Microplastics Decrease the Toxicity of ¹³⁷Cs in the Zebrafish Embryo-Larva

Large amounts of radionuclides and microplastics (MPs) have been released and will continue to be discharge into the environment. They will exist and interact in the aquatic environment over extended periods. However, the toxicological risks associated with their co-exposure remain poorly understood. In this study, the zebrafish (Danio rerio) embryos were exposed to ¹³⁷Cs (6.8 × 10⁴ Bq/L) in combination with 9.9 μm polystyrene MPs (PS-MPs, 10, 100 μg/L) for 7 days. Early developmental growth was significantly influenced in the ¹³⁷Cs-exposed groups. This was evidenced by delayed hatching, increased swimming total distance, and anxiety behavior (increasing swimming distance in the inner circle). Furthermore, transcriptomic analysis demonstrated that a higher number of differentially expressed genes were found in the ¹³⁷Cs group compared to other exposure groups. In ¹³⁷Cs groups, KEGG enrichment analysis highlighted significant disruptions in lipid metabolism pathways. ¹³⁷Cs can influence its neuro-related genes by inducing lipid metabolism toxicity, providing a mechanistic explanation for the observed locomotory abnormalities in larvae. Interestingly, during the early stage of development, MPs appeared to reduce the internal irradiation dose and toxic effect by absorbing the ¹³⁷Cs. Overall, this study enhances our understanding of the ecological risks posed by combined exposure to ¹³⁷Cs and MPs.