The seafood was also analyzed for seven PCBs or Aroclors.  Only the two shown in this graph were detected, and they were only detected in samples of "crab butter" (crab hepatopancreas) and halibut heads.  The presence and concentration of these PCBs is due in part to the fat content in these parts of the animals. 

The crab hepatopancreas functions like the liver of more complex species, removing toxins from the animal's system; this explains the PCBs and other toxic chemicals detected in the crab butter.  As for halibut heads, they contain a high proportion of fatty tissues, which tends to bind PCBs.

The concentrations of these two PCBs exceeded the EPA screening level for these chemicals.  In this case, the Study Team opted not to calculate a risk factor based on a subsistence consumption rate, because there was no information on how much crab butter or halibut heads a person might eat.  Although people sometimes eat these parts, it is unlikely anyone would eat an 8-ounce serving of crab butter every day for a lifetime.  So the exposure and dosage of PCBs is probably not at unsafe levels.