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may continue until the body burden of the toxicant reaches such levels 

 that the animal's death would result if the pollutant were released 

 into the blood stream by physiological activity. This may occur, as 

 in the case of chlorinated hydrocarbon pesticides (such as DDT and 

 endrin) stored in fat depots, when the animals's food supply is 

 restricted and the body fat is mobilized. The appearance of the 

 toxicant in the blood stream causes the death of the animal. Equally 

 disastrous is the mobilization of body fat to form sex products which 

 may contain sufficiently high levels of the pollutant so that the 

 normal development of the young is impossible. 



The biological magnification and storage of toxic residues of pollu- 

 ting substances and microorganisms may have another serious after-effect. 

 Herbivorous and carnivorous fish at lower trophic stages may gradually 

 build up DDT residues without apparent ill effect. Carnivorous fish, 

 mammals, and birds preying on these contaminated fish may be killed 

 immediately or suffer irreparable damage because of the pesticide 

 residue or infectious agent. 



A great deal of work must be done to determine the significance of 

 the phenomenon of biological magnification. We must develop techni- 

 ques for predicting potential hazards before toxic material is 

 introduced into the environment and economic noisons must be used 

 so as to minimize the possibility of biological magnification. 



