VI-128 



upon the development of organisms and communities. There is an urgent 

 need, therefore, for diversified programs to develop new indices of 

 toxicity at the individual, the population and the community levels, 

 with emphasis on long-term exposure at sublethal concentrations. 



Food Chain Effects 



The outright poisoning of various organisms is easily recognized. 

 Perhaps an even more important problem is the effects of various 

 toxicants present in concentrations which reduce the populations of 

 food organisms to such a low level that they are inadequate for the 

 forms deoendinq on them as a food supply. For example, fish such 

 as salmon, migrating downstream, will be feeding on their way to sea. 

 If these young fish are feeding on a sub-adequate food supply, then 

 they must be in a weakened condition for their subsequent journey 

 in the ocean and, thus, be more susceptible to attack by predators 

 and disease than they v.'ould be otherwise. Various kinds of pollution 

 such as toxic materials or heated effluents could cause such results. 



Another food food chain effect is the phenomenon of biological magnifi- 

 cation. Biological magnification is an additional chronic effect of 

 toxic pollutants (such as heavy metals, pesticides, radionuclides, 

 bacteria, and viruses) which must be recognized and studied. Many 

 animals, and especially shellfish such as the oyster, have the ability 

 to remove from the environment and store in their tissues substances 

 present at non-toxic levels in the surrounding water. This process 



