provide critical insights into the toxicological impacts of chronic PNP exposure on fish gut health, highlighting the potential risks to aquatic ecosystems and human health.