ichthyopathologist of our laboratory, O.N. Krylov (1973) on the influence 

 of chlorophos (Dipterex) on fish (see Table 1). 



TABLE 1. RELATIONSHIP OF LT50 (mg/liter) OF CHLOROPHOS FOR CURRENT 

 YEAR'S BROOD OF FISH AS A FUNCTION OF TIME OF EXPOSURE 



With an exposure of 96 hours, Coregonus peled was 1200 times more sensi- 

 tive to chlorophos than Cyprinus carpio , while with an exposure of 25 days, 

 it was only 64 times more sensitive. As a rule, the longer the exposure, 

 the less the difference is between sensitivities of species. 



Our ideas concerning the relative sensitivity of test organisms to toxic 

 substances are presented in Table 2. The relative sensitivity of the test 

 organisms used in the USSR is estimated on the basis of studies of the 

 GosNIORKh Water Toxicology Laboratory (Lesnikov, 1976, 1973; Krylov, 1973; 

 Alekseyev and Lesnikov, 1977; Stroganova, 1971), while the relative sensi- 

 tivity of test organisms used in the USA is based on the works of McKee and 

 Wolf, 1963, Mayer et a^., 1975; Meerle and Mayer, 1975; Sanders, 1977; 

 Sanders et al_., 1973; Mayer etaX., 1976, 1977; Carlson, 1972; Hermanutz et 

 al., 1973; Macek et aj_., 1976; Sauter et al., 1976; Snarski et a^., 1976; 

 Allison and Hermanutz, 1977; Pickering et aj_., 1977; Christensen et al ., 

 1977; Eaton etal., 1978; McKim, 1977; McKimet al., 1976; Benoit et al., 

 1976; Carwell et al., 1977; Spehar, 1976, Spehar et al., 1978; Hermanutz, 

 1977; McKimm et al., 1978; Lloyd, 1976; Lloyd et al. , 1976. Of course, this 

 table must be considered a first approach to the problem. We can see from 

 the data presented that some organisms, e.g., Salmo irideus , Cyprinus carpio 

 and Daphnia magna , are used in both countries, while the others are similar 

 in their sensitivity. At the present time, neither country uses the most 

 toxicoresistant species. Consequently, the data compared using today's test 

 organisms are comparable. 



The experimental differences are small in most cases, significant in a 

 few cases. 



EXPERIMENTS ON FISH 



In the USSR, experiments are performed on eggs, larvae, current year's 

 brood and second year fish, less frequently on older fish. The usual dura- 

 tion of acute experiments is not over 15 days. As in the USA, the LC50 is 

 determined for 96 and 120 hours, and the curve of median lethal time as a 

 function of substance concentration is studied. Subacute experiments, al- 

 lowing the boundary of chronic lethal effect to be determined and sublethal 

 effects to be revealed, last up to 3 months (90 days). Chronic experiments, 



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