method of the so-called fish-test both in the USSR and abroad, including 

 the USA. It should be noted that the time factor, i.e., determination of 

 the toxicity of a substance in a shortest possible time, becomes decisive 

 today. Therefore, the problem of rapid establishment of biological MPC of 

 chemical substances is the number one problem in both the scientific and 

 the commercial considerations, since the number of toxic substances 

 discharged into the waters grows at a frightening rate. 



The approaches of Soviet and American water toxicologists to solution 

 of this problem differ primarily in the importance attached to long-term 

 (chronic) and short-term (acute) experiments. In the USA there is a 

 method of estimation of the conventional harmless concentration of a toxi- 

 cant assumed to be 0.1 x TL (tolerance limit). The TL value is found in 

 short-term experiments (exposure of 24-96 hours). Such an approach 

 enables quick answers to the question of the degree of toxicity of a sub- 

 stance and its conventional harmless concentration. An essential disad- 

 vantage of this method is that the toxicity of many substances is dis- 

 played in prolonged (chronic) experiments at the concentrations much lower 

 than 0.1 x TL. 



The method of estimation of the MPC in the Soviet Union allows acquisi- 

 tion of more confident data about the toxicity of substances owing to pro- 

 longed observations of the survival of various aquatic organisms (from 

 fish to microbes), but is is very laborous and time consuming. This makes 

 it necessary to find a reliable, but time saving method of determination 

 of MPC. The main direction of the search is the experimental elaboration 

 of the transition from acutely toxic and threshold concentrations, to 

 maximum permissible ones. Here cooperative Soviet -American investigations 

 are needed with the application of the methods of physiological, biochemi- 

 cal and biophysical analysis for the quickest possible detection of the 

 symptoms of intoxication of varying aquatic organisms. 



The physiological and biochemical foundations of the determination of 

 the MPC (Lukyanenko, 1965, 1967, and 1973) allowed the development of the 

 method of physiological/biochemical indicators, the resolving capacity of 

 which is tens of times higher than that of the method of the "fish-test". 

 The method of the indicators allows detection of toxic effects of a sub- 

 stance by an understanding of the condition of one or another functional 

 system of the organism. This can be done in a much shorter time with the 

 indicator experiments than with the "fish-test", since the disturbances in 

 functions are observed long before the lethal effect. The choice of the 

 method of determination of the MPC of the investigated substance must be 

 based on the knowledge of toxicological dynamics of this substance and the 

 mechanism of its action, i.e., a clear idea of the most susceptible func- 

 tion or "target function" (Lukyanenko, 1973). 



Determination of the MPC of chemical substances entering water-bodies 

 is an important function, but not the only task of aquatic toxicology. 

 The diversity and complexity of the problems faced by aquatic toxicology 

 and ichthyo-toxicology implies a wide application of many modern methods, 

 primarily physiological and biochemical evaluation of the toxicity of in- 

 vestigated substances. 



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