A man collects plastic bottles to sell for recycling, in a landfill of Managua, Nicaragua, on January 11, 2013. Photo: Getty Images
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Scientists buried biodegradeable plastics for three years, found it doesn't degrade

Common method of making plastic "biodegradeable" seems to be useless, in some types.

Gardeners beware - those "compostable" bin bags might not so readily turn into soil. A study published in Environmental Science & Technology has found that many common biodegradeable plastics, aren't - and that recycling is a much better bet.

There are typically two ways to make plastics degrade faster than they otherwise would: either add stuff to them to make them break down faster, or make them out of biological materials like vegetable oil or corn starch. The researchers, from Michigan State University, were specifically interested in the first set, and did what has to be done when testing how fast something rots - they buried a bunch of different plastics, for three years, and then dug them up again to see what had happened. The results don't bode well for the efficacy of additives.

Typically, plastics made from petroleum can take hundreds of years to decompose, yet getting precise estimates for the timeframes involved can be difficult. After all, most modern plastics haven't been around anything like the amount of time we think they'll take to break down - and the thing that makes plastics so useful as packaging, that they're unappetising to bacteria, makes them also an environmental terror. It's not just about plastic bags caught in trees; the plastics that form the Great Pacific Garbage Patch, a vast gyre of debris, form an ongoing natural disaster that is entirely human-made.

Recycling is, of course, one option to prevent the problem in the first place; another is making plastics biodegradeable, so that they either break down into other, harmless molecules, or into something small enough that bacteria might consider it food. But designing material that is able to maintain its strength and durability during everyday use while also breaking down when exposed to sunlight is a challenge, as is creating a material that breaks down in both landfills (airless, warm, dark, compressed) and stuck in a hedge or river (light, airy, varying temperature).

For this study, the researchers looked at two specific types of plastic - polyethelene, and polyethylene terephthalate, both of which are extremely ubiquitous as packaging material, especially for containers like plastic bottles - with five different additives (that supposedly improve biodegradeability) in three different environments: buried with oxygen (as in compost); buried without oxygen (as in a landfill); and simply bured in soil.

No matter the additive, and no matter the environment, they didn't find anything that appeared to have made the plastics decompose quicker than without. In a statement, the authors recommend "the proper management of waste plastics" instead - which means, for now, if you want to do the right thing by the environment, either use something known to degrade properly, recycle it before it gets into the ground, or (and possibly the easiest option in many situations) not using plastic at all in the first place.

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.

Photo: Getty Images
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What do Labour's lost voters make of the Labour leadership candidates?

What does Newsnight's focus group make of the Labour leadership candidates?

Tonight on Newsnight, an IpsosMori focus group of former Labour voters talks about the four Labour leadership candidates. What did they make of the four candidates?

On Andy Burnham:

“He’s the old guard, with Yvette Cooper”

“It’s the same message they were trying to portray right up to the election”​

“I thought that he acknowledged the fact that they didn’t say sorry during the time of the election, and how can you expect people to vote for you when you’re not actually acknowledging that you were part of the problem”​

“Strongish leader, and at least he’s acknowledging and saying let’s move on from here as opposed to wishy washy”

“I was surprised how long he’d been in politics if he was talking about Tony Blair years – he doesn’t look old enough”

On Jeremy Corbyn:

"“He’s the older guy with the grey hair who’s got all the policies straight out of the sixties and is a bit of a hippy as well is what he comes across as” 

“I agree with most of what he said, I must admit, but I don’t think as a country we can afford his principles”

“He was just going to be the opposite of Conservatives, but there might be policies on the Conservative side that, y’know, might be good policies”

“I’ve heard in the paper he’s the favourite to win the labour leadership. Well, if that was him, then I won’t be voting for Labour, put it that way”

“I think he’s a very good politician but he’s unelectable as a Prime Minister”

On Yvette Cooper

“She sounds quite positive doesn’t she – for families and their everyday issues”

“Bedroom tax, working tax credits, mainly mum things as well”

“We had Margaret Thatcher obviously years ago, and then I’ve always thought about it being a man, I wanted a man, thinking they were stronger…  she was very strong and decisive as well”

“She was very clear – more so than the other guy [Burnham]”

“I think she’s trying to play down her economics background to sort of distance herself from her husband… I think she’s dumbing herself down”

On Liz Kendall

“None of it came from the heart”

“She just sounds like someone’s told her to say something, it’s not coming from the heart, she needs passion”

“Rather than saying what she’s going to do, she’s attacking”

“She reminded me of a headteacher when she was standing there, and she was quite boring. She just didn’t seem to have any sort of personality, and you can’t imagine her being a leader of a party”

“With Liz Kendall and Andy Burnham there’s a lot of rhetoric but there doesn’t seem to be a lot of direction behind what they’re saying. There seems to be a lot of words but no action.”

And, finally, a piece of advice for all four candidates, should they win the leadership election:

“Get down on your hands and knees and start praying”

Stephen Bush is editor of the Staggers, the New Statesman’s political blog.