Decomposing Plastics at Sea

A boy points out styrofoam debris from the ocean. (Saido/Nihon University)
Billions of pounds of plastic waste are floating in the world’s oceans. Scientists are reporting that even though plastics are reputed to be virtually indestructible, they decompose with surprising speed and release potentially toxic substances into the water.

“Plastics in daily use are generally assumed to be quite stable,” said Katsuhiko Saido, a chemist with the College of Pharmacy, Nihon University, Chiba, Japan. “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's team found that when plastic decomposes it releases potentially toxic bisphenol A (BPA) and PS oligomer into the water, causing additional pollution. Plastics don't usually break down in an animal’s body after being eaten, but the substances released from decomposing plastic are absorbed. BPA and PS oligomer can disrupt the functioning of hormones in animals and seriously affect reproductive systems.

A new method developed by the research team simulates the breakdown of plastic products at low temperatures, such as those found in oceans. The process involves modeling plastic decomposition at room temperature, removing heat from the plastic, and then using a liquid to extract the BPA and PS oligomer.

According to Saido, styrofoam is typically crushed into pieces in the ocean and finding these is no problem. But when the scientists were able to degrade the plastic, they discovered that three new compounds not found in nature formed - styrene monomer (SM), styrene dimer (SD), and styrene trimer (ST). Styrene is a suspected human carcinogen. BPA ands PS oligomer are not found naturally, so must have been created through the decomposition of the plastic. Trimer yields SM and SD when it decomposes from heat, so trimer also threatens living creatures.

(American Chemical Society)

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