Ammonium Perchlorate Disruption of Thyroid Function in Natural Amphibian

We examined indices of thyroid development in tadpoles from ammonium perchlorate (AP)-exposed sites. Bullfrog (Rana catesbeiana) tadpoles collected from a reference site exhibited normal developmental features, with many completing metamorphoses. In contrast, tadpoles collected from the AP contaminated site exhibited a 5-fold lower hindlimb/snout-vent length ratio than tadpoles from the reference site. The volume of the thyroid gland was 2.5-fold larger in the tadpoles from the reference site, presumably because they had progressed to late prometamorphosis and early metamorphic climax. Premetamorphic western chorus frog tadpoles (Pseudacris triseriata) inhabiting an ephemeral pond contaminated with AP exhibited gross morphological abnormalities of the thyroid including colloid depletion and follicle cell hypertrophy. We conclude that tadpoles exposed to AP-contaminated pond water early in larval life exhibit delayed development ofthyroid-hormone sensitive structures. Additionally, there are abnormalities in the developing thyroid gland that seem to depend upon the window of AP exposure. The potential impact of thyroid disruption on development and reproduction in amphibian populations will be discussed.