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 Maryland’s 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 UMBI’s 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 19^th 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 don’t 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 Baltimore’s 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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