FactCheck: Tesco's degradable bags
Updated on 13 September 2007
Are Tesco's carrier bags really better for the environment? The FactCheck Green season continues.
The Background
They're a marvellously cheap and handy way to take home your shopping, and we use billions of them every year.
But shopping bags either end up in landfills - where they're wasted - or littering the countryside, where they linger for years, looking untidy and potentially harming wildlife.
So supermarkets and other retailers have been quick to adopt a supposedly green alternative - a 'degradable' bag which breaks down in the environment, instead of causing litter.
An impressive number of companies have started using degradable bags - Co-op, Tesco, Sainsbury's and many others.
As the Tesco website proudly claims, "An estimated 719 million degradable carrier bags have since been used by our customers, which means that the equivalent of 6,035 tonnes of non-degradable plastic has been offset."
Degradable plastics are even taking off beyond the world of carrier bags - other users, such as the makers of magazine cover bags and food packaging, are increasingly starting to use degradable plastics.
But are they really as green as their proponents say they are?
Green campaigners have always been against them. Friends of the Earth has said that they offer "offer virtually no environmental advantage over conventional plastic bags".
And there's a strong chance that greater use of degradable plastics could jeopardise efforts to recycle other plastics, too.
The analysis
First of all, it's worth clarifying exactly what 'degradable' means.
'Degradable' bags are made of similar plastic to normal carrier bags, but they contain a small amount of a mineral additive. This speeds up the chemical breakdown of the bag, reducing them to carbon dioxide and water in, as Tesco's website puts it, "as little as 60 days".
They're not the same as 'biodegradable bags', which rot down through the action of bacteria.
Green groups have criticised this strategy from a number of different points of view.
Ordinary people may confuse 'degradable' bags (which cannot be composted) with biodegradable bags, which can - potentially polluting their compost.
The 60 day figure has been disputed - in less than ideal conditions, plastic bags can persist in the environment for longer than sixty days.
This means that the main benefit of plastic bags - namely that they reduce the impact of plastic bags as a litter problem - is less great than proponents claim it is.
There are some other difficulties, too. In anaerobic conditions, such as inside a landfill they could break down into methane - which is a highly potent greenhouse gas.
Ordinary people may confuse 'degradable' bags (which cannot be composted) with biodegradable bags, which can - potentially polluting their compost.
And degradable bags could cause trouble with the recycling of other plastics.
Degradable bags aren't meant to be recycled, but they will inevitably end up being mixed in to the material that is sent to recyclers.
'All of our free carrier bags are degradable, which means that once in active landfill they will ultimately break down into CO2, water, minerals.'Tesco statement
If this happens, then the mineral additives will end up in whatever comes out the end of the process - causing that to break down faster, too.
The quantities of degradable bags are still quite small relative to the total volume of degradable waste. But if the trend towards using degradable plastics in other areas continues to gather pace, then they may start to cause problems for recyclers.
Andrew Green is the director of environmental affairs for BPI, Britain's largest recycler of plastic materials.
He told Factcheck: "Our concerns on degradable materials entering the waste stream is that they could break down once turned into new products.
This would be bad enough if large volumes of bin-liners degraded before they were used, but it is clearly an even bigger concern for our damp proof membranes and damp proof course products - which protect houses and buildings against moisture and gas vapours - and are intended to last!"
Tesco defended the use of degradable plastic bags, saying in a statement that: "All of our free carrier bags are degradable, which means that once in active landfill they will ultimately break down into CO2, water, minerals.
"It also means that if they are discarded they will rot down and not litter the environment."
The verdict
Degradable bags offer an attractive solution for retailers - they're a supposedly green alternative that doesn't cost them too much money to put in place, and doesn't require their customers to change their behaviour.
They do offer a partial solution to the biggest environmental impact of plastic bags, namely their contribution to the litter problem.
But they do have a number of downsides, which has brought a number of environmental groups to condemn them as the wrong solution.
Of course, the greenest thing to do is to use a reusable cotton bag, or a rucksack - or even a suitcase - but that's not as convenient as taking a disposable bag.
There are a number of other answers to the shopping bag problem - brown paper bags, or biodegradable plastic bags - but they also have problems associated with them.
But the degradable bag option offers relatively few benefits, and presents a number of difficulties which will get worse as they become more widely used.
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