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updated 8/27/2010 4:55:50 AM ET 2010-08-27T08:55:50

The concentration of plastic bits floating on the surface of the Atlantic has held steady for more than 20 years, found a new study, even as people use and discard ever-increasing amounts of plastic.

With growing concerns about plastic in the environment, the surprising new finding raises questions about where all that stuff is ending up.

“We know that the global production of plastic has increased at a very high rate, and we know that plastics in the waste stream have also increased over time,” said Kara Lavender, an oceanographer at the Sea Education Association in Woods Hole, Mass.

“We infer that plastic in the ocean is most likely increasing,” she added. “So how come we’re not seeing increasing amounts of plastic in areas where the plastic is accumulating? That’s the mystery.”

Although massive garbage patches have drawn lots of attention lately to plastic in the oceans, few studies have looked at exactly how much is out there and where it’s going. Lavender realized she had the perfect data set just waiting to be analyzed.

For nearly 40 years, the Sea Education Association (SEA) has been taking college students on educational semesters at sea. As part of the program, students have sampled surface waters by dragging a one meter-wide mesh net behind their live-aboard ship.

The net, which catches anything bigger than one-third of a millimeter wide, has been dragged throughout the western Atlantic, from Newfoundland to the southern Caribbean. When it comes back onboard after sampling a nautical mile, SEA students use tweezers to pick through the plankton, jellies, tiny fish and occasional tar balls.

Within the gooey brown mush, they count and record every single piece of plastic. For the new study, Lavender and colleagues compiled 22 years' worth of those numbers.

One of the work’s major findings, published this week in the journal Science, was to show for the first time that the highest concentration of plastic in the western Atlantic is centered in a region offshore at about the latitude of Atlanta. The bulk of the waste stretches from Virginia to Cuba.

To the surprise of Lavender and her colleagues, the study also showed no overall change in the amount of plastic snared from 1986 to 2008, even though they assume more plastic is making its way into the ocean.

“I expected to see the line go right up,” she said. “It took us a good year to decide, no, we have not seen an increase, no matter how you slice it.”

Where is all the missing plastic?

One theory is that it’s breaking down into really tiny pieces that the nets can’t catch. Another possibility is that it’s sinking below the surface, either because tiny organisms are growing on it and weighing it down, or because birds, fish and other animals are eating it and excreting it.

Or maybe the plastic is getting incorporated into tissues of animals that mistake it for food.

Each scenario offers consequences to be concerned about. When animals eat plastic, they can damage their insides, become malnourished, or consume chemical pollutants, which tend to stick to plastic like a sponge. These pollutants may then work their way through the food chain all the way up to people.

When drifting plastic becomes homes for colonizing organisms like barnacles, they can become vehicles for invasive species, added University of Hawaii oceanographer David Karl, whose recent work has shown that plastic is like the bottom of a boat -- an easy target for ocean slime.

Degenerating plastics also release chemicals with unknown consequences.

“Plastic is a chemical compound that does not naturally occur in nature,” Lavender said. “We could be altering the chemistry of the ocean.”

Of course, the findings could also be good news, Karl said. Maybe the plastic is simply washing back up onto shore. Or maybe people are being more careful with trash disposal and recycling, and less plastic is getting into the ocean, though he admitted that was a hard scenario to believe.

“This may be another unplanned experiment of humankind,” Karl said. “Since the 1950s, we’ve been putting plastic into the ocean. Now we’re trying to figure out where it’s gone and what it’s done and what the impact is ecologically.”

© 2012 Discovery Channel

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