Surface water mitigates the anti-metamorphic effects of elevated perchlorate concentrations in New Mexico spadefoot toad larvae (Spea multiplicata).

Perchlorate (ClO4-) has potential to negatively impact amphibian populations by inhibiting thyroid hormone production, and thus metamorphosis in developing larvae. However, variability exists in species sensitivity, and there is evidence suggesting that natural surface waters can mitigate the anti-metamorphic potential of perchlorate. New Mexico spadefoot toad tadpoles, Spea multiplicata, were exposed to natural surface waters spiked with nominal concentrations of 0, 1000, 1350, 1710, 3000, 5110, and 8000 μg/L perchlorate ion for up to 42 days. No consistent dose-response trends were observed in mortality, rate of metamorphosis, Gosner stage, mass, or length. This study suggests that perchlorate exposure to concentrations as high as 8000 μg/L in natural surface waters does not result in adverse effects on New Mexico spadefoot tadpoles and emphasizes the importance of using site-specific conditions and species when evaluating ecological risks in perchlorate-impacted areas.