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 Cu²⁺ significantly increased the mortality and malformation rates, impaired swimming ability, and exhibited dose-dependent toxicity. Compared to Cu²⁺ exposure alone, TDF exposure significantly reduced thyroxine (T4) levels in zebrafish, and the co-exposure further exacerbated this reduction. Cu²⁺ alone downregulated several HPT-related genes (e.g., TTR), whereas TDF exposure and co-exposure upregulated TTR expression. Regarding reproductive toxicity, Cu²⁺ 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 Cu²⁺, improveing our understanding of the combined ecological risks posed by pesticide and heavy metal co-contamination.