Size-dependent toxicity of microplastics induced gut cell apoptosis in brine shrimp Artemia parthenogenetica through p53 signaling pathway

Microplastics (MPs) are one of the most concerning pollutants that affects the health and growth of aquatic organisms. We characterized the MPs dispersion in the milli-Q water and seawater, and evaluated the effects of MPs on the gut epithelial cells of brine shrimp using three sizes of polystyrene (PS) microbeads (0.05, 0.5, and 5 µm, respectively). Results show that microbeads evenly dispersed in milli-Q water, but exhibited aggregation tendency in seawater associating with the particle size. Apart from a reduced survival rate, we observed the structure changes in the gut epithelium that the smaller size of PS microbeads resulted in an increased reactive oxygen species (ROS) and higher apoptosis-related genes expression. Moreover, exposure to all size of PS microbeads led to increased green fluorescence of J-monomer, indicating the declined mitochondrial membrane potential. Therefore, exposure to PS microbeads led to significantly size-dependent toxicity on brine shrimp. Especially, 0.05-µm PS microbeads were more toxic, leading to severe oxidative stress and activation of the p53-Bax-Bcl2 pathway, ultimately resulting in cellular apoptosis and gut damage. These findings are important to understand the mechanism of MPs toxicity and its potential ecological risks to marine aquatic animals.