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See Inside June 2011

The Smallest Hitchhikers

Marine microbes may hold the key to the ocean's disappearing plastic



Gary Bell Corbis

We know that at the heart of at least two ocean basins—the North Pacific and the North Atlantic—tiny plastic fragments the size of confetti or smaller are accumulating on the sea surface by the tens of thousands, the remnants of discarded grocery bags, cups, bottles and other waste.

Last year a group of researchers publishing in the journal Science reported a mystery: during a 22-year survey of plastic accumulation in the western North Atlantic, the scientists saw no increase in the amount of plastic, despite a surge in annual global plastic production from about 75 million to 245 million metric tons over the same period. Where was it going? New research shows marine microbes may be feasting on the debris.

On a recent cruise to the North Atlantic’s Sargasso Sea, scientists from the Sea Education Association (SEA) in Woods Hole, Mass., collected bits of plastic that, to the naked eye, looked relatively smooth and clean. But when they zoomed in on the one-centimeter-size slivers using an electron microscope, a new world appeared. “We saw that they were just covered with microbes,” says Tracy Mincer of the Woods Hole Oceanographic Institution.

What’s more, he observed individual microbes sinking into the plastic’s surface, eroding a footprint roughly twice their diameter. “They look just like hot coals burning through snow,” says Mincer, whose colleague presented the findings at the Fifth International Marine Debris Conference in Honolulu in March.

Mincer cautions that these observations are preliminary, but if they are confirmed, they would be the first evidence of marine microbes able to degrade plastic at sea. Whereas Mincer notes that bacteria’s ability to digest plastic in the warm, moist, nutrient-rich clime of landfills is well established, the ocean’s surface has long been considered too inhospitable an environment for biodegradation to occur. It is cold, turbulent and, particularly in the Sargasso Sea, devoid of nutrients.

The new research is crucial to understanding the fate of plastic at sea, says Kara Lavender Law of SEA, who is lead author of the Science paper that first reported the missing plastic. “If we can find how it’s broken down into its molecular components, that’s a really important revelation,” she says. 

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