using locally important fish as test animals and waters receiving the 

 tested wastes as diluents (Hart, Doudoroff, and Greenbank, 1945; 

 Doudoroff, oX at., 1951). The methods developed and recommended have 

 been widely adopted by other investigators, and by regulatory agencies 

 and industrial organizations in the United States and elsewhere. They 

 have appeared repeatedly, with some minor modifications or refinements, 

 in manuals of currently approved, standard practice, such as the eleventh 

 edition of "Standard Methods for the Examination of Water and Wastewater" 

 (American Public Health Association oX at., 1960) and the subsequent edi- 

 tions. Similar methods for evaluation of the toxicity of water pollutants 

 to organisms other than fish have been developed, but their use in the 

 United States outside of research laboratories has not yet been extensive. 



Chemical criteria of water quality can be very useful, and cannot be 

 entirely ignored in controlling pollution for the protection of aquatic 

 life. However, deficiencies in this area, even after the great technolog- 

 ical advances of recent years, are still very real and apparent. Thus, 

 frequent reliance on toxicity bioassays of effluents regulating the dis- 

 charge of toxic wastes is still necessary. Several ways in which these 

 toxicity tests can be used in controlling water pollution have been pro- 

 posed by biologists and tried by regulatory agencies. 



The maximum safe or harmless concentration of an industrial waste or 

 other toxicant in a receiving water cannot be directly determined, by per- 

 forming a toxicity test of short duration, e.g., a 96 hour test. Much 

 longer and more difficult tests can be successfully undertaken only in re- 

 search laboratories, and cannot be frequently repeated. When only the 

 acute toxicity of an effluent is known, its highest permissible concentra- 

 tion in the receiving water must be computed by some prescribed formula 

 that has been judged to be appropriate. For example, the concentration 

 found by experiment to be fatal in 48 hours to just 50 percent of test 

 animals, termed the 48-hour "median tolerance limit" or "median lethal 

 concentration" (LC 50 ), may be simply multiplied by a fractional "appli- 

 cation factor", e.g., 0.10, to obtain the permissible or presumably safe 

 concentration. This formula, with the application factor of 0.10, was 

 first recommended tentatively by the Aquatic Life Advisory Committee of 

 the Ohio River Valley Water Sanitation Commission (1955) as one believed 

 to be sufficiently but not unreasonably restrictive. That committee 

 noted, however, that smaller or larger application factors may be often 

 fully justifiable. The recent trend has been to reduce the permissible 

 concentrations, substituting the 96-hour LC 50 for the 48-hour value, and 

 using smaller application factors in the formula. More complicated 

 formulas have been proposed (Hart, Doudoroff, and Greenbank, 1945; 

 Doudoroff e* a£. , 1951; footnote No. 7). For some time they attracted 

 much favorable attention, but regrettably they have not proved 

 sufficiently useful for wide-spread adoption by regulatory agencies. 



For each of a large variety of toxic substances, an individual appli- 

 cation factor has been recently proposed (National Technical Advisory 

 Committee on Water Quality Criteria, 1968; Committee on Water Quality 

 Criteria, National Academy of Sciences and National Academy of 

 Engineering, 1972/1973). The recommended values are based on the results 



