months or more in closed vessels. This phenomenon can be attributed to DDVP 

 (dimethyldichlorovinylphosphate), a product formed upon decomposition of 

 chlorophos (dimethyloxytrichloroethylphosphonate) . An increase has been 

 found in toxicity during the first week in solutions of orthoxylene, though 

 the mechanisms of the process itself is not clear. 



Of works of this type performed in the USA, we would like to note an ex- 

 ceptionally interesting study by Mancy and Allen (1977), on the influence of 

 environmental factors on the toxicity of heavy metal ions. 



A second trend is estimation of the influence of a pollutant on the 

 hydrochemical processes in a body of water. This type of experiment is an 

 obligatory component of all water toxicology studies in the USSR. We found 

 no analogous studies in the USA. In these experiments, water is taken from 

 a natural reservoir and placed in an aquarium for study. In our laboratory, 

 water is taken from a reservoir with hard water (e.g., the Strelka River) 

 and another bo^dy of water with soft water (e.g.. Lake Ladoga). A series of 

 concentrations of the pollutant, usually 6-7 gradations, is created, with 

 pure water serving as the control. Analysis of pH, dissolved oxygen, BOD5, 

 BOD2o» permanganate and bichromate oxidizability, forms of nitrogen (am- 

 monia, nitrates, nitrites) are regularly analyzed, and changes in the con- 

 centration of the pollutant are observed. Many substances cause a decrease 

 in the content of dissolved oxygen and an increase in BOD, increasing the 

 saprobic nature of the medium. Toxic substances may significantly suppress, 

 either temporarily or throughout the experiment (usually 25-30 days) pro- 

 cesses of self-purification. Most frequently, processes of oxidation nitro- 

 gen are first suppressed, i.e., processes of formation of nitrites from am- 

 monia compounds and oxidation of nitrites to nitrates. In many cases, an 

 increase is found in the content of nitrites which cannot be explained by 

 oxidation of ammonia compounds and can be attributed only to denitrif ication 

 processes. 



Summing up all that we have said, we note that, with the exception of a 

 small number of tests used in one country and not in the other, the studies 

 in the two countries, the USSR and the USA, generally follow the same goals, 

 and at the present time are performed according to basically similar 

 methods, which is determined as we compare works performed in the two coun- 

 tries. The most difficult question is that of the maximum permissible 

 standardization of a minimum program of these investigations. 



It is hardly necessary to change the forms of application of the stand- 

 ards developed in one or the other of the countries--they are determined by 

 the specifics of our individual national systems. We can simply state that 

 the MPC system used in the USSR is equivalent in the nature of its scienti- 

 fic foundation to the concept of the "water quality criterion" used in the 

 USA, while the water quality "standards" used in the USA are more or less 

 equivalent to the "discharge norms" or "maximum permissible discharges" 

 (MPD) used here. 



The system of distribution of test organisms in terms of their relative 

 sensitivity to pollutants represents some difficulty, since the relationship 

 of sensitivity of species to various substances differs somewhat. At one 



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