Polyethylene microplastics perforate the chorion defense, triggering developmental cardiotoxicity at zebrafish

Polyethylene microplastics are pervasive environmental pollutants that pose potential risks to aquatic organisms. This study investigates the effects of polyethylene microplastics on zebrafish (Danio rerio, Hamilton 1822) embryo development, with a focus on whether the chorion, a protective barrier surrounding the embryo, is effective in blocking polyethylene penetration. Contrary to previous findings that suggested the chorion could prevent larger microplastics (>0.7 µm) from entering, our study demonstrates that polyethylene particles sized 1-4 µm can still negatively impact embryo development without dechorionation. Embryos were exposed to polyethylene at concentrations of 0.01, 0.1, and 1 mg l^-1, followed by RNA sequencing to assess gene expression changes. Despite no significant differences in survival, hatching, or body length between control and treated groups, a significant reduction in heart rate was observed at higher concentrations, indicating potential sub-lethal cardiotoxicity. Further, RT-qPCR validation confirmed significant downregulation of key heart development-related genes, particularly fbln1 and fn1b, in polyethylene-exposed embryos. These findings highlight the ability of polyethylene microplastics to penetrate natural barriers such as the chorion and induce physiological and developmental changes. Our results emphasize the need for further research into the long-term effects of microplastic exposure on aquatic ecosystems.