Seems to be a bit of debate out there on whether or not caesium-137 will work its way up the food chain in the earth's oceans and affect humans who eat food from the sea, so here is a little more information.
From New York Times/Asia Pacific:
http://www.nytimes.com/...
...Cesium 137 levels were 20 times the normal level about 1,000 feet from the effluent at the Fukushima Daiichi nuclear power plant. That is far less than the level of the other main radioactive isotope spilling from the plant, iodine 131. It was found in concentrations of more than 1,150 times the maximum allowable for a seawater sample a mile north of the plant.
Still, scientists say, cesium 137 poses the greater long-term danger to the marine food chain...
Affirmed by Rutgers Marine and Coastal Sciences professor:
...Cesium 137, on the other hand, has a half-life of 30 years. Worse still, it is absorbed by marine plants, which are eaten by fish and — like mercury — tends to become concentrated as it moves up the food chain.
“It’s worrisome in that CS 137 is leaking, although the levels are still low,” said Paul G. Falkowski, a professor at Rutgers University’s Institute of Marine and Coastal Sciences. “At some point this water that is pooling in various places is ultimately going to make its way out to the sea.” And if there is a lot of cesium 137 over an extended period “then you’ll have to worry.” ...
While not ringing alarm bells or saying to push the panic button, we darn well ought to, nevertheless, be paying close attention to the possibilities here. It should help us make better future choices with regard to the world's energy policies. How important is healthy food to the human species? If it's important, then we need to move it up the national and world priority list.
Those who say caesium concentrates in the muscles, rather than fat tissue like some other toxins are correct. Studies done on caesium levels marine mammals in 2006 were done by taking muscle tissue samples. Conclusions suggest caesium=137 presence in the marine mammals were relatively low at the time of these specific studies with the specific mammals tested. However, it was noted that levels of caesium in the mammals may have varied based on their diets.
http://www.sciencedirect.com/...
The fact that caesium-137 is still concentrated in the meat of reindeer in the regions around Chernobyl would be evidence that caesium does, in fact, work its weigh through the food chain and concentrate in meat.
http://www.quora.com/...
...This is certainly a concern in light of the recent report in the New York Times that cesium 137 emits radioactive particles for centuries and that such radiation from the Chernobyl accident 15 years ago is still concentrating in the meat of reindeer as far away as Norway and wild boar meat in Croatia at levels that cause a health hazard to the people who eat the meat...
Studies were done on arctic seals in 2002, indicating that caesium does work its way up the food chain and will concentrate in muscle, liver, and kidney.
http://www.sciencedirect.com/...
...Seals are high trophic level feeders that bioaccumulate many contaminants to a greater degree than most lower trophic level organisms. Their trophic status in the marine food web and wide-spread distribution make seals useful sentinels of arctic environmental change. The purpose of this investigation is to document the levels and bioaccumulation potential of radiocaesium in high latitude seal species for which data have not previously been available. The study was carried out on harp, ringed, and bearded seals caught north of the island archipelago of Svalbard (82°N) in 1999. The results are then compared with previous studies in order to elucidate factors responsible for bioaccumulation in Arctic seals. Concentrations of 137Cs were determined in muscle, liver and kidney samples from a total of 10 juvenile and one adult seal. The mean concentration in muscle samples for all animals was 0.23±0.045 Bq/kg f.w. 137Cs concentrations in both liver and kidney samples were near detection limits (≈0.2 Bq/kg f.w.)...
Studies done in the 50's verify the concern regarding caesium 137 working its way through the marine food chain.
http://books.google.com/...
...Cesium 137 and strontium 89 and 90 remain in solution while ruthenium 106, cerium 144, zirconium 95, yttruim 90 and 90 and niobium 95 are largely in the solid phase...
The long-lived and dangerous isotope, strontium 90, has a relatively high transfer percentage and long equilibrium or "residence" time; the same would be expected for cesium 137, which is alkali and should behave somewhat like potassium or rubidium...
One could fairly conclude that making every effort to keep radioactive contaminated water out of the fresh water and oceans of the planet should be a priority. And that, if the prevailing winds from Fukushima are blowing over the ocean rather than over land, this may pose less of an immediate threat to locals in Japan, but it is by no means a reason to say "all is well."
Updated by akmk at Wed Mar 30, 2011 at 05:33 PM PDT
An update on overall seafood concerns from the Guardian.
http://www.guardian.co.uk/...
Updated by akmk at Wed Mar 30, 2011 at 05:43 PM PDT
And back on land--food contamination remains high from iodine and caesium.
Wall Street Journal
http://www.guardian.co.uk/...
"...The Ministry of Health, Labor and Welfare said Wednesday that 43 farm product samples taken Monday in Fukushima prefecture in north of Tokyo showed 25 of them, that cover nine different kinds of vegetables including spinach and broccoli, contained high levels of radioactive iodine or cesium, surpassing permissible level for consumption.
For instance, a sampling of spinach contained radioactive cesium worth 34,000 becquerels per kilogram, higher than the acceptable level of 500 becquerels per kilogram for consumption..."