Combined exposure to fenvalerate and tebuconazole induces apoptosis, leading to developmental and endocrine toxicity in early life stages of Japanese Medaka (Oryzias latipes)

Abstract

Pesticide residues in aquatic ecosystems often occur as complex mixtures, posing significant risks to aquatic fauna. However, the toxicological effects of fenvalerate (FEN) and tebuconazole (TEB) on marine and freshwater aquatic organisms are poorly studied. To evaluate the impact of fenvalerate and tebuconazole on the early development of Japanese medaka (Oryzias latipes), embryos and larvae were exposed to FEN (3 × 10⁻³ mg/L), TEB (1 mg/L), and a combined treatment of FEN+TEB (1 × 10⁻³ mg/L + 0.1 mg/L). The results showed that the combined exposure significantly reduced hatchability, survival rate, and heartbeat rate, indicating a synergistic effect. Morphological abnormalities were observed in embryos and newly hatched larvae, such as pericardial edema, yolk sac extension, curved spine, and caudal fin abnormalities. Apoptosis was induced in both single and combined mixture toxicity, as evidenced by upregulated expression of pro-apoptotic genes (bax, p53, and caspase3). Furthermore, key genes in the hypothalamic-pituitary-gonadal (HPG) axis (cyp19a, cyp17, fshr, lhr, erα, erβ) and reproduction-related genes (vtg1 and vtg2) were downregulated, while star was upregulated in the binary mixture group. These results suggest that combined exposure to FEN and TEB induces synergistic toxicity, leading to increased mortality, developmental abnormalities, and endocrine disruption. This study enhances understanding of the molecular mechanisms underlying embryonic and larval development and underscores the importance of assessing the risk of pesticide mixtures in aquatic ecosystems.