Waterways the world over are reeling under the pressure from invasive species, many of which arrive in cargo-ship ballast water. A team at Louisiana State University has come up with a potentially promising approach to controlling the migration: Nuke the unwanted hitchhikers with microwaves.Dorin Boldor and colleagues note that globally, an estimated 10 billion tons of ballast water are pumped into and out of ships' tanks each year as they load and unload their cargo. They carry a rogue's gallery of organisms – from zebra mussels, sea squirts, and European green crabs, to various species of plankton, for instance. To deal with the problem, researchers have proposed a range of methods, including open-ocean exchange of ballast water, chemical treatments, heat, and ultraviolet radiation.
The group devised a system that pumped water through a cylinder that acted like the interior of a microwave oven. As water containing organisms moves through the cylinder, the team fired up a microwave transmitter that generated some 5 kilowatts of microwave radiation – roughly as much power as a small radio station's transmitter radiates. The best results came if the water was heated to about 131 degrees F. The team acknowledges that based on the lab results, this approach to killing unwanted guests would be expensive. But, they say, it has several advantages over other approaches, and its price could fall if the technology gains widespread use. The results appear in a recent issue of Environmental Science and Technology.