Alteration of larval development and metamorphosis by nitrate and perchlorate in southern leopard frogs (Rana sphenocephala).

Amphibians are sensitive to a great variety of agrochemicals. Nitrate compounds are commonly applied as fertilizers, whereas perchlorate salts occur as by-products of the military industry and in some nitrate fertilizers. Both compounds are highly soluble and can easily diffuse between ground and surface water, thus potentially affecting amphibians. Nitrate reduces embryonic and larval survival and development, whereas perchlorate has a well-known goitrogenic effect and inhibits metamorphosis. We present the results of an experiment that assessed the combined effects of these two chemicals on the development and metamorphosis of southern leopard frogs (Rana sphenocephala) larvae. Individual frogs were exposed in a block design throughout their larval stages until they metamorphosed. Nitrate at 100 mg/l increased larval mortality and reduced the growth of developing tadpoles. Perchlorate at 15 mg/l was not lethal to larvae, but inhibited metamorphosis, resulting in high mortality during metamorphosis compared with control animals. At 30 mg/l of perchlorate, larvae experienced increased mortality. Together, the chemicals exhibited additive effects on developmental rate and survival. When nitrate and perchlorate occur simultaneously in the environment, they can have greater effects on an amphibian population than either chemical alone.