of Henderson ^ al^, , (1959a, b) or in the present 

 study, would provide a basis for determining a 

 safe application level. Factors which might af- 

 fect the toxicity of a field dosage, such as a 

 possible interaction of DDT with organic and 

 inorganic materials, any variation in volume of 

 water per fish, stress situations, rainfall, or 

 contaminated runoff from insecticide treated 

 area (Young et^al_., 1951) should be considered 

 before application of the insecticide . 



The removal of food may actually prove 

 to be of more imminent danger to fish than the 

 toxicity of the insecticide, and evaluation of 

 effects of DDT might better.be based on inverte- 

 brate food organisms rather than on fish. DDT 

 and other chlorinated hydrocarbons are known 

 to be toxic to lower organisms in the fish food 

 chain, though specific TL/m values have not 

 been determined (Harrington et al., 1958). It 

 requires only an ounce or two of DDT per acre 

 to kill crustaceans (Leedy)^. The microfauna, 

 especially the protozoa, are relatively resistant 

 to the chlorinated hydrocarbons (DeWitt et al., 

 1960) . Even if over 50 percent of the lower 

 food-chain organisms survived, the dead ones 

 might be eaten by fish. Though DeWitt and 

 George (1960) report no harmful effects on fish 

 from eating insects killed by DDT sprayings, 

 Hoffman (1959) and Janzen (1960) report fish 

 affected by insects sprayed with DDT. The 

 amount of poisoned insects required to kill fish 

 varied considerably, however. 



It is obvious that use of standardized pro- 

 cedures in the laboratory results in comparable, 

 reliable, and reproducible data, but cannot 

 reproduce conditions of a particular natural 

 situation, which are never constant or identical 

 with other natural situations . 



Histopathological conditions 



Although bioassays with DDT are neces- 

 sary for estimation of fish survival after field 

 application, it seems of at least equal importance 

 to determine the physiological cause of death. 



Some research concerning effects of the DDT on 

 the tissues of exposed animals is now in progress 

 in several laboratories. Janzen (1960) has re- 

 ported that pesticides are concentrated in fish, 

 especially in the fatty tissues. Damage of liver 

 and kidney tissues, reduction of red blood cell 

 production, depressed growth rates, and reduced 

 efficiency of reproduction may result. These 

 conditions would suggest increased sensitivity to 

 diseases. Janzen pointed out that under stress, 

 such as lack of food, the DDT stored in the fat 

 is likely to be released into the system. The 

 effects of such a release are not yet known . Cope 

 (1959) reported storage of chlorinated hydro - 

 carbons in the kidney, pyloric caecum, and brain, 

 but none in the liver. In other chemical bioassays 

 conducted at his laboratory, DDT has been found 

 in tissues two years after exposure of trout (up 

 to .94 ppm DDT in the tissues) and whitefish (0.7 

 ppm DDT and 1.2 ppm DDE) . 



The determination of DDT concentrations 

 in tissues or even test solutions is difficult, and 

 no method has yet been established that is both 

 rapid and accurate. An elaborate paper chro- 

 matographic analysis for DDT was proposed by 

 Mitchell (1954) . The analysis is based on sub- 

 jective color comparisons with a standard and is, 

 therefore, subject to some error. Cope's results 

 mentioned above stem from a complex bipchemical 

 analysis of tissues requiring special equipment 

 and skilled technique. This procedure is still be- 

 ing perfected. Amounts of stored insecticide in 

 fish tissue depend on the compound and species. 

 Small amounts seem to be of no harm to the fish . 

 This is indeed fortunate as every assayed fish, 

 even from supposedly uncontamlnated waters, at 

 the Denver Laboratory has had some DDT in the 

 tissues . Mount?/ found high concentrations of 

 endrin in the liver, intestine, spleen, and kidney 

 of carp after 2-7 days of exposure . Similar and 

 more extensive assays have been performed on 

 quail and pheasant (Anon., 1951; DeWitt, 1955; 

 DeWitt et al ., L960) and the chlorinated hydro- 

 carbons have been found to accumulate in the 

 tissues of birds also, especially in the fat and 

 muscle. 



7/ Leedy, D. L. November 15, 1960 Draft report on (1) wildlife values and 

 (2) pesticide usage in conservation programs. U.S. Fish and Wildlife 

 Service, U.S. Department of the Interior 



8/ See footnote 4. 



12 



