Science & Environment

Can the oceans be cleared of floating plastic rubbish?

Plastic in seaweed
Image caption Hundreds of millions of tonnes of plastic are estimated to litter the world's oceans

Scientists are investigating ways of dealing with the millions of tonnes of floating plastic rubbish that is accumulating in our oceans.

They are a quirk of ocean currents - a naturally created vortex known as a gyre - where floating rubbish tends to accumulate.

The largest is in the North Pacific and covers an area twice the size of France. Others have since been discovered in the North Atlantic and most recently the South Atlantic.

Scientists now fear the same process is probably taking place in the South Pacific and Indian Ocean.

As well as damaging coasts and killing marine life who mistake the plastic for food, contaminants in the water, which attach to the plastic debris, are transporting waste chemicals across the world's oceans.

'Plastic munching'

At the UK's University of Sheffield, scientists are investigating how they could accelerate the speed at which the plastic breaks down by looking at micro-organisms already found in the sea that naturally feed on plastic.

Image caption Plastic-eating mico-organisms could be used to help break down floating plastic

Promising results have already been seen in finding out which microbes are attaching themselves to plastic in coastal waters around the UK.

The next stage will be to analyse how these enzymes work in the natural environment and how they might work in controlled environments where plastic would be the prominent carbon source.

But the researchers emphasise that even if they can narrow down the microbes and encourage their proliferation in an area like the plastic waste patch just found in the South Atlantic, this would be a very slow process.

"It's a bit like imagining how long it would take us to eat something the size of Canary Wharf," says the university's Dr Mark Osborn.

"If you have hundreds of thousands or millions of organisms colonising one piece of plastic then you can imagine the potential for scale up in terms of the rates of potential degradation."

Biological intervention to restore the ocean environment, otherwise known as bioremediation, is a relatively new field and would require careful assessment of any potential consequences.

And most current work is based on stopping plastic getting into the oceans in the first place.

'Diesel' plastic

In Ireland at a plastic fuel plant, Cynar, scientists are using waste plastic to make a synthetic fuel in a process known as plastic pyrolysis.

Plastic waste that would otherwise have ended up in landfill, is cleaned, dried and then heated to more than 300C (570F) in the absence of air.

The resulting molten liquid is turned into a gas which is then fractioned off to produce a diesel-like fuel.

"We do believe this is a terrific solution to a massive issue of landfill diversion as well as fossil fuel alternative," says Cynar's chief executive, Michael Murray.

Pyrolysis has the potential to be set up at waste disposal sites across Europe, with the fuel produced being used to power the waste disposal trucks and machinery.

But it costs money to establish the plants and burn the plastic, and this is only partly recovered by the cost of the fuel generated.

Much of the solution lies in more recycling says Murray, pointing out that only 50% of the 25m tonnes of plastic waste the EU produces every year is recycled.

Recycling and prevention

Image caption The variety of plastics and packaging makes recycling far more complicated and difficult

The challenge is to prevent it reaching landfill in the first place.

Our plastic lifestyle is at the heart of the problem according to Richard Thompson, professor of marine biology at the University of Plymouth.

Varying colours of plastic and different components such as sports caps which are made of different plastic types, make them harder to recycle compared to clear and strong plastic.

Despite campaigns to improve recycling, many plastics - such as food packaging packaging - are still not recyclable.

"The diversity of different polymers and different forms of packaging we use... is compromising the recyclability of the product," Professor Thompson explains.

"The best way to solve this problem is to close the loop, to turn a bottle back into a bottle," he says.

Eighty percent of the plastic in our seas has come from the land where it has either been flushed through drains or blown off landfill sites.

Until there is an effective alternative to dumping, the floating plastic in our oceans will continue to accumulate.

Costing the Earth, Fake Plastic Sea will be broadcast on BBC Radio Four on Wednesday 6th October at 9pm and after on BBC iPlayer

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