sensitive organism; the large pond snail, Liumta ^tagnaUs as an organism 

 of intermediate sensitivity; and the guppy, Lefa-c6-tei inticulaJiu,, a fish 

 of least sensitivity. The duration of the test is five days at a tempera- 

 ture of 17-22 °C. Survival and general condition (behavior) are the 

 criteria of toxicity to the organism. Toxicity is estimated using a five 

 degree system: 



1. First Degree. Very acutely toxic. All organisms of 

 the three species die within the first day. 



2. Second Degree. Acutely toxic. All organisms of the 

 organisms of the three species die within five days. 



3. Third Degree. Toxic. From 70 to 100 percent of the 

 Vaphnia die; not more than 20 percent of the pond snails 

 expire; and all guppies survive. 



4. Fourth Degree. Slightly toxic. The mortality of Vaplmia. 

 does not exceed 30 percent; and all of the pond snails and 

 guppies survive. 



5. Fifth Degree. Conventionally non-toxic. All of the or- 

 ganisms of the three species survive, and by outward ap- 

 pearance and behavior do not differ from control organisms. 



When the variability in the degree of toxic waste water is considered, 

 control of periodically diluted waste water is recommended. In this re- 

 gard, waste water is diluted in the following order: (initial), 5, 10, 

 100, 500 times with clean water from a river or brook containing no toxic 

 substances. The scheme of the tests is identical to the initial waste 

 water. The results obtained are expressed graphically by plotting the 

 degree of dilution against the degree of toxicity. The resultant slope 

 of the curve suggests either the rate of increase characterizing the toxi- 

 cological danger of the waste water, or the rate of loss of the toxicant 

 with dilution. 



The first variety of control of toxicity may be used for differential 

 determination of the degree of toxicity of waste waters discharged from 

 different sources within a single industry. This enables the detection 

 of the most dangerous sources and allows these waters to be directed to 

 special treatment. 



The Second Variant 



The waters of large rivers, reservoirs and lakes do not possess the 

 acute toxicity of waste waters, although they receive these waters. How- 

 ever, even in low concentrations, a prolonged influence of toxic 

 substances on aquatic organisms leads to death or diminution of the num- 

 bers of the most sensitive of these organisms. These conditions transform 

 individual aquatic communities and the ecosystem as a whole. Therefore, 

 toxicological control is also necessary for the waters of rivers, reser- 

 voirs, and lakes which undergo anthropogenic influence. 



