Early neurotoxic effects of commercial 2,4-D formulation in zebrafish: A multibiomarker approach

Commercial formulations of 2,4-dichlorophenoxyacetic acid (CF2,4-D) are widely used in agriculture and frequently detected in aquatic environments, yet their neurotoxic effects remain poorly understood. We investigated behavioral, histological, stereological, and biochemical responses in adult zebrafish (Danio rerio) after 7-day exposure to CF2,4-D (0.03; 0.3; or 3.0 mg/L). Exposure to 3.0 mg/L induced anxiety-like behavior, evidenced by reduced vertical exploration, altered light-dark preference, and increased thigmotaxis. No histological or stereological changes were detected in the telencephalon. CF2,4-D reduced oxidized glutathione (GSSG) without affecting the GSH/GSSG ratio, suggesting maintenance of redox homeostasis. Conversely, increased nitrite and total protein levels indicated nitric oxide production and stress-related responses. The Integrated Biomarker Response index increased markedly at 3.0 mg/L, indicating higher biological disturbance under the experimental conditions. Collectively, these findings demonstrate that CF2,4-D induces neurobehavioral and biochemical disturbances, with functional alterations occurring prior to detectable structural changes in the brain.