DEVELOPMENTAL IMPACTS OF FLUORIDE AND ITS REMEDY ON Xenopus laevis’ THYROID GLAND

Abstract

Fluoride is known to cause several non-skeletal health effects including neural, kidneys, endocrinal, thyroid gland, and disorders of the liver as well as interfering with metabolic processes when the doses are high. This study sought to evaluate developmental impacts of fluoride in the Xenopus laevis and the remedies using different treatments. The specific objectives of the study were to: evaluate acute toxicity of fluoride using Xenopus laevis embryos (FETAX test); reverse acute impacts of fluoride in Xenopus laevis embryos using T4 and KI; evaluate chronic toxicity of fluoride in the Xenopus laevis tadpoles and evaluate the effects of KI, T3, T4, and Methimazole on chronic toxicity of fluoride in Xenopus laevis tadpoles. This study used experimental research design. Breeding of the adults was done according to Frog Embryo Teratogenesis Assay Xenopus (FETAX) test. The fertilized eggs were divided into two groups for acute and chronic experiments. Eggs set aside for acute toxicity were used to set the experiment to test the effects of fluoride in the tadpoles and the ability of T4 (2 ppm) and Iodine (0.5 ppm) to reverse the effects. The setting of the experiment was set up the same way as the test for fluoride effects except; the LC50 calculated from the first part (452.8 ppm), was used as the standard test. Descriptive statistics, Abbott’s adjustment, probit analysis (used to determine LC50 and EC50) and ANOVA was used to analyze the data. Teratogenic index was used to ascertain the degree of teratogenicity of the compounds. Development in chronic experiments was determined through the staging criteria of Nieuwkoop and Faber (1994). SVL was measured by using the cranial aspect of the vent as the caudal limit for the measurement. This was done using Motic® imagery software. Fertilized eggs were cultured for 17 days to attain stage 51. Tadpoles were fed with t- bites throughout the pre- exposure period (after NF stage 45/51) and throughout the experimental period. Iodine concentration was maintained at 0.5 ppm. Tadpoles exposed in AMA test were used to test for the thyroid gland impacts from the chemicals exposed to the Xenopus laevis. The study findings indicated that the tadpoles exposed to Fluoride exhibited abnormal behavior including non-response to touch even though they were still alive as they had visible heart palpitations. The level of significance of survival in the tadpoles was p<.005. Malformations across all the treatments were recorded. The tadpoles treated with F were insensitive to touch and remained completely immobile at 800 ppm F although were still alive because of visible heart palpitations. The study results revealed that the level of significance for the T4 treated tadpoles was p>.005, while those treated with Iodine p<.005. Comparing the response of the tadpoles between the Iodine treated and the T4 treated tadpoles showed that there was no significant difference between the responses as the p value was p>.005. Persistent exposure to fluoride multiplied the mortality, inhibited metamorphosis, and delayed development in tadpoles in both the acute and chronic experiments. T3 treated tadpoles recorded 100% mortality across all its combinations before end of experiment. All the treatments were able to reverse the impacts of fluoride exposure across all the concentrations although not fully. The study recommends the use of Xenopus laevis for similar studies as they are just as effective and for all relevant authorities to use this data to make all decisions.