SECTION 7 

 AMMONIA AND NITRITE TOXICITY TO FISHES 

 Rosemarie C. Russo and Robert V. Thurston 



AMMONIA 



Introduction 



Ammonia is a serious pollutant to aquatic life. It enters natural 

 water systems from several sources, including agricultural and industrial 

 wastes, and inadequately oxidized sewage effluents. Ammonia is also a 

 natural biological degradation product of nitrogenous organic matter. 



The toxicity to fishes of aqueous solutions of ammonia or ammonium 

 salts is attributed to the un-ionized (undissociated) chemical species 

 (NH 3 ) (Chipman, 1934; Wuhrmann, zt al. 1947, Wuhrmann and Woker, 1948; 

 Hemens, 1956), with the ionized species (NH4 + ) considered nontoxic, or 

 significantly less toxic (Tabata, 1962). The concentration of un-ionized 

 ammonia is dependent on the chemical and physical characteristics of the 

 water, and therefore the toxicity of ammonia to fishes is dependent in 

 part upon the effect of these variables on the aqueous ammonia equilibrium. 

 The most important factors affecting this equilibrium are pH, temperature, 

 and ionic strength. The concentration of un-ionized ammonia increases 

 with increasing pH and temperature, and decreases with increasing ionic 

 strength. 



The toxicity of ammonia to fishes is also influenced by dissolved 

 oxygen and free carbon dioxide. A decrease in the dissolved oxygen concen- 

 tration increases the toxicity of ammonia (Downing and Merkens, 1955; 

 Merkens and Downing, 1957), possibly because of increased ventilation by 

 the fish and a corresponding increase in the rate of flow of ammonia 

 across the gill tissues. Lloyd and Herbert (1960) reported that in waters 

 of low CO2 concentration the toxicity of ammonia may decrease, and attri- 

 buted this to a reduction of pH at the gill membrane surface, brought 

 about by the expiration of CO2. Other factors which exert an effect on 

 ammonia toxicity include previous acclimation of fish to low ammonia con- 

 centrations (Vamos, 1963; Malacea, 1968; Lloyd and Orr, 1969), physical 

 stress (Herbert and Shurben, 1963), and fish size (Penaz, 1965). Several 

 researchers have investigated the toxic effect of ammonia in combination 

 with other poisons (Herbert, 1962; Herbert and Shurben, 1964; Herbert and 

 Van Dyke, 1964; Vamos and Tasnadi, 1967; Brown, 1968; Brown, ztal., 1969) 

 It is clear that the effects of the toxicants studies are generally 

 additive; sometimes proportionally, but not always. 



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