UV-aged microplastics induces neurotoxicity by affecting the neurotransmission in larval zebrafish

Microplastics (MPs) are nearly ubiquitous in aquatic ecosystems and may affect aquatic organisms. In this study, virgin and aged polystyrene MPs (PS-MPs) of size 1 μm were selected to analyze their adverse effects on larvae zebrafish. Exposure to PS-MPs significantly reduced the average swimming speed of zebrafish, and the behavioral effects caused by aged PS-MPs on zebrafish were more pronounced. Fluorescence microscopy revealed that 10-100 μg/L of PS-MPs accumulated in tissues of zebrafish. As an endpoint of neurotransmitter concentration, exposure to aged PS-MPs at doses ranging from 0.1 to 100 μg/L significantly increased the dopamine (DA), 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (GABA), and acetylcholine (ACh) levels in zebrafish. Similarly, exposure to aged PS-MPs significantly altered the expression of genes related to these neurotransmitters (e.g., dat, 5ht1aa, and gabral genes). According to Pearson correlation analyses, neurotransmissions was significantly correlated with neurotoxic effects of aged PS-MPs. Thus, aged PS-MPs cause neurotoxicity in zebrafish through their effects on DA, 5-HT, GABA, and ACh neurotransmissions. The results highlight the importance of the neurotoxicity of aged PS-MPs in zebrafish, which has important implications for the risk assessment of aged MPs and the conservation of aquatic ecosystems.