cal substances entering the water body. This effect may result in the form- 

 ation of complex compounds, suppression or stimulation of the bacteriof lora, 

 and the appearance of free radical compounds if photosynthetic oxygen and 

 some other factors are present in the environment. 



This indicates that when determining the Maximum Permissible Concentra- 

 tion for toxic substances, it is necessary to take into account the influ- 

 ence of exogenous metabolites of algae on toxic compounds and likewise it 

 is necessary to determine biologically dangerous concentrations of the 

 natural metabolites for fish and other aquatic organisms. 



This information examines the possibility of determining, for fish, the 

 threshold and biologically dangerous concentrations of metabolites of blue- 

 green algae that cause "blooms". 



During cell reproduction of Microcystis , the main stimulus for algae 

 "blooms", the environment accumulates exogenous metabolites which have a 

 high biological activity (Goryunova, 1966; Sirenko, 1971). They in- 

 clude polyphenol compounds, and likewise polynucleotides. We determine 

 that in concentrations up to about 0.28 ppm, phenol compounds suppress the 

 growth of other examples of algal flora, not affecting the life processes 

 of the species-producer. When the concentration of phenol compounds in- 

 creases to 1.3 ppm, autoinhibition of the algal growth and reproduction is 

 observed . 



This indicates the role of the metabolite concentrations in the cell- 

 division regulation processes; in this case, it concerns the algae cells in 

 culture and natural conditions. If we changed the concentration, we would 

 be able to regulate to a definite limit the number of algae cells in a pop- 

 ulation. 



The metabolites produced by algae are not of less importance for the 

 life processes of other aquatic organisms entering into communities and im- 

 portant in the self -purification processes. For example, the effect of 

 blue-green algae metabolites on the decrease in the producing capacity of 

 Daphnia was shown (Braginskiy et al . , 1965). 



As for fish, there has been little study of the influence of natural 

 blue-green algae metabolites on them. The threshold and biologically dan- 

 gerous concentrations of these metabolites for all practical purposes, have 

 not been formulated. 



At present, when determining the maximum permissible concentration of 

 some basically artificial substances entering the water body, the following 

 criteria are usually considered (Stroganov, 1972): 



1. Mineralization processes of organic substances. 



2. Oganoleptic indices of water and water organisms (especially 

 of fish). 



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