Posts Tagged ‘plastic eating bacteria’

Update on Ocean Plastic Pollution

Wednesday, June 8th, 2011

About the best we can do as environmentalists is to look for some good news in the huge mess of bad news.

So here is some: though the production of plastics has continued to increase over the past couple of decades, the amount polluting the ocean does not appear to be increasing. This is unexpected.

Ocean currents and winds concentrate plastic and other debris in the five great subtropical gyres – the most notorious being the North Pacific Gyre.

The five subtropical gyres, regions of convergence, products of the ocean currents and winds. The North Pacific Gyre is also rudely called the Great Pacific Garbage Patch (coastalcare.org)

To understand whether plastic pollution in the gyres has been increasing, we need a long-term study covering a very large area, supported by a convincingly large set of data. Such a study is extremely rare, for funding agencies don’t really want to wait 20 years to see results.

Hence the beauty of the study published in Science last September. Sea Education Association offers university credits in oceanography on sailing research vessels. For 22 years, from 1986 to 2008, over 7000 lucky undergraduates and faculty scientists conducted 6100 surface plankton tows from sailing research vessels in and around the North Atlantic Gyre, known as well as the Sargasso Sea.

The North Atlantic Gyre, also called the Sargasso Sea, is largely a product of the impact of the immense Gulf Stream (rtseablog.com).

Plastics in the ocean gradually break up into smaller and smaller bits, called microplastics. Up to a few mm in diameter, these float just below the water surface, easily sampled by the plankton nets. More than 64,000 plastic pieces were picked out of the plankton samples, most from 30-38 degrees latitude, and most concentrated at the latitude of Atlanta. Abundance of microplastics should have increased over the 22 years.

Microplastics were particularly abundant in the eastern part of the North Atlantic Gyre (science.org)

Unexpectedly, they didn’t. Despite the four to five fold increase in global plastics production and in discarded plastics in US municipal waste over that time, the amount of plastics collected each year of the study stayed about the same.

Why, you ask? Most of the plastics come from the US eastern seaboard: have the beaches of the eastern US been cleaned more successfully? Are people really discarding less, recycling more? Much in the past has also come from ships, which are now prohibited from dumping plastics at sea. As well, efforts to prevent or recover spills of resin pellets, the raw material of plastic products, have increased. But these are still not sufficient explanations.

There is a further possibility. Microbiologists have found that bacteria – of the Vibrios group of bacteria – appear to be eating away the surfaces of the microplastics. This could be very good news, provided they are actually digesting the polymer molecules and breaking down associated toxins. If they only accumulate the polymers and toxins, and in turn pass them on to whatever grazes on them, then the news is interesting, but not so good.

Electron micrograph of bacteria grazing on a microplastic fragment pulled from the Sargasso Sea (nature.com)

Plastics producers are also taking some limited action: in March, at a conference on marine debris, 47 companies signed a pledge. They agreed to try to reduce marine debris, help look for solutions to the debris problem, promote enforcement of existing laws, promote knowledge of eco-efficient waste management, enhance recovery of plastic for recycling, and prevent further loss of resin pellets. Certainly good intentions.

It all helps. Sea birds, marine mammals, sea turtles and large fish will still be entangled, strangled and suffocated by plastic garbage and fishing gear, and microplastics are hardly nourishing food for any except the bacteria.

But it isn’t getting worse.