U.S. Water News Online
EAGLE HARBOR, Wash. -- Ferry passengers traveling to and from Bainbridge Island no longer see the remnants of the last creosote plant on the south shore of Eagle Harbor.
The plant, defunct for about a decade, was dismantled this spring as part of an extensive cleanup mounted by the Environmental Protection Agency with input from half a dozen other state and federal agencies.
But the EPA faces a legacy that can't be dismantled as easily. On shore, oily wastes foul the groundwater and the soil below it, in some spots going deeper than 70 feet. And in Eagle Harbor, a cap of clean fill entombs wide swaths of the harbor floor where sediments are most heavily contaminated with toxic polycyclic aromatic hydrocarbons (PAHs).
Now scientists from the University of Washington (UW) have some good news from the muddy bay bottom here. Bacteria on the floor of the bay like eating the polluting residue of creosote so much that samplings show 10 times as many microorganisms at the bottom of Eagle Harbor as at nearby clean bays.
"Maybe there's some hope for a natural cleanup," said Jody Deming, a UW oceanographer who is a principal investigator on a $4 million study of Eagle Harbor financed by the Office of Naval Research. "It's surprising because these polluting molecules are so hard to break down."
Deming said researchers are trying to determine which microorganisms recycle PAHs into harmless minerals and what actions might help or hinder their activity. Organisms that can help clean up pollutants and industrial wastes on land are well known, but the work at Eagle Harbor is one of the first in the nation to investigate the role of such organisms in marine sediments.
"One beauty of bioremediation is that it taps into the lower end of the food web," said Deming. "The expectation is that you can keep PAHs from making their way higher in the food web if they are recycled into harmless minerals at the microbial level."
Very little is known about the microorganisms surviving in such heavily polluted sites, said Deming, who added that researchers have encountered surprises at Eagle Harbor. For instance, she said, scientists thought that most of the microorganisms in such heavily polluted sediments would be specialists adapted to living off contaminants. Instead, sediment samples show a wide diversity of organisms.
Given the level of contamination, researchers also speculated there might be fewer organisms here than in clean sediments. But results thus far show the sediments are teeming with life. There are about 10 times as many bacteria per ounce of sediment as there are humans on Earth. The numbers found in some of the contaminated sediments have even surpassed those found in samples taken from some clean sites.
Scientists have also discovered that microorganisms needing oxygen to fuel their activities (aerobic) and those operating in oxygen-starved environments (anaerobic) are both recycling PAHs in the marine sediments at Eagle Harbor.
It's important to learn more about the conditions under which these organisms function in marine sediments, Deming says. For example, it's encouraging to know that an oxygen-starved environment does not halt the natural cleaning activities because humans create such environments when they put layers of clean fill over contaminated sediments.
Currently, spreading clean fill appears to be a reasonable way of holding contaminated marine sediments in place, and the Puget Sound region is at the forefront in using this approach, according to Deming. At Eagle Harbor, a cap covers sediments contaminated with PAHs from the creosote plants as well as heavy metals, such as mercury, left behind from ship-building activities.
It's too early to say how thoroughly bacteria are in converting the creosote pollution to harmless carbon dioxide. These bacteria are not aiding in removing the heavy metal contamination here, said Deming.
However, Deming said the discoveries could mean agencies should take a longer view of toxic cleanups, giving nature more time to work. And government might want to modify its strategy by capping polluted bottoms with a thinner layer of clean sand than is now the case. The porosity and permeability of the cap is important, she said, because there needs to be a certain amount of water between grains for the microorganisms to function optimally.
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