Lethal and Sublethal Effects of Nitrogen Fertilizer Ammonium Nitrate on Common Toad (Bufo bufo) Tadpoles

Abstract.

The impact of elevated ammonium nitrate concentrations on the survival and development of common toad (Bufo bufo) tadpoles was investigated in the laboratory. 1,704 mg/L and 1,637 mg/L nitrate (equivalent to 2,198.7 mg/L and 2,112.3 mg/L ammonium nitrate) were recorded as 96 h and 168 h LC50s respectively. These are well above field levels (10–250 mg/L) observed in freshwater in Britain. The exposure of tadpoles to nominal concentration of 100 mg/L nitrate for 24, 48, and 72 h caused a significant decrease in their activity but no clear reduction in food consumption or delay of the development. In subchronic exposures at the nominal concentrations of 50 and 100 mg/L nitrate, the metamorphosis started earlier and took less time to complete than in the control. However, some of the results were equivocal, at 50 mg NO₃/L the metamorphs were significantly larger than the controls, while at 100 mg NO₃/L metamorphs were not significantly different from the controls. Certain deformities and unusual swimming patterns were also found in tadpoles exposed to various concentrations of ammonium nitrate.