Steve Connor, The Independent 20 Aug 09;
Scientists have identified a new source of chemical pollution released by the huge amounts of plastic rubbish found floating in the oceans of the world. A study has found that as plastics break down in the sea they release potentially toxic substances not found in nature and which could affect the growth and development of marine organisms.
Until now it was thought that plastic rubbish is relatively stable chemically and, apart from being unsightly, its principle threat to living creatures came from its ability to choke or strangle any animals that either got caught in it or ingested it thinking it was food.
But the latest research suggests that plastic is also a source of dissolved substances that can easily become widely dispersed in the marine environment. Many of these chemicals are believed to toxic to humans and animals, the scientists said.
The scale of plastic pollution in the sea has only been widely recognised in recent years when sailing yachts reported vast areas of ocean, such as an area estimated to be twice the size of Texas in the North Pacific, that seem to be permanently covered in a layer of floating marine litter caught up in swirling ocean currents or gyres.
Some of the items were found to be many decades old, suggesting that the plastic took a long time to degrade. However, a study by Katsuhiko Saido at Nihon University in Chiba, Japan, has found that plastics degrade relatively quickly in the conditions and temperatures that were designed to simulate the environment of the open ocean.
“Plastics in daily use are generally assumed to be quite stable. We found that plastic in the ocean actually decomposes as it is exposed to the rain and sun and other environmental conditions, giving rise to yet another source of global contamination that will continue into the future,” Dr Saido said.
“To date, no studies have been conducted on plastic decomposition at low temperature in the environment owing to the mistaken conception that plastic does not decompose. The present study was conducted to clarify that drift plastic does indeed decompose to give rise to hazardous chemicals in the ocean,” he said.
The scientists found that when plastics decompose in the ocean they release a range of chemicals, such as bisphenol A and substances known as polystyrene-based (PS) oligomers, which are not found naturally. Bisphenol A has been implicated in disrupting the hormonal system of animals.
A common form of plastic rubbish is styrofoam, which soon gets crushed into small pieces in the sea. However, it also releases substantial quantities of a toxic substances called styrene monomer, which is known to cause cancer, as well as styrene dimers and trimer, which are suspected of being carcinogenic. The trimer also breaks down into the toxic monomer form.
Findings from the study were released yesterday at the American Chemical Society meeting in Washington. Dr Saido said that samples of seawater collected from the Pacific Ocean were found to be contaminated with up to 150 parts per million of some of these components of plastic decomposition.
“This study clearly shows new micro-pollution by compounds generated by plastic decomposition to be taking place out of sight in the ocean. Thus, marine debris plastics in the ocean will certainly give rise to new sources of global contamination that will persist long into the future,” he said.
It is estimated that there could be hundreds of millions of tons of plastic rubbish floating in the world’s oceans. In Japan alone, it is calculated that 150,000 tons of plastic is washed up on its shores each year.
Study says plastic decomposes at sea
Yahoo News 19 Aug 09;
WASHINGTON – Environmentalists have long denounced plastic as a long-lasting pollutant that doesn't break down. A new study indicates that, in the oceans, plastic does decompose, but says that's not a good thing either.
Thousands of tons of plastic debris wind up in the oceans every year, some of it washing up on coasts, some being swirled by currents into the Great Pacific Garbage Patch between California and Hawaii, said to be larger than Texas.
"Plastics in daily use are generally assumed to be quite stable," Katsuhiko Saido, a chemist at Nihon University, Chiba, Japan, said in a statement.
"We found that plastic in the ocean actually decomposes as it is exposed to the rain and sun and other environmental conditions, giving rise to yet another source of global contamination that will continue into the future," said Saido, who presented his findings at the annual meeting of the American Chemical Society on Wednesday.
Saido reported that the decomposing plastics release potentially toxic chemicals such as bisphenol A and PS oligomer, which can disrupt the functioning of hormones in animals.
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On the Net:
American Chemical Society: http://portal.acs.org/portal/acs/corg/content
Plastic Breaks Down in Ocean, After All -- And Fast
Carolyn Barry, National Geographic News 20 Aug 09;
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, a derivative of styrene trimer, is a known 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.
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."
