Polyethylene microplastic exposure and concurrent effect with Aeromonas hydrophila infection on zebrafish

Microplastics are widely distributed in the environment, raising significant concerns owing to their potential negative effects on humans. Zebrafish were used in this study to assess the toxicity of microplastic exposure. Adult zebrafish were exposed to polyethylene (PE) microplastics with smooth clustered sphere shapes and diameters of 75-100 µm for 35 days. Survival rates of the zebrafish were not significantly affected, whereas growth rates were. Analyses on oxidative stress-related enzyme activities showed that glutathione (GSH), glutathione peroxidase (GSH-PX), and glutathione s-transferase (GST) production in the intestines was stimulated when exposed to low concentrations of microplastics (0.1 and 1 mg/L), while superoxide dismutase (SOD), catalase (CAT), GSH, and GSH-PX production was suppressed when exposed to 10 mg/L microplastics. Enzyme activities in the muscles were much less affected. Intestinal injuries and changes in colony structure in the intestines were observed in zebrafish following exposure to microplastics. After 35 days of exposure, concurrent exposure to microplastics and Aeromonas hydrophila did not increase zebrafish mortality compared with those challenged by bacteria alone. This study confirms that intestinal enzyme activities of zebrafish are altered by exposure to PE microplastics but mortality and bacterial infection were not significantly affected under the tested conditions.