HARBOR MUD BREAKS PCB BONDS
INNER HARBOR, BALTIMORE, MD -- Dealing with tons of
PCBs in the environment, released for many decades, has long
challenged environmentalists and regulatory agencies. Now scientists
with the University of Marylands Biotechnology Institute
(UMBI), are beginning to find some answers, at the bottom of
Baltimore Harbor.
Something in the mud breaks down the toughest chlorine
bonds of PCB, or polychlorinated biphenyl, molecules.
In experiments with the mud, repeated many times at
UMBIs Center of MarineBiotechnology (COMB), and the Medical
University of South Carolina, the scientists may have revealed the
first known complete dechlorination of PCBs in nature, an essential
step to breaking down the banned, toxic materials.
Kevin Sowers, a research associate professor at COMB,
reported in the journal Applied and Environmental Microbiology that
there is probably no single PCB-eating organism in the mud. Instead,
clusters of 12 or more PCB-degrading microbes are likely working
together, each breaking a different kind of chlorine bond on PCB.
Sowers and colleagues tested the mud on Aroclor 1260,
one of the more persistent commercial PCBs in the environment.
"We want to know how they are degraded because it would be nice
to know there are natural processes at work," he says. " We
might find a way of promoting and improving them."
Beginning in the 19th
century, PCBs were made from petroleum as excellent insulators for
electric power equipment and other electronics. But in 1977, the
federal government banned them because of possible environment and
human health hazards.
In water, particles of PCBs dont dissolve well.
They attach to sediment and getcovered over. "Unless there is
some turnover, a lot of PCBs stay hidden," says Sowers.
PCBs build up in fish and marine mammals and can reach
levels thousands of times higher than in the water itself, according
to the U.S. Environmental Protection Agency.
"There are organisms out there doing this, but we
did not start out trying to isolate them," says Sowers. Instead,
the scientists are using molecular probes to narrow down thousands of
candidate microbes in the mud. The probes, a standard biotechnology
tool, will then be available to locate PCB-degrading microbes in
other locations, he says.
"The reason we chose the harbor is because of the
old electric power plant there. The electric railroads used to serve
the shipping industry on the docks," he explains. Previous
studies had shown that near Baltimores historic Power Plant,
bottom sediments contain up to 2 parts PCBs per million parts mud. He
says they occur "at significantly lower levels" in nearby
Chesapeake Bay.
Despite the experiment results, Sowers cautions there
may not be simple solutions to cleaning up PCBs in the environment
because they are a "mixed waste." Aroclor is a mixture of
different forms of PCB. Each form may require a different set of
bacteria for a complete dechlorination, he notes.
Previously, scientists have reported only partial
dechlorination in nature, such as the breaking of chlorine bonds in
what chemists call the meta and para positions on PCB
molecule. However, the COMB report was the first significant breaking
of chlorine bonds in an ortho position, a distinction
indicating the potential for complete dechlorination for the first time.
The few previous scientific reports from other
laboratories of possible complete dechlorination of a PCB--including
breaking ortho bonds--could not be repeated, says Sowers. "But
in our study, we went back, got more mud, started a brand new culture
and again broke these chlorine bonds." The results took only 21
days, he says.
Similar dechlorination of PCBs may be happening at the
bottom of the harbor in Charleston, South Carolina, according to
preliminary results by Sowers and co-researcher Harold D. May,
Medical University of South Carolina. The research is funded by the
Office of Naval Research.
PCBs are either oily liquids or solids that are
odorless, tasteless and nearly colorless. Before 1977, they entered
the air, water and soil during their manufacture and use. They can
still be released today from hazardous waste sites, improper disposal
of old electrical equipment or from electrical transformers
containing PCBs.
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