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nature news homenews archivespecialsopinionfeaturesnews blognature journal Published online 30 March 2011 |Nature | doi:10.1038/news.2011.195 News Algae holds promise for nuclear clean-up Organism's ability to distinguish strontium from calcium could help in dealing with nuclear waste. Richard A. Lovett 
Strontium-eating algae could help clean up after nuclear accidents.CLAUDE NURIDSANY & MARIE PERENNOU/SCIENCE PHOTO LIBRARYCommon freshwater algae might hold a key to cleaning up after disasters such as Japan's Fukushima nuclear accident, scientists said yesterday at a meeting of the American Chemical Society in Anaheim, California.
The algae, called Closterium moniliferum, are members of the desmid order, known to microbiologists for their distinctive shapes, said Minna Krejci, a materials scientist at Northwestern University in Evanston, Illinois. But the crescent-shaped C. moniliferum caught Krejci's eye because of its unusual ability to remove strontium from water, depositing it in crystals that form in subcellular structures known as vacuoles — an knack that could include the radioactive isotope strontium-90.
Strontium is very similar in properties and atomic size to calcium, so biological processes can't easily separate the two elements. That makes strontium-90 a particularly dangerous isotope: it can infiltrate milk, bones, bone marrow, blood and other tissues, where the radiation that it emits can eventually cause cancer.
"That's what makes strontium-90 one of the dominant health risks of spent fuel for the first 100 years or so after it leaves the reactor," says Krejci. The radioisotope has a half-life of about 30 years.
Unfortunately, reactor waste and accidental spills can contain up to ten billion times more calcium than strontium, making it very difficult to clean up the strontium without also having to dispose of a mountain of harmless calcium. "We need a highly efficient and selective method of separating it," says Krejci.
Enter C. moniliferum. The organism has no particular interest in strontium: it mostly collects barium. But strontium is midway between calcium and barium in size and properties, so any of it that happens to be around gets crystallized as well. Meanwhile, even though calcium is far more abundant than either of the other two elements, it is different enough to barium that it gets left behind.
The result is a crystal that is mainly composed of barium, but is massively enriched in strontium.
How do they do that?Much of Krejci's research so far1 has focused on trying to work out how the algae generate the crystals, with an eye to making the process even more strontium-selective. For the moment, she knows that the organism isn't purposefully bringing excess barium and strontium through its cell walls. Rather, she says, the crystals appear to form because the vacuoles in which they collect are rich in sulphate. Barium and strontium have relatively low solubility in sulphate solutions, so any barium and strontium that make their way into these vacuoles easily precipitate out to form crystals.
Microbiologists don't know whether the crystals have any function for the organism. Perhaps they are simply waste, forming by accident in vacuoles that serve as storage depots for sulphate, said Krejci.
Whatever purpose the crystals serve, Krejci's research has found that it is possible to enhance the uptake of strontium by tailoring the amount of barium in the algae's environment. This, she says, means that it might prove possible to seed nuclear waste, or a spill of radioactive material, with barium to encourage the algae to grab the strontium — easy to do, she says, because "it would only be a small amount" of barium.
It might also be possible to improve the process by tinkering with sulphate levels in the environment, thereby changing the amount of sulphate in the vacuoles. "Once we learn about how the cells respond to conditions, we can think of more elegant ways to manipulate them," says Krejci.
Once isolated by the algae, the strontium could be sequestered in high-level nuclear waste repositories, while the rest of the waste could go to a less expensive lower-level repository, saving space and money. Currently, Krejci says, there are hundreds of millions of litres of stored nuclear waste in the United States alone, much of which contains strontium. "So we know it's a big problem," she says.
Radiation exposureKrejci and her colleagues have not yet tested how well the algae survive in the presence of radioactivity. But even if the organisms respond poorly, she says, they would probably live long enough to start removing strontium, because the process begins quickly. "The cells precipitate crystals within 30 minutes to an hour," she says. And if more are needed, "they are easy to culture".
Gija Geme, a chemist at the University of Central Missouri in Warrensburg, organized the symposium at which Krejci presented her work. Geme, who grew up in an area of Russia not far from Chernobyl and so has a personal interest in nuclear clean-up, was one of the few people at the meeting who knew the significance of Krejci's presentation in advance: the talk's title, focusing on biomineralization, did not mention Japan, radioactivity or nuclear accidents.
