SECTION 16 

 RECENT ADVANCES IN THE STUDY OF NITRITE TOXICITY TO FISHES 



Rosemarie C. Russo^ 



Nitrite has not until recently received much attention as a toxicant to 

 aquatic organisms. However, it has been established that nitrite is very 

 toxic to fishes and aquatic invertebrates. Furthermore, nitrite has been 

 implicated in the formation of N^-nitroso compounds (Archer et a^. 1971; 

 Wolff and Wasserman 1972; Mirvish 1975), and nitrosamines have been shown 

 to be carcinogenic to zebra fish ( Brachydanio rerio ), rainbow trout (Salmo 

 gairdneri ), and guppy ( Lebistes reticulatus ) (Stanton 1965; Ashley and 

 Halver 1968; Sato et al . 1973). Recently nitrite has been reported to in- 

 duce cancer in rats directly, rather than through formation of nitrosamines 

 (Newberne 1979). 



In the past few years much research has been done to investigate the 

 toxicity of nitrite to aquatic organisms. This includes the study of 

 nitrite toxicity to additional fish species, the effects of water chemistry 

 conditions on nitrite toxicity, and some work on the mode of toxic action 

 of nitrite. 



Nitrite is produced as an intermediate product in the nitrification pro- 

 cess. In this process, the biological oxidation of ammonia to nitrate, 

 Nitrosomonas bacteria convert ammonia to nitrite, and Nitrobacter converts 

 nitrite to nitrate. The effectiveness of the conversion process is affected 

 by several factors, including pH, temperature, dissolved oxygen concentra- 

 tion, numbers of nitrifying bacteria, and presence of inhibiting compounds. 

 Under normal circumstances the first conversion, ammonia to nitrite, is the 

 rate-limiting step in the process; the second conversion, nitrite to ni- 

 trate, is relatively rapid. For this reason, nitrite is generally present 

 in only trace amounts in most natural freshwater systems. In sewerage 

 treatment plants utilizing the nitrification process, the process may be im- 

 peded, causing discharge of nitrite at elevated concentrations into the re- 

 ceiving water. Also, water reuse systems using the nitrification process 

 may malfunction, resulting in increased nitrite levels in the treated water. 



^Fisheries Bioassay Laboratory, Montana State University, Bozeman, 

 Montana 59717. 



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