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Topic Name: Cost-effective methods for on-site PCB remediation
Category: Environmental Fluid Mechanics
Research persons: Kristi Ritalahti and Frank Löeffler of the Georgia Institute of Technology.
Location: Rensselaer Polytechnic Institute (RPI), 110 8th St., Troy, NY 12180. (518) 276-6000, United States
Details
Researchers at Rensselaer Polytechnic Institute have discovered a tiny
bacterium that could one day transform the way we remove polychlorinated
biphenyls (PCBs) from our environment. The organism could be the key to
developing methods that help detoxify commercial PCB compounds on site — without
the need for dredging.
The results will appear in the April 15 issue of Applied and
Environmental Microbiology.
Commercial PCBs, which were banned from production in the United States in
1977, were once commonly used by industry. The compounds are mixtures of 70-90
different molecular forms that vary in the number and positions of chlorine
atoms, making them difficult to degrade. To date, the most commonly used method
to remove PCBs from the environment is to dredge and then deposit the sediments
in a landfill.
In order to detoxify PCBs the strong bonds between the chlorine atoms and the
biphenyl compounds that make up the PCB atomic structure need to be broken, a
process known as dechlorination. More than two decades ago, scientists
discovered that PCBs were slowly being dechlorinated by naturally occurring
microbes, but despite years of research, the exact microbes responsible have
remained elusive — until now.
“For the first time we have been able to cultivate in defined media naturally
occurring bacteria that can extensively dechlorinate PCBs right at the site of
the contamination,” said Donna Bedard, professor of biology at Rensselaer and
lead author of the paper. “This is a major step toward the development of
cost-effective methods for on-site PCB remediation.”
Bedard used sediments from the Housatonic River in Massachusetts — an area
known to be contaminated with PCBs — to develop sediment-free cultures and to
identify the bacteria that were breaking down the PCBs. Using molecular
techniques, the research team determined that the microbes that are
dechlorinating the PCBs belong to a group of bacteria known as
Dehalococcoides (Dhc).
Dhc are “strict anaerobic” bacteria, which means they cannot survive
in the presence of oxygen. They are frequently involved in natural remediation
of chlorinated solvents such as trichloroethylene (TCE), but this is the first
time it has been demonstrated that Dhc can dechlorinate complex
commercial PCB mixtures.
After identifying the Dhc bacteria, Bedard and her team proved that
the anaerobic bacteria thrive on the PCBs, much as humans thrive on oxygen. The
microbes replace the chlorines on the PCBs with hydrogen, which fuels their
growth and begins the PCB degradation process.
The discovery of the Dhc bacteria’s unique abilities could one day
alter the way we treat PCB contaminated water bodies, according to Bedard.
“Now that we have identified the PCB-dechlorinating bacteria and learned how
to cultivate them in the laboratory, we can begin to understand the processes
that they use to dechlorinate PCBs and tap their unique abilities to create new
technologies that efficiently and safely remove commercial PCBs from our
environment,” she said.
The research was funded through a grant from the National Science Foundation.
Bedard was assisted in her research by Kristi Ritalahti and Frank Löeffler of
the Georgia Institute of Technology.
About Rensselaer
Rensselaer Polytechnic Institute, founded in 1824, is the nation’s oldest
technological university. The university offers bachelor’s, master’s, and
doctoral degrees in engineering, the sciences, information technology,
architecture, management, and the humanities and social sciences. Institute
programs serve undergraduates, graduate students, and working professionals
around the world. Rensselaer faculty are known for pre-eminence in research
conducted in a wide range of fields, with particular emphasis in biotechnology,
nanotechnology, information technology, and the media arts and technology. The
Institute is well known for its success in the transfer of technology from the
laboratory to the marketplace so that new discoveries and inventions benefit
human life, protect the environment, and strengthen economic development.
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