Plastics decompose fast in water

In the first study to look at what happens over the years to the billions of pounds of plastic waste floating in the world’s oceans, scientists are reporting that plastics - reputed to be virtually indestructible - decompose with surprising speed and release potentially toxic substances into the water.

Reporting at the 238th National Meeting of the American Chemical Society (ACS), the researchers termed the discovery 'surprising'. Scientists always believed that plastics in the oceans were unsightly, but a hazard mainly to marine animals that eat or become ensnared in plastic objects.

'Plastics in daily use are generally assumed to be quite stable,' said study lead researcher Dr Katsuhiko Saido of Nihon University in 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.'

He said that polystyrene begins to decompose within one year, releasing components that are detectable in the parts-per-million range. Those chemicals also decompose in the open water and inside marine life. However, the volume of plastics in the ocean is increasing, meaning that decomposition products remain a potential problem.

Saido, a chemist with the College of Pharmacy at Nihon University, said his team found that when plastic decomposes it releases potentially toxic bisphenol A (BPA) and PS oligomer into the water, causing additional pollution.

Plastics do not usually break down in an animal’s body after being eaten. However, the substances released from decomposing plastic are absorbed and could have adverse effects. BPA and PS oligomer are sources of concern because they can disrupt the functioning of hormones in animals and can seriously affect reproductive systems.

Saido also described a new method to simulate the breakdown of plastic products at low temperatures, such as those found in the oceans. The process involves modelling plastic decomposition at room temperature, removing heat from the plastic and then using a liquid to extract the BPA and PS oligomer.

When the researchers degraded styrofoam using the method, they discovered that three new compounds, which are not found in nature, formed.

They are styrene monomer (SM), styrene dimer (SD) and styrene trimer (ST). SM is a known carcinogen and SD and ST are suspected to cause cancer. BPA and PS oligomer are not found naturally and, therefore, must have been created through the decomposition of the plastic.