Gunning for the gut: tiny particles might fight invasive zebra mussels.

By modifying a method used to flavor foods, researchers have made a substance that poisons the zebra mussel. That invasive species clogs water pipes that feed power plants and other facilities.

Around the Great Lakes and along much of the Mississippi watershed, facility operators lose about $1 billion each year to the mussel. They fight it with various toxicants, including chlorine and potassium salts.

Each mussel defense faces a test. "Either it's got to be toxic to zebra mussels and innocuous to other organisms, or you need to remove it or inactivate it" before it enters the environment, says Charles R. O'Neill of the New York Sea Grant at Cornell University, who studies aquatic invasive species.

Furthermore, he says, when zebra mussels detect a toxicant, they sometimes stop filtering water for days or weeks while the chemical dissipates.

Scientists at the University of Cambridge in England set out to make a substance that mussels would take in without recognizing as poison and that would be unlikely to harm other creatures. Some funding came from BioBullets Ltd., a London company founded by David C. Aldridge

and Geoff D. Moggridge, two of the researchers.

The scientists produced and tested the new substance with assistance from TasteTech Ltd. of Bristol, England, which manufactures commercial food flavorings.

To make the mussel poison, TasteTech mixed potassium chloride with hydrogenated vegetable oil and a soaplike surfactant that "encourages the fat to coat the potassium chloride," says Moggridge. When sprayed into a chamber of cool air, the mix, re solidified into spherical droplets with typical diameters between 45 and 165 micrometers.

In tests in water spiked with the spheres, zebra mussels took them in and retained some in their bodies, as if they were food particles worth digesting. About 60 percent of mussels died when exposed to the spiked water for 12 hours, Aldridge, Moggridge, and Patti Elliott report in an upcoming Environmental Science & Technology. The same concentration of potassium chloride added directly to the water, along with inert spheres, caused few if any deaths.

Disguising the toxicant as food, so that mussels won't reject it, is a good strategy, O'Neill says. "I've never seen anyone try this approach before" he says.

Biologist Robert F. McMahon of the University of Texas at Arlington says, "Zebra mussels take this stuff out the water column and concentrate it in their digestive systems to levels that are toxic." Aquatic organisms that don't filter feed, as mussels do, would take in only inconsequential amounts of the toxicant, he adds.

Long-term consequences for species other than zebra mussels should be minimal because after 2 hours in water, most of the particles fell apart, denuding the remaining potassium chloride, Moggridge says.