Keywords: 
• perfluorooctanesulphonic acid potassium salt (PFOS) /
• ZnO nanoparticles (Nano-ZnO) /
• zebrafish /
• hypothalamic-pituitary-thyroid axis /
• thyroid hormone

Abstract: Perfluorooctanesulphonic acid potassium salt (PFOS) and ZnO nanoparticles (Nano-ZnO) are widely distributed in the environment. However, the potential toxicity of co-exposure to PFOS and Nano-ZnO remains to be fully elucidated. Our present study investigated the effects of co-exposure to PFOS and Nano-ZnO on the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish. The embryos were exposed to PFOS (0.2, 0.4, 0.8 mg·L^-1) single solutions, Nano-ZnO (6.75, 12.5, 25 mg·L^-1) single solutions and PFOS plus Nano-ZnO (0.2+6.75, 0.4+12.5, 0.8+25 mg·L^-1) mixture solutions for 15 days. We analyzed development toxicity, the whole-body content of TH and the expression of genes (corticotropin-releasing factor (CRF), thyroid-stimulating hormone (TSHβ), sodium/iodide symporter (NIS), thyroglobulin (TG), thyroid peroxidase (TPO)) related to the HPT axis. Compared with single-exposure groups, the body length and survival rate decreased, the malformation rates increased in co-exposure groups. The triiodothyronine (T3) levels increased and the thyroxine (T4) content decreased in co-exposure groups. Compared with the exposure to PFOS and Nano-ZnO alone, the expression of genes (CRF and NIS) significantly up-regulated and the expression of genes (TSHβ and TG) significantly down-regulated in co-exposure groups. In addition, the expression of TPO gene was unchanged in both the single and co-exposure groups. Our results were the first evidence for the thyroid-disrupting effects of PFOS and Nano-ZnO co-exposure in zebrafish. The results also provide insight into the mechanism of disruption of the thyroid status by PFOS and Nano-ZnO.