Degradable plastics often do not decompose

Much of the biodegradable plastic labeled as “home compostable” does not fully decompose in compost. For this reason, plastic residues end up in the soil with the compost, reports scientists from University College London after a study with thousands of consumers in Great Britain. The study, published in the journal Frontiers in Sustainability, further shows that many products are inadequately and misleadingly labelled, leading to incorrect disposal of biodegradable plastics.

Global plastic pollution is one of the greatest environmental challenges of our time. According to an OECD report, only 9 percent of the plastic produced worldwide is recycled. Half of it ends up in landfills, 19 percent is incinerated and 22 percent escapes any form of waste disposal - it ends up in nature or on uncontrolled dumps.

In response to the plastic waste crisis, many countries are scrambling to ban unnecessary single-use plastic or make plastic packaging recyclable, reusable, or compostable. According to the researchers, the proportion of bioplastics in the total plastic produced is currently around one percent.

Compostable plastics are materials that can be biodegraded in a composting facility as quickly as other known compostable materials, leaving no visible or toxic residue. One of the theoretical benefits of developing compostable plastics is that some products are too small or too dirty to be recycled or reused with traditional plastic waste.

In addition to the biodegradable plastics, which can only be composted industrially in special plants, there are those that, according to the manufacturer, also decompose in domestic compost. In order to check to what extent this is actually possible, the research team led by Danielle Purkiss developed a comprehensive citizen science project: the large compost experiment. Over a period of two years, the scientists collected data from citizens on the disposal of degradable plastics.

In an online survey, around 9,700 participants gave their opinion and behavior on the subject of "compostable plastics". 85 percent of the participants said that they would rather buy products whose packaging is labeled as "compostable" or "biodegradable". In addition, 84 percent stated that they compost waste at home. According to the researchers, this motivation for home composting is well above the average of 34 percent of the British population.

In the next step of the project, 1,648 of the participants agreed to compost compostable plastic waste at home. Using photos, the scientists found that many participants had problems labeling and identifying the plastic waste. A sample of 50 images showed: 46 percent of the plastics were not labeled as "home compostable" and another 14 percent were labeled as "industrial compostable". "This shows that there is currently a lack of clear labeling to ensure the public can properly dispose of compostable plastics§, lead author Danielle Purkiss is quoted as saying in a press release from her university.

But an even more startling finding is that 60 percent of the plastics labeled “home compostable” didn’t fully decompose in home compost bins. "Apparently compostable packaging - even those certified 'home compostable' - cannot properly degrade under home composting conditions in the UK," Purkiss is quoted as saying. "As a result, the plastic gets into the soil and contaminates it."

According to the scientists, uncontrolled home composting is proving to be inefficient. In their view, it would be better to send compostable plastics to industrial waste plants, where composting takes place under controlled, biotechnological conditions.

Many experts fundamentally doubt that biodegradable plastics have any significant use. The Federal Environment Agency (UBA), for example, writes that biodegradable packaging has no advantages compared to packaging made of conventional or bio-based plastics. More useful is the multiple use or recycling of stable and durable material. Even biodegradable single-use products would not bring any advantages: "Single-use products are short-lived and - in contrast to reusable products - generate unnecessary waste, regardless of whether they are biodegradable or not."

According to the UBA, such products may not be disposed of in the organic waste bin, but belong in the yellow bin. Collection bags for organic waste that are marked as biodegradable are only allowed to be disposed of with the appropriate certification and only if the local waste disposal company has given their approval.

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