BOSTON -- One might say that General Electric Co. is practicingbioremediation without a license.
Physical chemist Daniel Abramowicz, manager of GE'sEnvironmental Development Program, told a plenary session ofa "Science Innovation" conference here on Tuesday that thecompany's bioremediation of polychlorinated biphenyl (PCB)contamination was proceeding despite no identification of theanaerobic microorganisms breaking down the PCBs.
The Environmental protection agency has not testedthe approach.
Under EPA regulations, GE bears a heavy share ofthe responsibility for cleaning up rivers and soil contaminatedby PCBs. Until PCBs were banned in the late 1970s, thecompany used them as fire-resistant dielectric fluids intransformers and to impregnate capacitors.
Before addressing a plenary session of the conference,organized here by the American Association for theAdvancement of Science, Abramowicz said at a press briefingthat the same deficit of chemical reactivity that makes PCBsuseful in fire resistance renders them resistant to degradationby natural microorganisms.
The biphenyls consist of two aromatic carbon rings graspinganywhere from one to 10 chlorine atoms (in theory; five inpractice). The more chlorines, the less reactivity and thegreater industry's acceptance of PCBs.
"For a long time," Abramowicz explained, "people usedunchlorinated mineral oils in transformers. Transformerscaught fire; buildings would burn down. PCBs, being lessreactive, reduced risk of fire."
PCBs also found special applications in 209 separateformulations as lubricants, heat-transfer and hydraulic fluids,plasticizers, flame retardants, coatings and adhesives.
During 50 years of use, industry produced some 1.4 billionpounds of PCBs, of which several hundred million werereleased into the environment, largely in river sediments; 250million are still found in utility transformers and condensers.
"These compounds, commonly believed to be indestructible,have repeatedly been shown to biodegrade in naturalenvironments," Abramowicz said. This breakdown essentiallyconsists of microorganisms stripping chlorine atoms off of thecarbon rings one at a time.
Two classes of bacteria share this natural bioremediation chore.Deep in sediment, oxygen-shunning anaerobic microbesreductively remove the first two chlorine ions of apentachloride PCB. Then aerobic ones take over, oxidatively, toknock off another one or two chlorine ions. In nature, thisdehalogenation process takes a very long time, measured inmonths and years. And it never quite gets rid of every lastchlorine ion.
"We at GE discovered this reductive process in PCBs; others didso in other chlorinated products," said Abramowicz. His theme,he declared, is that "anaerobic dechlorination of thesechlorinated compounds really represents the future ofbioremediation. We now have the first evidence that thissequential anaerobic-aerobic process is going on naturally inthe environment," he said.
GE's first operational test of the theme is gearing up in Wood'sPond, a 10-acre impoundment basin along the Housatonic Riverin western Massachusetts.
The pond is impounding decades-worth of PCB contaminantsfrom a nearby GE transformer plant. (Since 1976 thosetransformers have used silicon-based fluids, which are slightlyless fire-resistant and dielectric than the now-prohibited PCBs.)
Field tests on the Housatonic began a year ago, and thedegradation process is proceeding slowly. It's being stepped upby a proprietary GE selective chemical cocktail that includesfood additives to nourish the bugs. Patent applications wererecently filed for the cocktail.
"We are considering adding this chemical to a time-releasecompound deposited on the sediment surface where the PCBsare. First, it would stimulate organism growth, then --hopefully -- cause anaerobic activity," said Abramowicz.
What worries GE's bioremediators is the EPA. "The agency hasnot yet tested our anaerobic-aerobic approach," Abramowiczobserved.
The traditional way of cleaning up a Superfund body of wateris by diverting the water, digging up the sediment and taking itaway. But at Woods Pond, "dredging has been eliminated fromconsideration because the site sits in a valuable ecosystem."
The chemical-assisted natural anaerobic/aerobic process will, ifit works, convert the tetra- and penta-chlorinated biphenyls tolighter, but still chlorinated, products, anathema by EPA'scurrent regulations.
"But there's a rather strong movement under way to re-evaluate, re-regulate PCBs," the GE scientist observed hopefully."Everyone recognizes that you can no longer treat 209compounds as if they are identical. And we do get two or threeorders of magnitude decrease in the toxicological profile peopleare measuring."
Unless this regulatory relief comes within five years -- theestimated time it will take the microbes to do their thing -- hefears "we'll lose the battle and have to dredge the material outanyway."
Abramowicz said the slow rate at which natural degradationworks "may be at the heart of why anaerobes are so hard toisolate. Though probably fast enough on an environmental timescale, it's a real hindrance in the lab." As for biotechnology, hesaid, "We have not tried something like a dye or antibody orfluorescent probe. We don't know what we would attach themto. We don't know what DNA is involved in this process."
He pointed out that the whole sediment is complexmicrobiologically as well as chemically. "There are probably 10to the eighth power different kinds of organisms in that bottleof sediment on your desk. Which is the one you're after? Wedon't know if our anaerobe is present in one in ten million, onein a million, or one in 100,000."
Dismissing more microbiology, he concluded, "Merely lookingunder a microscope or plating colonies looking for differentmorphologies, mixing and matching -- we've done all thesethings, and none of it has been successful, to be honest. Sowe're abandoning that approach because we've been at it for ayear and a half, and I'm ready to try something else." He andhis team are planning to move from contaminated sediments tosoils and ask the question: Are soils recalcitrant todechlorination, or do they just lack water?
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.