Direct effect of ammonia on three species of North American anuran amphibians

Leopard frog (Rana pipiens), green frog (Rana clamitans), and American toad (Bufo americanus) embryos were exposed to different un-ionized ammonia (NH(3)) levels over an ecologically relevant range (0-2 mg NH3/L H2O). Hatching success and prevalence of deformities were recorded after acute exposures (3-5 d duration) at 23 degrees C and pH 8.7. Green frog tadpoles were exposed to different NH3 levels in a subchronic experiment (114 d), and growth, survival, and metamorphosis were monitored. Survival declined, the prevalence of deformities increased, and growth and development were slow in anuran embryos and tadpoles exposed to NH3 concentrations in excess of 0.6 mg/L (green frogs) or 1.5 mg/L (leopard frogs). No effects were observed in American toads up to a concentration of 0.9 mg/L NH3. It appears from the few data available that anurans may not be particularly sensitive to NH3 when compared with many fish species and that water quality criteria determined using data collected on fish species will be protective for many anuran amphibians. The NH3 concentrations that caused negative effects in these experiments are higher than measured values for water in the Fox River-Green Bay ecosystem (WI, USA) but lower than for pore sediment water. In this ecosystem, anuran amphibians are potentially exposed to hazardous levels of NH3 when they hibernate on the bottom or buried in sediments or during episodic releases of NH3 from sediments.