Hepatotoxic effects of low-concentration exposure to the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in adult male zebrafish (Danio rerio)

2,4-Dichlorophenoxyacetic acid (2,4-D) is an herbicide widely used around the world. It has been detected in water samples, with a half-life ranging from 15 to 300 days depending on environmental conditions. This study aimed to investigate the effects of a commercial formulation containing 2,4-D on oxidative stress markers, as well as on liver histopathological and histochemical parameters, in adult male Danio rerio for 7 days. The results revealed structural and vascular lesions in the livers of zebrafish across all groups exposed to 2,4-D (at concentrations of 0.03, 0.3 and 3.0 mg/L). Analysis of the Histopathological Alteration Index suggests severe (3.0 mg/L) or moderate (0.03 and 0.3 mg/L) liver impairment in zebrafish exposed to 2,4-D. Exposure to the herbicide also led to a reduction in acid polysaccharides (0.03 and 3.0 mg/L) and glutathione (GSH) levels (at concentrations of 0.03 and 3.0 mg/L), and increased levels of the oxidized glutathione (GSSG) (at concentrations of 0.03 and 0.3 mg/L). No significant changes in lipid peroxidation levels were observed. These findings suggest that as little as 7 days of exposure to permissible concentrations of 2,4-D (0.03 mg/L) or higher (0.3 and 3.0 mg/L) can negatively affect biochemical, histochemical, and histopathological parameters, as well as the integrated biomarker response index in the liver of adult zebrafish. This study provides the first evidence of the hepatotoxic effects of the herbicide 2,4-D in adult male Danio rerio .