necessarily evidence of its danger to a population. These factors serve only 

 to warn about toxic effects under conditions of optimal temperature. When 

 the temperature of water is raised to 30°C, the toxicity of a given substance 

 for organisms can be increased by hundreds, thousands, and tens of thousands 

 times. This has been demonstrated in experiments with cadmium on Daphnia 

 magna (Braginsky and Scherban 1978). Therefore, the question of the "patho- 

 logical" reactions of aquatic populations to toxic effects is inseparably 

 linked with ambient temperatures. 



The existence of populations, as opposed to individuals, is in itself 

 protective, since an irregular distribution of a toxic agent within popula- 

 tion predetermines the possibility of preserving some quantity of resistant 

 individuals. This was noted in natural communities of the blue-green algae 

 treated with algaecide preparations. Luminiscence microscopy data showed 

 that from 0.5 to 20 percent of the total quantity of algae was unaffected by 

 algaecides. In experiments with aquatic invertebrates, uneven mortality of 

 test organisms was observed, although it was not possible to connect this 

 phenomenon directly with the level of toxicant accumulation in the animals' 

 body. 



An irregularity of toxicant distribution among fish populations was con- 

 firmed analytically by gas chromotography for extracts of DDT in organs and 

 tissues. When studying accumulation levels of this pesticide in fish popu- 

 lations, fluctuations in cerebral fat tissue from to 40 mg/kg were ob- 

 served, consistent with a normal distribution range. It is natural that 

 fish with DDT levels exceeding the critical values (3 mg/kg of cerebrum 

 weight) are in a state of deep pathology; a cumulative intoxication which 

 does not affect the entire population (Braginsky, et al^. 1979). 



All analogeous phenomena are undoubtedly similar, and subject to the law 

 of survival of the species since the history of the earth, toxic factors are 

 not new. They probably functioned constantly in the early stages of the de- 

 velopment of the planet, with respect to high concentrations of ammonia, 

 methane, phosphorus and other toxic agents in water. The "chemical weapon" 

 is of importance to interspecies relations, and where this weapon was used, 

 protective measures were created. Apparently these measures are also ef- 

 fective with respect to toxicants of anthropogenic origin. Whatever the me- 

 chanism is for populations reaction to toxic effects, the ultimate result 

 should be a decrease of population abundance. Occasionally, the population 

 may even increase, when concentrations promoting reproduction are favored. 

 In any case, the question where "normalcy" ends and "pathology" begins is a 

 controversial consideration. It must be noted that deceleration or accele- 

 ration of a population's reproduction rate, or fluctuations in its range of 

 abundance are not something fatal or unfamiliar. Sequential sigmoid fluctu- 

 ations of population quantity are characteristic of life on earth; there- 

 fore, it is hardly appropriate to speak about pathology in the same sense in 

 which the term is used in medicine. 



38 



