It would seem with all the health conscious organic food affectionados, there would be more information on foods high in natural ionizing radiation. Really, the organic food guys are trying to avoid part per billions of pesticides, hormones and inorganic fertilizer elements. It would seem that they would have stepped up to the plate to warn the world of all the radiation in certain foods. The best list I have found so far is at this site at Idaho State University.
This list is pretty basic as far as individual foods. With the exception of Brazil Nuts, the list may be useful for types of food stuffs. At least it gives a little bit of insight.
The propagation part of plants seem to be highest in radiation, so the root vegetables and seed portions should be the highest source of radiation in the plant. That is not a definite, but it makes some sense. Leafy vegetables should have radiation levels proportional to their potassium content. Since cesium 137 is chemically similar to potassium, it is likely that vegetables high in potassium would also tend to be higher in cesium if grown in an area with radiation fallout. Since the first atomic bomb tests, wine has traces of cesium 137, which seems to support that thought.
It would seem reasonable that farmers and gardeners that want to reduce the Cesium uptake of their crops would increase the potassium in their soils. The plants would fill their potassium needs more easily with the abundant potassium instead of scrounging around for traces of Cesium. Since the potassium content of the vegetables is lower in Becquerel/kilogram than the limits set by governments, it is unlikely that plants would shift gears to absorb more Cesium than potassium. To me that would indicate that most of the excess radiation contained in food stuffs would be external to the plants. Rinsing vegetables well before serving should then significantly reduce the exposure to radiation fallout.
Meats are a little different. Pork and sheep that are mainly feed in pastures would tend to absorb more fallout. Pork especially since they are rooting feeders. They would ingest more soil with the fallout. Sheep feed close to the ground so they also would tend to be higher as well as free range poultry. So to reduce the amount of radiation farm animals absorb, their feed should be limited to the least amount of radiation possible. Milk producing cattle are pasture feed primarily. Milk is susceptible to higher radioactive iodine levels early in a nuclear event which reduces quickly with the decay of the iodine 131 and rain rinsing the radiation off the grass leaves into the soil. Cattle generally consume less soil when grazing.
Radioactive cesium is the primary isotope of concern after the first month of an incident. With its half life of 30 years versus many millions of years for potassium 40, it only takes a small percentage of cesium replacing potassium to make a large increase in radiation activity. Cesium and potassium have similar biological half lives of 70 to 100 days, so it is quite possible that animals fed high potassium feeds would reduce Cesium levels in the meat and other products.
How effective is blocking with potassium? That is kind of hard to say. The Becquerel reading is decays per second or pops per second. It takes a tiny fraction of Cesium to produce the equivalent counts per second of the huge amount of potassium. A single Cesium 137 atom is about a billion times more likely to pop in its biological half than a potassium atom. On the other hand, only a very small amount of Cesium would need to be replaced to prevent a lot of pops. So reducing the likelihood of absorbing Cesium is much better than trying to get rid of it.
The banana dose, while not perfect, does give a pretty good indication of risk. White potatoes have a natural Becquerel reading of 126 per kilogram. That is close to the 130 Bq/kilogram for bananas, 126 for carrots, 111 for red meat, and 172 for raw lima beans. Brazil Nuts which seem to not be harmful, have an average around 350 Bq/kg with a high of about 465 Bq/kg. Most of the Brazil nut radiation is from Radium 226 which has a half life of 1600 years. Radium 226 is an alpha particle emitter with energy of about 5000 KeV per decay. While alpha particles travel less than Beta particles or gamma rays, the energy is significant. Brazil nuts by the way have radium levels nearly 1000 times higher than most foods. That just gives you an indication of how flexible the radiation level can be in the body without significant damage. So the 500 Bq/kg limit in Japan is quite safe as are the 600 Bq/kg in the EU and the 1000 Bq/kg in the UK for sheep meat, unless the body absorbs more than a normal percentage of the more active isotopes.
The main concern should be good nutrition and healthy lifestyle. Good nutrition with normal electrolyte levels and regularity, helps the body prevent absorption of excess amount of the stronger radiation. Normal body weight would also reduce absorbed radiation. Active lifestyles burn more calories which would reduce the biological half life of radiation in the body. Home remedies and special diets may be of some help, but good health is the best defense.
While I was researching to provide a more comprehensive list a natural radiation levels in foods, I could not help but notice the similarity of radium 226 decay energy and plutonium 239 decay energy. Pu239 is also an alpha particle emitter with just a little higher energy than radium 226. A very small amount of Pu239 was released at Fukushima. Since Ra226 has a half life of 1600 years and Pu239 a half life of 24,000 years, milligram per milligram, naturally occurring radium is more dangerous than plutonium. While both are dangerous, it seems that plutonium fears may be a bit overstated. The Radium Girls were workers employed to paint watch dials with radium for glow in the dark operation. The workers ingested radium from licking their paint brushes to smooth the tips. Research on the dial painters determined a threshold of 0.1 microcurries (3700 Becquerel) of radium which was established as the tolerance level for radium. The Argonne National Laboratory performed further research finding that 1000 times normal radium 226 levels is a suggested threshold for radium induced malignancies. Interesting that threshold is verified by Brazil nuts.
Inhalation of radium or plutonium is much more hazardous than ingestion. Approximately 20% of the radium and one percent of the plutonium ingested with be absorbed in the blood stream. Once in the bloodstream, both radium and plutonium are likely to treated as calcium in the body. This is not to say we should add plutonium to our diets, just that naturally occurring isotopes are so similar to the nasty man made ones, that natural dietary radioisotopes give a better clue of what to expect.
There is no way anything I write will calm many fears, but if some of the health food guru's look at the facts, they may be able to have more influence. Everything I have read so far indicates there is no governmental or nuclear industry conspiracy to force us to accept dangers. If the health food gurus devoted a little more time to natural radioactivity and how it compares to the unnatural radioactivity things would be more understandable for the general public. One thing they should more greatly research is natural iodine in various foods such as sea foods and kelps. Natural iodine does help block radioactive iodine, but daily doses need to be on the order of 120 milligrams to make a difference early in an event. Most that I have seen do responsibly recommend stable iodine tables, but a few are misleading. Another thing they may wish to research is the odd radiation paradox. Relatively low levels of radiation in addition to normal background seem to have produce a vaccine effect helping to reduce cancer risk.
Added resources: http://www.fda.gov/downloads/Food/FoodSafety/FoodContaminantsAdulteration/TotalDietStudy/UCM184305.pdf This is a pretty in depth study that generally confirms the other one.
I found another US study that generally confirms the 1000 Bq/kg limit for most accidental release isotopes except Plutionium 239. That study lists that Pu239 is 100 times more dangerous, but did not include Radium 226. It did list the biological impact of Pu239 at 1.7 e-5 Sv/Bq. Since only an extremely small amount of plutonium has been released and radium 226 is much more abundant, it would be interesting to see a more direct comparison.
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