If you chuck biodegradable packaging in your food waste bin, or in with your garden compost, it might not end up where you expect it to, according to a scientist. 

Professor Mark Miodownik, a materials scientist at UCL, said items such as disposable cutlery, coffee cups, and wet wipes could take years to biodegrade – and even have the unintended consequence of contaminating your waste.

“The public really need to know that when something says it’s ‘compostable’, it is not going to disappear as soon as you drop it and it may not actually be good for the environment,” he said, speaking at the Cheltenham Science Festival. 

“Even on a home compost heap, these products may not biodegrade for years because the conditions are not right.”

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Professor Miodownik added that these products may even lead to an increase in littering as people leave them in grass or hedges – thinking they will simply biodegrade.

“Many people put them in the bin, where they do not look any different to regular plastic so are not separated out and end up burned or in landfill,” he said. “Or they put them in with the food waste, which is actually worse, because it is not dealt with in the same way and can contaminate the process.”

At the moment most biodegradable or compostable products end up in landfill where they will not biodegrade, he said, which “raises the question of what the point is”. 

How can we avoid the problem? “People should really be staying away from single-use materials,” he said. 

In April, a study by scientists from the University of Plymouth found biodegradable and compostable bags were intact enough to carry shopping three years after being exposed to air, soil and sea – the same conditions they would encounter if left as litter.

When exposed to air, they all disintegrated into fragments but did not completely disappear. The compostable bag was found to break down in sea conditions within three months – however it was found still present in soil after 27 months, the researchers said.