Maternal exposure to chiral triazole fungicide tebuconazole induces enantioselective thyroid disruption in zebrafish offspring

Pesticides could induce long-term impacts on aquatic ecosystem via transgenerational toxicity. However, for many chiral pesticides, the potential enantioselectivity of transgenerational toxicity has yet to be fully understood. In this study, we used zebrafish as models to evaluate the maternal transfer risk of tebuconazole (TEB), which is a chiral triazole fungicide currently used worldwide and has been frequently detected in surface waters. After 28-day food exposure (20 and 400 ng/g) to the two enantiomers of TEB (S- and R-TEB) in adult female zebrafish (F0), increased malformation rate and decreased swimming speed were found in F1 larvae, with R-TEB showing higher impacts than S-enantiomer. Additionally, enantioselective effects on the secretion of thyroid hormones (THs) and expression of TH-related key genes along the hypothalamic-pituitary-thyroid (HPT) axis were found in both F0 and F1 after maternal exposure. Both the two enantiomers significantly disrupted the triiodothyronine (T3) and thyroxine (T4) contents in F0 with different degrees, whereas in F1, significant effects were only found in R-TEB groups with decreasing of both T3 and T4 contents. Most of the HPT axis related genes in F0 were upregulated by TEB and more sensitive to R-TEB than to S-TEB. In contrast, most of the genes in F1 were downregulated by both R- and S-TEB, especially the genes that are primarily responsible for thyroid development and growth (Nkx2-1), TH synthesis (NIS and TSH beta) and metabolism (Deio1). Findings from this study highlight the key role of enantioselectivity in the ecological risk assessment of chiral pesticides through maternal transfer.