Impact of fluoride on thyroid function and histopathology in cyprinus carpio: Implications for aquatic ecosystems

Fluoride pollution in freshwater bodies is becoming alarming because it interferes with the endocrine system of water-dwelling organisms. In this study, we evaluated the effects of sublethal fluoride levels on thyroid hormone levels and histological alterations in Cyprinus carpio, a popular model fish species used in ecotoxicity experiments. The low, medium, and high fluoride groups received 1, 5, and 10 mg/L fluoride, respectively, and thyroxine plasma levels (T4) and triiodothyronine plasma levels (T3) were assessed at 7, 14, 21, and 35 days. The findings revealed that both T4 and T3 levels significantly decreased with increasing dose and ranged from to 10-41 % lower than controls in the 10 mg/L fluoride group. On day 35, T4 levels were reduced by 42 % and T3 levels were reduced by 50 % in the high fluoride exposure group compared to those in the control group. Changes in the thyroid gland were observed under a light microscope that included, but were not limited to, small follicle size, epithelial hypertrophy, and epithelial hyperplasia, especially in the high-fluoride group. These results suggest that elevated fluoride exposure causes a hormonal imbalance in Cyprinus carpio by affecting thyroid hormone biosynthesis and functionality, which may result in growth and reproductive failure. The eminent dose-response data on fluoride concentration and the degree of thyroid disruption clearly emphasise the severe endocrine-disruptive effects of fluoride at increased concentrations. The results of the present study agree with those of other studies that have described the inhibitory effect of fluoride on thyroid function in different fish species. Therefore, we conclude that fluoride may be a potent endocrine disruptor in the environment. As thyroid hormones play significant roles in metabolic and physiological functions in fish, these findings underscore the importance of improving fluoride standards in freshwater habitats. Research on the molecular pathways that lead to thyroid dysfunction when exposed to fluoride and other effects of this chemical substance on the environment.