Confocal microscopy of C. moniliferum, an algae that takes up strontium and could be used in cleaning up radioactive contamination. Image: Minna Krejci/Joester Laboratory of Northwestern University. |
In 1963,
Dr. Louise Reiss completed a study of thousands of baby teeth collected from
children born in the 1950s and ’60s that showed the world that fallout from
weapons testing was accumulating in humans.
She had
tested the teeth for strontium-90, a radioactive isotope so similar to calcium
that our bones can use it as a building block instead. But 50 years after her
discovery, we still have no good way to clean up strontium-90.
Using the
Advanced Photon Source at the U.S. Department of Energy’s Argonne National
Laboratory, a group of Northwestern University and Argonne scientists have
figured out the secrets of algae that can preferentially take up strontium over
calcium—a task so difficult that it’s not easily done even in a laboratory. The
algae could form the basis of new technologies to clean up contaminated land or
water.
Strontium-90
is one of the deadly isotopes produced by nuclear weapons and reactors. If it’s
ingested in contaminated food or water, the human skeleton may take it up
instead of calcium—where it can sit for decades, poised to trigger bone cancer
or leukemia.
“The
difficulty with cleaning up strontium-90 from the environment is that it’s so
similar to calcium and barium that scientists even have trouble doing it in the
laboratory, with sophisticated equipment,” explains lead author Minna
Krejci, who has a joint appointment at Northwestern and Argonne.
“The
ability to differentiate the two is rare even in nature. This green alga is one
of the few organisms with that ability.”
Biologists
had discovered that the green algae Closterium
moniliferum forms crystals using strontium isotopes, but no one
knew how.
Krejci and
the team used a type of imaging called X-ray fluorescence microscopy to track
the movement of metals through the components of a cell. By comparing the data
with physical photos of the cells taken with an electron microscope, they found
that high concentrations of sulfur in the vacuoles—the cell’s storage
compartments—meant more strontium pulled up into crystals. This type of mechanism
is called a sulfate trap.
If the
mechanism could be harnessed, the algae could be released in contaminated areas
to sequester the strontium, the researchers suggest. Previously, even the best
known methods for removing strontium-90 pulled in too much calcium along with
the strontium to be efficient. Methods for removing strontium might also
someday be useful in recycling nuclear fuel.
The
discovery is also useful in the context of learning how organisms use metal
atoms in everyday functions.
“About a third of the proteins in your body interact with metals; for
example, iron in blood cells and calcium in bone,” explains Argonne physicist Lydia Finney. “It’s a rapidly
developing area of science, and the techniques we’ve developed at the APS are
really helping it to grow.”
