Microbes hasten breakup of PCBs

Inner Harbor findings unique

reasons still unclear to researchers

July 17, 1999|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

There's something lurking in Baltimore Harbor mud that seems to be chewing up the toxic PCBs left there by decades of industrial activity. If scientists can figure out what's going on, they might find ways to unleash the microbes on tainted waterways across the country.

Kevin Sowers, a microbiologist at the University of Maryland's Center of Marine Biotechnology (COMB) has been pulling muck from the harbor slips around his laboratory at the Columbus Center, cultivating the microbes that live in it, and watching them slice up the PCB molecules.

"We don't know a lot of what's going on down there," said Sowers. "That's part of what we're trying to find out."

Sowers and Harold May, of the Medical University of South Carolina, report on their work in the current issue of the journal Applied and Environmental Microbiology.

PCBs, or polychlorinated biphenyls, are extremely stable, oily, colorless liquids. They were used for most of this century as coolants and insulators in electrical transformers and capacitors. They were prized because they did not evaporate, flame up or explode when they got hot.

But that chemical stability has proven to be an environmental curse.

The U.S. government banned the manufacture or use of PCBs in 1977, after they were linked to cancer, reproductive disorders and liver abnormalities. Strict controls were then placed on their disposal.

Their chemical stability made them a persistent hazard wherever they had been spilled or dumped. They stick to bottom muds in rivers and harbors, spread through the environment and up the food chain, concentrating dangerously in fish and other predators.

A 1975 study found PCBs in Baltimore harbor muds at levels ranging from 1 to 10 parts per million. One of the worst spots seemed to be in the Inner Harbor, in the slips beside the old United Railway and Electric Co. The Pratt Street building has since been recycled as the Power Plant, housing restaurants and a bookstore.

Curiously, a 1997 study by the University of Maryland's Chesapeake Biological Laboratory found that PCB levels in the harbor had fallen sharply since 1975. The worst spot was still the muck beside the Power Plant, but levels had dropped to no more than 2.1 parts per billion, Sowers said.

"You have to remember there's been a lot of dredging," he cautioned. It's not clear whether the vanished PCBs were broken down by microorganisms, or simply carted away. "Before we can answer that, we have to be able to monitor the organisms and see if there's any activity or not."

A look at saltwater

That's what Sowers and May have been up to, in a three-year, $450,000 study supported by the Office of Naval Research.

Chatting over a beer one day, they realized that all the research on the natural breakdown of PCBs had been done in fresh water. So, they pulled some muck from the brackish slip between the Power Plant and the Columbus Center, and ran some tests.

To their surprise, the tests showed that something in the mud -- presumably microbes -- was breaking up the PCB molecules more thoroughly than at any freshwater sites.

Something similar had been reported elsewhere, but it had never been reproduced, so its validity was suspect. Sowers got more and more harbor mud, and got it to work again and again. May has reported preliminary signs of the same phenomenon in the harbor in Charleston, S.C.

PCB molecules are like double necklaces of carbon atoms with baubles of chlorine hanging from them. Breaking them down into harmless elements requires first snipping off each of the chlorines, and then cutting up the carbon rings, or phenyls.

Where there's oxygen available, and not too much chlorine, naturally occurring microbes can do the job. Where oxygen is absent -- deep in bottom muds -- the process is much slower. There, microbes can snip off some of the chlorines, but those attached by particular chemical links called "ortho" bonds are especially stubborn.

"The process would stop there," Sowers said. Except in Baltimore. "When we went into the Baltimore muds, we would see it within 21 days." In just three weeks, the ortho bonds had been cut, clearing the way for further breakdown.

Sowers suspects that clusters of microbes -- perhaps as few as six species -- work together on the PCBs. But no one has yet been able to isolate or identify them, or show how they do it.

It's not even clear yet whether the microbes are actually eating the PCBs to capture energy from them, or breaking them down by accident as they go about unrelated microbial business.

Why does it happen in Baltimore mud, and not in the PCB-laden Hudson River? Sowers said it could be a fortunate mix of microbial species peculiar to the Patapsco River. Or maybe it's just the local mix of PCBs. (Hundreds of variations were made and used, often in blends.) It might also be just the right mix of temperature, salinity or some other environmental factors.

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