By the end of the first day of detoxication in pure water, the state of 

 the majority of fish did not differ from that of the controls. They ac- 

 tively swam, obviously reacted to external stimuli, and consumed food. The 

 fish exposed to the point of equilibrium loss during intoxication, restored 

 horizontal positioning in pure water only at intervals, ultimately sinking 

 to the bottom and dying on the second day. The survivors did not differ 

 from controls after 25 days of detoxification. They were again subjected 

 to the action of the toxicants. During a repeated 5-minute exposure with 

 concentrated sewage, the inverted position was observed. In diluted 

 sewage, unstable reactions were noted, but an equilibrium state was re- 

 corded. In pure water, the roach exposed to the concentrates died on the 

 third day, 20 percent of fish exposed to weak dilutions survived (Figure 2). 



The dynamics of perch survival rate in pure water after 7 minutes expo- 

 sure is illustrated in Table 3. A situation similar to that described above 

 was observed when fish were exposed to concentrated and weakly diluted in- 

 dustrial wastes (boiling shop, evaporating and hydrolysis shops), and to the 

 waters of a natural waste water receiver, the isolated bay of a reservoir. 



Experiments determining reversibility of intoxication in fish after a 

 brief exposure to effluents from a heat-and-power station were also re- 

 vealing, since they are considered to be relatively pure by industry. After 

 fish were exposed to effluents from a heat-and-power station diluted in 

 ratios of 1:5, 1:10, and 1:25 for 6, 10, and 24 minutes, respectively, only 

 a minor suppression of activity was observed. At the dilution 1:5 there was 

 a thin coating of coal observed on the fins. Mortality during the 10 day 

 period of detoxification was only 20 percent. However, additional exposure 

 of fish at the same dilutions of wastes for 7, 16, and 24 minutes led to the 

 death of the fish after 20 minutes in the first case, after a day in the se- 

 cond case, and only at a dilution of 1:25 did 40 percent of the experimental 

 fish survive (Table 4). These examples convincingly demonstrate the high 

 toxicity of treated wastes of sulphate pulp manufacturing. 



The results of the experiment given in Table 5 are good evidence for the 

 dependence of the result on the duration of exposure. 



The data show that only a four minute difference in exposure marked ef- 

 fects in the outcome of intoxication. 



The dependence of the reversibility rate on concentration in roach lar- 

 vae is shown in Table 6. 



As was demonstrated earlier, the main factors determining the resistance 

 and degree of restoration of activity, are the duration of exposure and the 

 concentration of the toxicant. This is also demonstrated in Table 7, which 

 shows that the purified wastes from treatment plants loose their toxic pro- 

 perties to a considerable degree, and although there are some symptoms of 

 intoxication, life activity is restored in pure water. Table 8 gives an in- 

 dication of the reaction of juvenile fish of various species to toxicants. 



Thus, an extensive investigation into the pattern of intoxication from 

 effluents and its possible reversibility demonstrated that even brief expo- 



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