Scientists have discovered that sunflowers can pull radioactive contaminants out of the soil. Researchers cleaning up the Fukushima site in Japan are putting the flowers to the test. The idea was tried back in the mid-1990s near the Chernobyl power plant meltdown. Soil scientist Michael Blaylock, who worked on that project, and who is vice president of systems development at Edenspace Systems Corp in the U.S., tells Living in Japan's Bruce Gellerman how this clean-up-by-plant works.
GELLERMAN: So, sunflower plants and nuclear power plants - what's the connection?
BLAYLOCK: Well, the connection there is really that sunflowers are really good at taking up certain radioactive isotopes. And that’s really the connection between the sunflowers and the nuclear power plants.
GELLERMAN: So basically the plant just kind of grows, and as it grows, it’s sucking the radiation out of the soil?
BLAYLOCK: That’s correct. Those radioisotopes mimic some of the nutrients that the plant takes up normally. And so the plant really doesn’t distinguish between those radioactive isotopes and some of the nutrients like potassium and calcium that it takes up as a matter of course.
GELLERMAN: Well, you worked at Chernobyl back in the mid-1990s. Did it work?
BLAYLOCK: It was very effective for the water. The soil was a little bit of a different story because cesium in soil is a little bit tricky. Strontium is in soil, too. If you can’t take both of them out, taking just the strontium doesn’t necessarily get you to where you want to be if you leave the cesium around.
GELLERMAN: So why is cesium harder to get out than strontium?
BLAYLOCK: Well, cesium mimics potassium. The clay layers on a very small scale, the atomic structure, they have what we call, for lack of a better word, a cavity in between those clay layers. And the potassium fits very nicely into those cavities and that’s the way that soils retain potassium. Cesium, being very similar to potassium, fits in those same cavities and it becomes fixed in the soil and it is very difficult for it to come out. Whereas strontium is very similar to calcium and calcium is in a form that is very available to plants - we don’t have that problem.
GELLERMAN: Well, we’re trying this at Fukushima. Do you think it could actually work there?
BLAYLOCK: It could, given the right set of circumstances. You know, one thing we found in Chernobyl is, we came there a number of years after the fact. And so that gave plenty of time for that cesium to become fixed in the soil, and it’s going to become very dependent on the soil types. You know, soils that have very high mica contents, certain clays, are going to be very difficult to remove the cesium from, once the cesium gets fixed. But under the right set of circumstances, they could be effective in removing those contaminants from the soil.
GELLERMAN: So which part of the plant stores the radioactivity?
BLAYLOCK: You don’t want to have to dig up roots – that’s a very difficult process. It can be done but it’s much easier to harvest leaves and stems. So we focus our efforts on those plants that do a good job of translocating from roots to shoots.
GELLERMAN: Is the sunflower the best plant for this?
BLAYLOCK: Sunflowers are attractive because they grow well and produce a lot of biomass quickly. It doesn’t take a lot of management to grow sunflowers as compared to some other crops; they are adaptable to a lot of different climates. So, I don’t know that it is the best plant, but it is certainly one that meets the criteria that we need.
GELLERMAN: So when you harvest the plant, it’s radioactive!
BLAYLOCK: Yeah, the biomass, or the harvested material, would be radioactive.
GELLERMAN: What do you do then? How do you get rid of the radioactivity in the plant?
BLAYLOCK: The real process here is, what we’re trying to do is, concentrate that radioactivity from the soil, which is a fairly low concentration, to a much higher concentration in the plant material. You still have to dispose of that plant material, but you move that particular contaminant or radioactive isotope from silica, aluminosilicate matrix in the soil, which is very difficult to deal with, to a carbon-based substance in the plant material. You concentrate that, so you have a lot less material to dispose of, and you can leave that soil, which is a resource that’s hard to replace – you can leave that soil in place and just remove the contaminant.
GELLERMAN: And the radiation doesn’t kill the plant as this is happening?
BLAYLOCK: Typically not. If they’re high enough to where they’re going to affect the plant growth, it’s not going to be an area that’s suitable for this type of approach.
GELLERMAN: I can see unexpected consequences from something like this. I mean, here you have these sunflower plants, and the seeds dry, and birds eat the seeds and then they fly off, and they’re radioactive.
BLAYLOCK: Yeah, that could be a risk. I mean, typically, when we performed this, we would always harvest plants before they seeded out because the main idea is to harvest biomass. You want to produce as much vegetative material as possible. And once the plants start producing seeds, its flowers start forming, it’s not producing a lot more vegetative matter to remove that contaminant, so typically once the plant flowered, we harvested and we would replant again. We’re not interested in producing seeds.
GELLERMAN: What about the hard-nosed question about money? How much does this cost relative to other technologies?
BLAYLOCK: Relative to other remediation technologies, it’s not that expensive. But when you factor in that there’s sampling and disposal of the material, it’s certainly not free, but, you know, on a cost basis as compared to the cost of storing soil for a very long period of time, very large quantities of soil, it’s a very attractive option.
GELLERMAN: You know, there’s something very special about sunflowers. I mean, they’re beautiful. And there’s something poetic, I think, going on here because they’re also an anti-nuclear symbol.
BLAYLOCK: Yeah, it is an interesting set of circumstances. And to see a field of plants out there growing in an area that previously was not vegetated, and you’d be able to harness nature to do some of the things that we need to do to, you know, correct our mistakes, it is something that’s very pleasant to look at and to see. And it’s one of those touchy-feely things that you feel really good about.© 2011 Living on Earth. Used with permission of Living on Earth and World Media Foundation. www.loe.org Living on Earth is the weekly environmental news and information program distributed by Public Radio International. Use of material does not imply e