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I read yesterday that sunflowers were used and to cleanup radioactivity at Chernobyl and the Atomic Bomb sites in Japan and may be used as part of a campaign to clean up the Fukushima area.

But my questions are:

  1. How does a sunflower absorb radioactivity?
  2. Is there a way to measure how well the sunflowers are working?
  3. Can sunflowers planted in not particularly radioactive places concentrate otherwise harmless radiation?

I was tempted to ask this on Skeptics.SE, but there's not much to be skeptical about, except whether or not it's a good idea

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This is rather interesting: ""Almost 10,000 packets of sunflower seeds at 500 yen ($6) each have so far been sold to some 30,000 people, including to the city of Yokohama near Tokyo, which is growing sunflowers in 200 parks, Handa said."" By this priice, the usual bird food in wintertime in Germany would be some billions of Dollar. This story is eiter nonsense or betrayal of good-will- people! –  Georg Jul 29 '11 at 14:41
    
This question reminds me of a computer game I saw on store shelves recently in the U.S. ---> Plants Versus Zombies. Growing sunflowers is evidently critical to victory over a gruesome death. –  Vintage Jul 29 '11 at 17:56
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2 Answers

up vote 10 down vote accepted

It may have something to do with the growth rate of sunflowers. During peak growing times sunflowers can grow inches in a single day, which likely results in them drawing more water out of the ground, allowing them to concentrate the radioactive materials through deposition in the plant matter at a faster rate than other plant organisms. I would suspect you could monitor the process with standard instruments, which are pretty sensitive to the presence of particle decay. I doubt that there is any serious risk of activity accrual in areas that are not already contaminated.

Edited to add: A quick search on the Google points out that sunflowers are good at absorbing heavy metals via rhizofiltration.

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This is a stretch, but could sunflowers planted around a house help remove radon from a basement. I read that besides cesium-137 sunflowers can remove other isotopes. –  Peter Turner Jul 29 '11 at 12:53
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@Peter Turner: Quite unlikely. The original article linked specifically noted that sunflowers extracted cesium because it's chemically similar to potassium (kalium). Cesium is currently the main troublesome isotope near Fukushima (Iodine is pretty much gone). Sunflowers may also be able to extract other ions from the soil. However, radon is entirely different - it's a gas, for instance, and doesn't react chemically. So sunflowers would be not very likely to remove radom from the soil - and they certainly wouldn't grow in basements. Also, this gets you sunflowers with radioactive cesium in them –  MSalters Jul 29 '11 at 13:31
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  1. As your second link states, sunflowers absorb ions from the soil. That's how they get nutrients to grow, but the same chemical mechanism will absorb cesium atoms - cesium is very soluable in water. The explosion at Fukushima ejected two isotopes with a particular danger to humans, 137Cs (cesium) and 131I (Iodine) Because the latter has a half-life of only 8 days 135Cs is currently the main cause of radioactivity in the area. Therefore, sunflowers grown in the Fukushima area will absorb the radioactive Cesium-137 isotope.

  2. The effect is quite easy to measure: the sunflowers themselves become radioactive because they contain radioactive Cesium-137 atoms. In particular, Cesium-137 gives off characteristic gamma rays through the decay via Barium-137m.

  3. Not really. Banana's are far more effetive in that respect.

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