The aquatic problems of microplastics

Helen: Plastic debris - it's a growing ocean concern, and for a while now it's been known that a growing abundance of the plastic that's hanging around in the marine environment comes in the form of tiny particles, or microplastics, that are less than 1 mm in size. But where's it all coming from? That's the big question tackled by a team of researchers led by Mark Browne from the University of California, Santa Barbara and Richard Thompson from Plymouth University.

Their paper first came out late last year, and I had a chance to catch up with Richard and find out more about their forensic approach to identifying the source of polluting plastic.

Richard: 2004 we published a paper showing that small fragments of plastic, microscopic pieces, some less than the diameter of a human hair were accumulating in the oceans and that they had increased over time. So the key question was "where is that material coming from and to what extent was it causing harm." And over the last 10 years we've examined a number of different roots at the University of Plymouth, we've looked at razor fragmentation of larger items of debris and we know they contribute to the picture. We've looked at direct releases of small pieces of plastic into the environment, pieces of plastic, for example, that are used as abrasive scrubbers in cleaning products. Pieces less than a millimeter or so in size and yet many tones released to the oceans through sewage and waste water.

But another line of inquiry that we wanted to pursue was some of the material, the microscopic material, we were finding was fibrous in shape and it occurred to us that some of this could be resulting from the cleaning both at home and at in industrial settings of fabrics and textiles resulting in accumulation of small fibres that wouldn't necessarily be removed by any form of sewage treatment.

Helen: Richard, Mark and their team set out and took samples of sediments from shorelines in 18 sites spanning the globe, on six continents, and found microplastic everywhere. The team them zeroed in on the possible source of these fibres.

Richard: We found quite substantial quantities of fibres being released at the end of a washing machine pipe. We found similarly fibres being released from sewage treatment plants and we found in the UK despite the fact that dumping of sewage sludge stopped over ten years ago there was abundance of this kind of synthetic fibre at sites that were formerly used as dumping grounds than in nearby reference sites.

Helen: So what is the likely impact of all this plastic on marine life?

Richard: We know from laboratory studies that creatures with a range of different feeding mechanisms: barnacles and muscles that filter their food from the water column, marine worms that live in sediments and effectively strip their organic matter from those sediments, and detritivores things like sand hoppers that live at the top of the shore. All of those creatures will ingest material of this size in laboratory exposures and indeed with the muscles we did here at Plymouth showed that after a single exposure and then moving the muscles to clean conditions, even after more than 40 days, those muscles have still got plastic in their system.

And so there is some suggestion that these small fragments of plastic can accumulate in the tissues of organisms in a way that we wouldn't expect from the natural food source. That still doesn't prove that it is doing those creatures any harm but I think it is an important step on the way to establishing what harm it might cause. You need to know where this kind of material is, what creatures might be eating it, and then you can look at a kind of risk assessment to exposure pathway.

Helen: It's well known that larger animals, especially marine birds, can get tangled in bigger plastic debris, they choke and fill up their stomachs when they try and eat it, and its possible that for smaller animals, these smaller bits of plastic could have a similar effect.

A further concern, surrounds the possibility that very small pieces of plastic could transport and release chemicals found in the environment from other sources.

Richard: A lot of the chemicals of concern here are hydrophobic in nature and so they will latch on to plastics in preference to water. So a small piece of plastic exposed in the sea within a space of a week or so will dissolve a concentrate on its surface, concentrations of some of those chemicals that can be many, many fold the concentrations in the surrounding sea water. So that's a potential if those plastics are then eaten, different chemical environment could those chemicals then be released.

And that's in addition to existing concerns about some of the chemicals that are used in the production of a variety of plastics. Used with good purpose in mind, but things we are now regulating from a human health perspective such as thalates in plastics. So some of the chemical additives that are introduced for functionality might also be released more readily when you are dealing with very small particles.

So I think the overriding message here is that these small synthetic fibres are an additional part of the problem, they are an additional source of these microscopic particles which has really been the overarching aim of our studies to examine.

Helen: A team in Japan are running a project called International Pellet watch - Velellas (by-the-wind-sailors) and plastic confetti in the North Pacifc Plastic Gyrethey're asking members of the public to send in tiny particles of plastic -  so they can analyse and map out the global distribution of these hydrophobic organic pollutants that stick to plastic in the ocean - so if you want find out what chemicals are found on your local beach then check out pellet watch.org.

Plastic debris in the oceans is obviously a huge topic with all sorts of conservation implications, and you can find out more from a recent report that Richard co-wrote for the Global Environment Facility, you can download that from our website.

But as his study showed, if all these plastic fibres are washing out of our clothes - up to 1900 fibres each time a single fleece is washed, the team estimate - then is the solution simply to get the washing machine engineers to come up with better filters so these fibres don't end up in sewage water in the first place?

Richard: Its part of the picture, fixing the quantities of small synthetic fibres passing from waste water pipes is not to solve the problems of pollution of the oceans by solid marine debris, a large proportion of which is plastic items , rope, netting, packaging and what we're discussing here with respect to fibres in washing machines is part of the story but is not going to solve it on its own. 

Find out more:

Browne et al (2011). Accumulation of microplastic on shorelines worldwide: sources and sinks.
Environmental Science and Technology.

Marine Debris as a global environmental problem - Global Environment Facility report [PDF]

Pellet Watch