Responses of metamorphosis and immune function to perchlorate exposure in spadefoot toads

The immune system responses to perchlorate in species of toads that are native to the western United States were investigated because it has been found in previous research that perchlorate exposure has the secondary effect of immunotoxicity in amphibians due to inhibited thyroid function. Spadefoot toads, Spea multiplicata and Spca bombifrons, w ere caught as tadpoles from a playa lake near Lubbock, Texas. The tadpoles were exposed to environmentally relevant concentrations of sodium perchlorate, 0, 20 )µg/L and 150 µg/L, in addition to a very high concentration of 100 mg L until they metamorphosed. As soon as the tadpoles completed metamorphosis, they were removed from the perchlorate and allowed to grow to a size that would provide adequate spleen cells for use in a lymphocyte proliferation assay. The endpoints assessed were body weight, body length, spleen weight, number of spleen cells, white blood cells in blood, red blood cells in blood, white blood cell differential counts, background proliferation of spleen cells, and spleen cells' proliferative response to a mitogen.

Although previous research found significant effects to the immune system of amphibians due to perchlorate exposure, the results of this experiment did not find effects. The rates of metamorphosis were not significantly different (p=0.0093), although three out of four treatment groups followed a dose-dependent pattern. In contrast, the mortality rates of the treatment groups were significantly different, although a dose-dependent pattern could not be discerned. The mortality was most likely due to conditions other than the perchlorate exposure, but perchlorate had some influence on mortality. Although mortality was affected differently by the various concentration of perchlorate, there were no significant metamorphosis or immune system effects among the exposure groups.