Re: how many pcb's are enough to kill and orca/killer whale

PCBs (polychlorinated biphenyls are chlorinated aromatic 
hydrocarbon chemicals that have been in commercial use for over 50 
years. They are resistant to degradation and persist for long periods 
of time in the environment. In 1979, EPA prohibited the manufacture 
of PCBs in the U.S. and provided for severe restrictions and an 
orderly phaseout of all uses during a 5 year period. There is a wealth 
of data in the scientific literature on its toxic effects, and they are such 
a low order of acute toxicity to be labeled as legally nontoxic. From 
animal studies, PCBs are also described as a relatively low order of 
toxicity chronically. In rodents PCBs, similar to all chlorinated 
hydrocarbon compounds, produced liver tumors and cancer. They 
have not been shown to cause liver cancer in other species, 
including humans.  There have been no studies on the toxicity of 
PCBs in orca whales. It is not logical to think  that Puget Sound will 
be highly polluted by PCBs in the future. That is not to say that other 
commercial products may enhance pollution within these waters.