Dirty Bay Self-Cleans

While Dr. Deheyn is studying metals in the bay, Dr. Lovley is studying a different form of pollution. "What we've been doing for a number of years is looking at the potential for polycyclic aromatic hydrocarbons to be degraded in the absence of oxygen. There's very little oxygen available to microorganisms in sediments or in the mud at the bottom of harbors. It was thought that once polycyclic aromatic hydrocarbons got into the sediments that microorganisms would not be able to degrade them, because they needed oxygen in order to break them down. But -- and we first saw this in San Diego a number of years ago -- we saw in sediments from the bay that organisms had the potential to oxidize these polycyclic aromatic hydrocarbons to carbon dioxide, which of course is harmless, using sulfate naturally present in the sea water. Now that I'm in Massachusetts, we had better access to Boston Harbor sediments, and we more carefully looked at the degradation of the polycyclic aromatic hydrocarbons that are present in the sediments. We also for the first time looked at some of the larger polycyclic aromatic hydrocarbons that are of most concern -- some of the nastiest ones, the biggest ones -- and found that they were degraded."

Like the metals, the primary cause of polycyclic aromatic hydrocarbons is shipping. "Most of the sites that we looked at were fairly heavily contaminated with some kind of petroleum input and creosote from wooden pier pilings. Those are the major sources, though they come from a variety of sources."

Lovley's research over the past nine years has been funded by grants from the Office of Naval Research. "We've had three different grants," he says. "They're typically in the range of $300,000 to $400,000 for three years."

The next step in his research, he explains, "is sequencing a genome of one of the organisms -- they're known as sulfate reducers -- that can carry out this reaction. We're getting more into the molecular biology of the organisms themselves because now we know that they do it, but it's not understood how they do it. Once we know, maybe we can change conditions a bit to promote their activity. With environmental restoration, which is the stuff that I've worked on, the more we understand about the microorganisms, the better we can manipulate their activities to speed up contaminant degradation."

Lovley's research challenges another prevailing notion: that you have to dredge in order to remove contaminated soils. "I think that's one of the major outcomes of this," he says. "It just shows that there's a greater self-purification capacity in these environments than was previously recognized."

Asked about dredging in relation to contaminants, Deheyn answers, "Once the metals are bonded to the sediment -- and they are deep, like a few feet below the bottom -- they are not available. So a starfish, a crab, whatever, would not be exposed to the sediment that is down there below. So the sediment could be highly toxic, but the water could be clean, and the organism that is living in it could be noncontaminated and would not be exposed to toxicity. If you start digging, mixing everything back into the water, the chemical bond between the contaminant and the sediment will be loosened, and the chemical might be released into the water looking for something else to bond to. It is like starting the whole pollution process again. But you also have to keep in mind that the bay naturally fills up with sediment, and ten years from now, if you don't remove sediment, you will be able to walk across the back of the bay."

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