Andreas Späth

All the plastic in the sea

2014-07-21 14:13

Andreas Wilson-Späth

The fact that much of the plastic waste humanity dumps into the world’s oceans tends to accumulate in five large floating islands of garbage (two in the Atlantic and Pacific each, and one in the Indian Ocean) is common knowledge these days.

These huge vortices act as conveyor belts that accumulate the floating bits of plastic released from the continents, but exactly what happens to the plastic in them over long time periods is less well understood.

Now a new study evaluating data from an around-the-world cruise, several regional surveys and additional recent investigations has shed some light on the issue.

The researchers confirmed that the distribution pattern of floating plastic debris on the open ocean agrees with expectations, being concentrated mostly in the five known garbage patches – there is one to the east and one to the west of our own South African shoreline.

According to lead author Andrés Cózar of the University of Cádiz in Spain, “some illustrations of the plastic garbage patches in the media have not been accurate. They are enormous areas (millions of square kilometers) with dispersed but ubiquitous small plastic fragments, mainly in the order of millimeters and centimeters in size. Surface plastic concentrations in these regions are in the order of kilograms (or millions of fragments) per square kilometer”.

Cózar and his collaborators were surprised by the quantity of plastic they found. They estimate that there are currently between 7 000 and 35 000 tons of plastic floating in the worlds open oceans. But that’s much less – in the order of 100 times less – than what they expected.

Since the 1970s somewhere in the region of 100 000 tons of plastic have been released into open ocean surface waters, making for tens of thousands of tones of unaccounted for plastic. Where has it all gone?

“An unknown mechanism is removing plastic from the surface water at a fast rate,” says Cózar, ”and a large amount of plastic could be being transferred to the food chain and the ocean interior”.

We know that bits of plastic floating in the sea get broken down into ever smaller fragments as a result of exposure to sunlight and waves, but they don’t just disappear. In fact, they can last for hundreds of thousands of years.

The authors of the study believe that one possibility is that much of the plastic ends up fragmented into tiny micrometer scale particles which are not collected by conventional sampling nets and therefore remain practically invisible. Other explanations include a slow sinking of tiny plastic particles into the deeper reaches of the ocean and widespread ingestion by marine organisms, especially zooplankton and small species of fish.

The bottom line is that we really don’t know exactly what happens to a very large portion of the plastic rubbish we’re dumping into the sea (which, by the way, amounts to only about 0.1% of the annual global plastic production). There is growing evidence, however, that considerable quantities of it make their way into the marine food chain and that its ultimate destination may very well be your dinner plate.

“Marine plastic pollution has reached a planetary scale within only two to three human generations of using plastic materials,” explains Cózar. “We still don’t really know the consequences that this pollution is having on our oceans, but the effects will occur on a global scale. There are enough signs to suggest that plankton eaters, such as small fishes, are important conduits for plastic pollution and associated contaminants. If this assumption is confirmed, the impacts of sustained plastic pollution could extend to ocean predators on a large scale”.

The solution is really quite simple: let’s cut down on the vast quantities of plastic we produce, buy, use and throw away every day.

Cózar believes “that we need to tackle the problem at source. The amount of persistent plastic materials discarded globally is huge, and the global production of plastic will likely continue to increase in the coming decades. Plastic materials are key, and almost necessary, for human development in medicine, science, conservation and just about anything else, but we need to change the ways in which they are designed and used in order to improve the efficiency of usage and the recovery of plastic resources”.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
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