Although plastic has long been considered indestructible, some scientists say toxic chemicals from decomposing plastics may be leaching into the sea and harming marine ecosystems. Contrary to the commonly held belief that plastic takes 500 to 1,000 years to decompose, researchers now report that the hard plastic polystyrene begins to break down in the ocean within one year, releasing potentially toxic bisphenol A (BPA) and other chemicals into the water.

“Plastics in daily use are generally assumed to be quite stable,” chemist Katsuhiko Saido of Nihon University in Japan said in a press release. “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.” Saido presented the work Wednesday at the American Chemical Society meeting in Washington, D.C.

Several noxious plastic byproducts, including BPA and a substance called styrene trimer, have been detected in small quantities in the ocean, but Saido says this is the first time anyone has shown a direct connection between decomposing plastic and the hazardous chemicals. Both BPA and components of styrene trimer have been shown to disrupt hormone function and cause reproductive problems in animals.

The Japanese researchers devised a method to simulate plastic breakdown at 30 degrees Celsius (86 degrees Fahrenheit) in the lab, and they compared the chemical byproducts from their experiment with what they found in water and sand from the Pacific Ocean. Based on the speed of plastic decomposition and the amount of drift plastic found along the coasts of Japan, the scientists concluded that noxious chemicals in the water are probably coming from the breakdown of polystyrene, which is used to make Styrofoam.

But not all researchers are convinced the lab experiment accurately reflects what’s going on in the ocean. “Polystyrene is actually heavier than seawater, so before it ever chemically breaks down or degrades, it may be sinking to the bottom,” said ocean researcher Charles Moore of the Algalita Marine Research Foundation, who was not involved in the study. Because temperatures are much lower at the bottom of the ocean and there’s very little light to cause photodegredation, Moore said it’s unlikely that the plastic would break down once it sunk. “Food doesn’t even biodegrade at the bottom of the ocean,” he said. “There is so little activity going on down there.” In addition, Moore said ocean temperatures across most of the world are much lower than the 30 degrees Celsius the researchers used in their lab simulation.

Even if polystyrene breaks down in some regions of the ocean, pollution expert Joel Baker of the University of Washington questions whether the amount of chemicals released would be significant compared to the vast size of the ocean itself. “There’s a little bit of hyperbole going on here,” Baker said. “There’s no question that there’s too much plastic in the ocean, and we should try to reduce that. But whether it’s an important source of chemicals for the ocean is much less clear.”

But regardless of whether its chemicals leach into the water, the shear volume of plastic floating in the sea makes it a major polluter, Moore said. Discarded plastic junk makes its way from gutters and storm drains into rivers and streams, and eventually flows into the ocean, where it gets trapped by currents and creates vast regions of plastic soup. On a voyage back from Hawaii in 1997, Moore discovered a floating island of garbage larger than the state of Texas, which has since been dubbed “The Great Garbage Patch.”

Plastic poses the biggest threat to marine animals that confuse garbage with dinner and end up digesting large quantities of polystyrene. Even if polystyrene isn’t decomposing in the water, Moore said it could be breaking down in the digestive tracts of fish and marine mammals. “Every size of organism,” he said, “every creature in the food web in the ocean, from the smallest filter feeders to the largest whales, is consuming plastic.”

(Por Hadley Leggett, Wired, 19/08/2009)