Morphological and functional changes in the thyroid gland of methyl thiophanate-injected lizards, Podarcis sicula.

The thyroid has been shown to be a target organ for environmental chemicals, specifically endocrine-disrupting contaminants. Reptiles are particularly suitable as contaminant biomonitors due to their persistence in a variety of habitats, wide geographic distribution, longevity, and, in many cases, site fidelity. Methyl thiophanate is a systemic broad-spectrum fungicide used to prevent and control plant diseases caused by various fungi. The aim of this study was to develop an integrated biological model for monitoring the ecotoxic effects of thiophanate-methyl fungicide on the thyroid of the lizard Podarcis sicula. The results of this study indicate that both structural and functional differences in the thyroid gland of the lizard exist in the animals exposed to methyl thiophanate. Structurally, animals exposed to methyl thiophanate showed decreased epithelial cell height; the nuclei of the thyroid cells were small and elongated with dense chromatin and a greatly reduced cytoplasm. The colloid was retracted with few reabsorption vacuoles. Functionally, the same animals exhibited decreased T4 and T3 plasma levels compared to control animals. Methyl thiophanate administration produced statistically significant inhibition on serum thyroid-stimulating hormone levels and this is the mechanism for altering thyroid function. This study highlights how thyroid gland disruption, both structural and functional, in lizard and other nontarget organisms might also have an environmental aetiology.