Developmental toxicity, immunotoxicity and cardiotoxicity induced by methidathion in early life stages of zebrafish

Methidathion is a highly effective organophosphorus pesticide and is extensively utilized for the control of insects in agricultural production. However, there is little information on the adverse effects and underlying mechanisms of methidathion on aquatic organisms. In this work, embryonic zebrafish were exposed to methidathion at concentrations of 4, 10, and 25 mg/L for 96 h, and morphological changes and activities of antioxidant indicators alterations were detected. In addition, the locomotor behavioral abilities of zebrafish exposed to methidathion were also measured. To further explore the mechanism of the toxic effects of methidathion, gene expression levels associated with cardiac development, cell apoptosis, and the immune system were tested through qPCR assays. The findings revealed that methidathion exposure could induce a decrease in survival rate, hatchability, length of body, and increase in abnormality of zebrafish, as well as cardiac developmental toxicity. The LC50 value of methidathion in zebrafish embryos was determined to be about 30.72 mg/L at 96 hpf. Additionally, methidathion exposure triggered oxidative stress in zebrafish by increasing SOD activity, ROS, and MDA content. Acridine orange (AO) staining indicated that methidathion exposure led to apoptosis, which was mainly distributed in the pericardial region. Furthermore, significant impairments of locomotor activity in zebrafish larvae were induced by methidathion exposure. Lastly, the expression of pro-inflammatory factors including IFN-γ, IL-6, IL-8, CXCL-clc, TLR4, and MYD88 significantly up-regulated in exposed zebrafish. Taken together, the results in this work illustrated that methidathion caused developmental toxicity, cardiotoxicity, and immunotoxicity in embryogenetic zebrafish.