Morphological and Functional Changes in the Thyroid Gland of Methyl Thiophanate-Injected Lizards, Podarcis sicula

Abstract The thyroid has been shown to be a targetorgan for environmental chemicals, specifically endocrinedisruptingcontaminants. Reptiles are particularly suitableas contaminant biomonitors due to their persistence in avariety of habitats, wide geographic distribution, longevity,and, in many cases, site fidelity. Methyl thiophanate isa systemic broad-spectrum fungicide used to prevent andcontrol plant diseases caused by various fungi. The aim ofthis study was to develop an integrated biological modelfor monitoring the ecotoxic effects of thiophanate-methylfungicide on the thyroid of the lizard Podarcis sicula. Theresults of this study indicate that both structural andfunctional differences in the thyroid gland of the lizardexist in the animals exposed to methyl thiophanate.Structurally, animals exposed to methyl thiophanateshowed decreased epithelial cell height; the nuclei of thethyroid cells were small and elongated with dense chromatinand a greatly reduced cytoplasm. The colloid wasretracted with few reabsorption vacuoles. Functionally, thesame animals exhibited decreased T4 and T3 plasma levelscompared to control animals. Methyl thiophanate administrationproduced statistically significant inhibition onserum thyroid-stimulating hormone levels and this is themechanism for altering thyroid function. This studyhighlights how thyroid gland disruption, both structuraland functional, in lizard and other nontarget organismsmight also have an environmental aetiology.