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UK study says compostable plastic is not yet an environmentally viable option

While industrial composting is an effective way of reducing waste in landfills, researchers say compostable plastic is not yet adapted for home composters as marketed.

(CN) — In a world where roadside litter and ocean pollution is the norm, the idea of compostable and biodegradable plastics seems like a win-win solution for consumers and the environment. However, a recent study from the United Kingdom indicates that compostable plastics may not be the game changer it's thought to be, especially for home composters.

The study published in Frontiers in Sustainability on Wednesday documents a citizen science experiment, The Big Compost Experiment, where researchers instructed 1,648 citizens in the UK to test the performance of compostable plastics at home — plastics that could replace single-use plastics by 2025.

Yet, what the study found was that not only are consumers confused about which plastics are compostable, but that when participants composted the correct materials, even those items did not fully decompose.

“Despite our best efforts to guide the participants only to compost items marked clearly as ‘home compostable,’ many items that are marked as industrially compostable or just as biodegradable have been entered into the experiment,” wrote lead researcher Danielle Purkiss of University College London.

Out of a random sample of 50, Purkiss’ team found 46% of plastic items showed no identifiable certification or standards labelling.

“Our evidence reported in this paper shows that citizens don’t understand these complexities of compostable or biodegradable packaging and yet are enthusiastic about buying them,” Purkiss wrote, noting that 85% of participants reported as much.

Purkiss added that citizens are also confused about what the labels on compostable and biodegradable packages mean, citing that 60% of samples items tested in home composting experiments were not certified home compostable.

Of the 1,307 results submitted to the study, 55% of composted plastics were still clearly visible after the experiment, while another 11% of results indicated there were small pieces left behind. Only 34% of plastics submitted fully decomposed within participant home composting timeframes. Even worse, 61% of certified packaging did not decompose at all.

“This is not a labelling problem but one of materials science,” Purkiss wrote, explaining how the current composition of compositable plastics in the market do not reliably break down in the wide range of at-home compost bins.

The problem also extends to the current standards of composting certifications in the UK, the study reveals, where many products are labeled for industrial composting, yet there remains a lack of facilities to compost these items.

“Although the processing of compostable and biodegradable plastics is regulated under industrial organic waste management processes, the existence of systems of collection and industrial composting for this packaging are rare in the UK,” Purkiss wrote.

Additionally, Purkiss points out that since compostable and biodegradable plastics are currently incompatible with most recycling and industrial compost systems, the majority of these products are sent to the landfill or incinerators anyway.

“The typical fate of landfill or incineration is not usually communicated to customers, so the environmental claims made for compostable and biodegradable packing can be misleading,” wrote Purkiss.

All in all, the study led Purkiss’ team to conclude that compostable plastics are not the environmentally-friendly waste processing method it’s thought to be — or at least in the UK.

“The idea that a material can be sustainable is a widespread misconception,” Purkiss wrote. “Only a system of production, collection and reprocessing of a material can be sustainable. The type and amount of energy used to the fuel the process, the water usage and the by-products also contribute to its environmental footprint. This applies to compostable plastics as much as to normal plastics.”

Purkiss added: “Although the bio-sources of compostable plastics make this class of material more renewable, the fact there is no UK-wide system of collection is problematic. Most compostable plastics end up in landfill or are burnt. Neither is a good environmental outcome.”

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