pected as the causative agents. Subsequent laboratory tests in which mink 

 were fed various doses of DDT and dieldrin in excess of the levels found in 

 the fish did not reproduce the effects. However, 5 ppm PCB added to the 

 experimental diet markedly reduced reproduction, and 15 ppm totally 

 inhibited reproduction and caused death of the adults (Ringer, Aulerich, 

 and Zabik, 1972). These tests established that mink are highly sensitive 

 to PCB toxicity and clearly indicated that residues accumulated in Great 

 Lakes fish were responsible for death and reduced reproduction of commer- 

 cially reared mink. Because of the high losses resulting from feeding coho 

 salmon, fur farmers have discontinued the use of Great Lakes fish in mink 

 diets. 



The residues of PCB in Great Lakes fish pose a potential health hazard 

 to humans. To protect consumers the U.S. Food and Drug Administration has 

 restricted the distribution and sale of fish that contain more than 5 ppm 

 PCB; shipments of such fish from commercial outlets have been confiscated 

 and destroyed. This ruling has curtailed the commercial utilization of 

 most major food fish species in the Great Lakes. Although recreational 

 fisheries are not restricted, state health authorities have warned sport 

 fishermen to limit their consumption of Great Lakes fish. A new informa- 

 tion on PCB effects is developed, greater restrictions may be necessary. 



NEW TEST PROCEDURES 



The problems currently associated with PCB in the Great Lakes are only 

 a single example of the serious impact of synthetic organic chemicals on 

 aquatic ecosystems. Residues of other potentially harmful chemicals (e.g., 

 hexachlorobenzene, the chlorinated napthalenes, pthalate plasticizers) have 

 been found in increasing concentrations in aquatic systems. Clearly there 

 is a need to identify and restrict the distribution of harmful residues 

 before serious damage has occurred. 



Industrialized nations throughout the world have a responsibility to 

 develop new strategies for identification and control of harmful chemicals. 

 We can neither afford to wait to study these problems after contamination 

 has occurred, nor can we afford the time and resources to thoroughly 

 investigate each new chemical before it is released to the environment. It 

 is imperative that we develop a systematic approach for evaluation of new 

 materials and new technology. Important new efforts are being made to find 

 correlations between chemical structure and biological activity (Veith and 

 Konasewich, 1975). A chemical classification system based on physical pro- 

 perties, chemical structure, and biological activity would provide some 

 indication of potential hazard. Simple model ecosystems (Metcalf, Sanga, 

 and Kapoor, 1971) and food-chain models (Johnson, 1974) offer additional 

 promise for preliminary testing to identify harmful properties of chemicals, 



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