Nanoplastics transport in zebrafish brain: Molecular and phenotypic behavioral impacts

Nanoplastics (NPs) can accumulate in animal brain, but their kinetics and potential adverse impacts on the brain are not yet understood. This study compared the impacts of 200 nm (L-NPs) and 50 nm (S-NPs) NPs on the zebrafish (Danio rerio) brain at environmentally relevant concentration (500 μg L^-1), exploring how these nanoparticles were accumulated and removed, as well as their subsequent adverse effects at various biological levels. The bioconcentration factor and biological half-time in brain of L-NPs were 11.8 L kg^-1 and 1.54 d, while those for S-NPs were 18.9 L kg^-1 and 2.48 d, respectively. S-NPs displayed a higher tendency to accumulate and a slower elimination with a higher potential for long-term brain accumulation. Proteomic analysis of fish brain revealed that S-NPs exposure exhibited a higher level of differential expression of vesicle transport proteins. Transcriptomic analysis suggested that both NPs exposure significantly impacted pathways linked to inflammation and locomotion, while S-NPs additionally leading to increased enrichment of pathways associated with photoreceptor and phototransduction disorders. Both L-NPs and S-NPs caused damages in brain regions and even led to heightened oxidative stress across the whole brain regions. At the behavioral level, NPs induced abnormal patterns and feeding responses, and S-NPs further heightened the zebrafish sensitivity to light stimulation. Our study provides strong evidence of the risk of neurological diseases stemming from the prolonged accumulation of NPs in the brain, especially for the smaller-sized NPs.