Dr Richard Thompson, University of Plymouth
Chris - it's well known that a hell of a lot of plastic bags get used every year. The figure that was published a few years ago was that a trillion plastic bags alone are used annually and go into the millions of tonnes. A lot of it ends up in the sea.
Richard - Yes, a lot of plastic products are produced annually. Obviously quite a lot of that material goes into landfill and small quantities are recycled. However quite substantial amounts do enter the environment as litter or debris. It's estimated that about eight million items of litter go into the sea every day, and much of that is plastic.
Chris - And when it gets into the sea, what does it do? Does it bob around or does it break down?
Richard - Most of it is found floating on the surface. The majority of plastics are buoyant or neutrally buoyant so we find them on the surface or we find them on strand lines where they are washed up on shores throughout the world from the poles to the equator. We also find lots of plastic on the deep sea bed as well now. As plastics stay in the sea, they become fouled by marine organisms and this alters the overall density of the plastic object so that plastics that floated when they first entered the sea become negatively buoyant and sink to the seabed.
Kat - You mentioned marine organisms. Are there things in the sea that actually eat plastics?
Richard - Quite a lot of organisms will eat plastic. Usually what happens is that creatures seem to mistake plastic for what they might normally eat. To a turtle, for instance, a floating plastic carrier bag might look similar to the jellyfish it might usually eat. To a sea bird, small coloured fragments of plastic on the shoreline might well be confused for the food items that those birds may normally be eating.
Kat - It's a big problem not only with animals in the sea but animals in general. I remember seeing some terrible footage of some birds with rings from the top of beer cans stuck round their necks. Is that a problem as well and physically affecting animals?
Richard - There's a range of different problems. There's the physical problems you mentioned of entanglement and that can be for birds and particularly for marine mammals as well. Fish also get caught up and tangled. There are also problems if creatures eat plastic, such as leading to suffocation or blocking the digestive tract.
Chris - One thing the Japanese have been looking at is what happens to these tiny particles of plastic when marine organisms begin to filter and eat them. They have a theory that these tiny particles of plastic may be bio-concentrating, or in other words accumulating toxins and then leading those toxins to enter the food chain.
Richard - That is entirely possible. The mechanism that has been shown in the work in Japan is that plastics, when they're floating at the sea surface, will be very attractive to hydrophobic contaminants. Chemicals that have entered the marine environment from other sources, such as DDE, are hydrophobic in nature and will latch onto the surface of buoyant objects rather than be in the seawater. And so floating plastic debris can accumulate some of these contaminants to several orders of magnitude more concentrated than those chemicals were in the surrounding seawater. They are mopping up contaminants. Of course the question is when you have these concentrated contaminants, is there any danger of these contaminants coming off perhaps in a different circumstance such as the guts of an organism?
Chris - Are you worried?
Richard - I'm concerned about it and it's certainly something that we're working on at the moment at the University of Plymouth.