The effects of disturbance on hypothalamus-pituitary-thyroid axis in zebrafish larvae after exposure to polyvinyl alcohol

In recent years, considerable concerns have been raised regarding environmental pollution caused by water-soluble polymers (WSPs). Polyvinyl alcohol (PVA), used in the textile industry and in the manufacture of medical consumables, is one type of WSPs. After use, PVA is discharged and enters aquatic ecosystems, but most of it cannot be completely biodegraded in the environment. In this study, we investigated the effects of PVA on developmental toxicity and thyroid endocrine disruption using a zebrafish (Danio rerio) model. We treated zebrafish embryos with 10 g/L and 5 mg/L PVA for 96 h and found that the proportion of coagulated embryos significantly increased, resulting in a remarkable decrease in hatching rate and larval survival. The body length of zebrafish larvae in the exposed group was remarkably shorter than that of the control group (Control: 3.64 ± 0.03 mm vs. 10 g/L PVA: 3.46 ± 0.03 mm; p=0.001). Compared to the control group, the levels of T3 and T4 in embryos of the exposed group were significantly lower, while thyroid stimulating hormone (TSH) levels were significantly increased. Notable up-regulation of trh, tshβ, and tshr genes, as well as down-regulation of trα , tg, ttr, dio1, and dio2 genes, were observed in embryos of the exposed group. Collectively, these findings suggest that PVA negatively influences the development and function of the thyroid gland during zebrafish embryogenesis. These effects may be partly attributed to the disruption of hypothalamic-pituitary-thyroid (HPT) axis regulation. Therefore, raising awareness about the possible thyroid toxicity associated with PVA is crucial.