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.
Regarding the bolded part:
I believe that's called bioaccumulation. In short, plants, and other organisms at the bottom of the food chain receive most of the radiation or poisonous substance that is causing the problem because they make up over 90% of the total "biomass" of the environment. It's spread out over all of the bottom of the food chain, but they still get most of the radiation.
Then, something higher on the food chain eats them. It receives all of the poisonous substance, and will continue to receive it by eating more smaller organisms over its life. It cannot get rid of it, bodies aren't easily able to get rid of things that bioaccumulate (radiation, heavy metals). By the end of it's life, it might very well be full of poison or radiation, if there was enough of it.
Then something even higher on the food chain eats them, and in this mannerism, the poison keeps being concentrated into the top of the food chain. This causes more serious problems than it would if it were spread out over
all of the biomass.
I've avoided eating fish since Fukushima, and I'm worried that the consequences of the disaster will stick around for a long time.
