Most ‘compostable plastics’ in the UK end up in the soil without degrading

The researchers at University College London (UCL) also said that citizens are confused about the labels of compostable and biodegradable plastics, leading to incorrect plastic waste disposal.

A recent OECD report showed that plastic consumption has quadrupled over the past 30 years and yet only 9 per cent of plastic waste is recycled globally. Some 50 per cent ends up in landfills, 22 per cent evades waste management systems, and 19 per cent is incinerated.

In response to this pollution crisis, several countries have set targets to eliminate all single-use plastics and to make plastic packaging 100 per cent recyclable, reusable, or compostable by 2025.

Compostable plastics are becoming more common as the demand for sustainable products grows. The main applications of compostable plastics include food packaging, bags, cups and plates, cutlery, and bio-waste bags. But there are some fundamental problems with these types of plastics and they are largely unregulated, with exaggerated claims around their environmental benefits.

‘Compostable plastic’ describes a material that can undergo biological degradation in a compost site at a rate consistent with other known compostable materials, leaving no visible (toxic) residues.

However, compostable plastics are currently incompatible with most waste management systems and so they often end up either incinerated or put into landfill.

“The typical fate of landfill or incineration is not usually communicated to customers so the environmental claims made for compostable packaging can be misleading,” said corresponding author Danielle Purkiss.

The researchers designed The Big Compost Experiment to investigate what the public thinks about home compostable plastics, how we deal with them, and whether they fully disintegrate in our compost.

Participants from across the UK completed an online survey about opinions and behaviour surrounding compostable plastics and food waste before being invited to take part in a home composting experiment.

Those who joined in the home composting part were sent a request to search for traces of their chosen compostable plastic items in their composter.

The results show a general willingness to make sustainable choices by buying compostable plastics. However, participants showed confusion about the labelling and identification of these plastics.

Out of a randomised sample of 50 item images, the researchers found that 46 per cent showed no identifiable home composting certification or standards labelling and 14 per cent showed industrial composting certification.

“This shows that there is a current lack of clear labelling and communication to ensure that the public can identify what is industrially compostable or home compostable packaging, and how to dispose of it correctly,” said Purkiss.

But 60 per cent of the plastic certified as home compostable did not fully disintegrate in home compost bins.

“Compostable packaging does not break down effectively in the range of UK home composting conditions, creating plastic pollution,” Purkiss added. “Even packaging that has been certified as home compostable is not breaking down effectively.”

The experiment also showed that compost bins are important sites for biodiversity, with pictures sent in by the participants showing 14 different categories of organisms such as fungi, mites, and worms.