I don't know really, but pollutants tend to get more dangerously concentrated in predators up the food-chain (which may in turn be why sea lions and polar bears are effected, if the radiation is in fact what is harming them?). Even without consuming prey with radioactive materials in them I think orcas are already considered hazardous material if they wash up on shore.
This thread makes me wonder how the release of radioactive material from Fukushima will end up comparing to the long-standing Cold War practice of the Soviets disposing of nuclear waste and at times even entire reactor cores off the Arctic coasts of Novaya Zemliya. The radiation from those waters eventually contaminated much of the North Pacific, getting into things like salmon. Over the long run I don't really know how much of this radioactive material it takes for it to actually have a meaningful health impact on life thousands of miles away.
Either way, I'm curious to better understand the subject.
