Comparative effects of ammonium and nitrate compounds on Pacific treefrog and African clawed frog embryos

The effects of ammonium nitrate, ammonium chloride, ammonium sulfate, and sodium nitrate on survival and growth of Pacific treefrog (Pseudacris regilla) and African clawed frog (Xenopus laevis) embryos were determined in static-renewal tests. The 10-day LC50s for the three ammonium compounds for P. regilla ranged from 25.0-32. 4 mg/L NH4 -N. The 10-day sodium nitrate LC50 for P. regilla was 578. 0 mg/L NO3-N. LC50s for X. laevis exposed for 4 or 5 days to the three ammonium compounds ranged from 27.5-60.2 mg/L NH4-N. The sodium nitrate LC50 for X. laevis ranged from 438.4-871.6 mg/L NO3-N. The lowest LOAEL based on length or weight was 6.1 mg/L NH4-N for the two species. The lowest LOAELs for NO3-N were 111.1 mg/L for P. regilla and 56.7 mg/L for X. laevis. Calculated unionized NH3 comprised 0.5-1.8% of measured NH4-N concentrations. Potential harm to amphibian populations could occur if NH4-N and NO3-N in agricultural runoff or drainage impacts sensitive life stages for a sufficiently long period.