The toxicity of ammonia to fishes has been attributed to the un-ionized ammonia chemical species present in aqueous solution. Because the percent of total ammonia present as un-ionized ammonia (NH3) is so dependent upon pH and temperature, an exact understanding of the aqueous ammonia equilibrium is important for toxicity studies. A critical evaluation of the literature data on the ammonia–water equilibrium system has been carried out. Results of calculations of values of pKa at different temperatures and of percent of NH3 in aqueous ammonia solutions of zero salinity as a function of pH and temperature are presented.
Median lethal concentration values for acute copper toxicity to 3-10-g cutthroat trout (Salmo clarki) have been determined for nine different combinations of alkalinity, hardness, and pH. Equilibrium calculations were performed on the copper LC50 values; seven different soluble species of copper were considered: Cu2+, CuOH+, Cu(OH)2°, Cu2-(OH)22+, CuHC03+, CuC03°, and Cu(C03)22-. The acute toxicity of copper was inversely correlated with water hardness and alkalinity. At a given alkalinity, hardness determined the LC50; at a given hardness, alkalinity determined the LC50. At a given alkalinity and hardness, the concentrations of the copper species were determined by the pH of the water. Under the conditions tested, Cu2+, CuOH+, Cu(OH)2°, and Cu2(OH)22+ were toxic forms of copper to cutthroat trout; CuHC03+, CuC03°, and Cu(C03)22~w ere not toxic. Results of 11 96-h copper toxicity bioassays on 1-to 26-g rainbow trout (Salmo gairdneri) under uniform water chemistry conditions are also reported.
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