A seaweed soaks up TNT - and may help clean oceans

Tucked away in Donald Cheney's office desk is a cookie tin containing six paper-thin sheets of dried porphyra - a type of seaweed commonly known as nori.

It's the same stuff used to wrap sushi.

But the real surprise lies down the hall, where Dr. Cheney, a research biologist at Northeastern University in Boston, has transformed the Japanese treat into a "super sponge." So far, it can sop up and neutralize TNT leaking from unexploded shells in coastal bombing ranges. But if Cheney and other researchers are right, the seaweed has the potential to scrub everything from polluted rivers to oceans.

There's just one catch. The first edition of the cleanup seaweed is genetically engineered. Not only do current regulations prohibit its release into the environment, but some activists want to keep this version dry-docked.

"Whether it's genetically engineered salmon or seaweed, we're looking at biological pollution plain and simple," says environmentalist Brent Blackwelder of Friends of the Earth. "We have every indication from our experience with alien or invasive species that we don't want to go down that road because we don't know the consequences."

Not long ago, Cheney was focused on porphyra's dietary benefits. Then in 2002, the United States Office of Naval Research came knocking, wondering if the professor could possibly modify seaweed to detoxify leftover TNT seeping into the ocean at its coastal-training sites. The Navy was eager to clean up the residues from unexploded bombs dropped in its training sites.

Natural seaweed usually dies in heavily TNT-tainted waters. So Cheney and his graduate students began work on a genetically modified version that would thrive. Last month at a conference in Washington, D.C., they announced a breakthrough: a new seaweed strain that can absorb TNT and neutralize it 5 to 10 times as fast as any terrestrial plant can. The porphyra actually eats away at the nitrogen molecules that make TNT toxic, lessening its toxicity. So there's no need to gather and dispose of the seaweed.

"It's the first instance of a foreign gene being introduced into seaweed, enabling it to detoxify an ocean pollutant," Cheney says. He dubs this technique "marine phytoremediation," the seagoing version of the land-based process that uses plants to soak up pollutants. The results suggest that seaweed has the potential to be one of nature's best aquatic cleanup tools. He and other researchers are pushing the biological boundaries to develop varieties that can, for instance, filter nutrient pollution from salmon-farm aquaculture.

Even unmodified kelp can act like a pollution sponge when deployed around salmon pens to soak up fish waste and excess nutrients, says researcher Thierry Chopin at the University of New Brunswick at Saint John in Canada. "The Chinese have done this for centuries. We are just trying to refine the process [and] figure out how many tons of seaweed and shellfish we need to achieve a balance."

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