60% of UK compostable plastics do not fully disintegrate

A University College London study suggests that 60% of home-compostable plastics do not fully break down in compost bins at home, eventually ending up in our soil.

In addition to unearthing that an alarming number of compostable plastics do not disintegrate, the researchers discovered that people are often confused about the labels of compostable and biodegradable plastics, which results in plastic waste being disposed of incorrectly. The findings suggest that the sustainable plastic waste management system needs to be refined.

The study, ‘The Big Compost Experiment: Using citizen science to assess the impact and effectiveness of biodegradable and compostable plastics in UK home composting,’  is published in Frontiers in Sustainability.

Current efforts to combat plastic pollution

Plastic pollution is one of the most significant environmental threats globally, with a recent OECD report revealing that plastic consumption has quadrupled in the last three decades, with only 9% of plastic waste recycled worldwide, 50% ending up in landfills, 22% evading waste management systems, and 19% being incinerated. To tackle plastic pollution, various countries have introduced targets to eliminate all single-use plastics and make plastic packaging 100% recyclable, reusable, or compostable by 2025.

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What is compostable plastic?

Compostable plastics comprise materials that can biologically biodegrade in a compost site at a rate consistent with other known compostable materials, leaving behind no visible, toxic residues. They are becoming increasingly prevalent as the demand for sustainable products grows

Primary uses for composite materials include food packaging, bags, cups, plates, cutlery, and biowaste bags. However, issues persist with these materials as they are largely unregulated, and their environmental benefits are often exaggerated.

Moreover, compostable plastics are currently incompatible with most waste management systems, with there being no harmonised international standard for home compostable plastics, meaning they often end up incinerated or landfilled.

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

The UK plastic waste landscape

The researchers performed a three-part citizen-science study called The Big Compost Experiment to analyse plastic waste in the UK. Participants throughout the country completed an online survey of opinions and behaviour surrounding compostable plastics and food waste. They were then invited to participate in a home composting experiment. Finally, those who took part in the two stages were sent a request to search for traces of their chosen compostable plastics in their composter, with the team collecting the data over two years.

Purkiss explained: “Our study was created in response to feedback from the public and stakeholders from industry, policy, and third-sector organisations, which highlighted many systemic issues in the manufacturing, use, and disposal of compostable plastic packaging.”

Although the findings highlighted a general willingness to make sustainable choices by buying compostable plastics, participants were often confused about the labelling and identification of these plastics. In a randomised sample of 50 items, 46% displayed no identifiable home composting certification or standards labelling, with only 14% showing industrial composting certification. Shockingly, 60% of plastics certified as home compostable did not fully disintegrate in home compost bins.

“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.

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

The team explained that the best solution is to send compostable plastics to industrial composting facilities where conditions are regulated.

“We have shown that home composting, being uncontrolled, is largely ineffective and is not a good method of disposal for compostable packaging,” concluded Purkiss.

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