elusions about the toxicity of the water. Further evaluation requires 

 special chemical analyses, toxicologic investigations, and a detailed 

 ecological study of the water body. 



The quantitative aspect of application of biological testing is more 

 complex and requires an approach to the characteristics of measurable 

 functions. Any function changing under chemical action may function as 

 an indicator, although the more simply measured functions are advanta- 

 geous to use. Various functional disturbances in highly organized aquatic 

 organisms may be evaluated on the basis of application of various physio- 

 logical and biochemical methods (Komarovski , 1971, 1972; Malyarevskaya 

 and Birger, 1973) . 



At present, elementary statistical principles are being used in 

 biological testing. However, it is impossible to avoid the influence of 

 permanently acting factors (time, temperature) and yet, it is necessary 

 to reduce expenditures of time and labor to a minimum. The most reason- 

 able approach is the use of the principle of the All Factor Experiment 

 (AFE). The scheme AFE 2 2 enables the acquisition of reliable data from 

 four experiments. This seems applicable to the situation of stabilized 

 temperature, with due consideration of the factors of concentrations, and 

 time of action of toxicants. When three variable factors are considered, 

 the scheme AFE 23 gives confident information using eight experiments. 

 Such a material can be easily interpreted both analytically and graphi- 

 cally, using a system of three coordinates. With a mass accumulation of 

 data an electronic computer can be utilized. 



In conclusion, it should be noted that the development of the method- 

 ology leads to three variations of application: 1) qualitative tests for 

 toxicity of medium, 2) quantitative characteristics of toxic effect, and 

 3) quantitative determination of toxicants. The latter task is the most 

 complicated, and practically insoluble. In some cases, biological 

 testing lacks sufficient sensitivity when compared with chemical analysis. 

 For example, the test of Knepp compared with analytical chemical methods 

 has shown that this test detects the presence of some toxicants only at 

 concentrations equal to 5-10 MPC, which is certainly insufficient for a 

 quantitative conclusion. 



More indicative are the specific chemical tests, which reflect the 

 effect of a given substance, and provide a general indication of the 

 polluting substance. Concentrations are established by consecutive di- 

 lutions of the suspected toxicant. Parallel testing using a sensitive 

 species is employed. The effective concentration corresponds to the 

 dilution at which similar toxic effects are displayed. In view of the 

 difficulties of identifying numerous substances in natural water, and the 

 necessity for complex and expensive apparatus, often unsuitable for work 

 in the field, the quantitative tests may not only have analytical value, 

 but may also be more economic than direct determination of toxicants by 

 chemical methods. 



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