Bacteria could help clean groundwater contaminated by
uranium ore processing
Date:June 15, 2015
A strain of bacteria that "breathes" uranium may hold the key to cleaning up polluted groundwater at
sites where uranium ore was processed to make nuclear weapons.
A team of Rutgers University scientists and collaborators discovered the bacteria in soil at an old
uranium ore mill in Rifle, Colorado, almost 200 miles west of Denver. The site is one of nine such
mills in Colorado used during the heyday of nuclear weapons production.
The research is part of a U.S. Department of Energy program to see if microorganisms can lock up
uranium that leached into the soil years ago and now makes well water in the area unsafe to drink.
The team's discovery, published in the April 13, 2015 issue of PLOS ONE, is the first known
instance where scientists have found a bacterium from a common class known as
betaproteobacteria that breathes uranium. This bacterium can breathe either oxygen or uranium to
drive the chemical reactions that provide life-giving energy.
"After the newly discovered bacteria interact with uranium compounds in water, the uranium
becomes immobile," said Lee Kerkhof, a professor of marine and coastal sciences in the School of
Environmental and Biological Sciences. "It is no longer dissolved in the groundwater and therefore
can't contaminate drinking water brought to the surface."
Kerkhof leads the Rutgers team that works with U.S. Department of Energy researchers.
Breathing uranium is rather rare in the microbial world. Most examples of bacteria which can respire
uranium cannot breathe oxygen but often breathe compounds based on metals -- typically forms of
solid iron. Scientists had previously witnessed decreasing concentrations of uranium in groundwater
when iron-breathing bacteria were active, but they have yet to show that those iron-breathing
bacteria were directly respiring the uranium.
While the chemical reaction that the bacteria perform on uranium is a common process known as
"reduction," or the act of accepting electrons, Kerkhof said it's still a mystery how the reduced
uranium produced by this microorganism ultimately behaves in the subsurface environment.
"It appears that they form uranium nanoparticles," he said, but the mineralogy is still not well known
and will be the subject of ongoing research.
The Rutgers team was able to isolate the uranium-breathing bacterium in the lab by recognizing that
uranium in samples from the Rifle site could be toxic to microorganisms as well as humans. The
researchers looked for signs of bacterial activity when they gradually added small amounts of
dissolved uranium at the right concentration back to the samples where uranium had become
immobilized. Once they found the optimal uranium concentrations, they were able to isolate the
Exactly how the strain evolved, Kerkhof said, "we are not sure." But, he explained, bacteria have the
ability to pass genes to each other. So just like bacteria pick up resistance to things like antibiotics
and heavy metal toxicity, this bacterium "picked up a genetic element that's now allowing it to
detoxify uranium, to actually grow on uranium." His research team has completed sequencing its
genome to support future research into the genetic elements that allow the bacterium to grow on
What Kerkhof is optimistic about is the potential for these bacteria to mitigate the specific
groundwater pollution problem in Rifle. Scientists at first expected the groundwater to flush into the
Colorado River and carry the dissolved uranium with it, where it would get diluted to safer levels. But
that hasn't happened. Other potential methods of remediation, such as digging up the contaminated
soil or treating it with harsh chemicals, are thought to be too expensive or hazardous.
"Biology is a way to solve this contamination problem, especially in situations like this where the
radionuclides are highly diluted but still present at levels deemed hazardous," said Kerkhof. If the
approach is successful, it could be considered for other sites where uranium was processed for
nuclear arsenals or power plant fuel. While the problem isn't widespread, he said there's potentially
a lot of water to be concerned about. And the problem could spread beyond traditional places such
as ore processing sites.
"There is depleted uranium in a lot of armor-piercing munitions," he said, "so places like the Middle
East that are experiencing war could be exposed to high levels of uranium in the groundwater."
The above post is reprinted from materials provided by Rutgers University. The original item was
written by Carl Blesch. Note: Materials may be edited for content and length.
Nicole M. Koribanics, Steven J. Tuorto, Nora Lopez-Chiaffarelli, Lora R. McGuinness, Max M.
Häggblom, Kenneth H. Williams, Philip E. Long, Lee J. Kerkhof. Spatial Distribution of an Uranium-
Respiring Betaproteobacterium at the Rifle, CO Field Research Site. PLOS ONE, 2015; 10 (4):
e0123378 DOI: 10.1371/journal.pone.0123378
Although the following commentaries are from SCIENCE magazine published by the American
Association for the Advancement of Science with regard to spent nuclear waste and do not address
the deconstruction of the nuclear chain reaction, this is an important consideration. The recent news
that China is going to reuse their nuclear rods repeatedly, moving them to new reactors for many
years to come is a remarkable move forward for humanity and the environment.
IN THEIR POLICY FORUM “NUCLEAR WASTE: Knowledge waste?” (13 August, p 762), E.A. Rosa
et al. overlook a possible solution to nuclear waste: alternative fuel cycles, particularly the Thorium
Fluoride, Molten-Salt Reactor (Thorium MSR).
The use of Thorium as a fertile reactor input has the potential to greatly reduce high-level reactor
wastes (1). (Thorium-232 is bred by the reactor’s internal neutron flux to Uranium-233, which is then
efficiently fissioned by another neutron. A small proton accelerator can also do the breeding. U233
is unnatural, because of a short half-life, but fissions more easily than the U235 used in typical
reactors.) Adopting the MSR would further reduce waste by orders of magnitude (1,2) - there is not
solid fuel or refueling waste, and all fissiles entering the salts are consumed. …
TO READ THE REST OF THIS COMMENT: Science - AAAS
RESPONSE TO ALEXANDER CANNARA
CANNARA RECOMMENDS THE ADOPTION OF the Thorium Molten-Salt Reactor. We urge
caution. The nuclear industry has never fully realized safety and other promises, Grimes and Nuttall
(1) explain that the fissile Uranium-233 produced by the slow neutron capture of Thorium-232 “is
difficult to extract and handle, because it is produced together with other highly radioactive isotopes,
and the performance of thorium fuels is not well understood. The proliferation resistance credentials
of the thorium fuel cycle deserve greater scrutiny but appear promising.” These are precisely the
kinds of uncertainties and risks that should be part of a wider public discourse about energy
Eugene A. Rose, Seth P. Tuler, Baruch Fischhoff, Thomas Webler, Sharon M. Friedman, Richard E.
Sclove, Kristin Shrader-Frechette, Mary R. English, Roger E. Kasperson, Robert L. Goble, Thomas
M. Leschine, William Freudenburg, Caron Chess, Charles Perrow, Kai Erickson, James F. Short
TO READ THE REST OF THIS RESPONSE: SCIENCE AAAS
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