Reducing bacteria - number of bacteria and saprophytes 



growing on MPA (Lesnikov, 1973, 1975). 



N.S. Stronganov (19/5) added a series of experiments on aquatic plants 

 (elodea and others) to these tests. 



Investigations for each level are conducted to reveal the acute lethal, 

 the chronic lethal and the sublethal (inhibitory) effect of toxicants. Ana- 

 lysis of the dependence of survival time of organisms on the concentration 

 of toxic substances (Jones, 1957, 1964; Lesnikov, 19/3, 19/6) enables an 

 estimation of the duration of acute (short-term) and chronic (long-term) 

 experiments: 



Type of Experiments Invertebrates Fish" 



Acute 10 days 15 days 



Intermediate 1 month 3 months 



Chronic 3 months 6 months or longer 



The boundary between acute and chronic lethal concentrations was taken 

 to be a characteristic bend of the curve. Between chronic lethal and sub- 

 lethal concentrations, the position of the asymptote of Stroganov was used 

 as the determining factor. The bend for different species and substances 

 was typically between the 4-14th day of the experiment. The duration of 

 chronic experiments was determined by the detected cases of the remote 

 negative effect. 



For some organisms {Vaphviia, and certain algae) the methods of experi- 

 mentation on populations are established. For Vaphnia, the whole set of 

 population reactions such as logrythmic growth of the biomass, a regular 

 transition from parthenogenetic to bisexual reproduction, etc. are repro- 

 duced. It has been established that when a population reaches its satura- 

 tion biomass, its sensitivity to pollutants becomes 3-3.5 times greater 

 than before (Table 1). . 



TABLE 1 . CHANGES IN BOUNDARY CONCENTRATIONS OF 3 POLLUTANTS 

 INFLUENCING BIOMASS IN PAPHWIA MAGMA. 

 (Boundary concentrations are estimated on the basis of regression equation) 



85 



