Chronic Fluoride Toxicity Effects on Thyroid Iodine Metabolism in Xenopus laevis Tadpoles

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Ivy C. Ronoh


Chronic, dosage, mortality, histology, metamorphosis, fluoride, Xenopus laevis


Fluoride is abundantly found in the earth’s crust with most contamination of ground water occurring at levels of between 1-25 mg/l. The study aimed at evaluating the effects of chronic toxicity of fluoride (452.8µg/l) to Xenopus laevis tadpoles and to evaluate the possible interactions of 8.135µg/l triiodothyronine (T3), 11.652µg/l thyroxine (T4), 0.5µg/l Iodine and 0.005µg/l methimazole on iodine metabolism in the tadpoles. The experiments were done using Amphibian metamorphosis assay (AMA) test. The endpoints in the study were; daily observations to record the mortality of the tadpoles including any other observable changes in their behavior. For the whole duration of the experiment- 21 days, the development stages, hind-limb length (HLL), snout-vent length (SVL) and the body weights of the tadpoles were performed at the 7th and 21st day. Histology of the thyroid gland was evaluated at the termination of the experiment on day 21. Fluoride treated tadpoles showed a delay in growth and development of the tadpoles, Methimazole was able to inhibit the development of the tadpoles and prevent the tadpoles from reaching the climax of metamorphosis, T4, T3 were able to reverse chronic Fluoride toxicity in the tadpoles. The study recommends that Xenopus laevis is effective for use in laboratory experiments for study of toxicants.


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