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Scientists find “biodegradable” bags perfectly usable after three years in dirt

Uh oh.

Scientists find “biodegradable” bags perfectly usable after three years in dirt
[Photo: Lloyd Russell/University of Plymouth]

Roughly 50% of all plastics are discarded after a single use. And in the U.K., 100 billion new plastic bags are distributed every year. Given that plastic takes 1,000 years to decompose, it’s no wonder that we’re trying to escape an ocean of our own waste and why many retailers in the U.K. have started distributing compostable and biodegradable bags. Perhaps we can’t fix single-serve consumerism, but we can make these products disappear from the earth after being used–at least in theory.

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Unfortunately, new research from the University of Plymouth found that after three years in the dirt or water, so-called “biodegradable” bags were still in relatively good shape. Many were still perfectly functional bags that had lost little of their material or tensile strength, still able to carry five pounds of groceries. And even “compostable” samples didn’t always disappear without a trace. While more research is needed, the scientists concluded that biodegradable bags may not disappear from the environment much, if any, faster than traditional plastic ones.

Research Fellow Imogen Napper with one of the plastic bags tested as part of the study. [Photo: Lloyd Russell/University of Plymouth]

The study began over three years ago, as the researchers collected samples of bags from retailers around the U.K. They included a compostable bag, a traditional biodegradable bag, and two separate formulations of oxo-biodegradable bags (these are biodegradable bags made in such a way that they claim not to require microorganisms to break them down–meaning they should biodegrade predictably in any environment.)

The researchers put each of the bags into four situations simultaneously: one went into a black box in the lab (for a control), another was buried in a garden, a third was placed on a wall under the sun, and a fourth submerged in the Atlantic ocean. Every three months, they checked in on the bags to see what remained.

[Photo: Lloyd Russell/University of Plymouth]

Only one bag disappeared entirely in a single case: The compostable bag was 100% broken down after just 3 months in the water. Aside from that, “fragments or whole samples of each bag material type were present in all environments after 27 months, and some of the whole bag samples were still functional as plastic bags after 3 years in the natural environment,” the study’s authors write.

In open air, all the bags became brittle and lost their shape within 9 to 18 months. This condition was generally considered the most successful, which scientists attributed to the powerful UV rays put out by our sun breaking down the material. In soil, the bags lost their tensile strength over a three year period–anywhere from one quarter to two thirds of their weight capacity–but the bags themselves were still relatively intact. And in water, the biodegradable bags held up particularly well. That may sound surprising; wouldn’t water just dissolve them away? In fact, plastics have been found to be quite resilient in sea water, likely because microorganisms coat and protect the waste from damage.

The conclusions of the paper are particularly damning to biodegradable and compostable goods–goods the scientists point out could use more rigorous standardization and oversight. “It was not clear that materials which claimed to have enhanced degradation consistently deteriorated faster than conventional polyethylene,” the researchers write, meaning that biodegradable bags could be every bit as bad for the environment as plain old plastic ones. Ultimately, the researchers state that “Perhaps durability in the form of a bag that can and is reused many times presents a better alternative to degradability.”

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In other words, if you do end up grabbing a biodegradable bag at the supermarket, the best thing you can do for now is to use it again and again–and make sure it really is trash before you toss it out.

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About the author

Mark Wilson is a senior writer at Fast Company who has written about design, technology, and culture for almost 15 years. His work has appeared at Gizmodo, Kotaku, PopMech, PopSci, Esquire, American Photo and Lucky Peach

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