Pollution-trawling voyage finds ocean's plastic 'soup'

published 25 March 2011 by Ferris Jabr in New Scientist

If you trawl a fine mesh net through any of the globe's five subtropical gyres – giant ocean vortexes where currents converge and swirl unhurriedly – you will haul on deck a muddle of brown planktonic goop, the occasional fish, squid or Portuguese man-of-war – and, almost certainly, a generous sprinkling of colourful plastic particles, each no larger than your fingernail.

Every flake of plastic cup or shard of toothbrush handle is a sponge for persistent organic pollutants (POPs) – potentially hazardous compounds that do not degrade easily and cling to any hard surface they find. The fate of all this plastic determines not only the health of marine life, but also our own; if fish are feasting on these toxic morsels, then we probably are too.

Last month researchers from the 5 Gyres Institute in Santa Monica, California, and the Algalita Marine Research Foundation in Long Beach, California, sailed into Piriápolis, Uruguay. They had just completed the third leg of the first expedition ever to study plastic pollution in the South Atlantic subtropical gyre. In every single trawl, the team discovered plastic.

"This issue has only recently come to the public's attention," says Anna Cummins, co-founder of 5 Gyres. "We're trying to document the issue and get baseline information because there is such a scarcity of data."

Plastic dust

There are still significant gaps in the data the crew can collect, however. The nets that they use cannot capture plastic particles that are smaller than one-third of a millimetre across. "After a certain size these particles just disappear," says Cummins. "What is their ultimate state? They could very well break down to a size where they are ingested by fish."

Cummins also explains that trawling gathers plastic particles from surface waters only. Different kinds of plastic may be suspended at different depths – a dreadful rainbow of rubbish spanning the ocean from top to bottom – but no one has done the research to find out.

What 5 Gyres researchers are currently investigating, however, is whether surface-feeding fish are ingesting plastic – and if so, what that does to them. Chelsea Rochman, who studies marine ecology and ecotoxicology at San Diego State University in California, joined the 5 Gyres team in November for a month-long trawl in the South Atlantic. In addition to sampling the water and plastic, Rochman used a special net to collect around 660 lanternfish – a ubiquitous family of small bioluminescent fish that make up around 65 per cent of all deep sea fish biomass. Lanternfish inhabit the dim depths during the day, but swim to the surface at night to feed, so if any fish would have plastic in their guts, it would be these guys.

Back at her lab, Rochman has started analysing the water and plastic samples for the presence of POPs. She has also started slicing open the lanternfish so she can determine if they are eating plastic and whether POPs are accumulating in their tissues. Rochman wants to see whether fish caught in highly polluted areas of the gyres have more plastic in their guts and higher levels of POPs than those taken from less polluted waters. Confirming that distinction would suggest that fish are indeed consuming toxic morsels.

In another lab experiment, Rochman fed one group of fish a diet infused with plastic, and another group a plastic-free diet. Preliminary results show that the fish which ate plastic endured significant weight loss and liver damage. "We are going to look for tumours, cell death and congestion in the organs that filter toxins," she says.

Plastic, plastic, everywhere

Plastic in the ocean would not be so worrisome if only certain areas were polluted, but it appears to travel everywhere. Worse, it's hard to pin down exactly where, say, the remains of a candy wrapper blown out to sea in China will eventually drift. One tool is providing some answers, however. For at least two decades oceanographers have deployed thousands of Lagrangian drifting buoys, which are designed to map surface ocean currents rather than wind patterns or waves.

"We realised that our buoys are in fact a kind of marine debris," says Nikolai Maximenko of the University of Hawaii in Honolulu, who collaborated with 5 Gyres researchers to identify which areas of the ocean should have especially high levels of plastic pollution. Wherever the buoys gather most densely, the reasoning goes, is also where plastic particles should cluster. And that is what the researchers have found so far: all our plastic waste meets and circulates in the gyrating wastes of the ocean.

More surprising is that despite the lure of the gyres, the buoys – and, therefore, probably plastic in general – really get around. "It's amazing to see the global patterns," says Maximenko. "I just found out that one surface drifter went very close to the North Pole in summer 2009, and another made two loops around Antarctica."

What researchers have established so far is that the plastic in the oceans is persistent and pervasive. 

Investigations into what all this pollution means for wildlife and people are just getting started, but the early signs are not reassuring. "The ocean is not infinite. It doesn't have room for our waste," says Cummins.