Study shows majority of “home compostable” plastics don’t fully degrade

If you’ve ever been turning over your compost heap and found months-old “compostable” plastic items that were still mostly intact – well, you’re not alone. New research states that 60% of such plastics don’t fully biodegrade in home composting systems.

The findings are the result of a study undertaken by scientists from University College London, which began with ordinary citizens from across the UK completing an online questionnaire regarding their habits and opinions relating to compostable plastic and food waste.

Participants were then invited to take part in the Big Compost Experiment, which involved regularly checking their home compost for traces of previously discarded compostable plastic items, over a 24-month period. Those objects were placed in non-biodegradable open-mesh bags when initially put in the compost, so they’d be easier to find when later digging through it with a spade or trowel. Photos and descriptions of the unearthed items were submitted to the scientists.

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While a variety of different composting systems were used, the most common was an outdoor closed-bin setup, utilized by 64% of the 1,648 people who participated in the experiment. The supposedly compostable plastic items included things like disposable cutlery, cups, bags and newspaper wraps.

When the submitted data was analyzed, it was found that approximately 60% of items that were marked by manufacturers as being “home compostable” still hadn’t completely broken down after 24 months.

Additionally, based on a random sample of 50 item photos, it was noted that 46% of the items were not marked as being home compostable, while another 14% were marked as being specifically industrial compostable. Needless to say, this suggests that there is definitely some confusion – on the part of consumers – regarding which items can actually be tossed in the home compost heap.

Importantly, 83% of the participants stated that they use their compost as fertilizer in their gardens. This means that the un-composted plastic would make its way into the soil, and thus into the environment.

“We have shown that home composting, being uncontrolled, is largely ineffective and is not a good method of disposal for compostable packaging,” said Danielle Purkiss, corresponding author of the study. “The idea that a material can be sustainable is a widespread misconception. Only a system of production, collection, and reprocessing of a material can be sustainable.”

More details on the study are available in an open-access paper that was recently published in the journal Frontiers in Sustainability.

Sources: Frontiers, Big Compost Experiment


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