toxic in soft water than in hard water (Patrick, 

 unpublished data). For Nitzchia linearis a 50-per- 

 cent reduction in growth of the population in soft 

 water (44 mg/1 Ca-Mg as CaCOg) occurred as 

 follows: 0.288 mg/1 (CN) at 72 F, 0.295 mg/1 at 

 82 F, and 0.277 mg/1 at 86 F. For Naviciila semi- 

 nulum var. hustedtii, the concentrations that re- 

 duced growth of the population 50 percent in hard 

 water (170 mg/1 Ca-Mg as CaCOs) were as fol- 

 lows: 0.356 mg/1 at 72 F, 0.491 mg/1 at 82 F, 

 and 0.424 mg/1 at 86 F. 



Recommendation: Permissible concentrations of cy- 

 anide should be determined by the flow-through bio- 

 assay method described in the bioassay section. These 

 tests should be conducted with DO, temperature, and 

 pH at recommended levels for the factors under which 

 the cyanide (HCN) is most toxic or under local water 

 conditions at which it is the most toxic. 



Ammonia: The toxicity of ammonia has been 

 studied by several investigators but because of in- 

 adequate reporting and unsatisfactory experi- 

 mental control, much of the work is not usable. 

 Doudoroff and Katz (1950), Wuhrmann, et al. 

 (1947), and Wuhrmann and Woker (1948) give 

 a complete account of the pH effect on ammonia 

 toxicity and demonstrate that toxicity is dependent 

 primarily on undissociated NHjOH and nonionic 

 ammonia. They found no obvious relationship be^ 

 tween time until loss of equilibrium and total 

 ammonium content. They also demonstrated a 

 striking synergy between ammonia and cyanide. 

 McKee and Wolf (1963) state that toxicity is in- 

 creased markedly by reduced dissolved oxygen. 

 Field studies by Ellis (1940) and other observa- 

 tions lead to the conclusion that at pH levels of 8.0 

 and above total ammonia expressed as N should 

 not exceed 1.5 mg/1. It has been found that 

 2.5 mg/1 total ammonia expressed as N is acutely 

 toxic. 



Recommendation: Permissible concentrations of am- 

 monia should be determined by the flow-through bio- 

 assay with the pH of the test solution maintained at 

 8.5, DO concentrations between 4 and 5 mg/1, and 

 temperatures near the upper allowable levels. 



marine 



and estuarine 



organisms 



Others: Especially significant sources of wastes 

 that must be considered individually are derived 

 from tar, gas, and coke-producing plants, pulp 

 and paper mills, petroleum refining and petro- 

 chemical plants, waterfront boating activities, and 

 special-purpose laboratories. These problems are 

 discussed in the toxicity portion of the section on 

 water quality requirements for marine organisms. 



66 



