Toxicity effects of cadmium and β-cypermethrin on zebrafish by single and combined exposure: oxidative stress and histopathological evaluation.

Introduction: This study investigated the effects of cadmium (Cd) and β-cypermethrin (β-CP), both singly and in combination, on oxidative stress responses and tissue morphology in zebrafish. Methods: Through acute exposure experiments, we evaluated the acute toxicity and behavioral responses of zebrafish to these two compounds. Results: The LC50 values of contaminants for zebrafish at 24 h, 48 h, 72 h, and 96 h were 25.36, 22.94, 20.36, and 17.83 mg/L for Cd, and 6.41, 4.96, 4.23, and 3.75 μg/L for β-CP, respectively. The results showed that β- CP exhibited higher acute toxicity compared to Cd, with pronounced toxic reactions including body curling, convulsions, accelerated operculum flapping, and significantly reduced swimming ability. In contrast, cadmium (Cd) elicited milder acute toxicity symptoms yet significantly disrupted key oxidative stress parameters, including superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA). During the chronic co-exposure phase, the combined treatment of Cd and β-cypermethrin (β-CP) resulted in more severe toxicity than individual exposures, as supported by marked bioaccumulation of both contaminants and extensive histopathological impairments-such as neuronal degeneration in the brain, hepatocyte necrosis in the liver, and villus atrophy in the intestine. Quantitative assessments further indicated that the co-exposure provoked the strongest oxidative stress response, with the highest increases observed during the acute phase-reaching up to 75% for SOD, 51% for CAT, and 52% for MDA relative to the control group (P < 0.05). Discussion: This study revealed the severe toxic effects of combined exposure to Cd and β-CP on zebrafish, underscoring the need for increased attention to the potential ecological risks of heavy metal and pesticide pollution in aquatic environments.