concentrations are selected from data obtained in the acute and subacute 

 tests. The duration of the chronic test is from 1 to 3 months, but no 

 longer. To shorten the duration of the tests, it is expedient to use the 

 functional loading method, and on this basis to determine the condition of 

 the indicator function (selectivity imitated), established on the basis of 

 data from the subacute test. 



Special emphasis was given to ichthyotoxicological tests when setting 

 biological standards for MPC, since the toxicological indication of harm 

 is more dangerous than all components of the natural ecosystem, and conse- 

 quently, for the "health" of the water body. However, this does not mean 

 that in biological standard setting, it is always necessary to be ruled 

 solely by this sign. That principle is composed when actually setting hy- 

 gienic standards, and with whose agreement the MPC of the substance tested 

 is established according to the limiting factor of harm (general sanitary, 

 organoleptic or toxicological). For example, the standard may be estab- 

 lished according to the least concentration of the substance which demon- 

 strates an unfavorable influence on the water body. This criteria must be 

 preserved to the end that setting biological standards be fully self 

 justifying. 



Considerations of principles and methods for biological standard 

 setting for chemical substances stated in this report, and evaluations of 

 the level of pollution in water bodies require further development. 



REFERENCES 



Frisch, K. 1941. von. Z. vergl . Physiol. B. 29. 



Hasler, A.D. and W.I. Wisby. 1951. Trans. Am. Fish. Soc. V. 79. 



Lukiyanenko, V.I. 1965. In Coll.: Problems of Hydrobiology M. 



Lukiyanenko, V.I. 1967. Toxicology of fishes M. 



Lukiyanenko, V.I. 1968. Tez. dokl. na vsescuzn. nauchn. Konf. po vopr. 

 vodn. toksikol . M. 



Lukiyanenko, V.I. 1973. In. Coll.: Experimental aquatic toxicology. 

 Riga, issue 4. 



Neurath, H. 1949. Z. vergl. Physiol. B. 31. 



Rapoport, I. A. 1972. In Coll.: Scientific foundations of establishing 

 MTC in water medium and self-purification of surface waters M. 



Shultz, F. 1956. Z. vergl. Physiol. B. 38. 



Teichmann, H. 1957. Naturwissenschaften. B. 44. 



Walker, T.J. and A.D. Hasler. 1949. Physiol., zool. V. 22. 



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