Common 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.
Information access: http://www.nature.com/news/2011/110330/full/news.2011.195.html