[ RadSafe ] " Study Uncovers Bacteria's Worst Enemy "

[Jaro]

" the bacteria's worst enemy in a nuclear waste site may not be the
radioactive elements, but rather, the other toxic metals that might also be
found at the site.....common toxic metals, such as cadmium, nickel, and
chromium, are more likely to cause problems for the bacteria. "


http://www.spacedaily.com/news/nuclear-civil-05l.html
Study Uncovers Bacteria's Worst Enemy
Los Alamos NM (SPX) Apr 18, 2005

University of California scientists working at Los Alamos National
Laboratory have found that the successful use of bacteria to remediate
environmental contamination from nuclear waste and processing activities may
depend more upon how resistant the bacteria are to chemicals than to how
tolerant they are to radioactivity.
The results of a recent Laboratory study may help make bacterial
bioremediation a more widespread method for cleaning up sites contaminated
with actinides and other radionuclides.

In research published in the journal Environmental Microbiology, Laboratory
chemist Mary Neu and her colleagues describe their study of different
naturally occurring bacteria used to treat actinide contamination.

Actinides are the elements above atomic number 89 and are usually
radioactive.

The study's results indicate that actinide toxicity is primarily chemical,
rather than radiological, and so a bacteria's resistance to radiation does
not necessarily ensure a tolerance for radionuclides.
In fact, the bacteria's worst enemy in a nuclear waste site may not be the
radioactive elements, but rather, the other toxic metals that might also be
found at the site.

The study also shows that contrary to the conventional wisdom, when it comes
to these environmental bacteria, plutonium is less toxic than uranium and,
in general, actinides are less toxic than other types of metals.

This suggests that actinide toxicity will not impede bioremediation using
naturally occurring bacteria.

"This study" said Neu, "is exciting because even though we've known for
years that bacterial bioremediation can be a preferred method for cleaning
up actinide contamination, we've never really known whether or not
radioactivity or chemical toxicity will stifle the process.

"Our study found that actinides are chemically toxic to bacteria only at
high levels far, far above concentrations at contaminated sites, and that
common toxic metals, such as cadmium, nickel, and chromium, are more likely
to cause problems for the bacteria."

Generally, bacteria used for bioremediation are selected to target a
specific form and oxidation state of toxic pollutants, such as soluble
hexavalent uranium carbonate for uranium contamination.

However, a single chemical rarely contaminates soils and groundwater and
combinations of actinides, radionuclides, organic chemicals and metal
regularly exist at many nuclear sites.

Based on the results of this study, if bioremediation is to be effective at
these types of sites, the operative microorganisms must be able to grow,
function and do better than other bacteria in the presence of all kinds of
contaminants.

The study examined the effects of toxicity of actinides, metals and
chelators on different bacteria being evaluated for radionuclide
bioremediation, Deinococcus radiodurans and Pseudomonas putida, along with
the toxicity of plutonium on the bacteria Shewanella putrefaciens.
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