Toxicological Assessment of Microplastics in Zebrafish: Biochemical Responses and Histopathological Changes

This study investigated the effects of polyethylene microplastics (PE MPs) on zebrafish (Danio Rerio), focusing on their survival, growth, bioaccumulation, oxidative stress and histopathological changes. Zebrafish were treated with two sizes of PE MPs (50 and 100 µm) at concentrations of 0.1, 10, 50, and 500 μg L^-1 for 12 and 24 days. Survival rates were high (> 95%), with no significant effect on growth. Bioaccumulation of MPs was dose dependent, with higher retention in the liver and gut than in the gills. The smaller MPs (50 µm) dispersed more widely in the body, whereas the larger MPs (100 µm) were mostly retained in the digestive organs. Oxidative stress responses, indicated by increased activity of enzymatic antioxidants such as superoxide dismutase (SOD) and catalase (CAT), along with elevated levels of nonenzymatic antioxidants including glutathione (GSH), glutathione S-transferase (GST), and glutathione peroxidase (GSH-Px), were observed with higher concentrations and longer exposure periods. Elevated lipid peroxidation (LPO) levels suggested cellular damage due to oxidative imbalance. Histopathological investigation showed concentration-dependent structural damage in the intestinal epithelial cells with necrosis, infiltration, and lipid droplet formation in the hepatocytes, while there was minimal or no damage to the brain and kidney. These findings demonstrate that exposure to MPs can induce bioaccumulation and oxidative stress in aquatic organisms, highlighting the need for mitigation strategies and further research into the long-term ecological impacts of MPs in aquatic ecosystems.