Carolyn Barry
for National Geographic News
August 20, 2009
Though ocean-borne plastic trash has a reputation as an indestructible, immortal environmental villain, scientists announced yesterday that some plastics actually decompose rapidly in the ocean. And, the researchers say, that's not a good thing.
The team's new study is the first to show that degrading plastics are leaching potentially toxic chemicals such as bisphenol A into the seas, possibly threatening ocean animals, and us.
Scientists had previously thought plastics broke down only at very high temperatures and over hundreds of years.
The researchers behind a new study, however, found that plastic breaks down at cooler temperatures than expected, and within a year of the trash hitting the water.
The Japan-based team collected samples in waters from the U.S., Europe, India, Japan, and elsewhere, lead researcher Katsuhiko Saido, a chemist with the College of Pharmacy at Nihon University in Japan, said via email.
All the water samples were found to contain derivatives of polystyrene, a common plastic used in disposable cutlery, Styrofoam, and DVD cases, among other things, said Saido, who presented the findings at a meeting of the American Chemical Society in Washington, D.C., today.
Plastic, he said, should be considered a new source of chemical pollution in the ocean.
Cooking Up Plastic Soup in the Seas
The toxic compounds the team found don't occur naturally in the ocean, and the researchers thought plastic was the culprit.
The scientists later simulated the decomposition of polystyrene in the sea and found that it degraded at temperatures of 86 degrees Fahrenheit (30 degrees Celsius).
Left behind in the water were the same compounds detected in the ocean samples, such as styrene trimer, a polystyrene by-product, and bisphenol A, a chemical used in hard plastics such as reusable water bottles and the linings of aluminum cans.
Bisphenol A (BPA) has been shown to interfere with the reproductive systems of animals, while styrene monomer is a suspected carcinogen.
The pollutants are likely to be more concentrated in areas heavily littered with plastic debris, such as ocean vortices, which occur where currents meet.
(Related: "Giant Ocean-Trash Vortex Attracts Explorers.")
Plastic Breaks Down Fast
About 44 percent of all seabirds eat plastic, apparently by mistake, sometimes with fatal effects. And 267 marine species are affected by plastic garbage—animals are known to swallow plastic bags, which resemble jellyfish in mid-ocean, for example—according to a 2008 study in the journal Environmental Research by oceanographer and chemist Charles Moore, of the Algalita Marine Research Foundation.
Now, it seems, they also face the invisible threat of toxic, plastic-derived chemicals.
Once Styrofoam, for example, breaks down, the tiny polystyrene components start to sink, because they're heavier than water, Moore said. "So it's likely that this styrene pollutant is prevalent throughout the water column and not just at the surface."
Along with Moore, David Barnes, a marine ecologist from the British Antarctic Survey, doesn't think the Japanese team's lab results can be applied uniformly across the ocean, however. Water temperatures are typically much cooler than the 86 degrees Fahrenheit in the study, he said.
"We're talking about, effectively, what happens in [zones] of tropical and some subtropical coasts. And there, [the] study may be very important," Barnes said.
Ocean as "Plastic Soup"
Plastic hits marine creatures with a double whammy, Moore said. Along with the toxic chemicals released from the breakdown of plastic, animals also take in other chemicals that the plastic has accumulated from outside sources in the water.
"We knew ten years ago that plastic could be a million times more toxic than the seawater itself," because plastic items tend to accumulate a surface layer of chemicals from seawater, Moore said. "They're sponges."
Moore worries about the plastic-derived chemicals' potential damage to wildlife. The chemicals can potentially cause cancer in humans, he said, and simpler life-forms "may be more susceptible then we are."
Pollutants also become more concentrated as animals eat other contaminated animals—which could be bad news for us, the animals at the top of the food chain. (Read National Geographic magazine's "The Pollution Within.")
Moore estimates plastic debris—most of it smaller than a fifth of an inch (five millimeters)—is "dispersed over millions of square miles of ocean and miles' deep in the water column.
"The plastic soup we've made of the ocean is pretty universal—it's just a matter of degree," he said. "All these effects we're worried about are happening throughout the ocean as a unity."
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