Purdue scientists seek
Imagine a bug that could gobble up one of
the most widespread, persistent toxins in the environment.
Until recently, such a scenario has been wishful
thinking for environmental officials trying to clean up
polychlorinated biphenyls, which first contaminated industrial
sites throughout the country and now are so widespread
that they're found even in polar ice.
But within a year, researchers at Purdue University
and the University of British Columbia expect to be closer
to finding an enzyme that might be able to digest the
most stubborn of PCB toxins, said Jeffrey T. Bolin, a
Purdue biological sciences professor and a member of Purdue's
Markey Center for Structural Biology and Cancer Center.
The result could lead to more effective and
perhaps cheaper cleanups of the chemical, which is thought
to cause a variety of health problems.
Those answers, according to research that
will appear in the December issue of Nature Structural
Biology, will come from understanding how microorganisms
Although microorganisms, or "bugs,"
have been used to consume a host of other toxins, scientists
haven't found one capable of destroying all PCBs.
Bolin's team has figured out why.
Their research has shown that PCB molecules
either hopelessly bind to one of the enzymes in the bugs
or cause the enzyme to self-destruct. And that discovery
means it now may be possible to re-engineer a microorganism
that finally works, he said.
Ironically, it was PCBs' indestructible nature
and insulating qualities that made the chemicals popular
for use as coolants and lubricants in transformers and
But the chemicals' manufacture was banned
in 1977 because of health concerns. PCBs can cause skin
conditions and liver and respiratory problems and are
believed to cause cancer and thyroid and reproductive
problems. They also can cause developmental problems in
Still, PCBs have lingered at old industrial
sites, in sediment at the bottom of lakes and rivers and
in the food chain, where they settle in animals' and humans'
fatty tissue. They also evaporate and fall back to earth,
recontaminating soil and water.
The highest PCB concentrations are found
at industrial sites -- 21 of which in Indiana are being
cleaned up by state and local environmental agencies specifically
because of PCBs -- and in waterway sediment.
Cleanup can be expensive and time-consuming.
At one of the worst sites of PCB contamination in Indiana,
the former Westinghouse plant in Bloomington, more than
$200 million has been spent in the past five years to
incinerate the toxin on-site or ship tainted soil to a
hazardous waste landfill.
Neither method is perfect: Encasing PCBs in
a landfill does not destroy the chemical; burning them
creates other toxins. For now, though, they are the most
commonly used methods to remove PCBs.
A PCB-munching bug might prove to be less
costly and more effective in cleanups, said Tom Alcamo,
the EPA project manager for the Westinghouse site.
"It would be fantastic," he said.
"It could be an effective way to deal with PCBs."
But there still are significant challenges
to finding a bug that works.
Bioremediation might not work in every situation,
nor would it be practical for very high levels of contamination,
such as on barrels of the chemical, said researcher Lindsay
Eltis, associate professor of microbiology and biochemistry
at the University of British Columbia. It mostly would
be used on soil contaminated with an intermediate level
of PCBs, he said.
And because PCBs consist of multiple compounds
that are present in many different combinations, other
problems could crop up in other steps involved in the
destruction of the toxin, Bolin said.
Researchers will start with a version of enzyme
that works best, then try to force that organism to undergo
random mutations until they find one that works on PCBs,
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