Acute and chronic toxicity of ammonia to freshwater fish: A site-specific study

The toxicity of ammonia to the juvenile stages of the bluegill (Lepomis macrochirus) and the walleye (Stizostedion vitreum), and to the embryo, larval and juvenile stages of the fathead minnow (Pimephales promelas) was determined in support of the development of a site-specific water quality standard for ammonia in the Tittabawassee River at Midland, Michigan. There was little difference among the acute toxicities of ammonia (expressed as un-ionized ammonia nitrogen NH₃ -N) to the three species tested, with 96-h LC50 values of 1.04, 1.06 and 1.50 mg NH₃ -N/L for the bluegill, walleye and fathead minnow, respectively. Evaluation of the chronic data showed no concentration-related effects for hatching success and growth. However, there was a significant (α = 0.05) decrease in number of normal larvae at hatch and in larval survival at 0.26 mg NH₃ -N/L and higher. The maximum acceptable toxicant concentration fell between 0.17 and 0.26 mg NH₃ -N/L, or 0.21 mg NH₃ -N/L when expressed as the geometric mean of these values. Both the acute and chronic values derived during this study are similar to those reported in the literature, indicating that, in this case, Tittabawassee River water quality did not influence the toxicity of ammonia to the species tested.