mg/liter NH3, and 5 percent died at both 0.11 and 0.06. In four separate 

 tests of 3-5 weeks 1 duration, the LC50 values for rainbow trout fry were 

 between 0.5 and 0.6 mg/liter NH3 (Thurston, unpublished data). 



Deleterious effects of ammonia at sublethal concentrations have been 

 observed by a number of researchers. Reichenbach-Klinke (1967), in a 

 series of one-week tests on 240 fishes of 9 species at concentrations of 

 0.1-0.4 mg/liter NH3, observed swelling of and diminishing of the number 

 of blood cells, inflammations, and hyperplasia, irreversible blood damage 

 occurred in trout fry at 0.27 mg/liter NH3. He also noted that these low 

 NH3 doses inhibited the growth of young trout and lessened their resistance 

 to diseases. Smart (1976) observed a high incidence of disease, as well 

 as gill damage, in rainbow trout exposed to 0.30-0.36 mg/liter NH3 for up 

 to 36 days. Flis (1968) reported that a 35-day exposure of carp [Cypnlmti, 

 ca/iplo) to a concentration of approximately 0.1 mg/liter NH3 resulted in 

 extensive necrobiotic and necrotic changes and tissue disintegration in 

 various organs. 



Reduction in growth rates for rudd has been observed after 95 days at 

 concentrations greater than 0.1 mg/liter NH3 (Water Pollution Research, 

 1971) and for channel catfish at 0.14 mg/liter NH3 after 27 days 

 (Robinette, 19/6). Smith and Piper (1975) reported a reduction in growth 

 rates after 6 months and severe pathological changes in gills and livers 

 of rainbow trout after 12 months' exposure at 0.02 mg/liter NH3. For the 

 21-day period between egg hatching and swim-up stage, a reduction in 

 development of rainbow trout (length, weight, and sac absorption) was ob- 

 served at concentrations of 0.07 mg/liter NH3 and higher (Thurston, un- 

 published data). Concentrations as low as 0.002 mg/liter NH3 have been 

 reported to cause gill hyperplasia in fingerling chinook salmon 

 [Onconhynchui lAhawytAcha) in 6 weeks (Burrows, 1964. 



Rainbow trout have successfully spawned in the laboratory at 0.06 

 mg/liter NH3 and have produced significant numbers of viable fry (Thurston, 

 unpublished data). 



NITRITE 



Introduction 



Nitrite is present in only trace amounts in most natural freshwater 

 systems. In the process of nitrification, i.e., the biological oxidation 

 of ammonia to nitrate, nitrite is produced as an intermediate product. 

 Primary treatment sewage plants discharge large quantities of ammonia and 

 partially converted ammonia into receiving waters, and as the nitrifica- 

 tion process proceeds downstream from the discharge point, nitrite levels 

 above normal may be detected. Of the total nitrogen being discharged by a 

 secondary treatment sewage plant, a lesser percent will be ammonia and a 

 higher percent will be nitrate, but also the percentage of nitrite will in- 

 crease. This percentage is related, in part, to how complete the nitrifi- 

 cation process has been within the plant before discharge. In some cases, 

 the amount of nitrite being discharge may raise the concentration of 



78 



