regardless of how thorough they might be, was able to address the issues 



of which components were involved, and what degree of removal would be 



required. These questions could only be answered with a help of experi- 

 mental methods of investigation and establishment of the MPC. 



The impetuous development of aquatic toxicology and ichthyo-toxicology 

 during the last two decades has lead to a notable decline in sanitary- 

 hydrobiological investigations. However, the main object of these 

 investigations remains the water-bodies polluted with organic matter. 



Herein lies one of the reasons behind the development of the interest 

 of some toxicologists in ecological aspects of aquatic toxicology which 

 must actually be dealt with by sanitary hydrobiology. A distinct demarka- 

 tion of the tasks and methods of sanitary hydrobiology and aquatic toxi- 

 cology is needed not only for successful solution of specific problems 

 faced by each of the sciences, but also for establishment of fruitful 

 contacts when solving the problems of protection of waters from pollution. 

 It is to be emphasized that the evaluation of the effectiveness of biologi- 

 cal setting of standards for substances discharged into waters can be exer- 

 cised only from the criteria and methodology of sanitary hydrobiology, 

 which has as its object of study the water-body as a whole and its living 

 communities. 



In this regard, the indices of ecological health imposed by M.M. 

 Kamshilov, e.g., the oxygen concentration in the water; ratio of produc- 

 tion to destruction; character of benthic communities; and the distribu- 

 tion of indicator species; deserve deep attention. The organoleptic 

 symptom of harmfulness must also be included. This symptom implies the 

 influence of pollution on organoleptic properties of not only the water, 

 but also of the aquatic organisms, including fish. Unfortunately, this 

 aspect of fisheries investigation attracts scant attention in comparison 

 with the sanitary-hygienic setting of standards. It is enough to recall 

 that out of 420 established sanitary-hygienic MPC standards of harmful sub- 

 stances, more than a half (216) are limited by the organoleptic index, 147 

 by sanitary-toxicologic considerations, and 57 substances by the general 

 sanitary index of harmfulness. But within the fisheries MPC, only 15 

 substances of a total of /0 are limited by the organoleptic index. The 

 main reason for the poor use of the organoleptic index in the fisheries 

 MPC is an insufficient elaboration of the methods of objectively evaluating 

 the reaction of aquatic organisms, including fish, to changes in taste and 

 smell of the water caused by toxic substances. The methods of investiga- 

 tion of these reactions exist, in the form of conditioned reflexes which 

 still awaits wide application in ichthyological investigations. 



Nevertheless, the sensitivity of fish to the odors of many chemical 

 substances greatly exceeds that of a human being. Thus, Hasler and Wisby 

 (1951) discovered in fish the ability to detect phenol in concentrations 

 0.01 mg/1, or even 0.005 mg/1, using a conditioned reflex. These concen- 

 trations are considerably lower than the threshold for humans. These data 

 agree with the results of Neurath (1949) who reported that fish detect the 

 the smell of phenethyl alcohol at the concentrations 250 times lower than 

 humans. An even greater sensitivity of the eel to beta-phenethyl alcohol 



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