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"It's a hot topic right now," says Geme. "But when I put this symposium together, there was no tragedy [in Japan]. I was looking for any studies about sequestration of metals that would be of significance to society."
Geme urges Krejci's team not to spend too much time trying to discover precisely why the algae does what it does before they start testing the process with nuclear wastes.
"Sometimes, just getting it out is very, very important," she says. "I would like to see field studies using actual waste as soon as possible."?
References Krejci, M. R., Finney, L., Vogt, S. & Joester, D. ChemSusChem doi:10.1002/cssc.201000448 (2011). CommentsIf you find something abusive or inappropriate or which does not otherwise comply with our Terms or Community Guidelines, please select the relevant 'Report this comment' link. Comments on this thread are vetted after posting. #19444The algae might be able to consolidate the Strontium, but it can't alter the radioactivity of the isotope. While interesting, this article will unfortunately serve as fodder for the new nuclear deniers who will slant the information to their purposes by suggesting the algae will "clean it up." I suppose there is some utility in having all your nuclear waste in one pile, but ultimately, there is still a pile of nuclear waste to deal with. www.killingmother.blogspot.com.
Report this comment2011-03-30 12:48:53 PMPosted by: Kathleen Wood #19462We need conversion of radioactive waste into non-radioactive waste. And not from pile to heap! This algae is just a candidate among many know micro-organism for consolidation of wastage via their metabolic pathways. It seems some investigators are distorting the scientific facts for their vested interest and trumpeting through high impact prestigious journals such as Nature.
Report this comment2011-03-30 03:18:52 PMPosted by: Alok Mishra #19484Unlike the Chernobyl incident in 1986, the radioisotopes released in Fukushima that are now reaching California and Western Europe comprise mostly the highly volatile Xenon (^133^Xe), Iodine (^131^I), and Cesium (^137^Cs). It appears that radio-strontium (^90^Sr), the isotope that was responsible for a significant amount of the radioactive fallout after Chernobyl, was not released in significant amounts into the atmosphere. The crews that are, under great personal risk, working to secure the severely damaged reactors deserve our admiration. While most of the world is watching their progress with bated breath, a political debate has flared up about the risks and benefits of nuclear power. Irrespective of any political opinion, it is very important to realize that even if we were to turn off all nuclear reactors tomorrow, we would still have to deal with a very large amount of spent nuclear fuels and radioactive wastes that already exist. In fact, the Department of Energy (DoE) of the United States of America alone has >300 million liters of radioactive tank sludge that await separation and safe storage.
The selective removal of particularly problematic isotopes such as ^90^Sr and ^137^Cs from such wastes, their concentration into small volumes, and safe storage is thus a matter of considerable importance, not only in times of crisis, but for decades to come. This is a non-trivial problem as we cannot simply turn a radioactive element into a non-radioactive one, but we essentially need to store it at a safe location for as long as it takes for the radioactivity to decay. At half-lifes of ~30 years for ^90^Sr and ^137^Cs, this will take a few hundred years. Right now, the volume of radioactive material is large, which makes storage expensive and creates a variety of problems (such as leakage from tanks). Creating a concentrate of the really dangerous stuff would make it much less expensive to store safely. Consequently, around the world groups of researchers are dealing with the fundamental science and engineering solutions to this problem.
The motivation for the research described in the paper covered by this news feature is in part personal a?? I (Derk Joester) vividly remember the Chernoby fallout coming down over southern Germany when I was a teenager. However, when my team started looking into the mechanism of sequestration of Sr and Ba in the desmid green algae several years ago, no nuclear disaster was anticipated. Instead, the idea was to seek mechanistic insight and inspiration from this rare ability, with potential applications in both direct bioremediation or in the development of more selective ion-exchange processes for nuclear waste treatment. We describe our first important steps in this direction in the ChemSusChem paper, which, coincidentially was accepted before the earthquake in Japan. It is a great relief that so far no ^90^Sr has been released in Fukushima, and we very much hope that there wona??t be. Research into sustainable treatment of nuclear waste and environmental remediation will, however, remain important for many years to come.
Actinomycetes known to eat up almost anything including TNT too should be looked for nuclear clean up process.
Anurag chaurasia,ICAR,India
anurag@nbaim.org.in,anurag_vns1@yahoo.co.in,+919452196686(M)
Image caption: "Strontium-eating bacteria...". It`s not bacteria – it`s eukaryot
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