Synergistic thyroid disruption and reproductive toxicity induced by co-exposure of triadimefon and copper in zebrafish embryos

The co-occurrence of pesticides and heavy metals in aquatic ecosystem poses a significant threat to biota, yet the interactive toxicological effects and mechanisms remain poorly understood, especially during their early developmental stages. In this study, we employed zebrafish embryos as a sensitive model to investigate the combined effects of fungicide triadimefon (TDF) and copper (Cu 2 + ) on endocrine regulation via the hypothalamus-pituitary-thyroid (HPT) and hypothalamus-pituitary-gonadal (HPG) axes. Our results showed that both individual and combined exposures to TDF and Cu 2+ significantly increased the mortality and malformation rates, impaired swimming ability, and exhibited dose-dependent toxicity. Compared to Cu 2+ exposure alone, TDF exposure significantly reduced thyroxine (T4) levels in zebrafish, and the co-exposure further exacerbated this reduction. Cu 2+ alone downregulated several HPT-related genes (e.g., TTR ), whereas TDF exposure and co-exposure upregulated TTR expression. Regarding reproductive toxicity, Cu 2+ exhibited a stronger inhibitory effect on key HPG genes (e.g., cyp19a ) compared to TDF; however, co-exposure significantly enhanced these inhibitory and induced the upregulation of genes such as StAR . The results of this study provide insights into the dual disruption of thyroid and reproductive endocrine functions by TDF and Cu 2+ , improveing our understanding of the combined ecological risks posed by pesticide and heavy metal co-contamination. • Co-exposure of TDF and copper increased developmental and behavioral toxicity. • Copper exerted stronger reproductive toxicity in zebrafish than triadimefon. • TDF reduced thyroxine levels, worsened by copper presence. • Different changes in HPT and HPG-related genes revealed dual endocrine disruption.