toxins in wastewater are expensive. No matter how expensive it may be, man 

 must pay the price. The relationship between the cost of purification of 

 water, the number of species of hydrobionts living in the water for a given 

 level of pollution, and the degree of disruption of aquatic ecosystems can 

 be expressed by the graphs of Figure 3. 



A decrease in the purity of waste water (sewage and flood water, water 

 polluted by water transportation, etc.) leads to a sharp decrease in the 

 number of species; perhaps, first of all, a significant decrease in commer- 

 cial species and, along with this, a significant increase in disruptions in 

 the aquatic ecosystem. Money saved in reduced purification leads to money 

 lost due to disruption of the normal (favorable for man) aquatic ecosystem. 



Limitations of chemical pollution by means of the MPC significantly im- 

 prove the situation, but do not guarantee complete safety. We must assume 

 that: 1) the ecosystem includes more sensitive organisms than those which 

 have been used in biologic testing to establish the MPC. Elimination of 

 these species from the community may have an influence on the entire eco- 

 system. 2) Long-term after-effects may result from the influence of chemi- 

 cal pollutants on various vital processes of aquatic organisms. However, 

 these two questions must now be stated as issues for the future. Even if 

 all industrial enterprises, cities and large population centers purified 

 their waste water to harmless concentrations for aquatic organisms, toxic 

 substances would still reach reservoirs from the atmosphere and with water 

 running off the surface of the land. We must assume that the body of water 

 can handle this quantity of pollutant. If the self-purifying capacity of a 

 body of water is somewhat greater than is currently being used, this excess 

 amounts to a reserve of strength in the aquatic ecosystem. At the present 

 time, many reservoirs cannot cope with the large quantities of chemical com- 

 pounds entering them. They are functioning beyond the limits of the normal 

 (useful for man) capacity of self-purification. As a result of this, any 

 new addition of toxins to a body of water only increases the harmfulness of 

 the water system for organims which are useful to man. As is shown in 

 Figure 1, an aquatic ecosystem consists mainly of three functional groups of 

 organisms, which perform vital processes at different rates. The rates are 

 determined not only by the specifics of the organisms, but also by the en- 

 vironment (temperature, gas and salt composition and presence of toxins). 

 Therefore, we must always consider that, for example, self-purification pro- 

 cesses do not occur as rapidly as we would like, so that commercial species 

 disappear. This disagreement between rates of self-purification and quanti- 

 ties of chemical pollution leads to long-term disruption of all hydrobiolo- 

 gic processes characteristic for pure reservoirs. 



Based on the requirements of a reservoir in terms of preservation of 

 hydrobiologic processes assuring pure water of good quality and productivity 

 of valuable commercial species, the following four principles should be used 

 as a basis for standardization of water quality in fresh surface bodies of 

 water: 



1. The principle of priority in the use of reservoirs. All large and 

 medium sized reservoirs are used by many users, whose requirements for water 

 quality vary greatly. The highest requirements for water quality are those 



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