At a Glance

Researchers tested biodegradable, oxo-biodegradable and compostable plastic bags.The bags were left out in the open, buried and submersed in sea water.Three years later, the biodegradable bags could still carry five pounds of groceries.

After being exposed to the elements for three years, plastic bags labeled biodegradable are still able to carry about five pounds of groceries, a study has found.

Researchers from the University of Plymouth tested biodegradable, oxo-biodegradable, compostable and conventional plastic bags in three environments: open air, buried in soil and submersed in seawater, according to the study published Sunday in the journal. The bags were widely available from retailers in Great Britain.

The biodegradable, oxo-biodegradable and conventional plastic bags were still capable of carrying a box of cereal, pasta, crackers, cans of Coke, bananas and oranges after being in the soil or the marine environment for more than three years, the study found.

“After three years, I was really amazed that any of the bags could still hold a load of shopping. For biodegradable bags to be able to do that was the most surprising," said Imogen Napper, who led the study as part of her doctoral program at Plymouth. "When you see something labelled in that way, I think you automatically assume it will degrade more quickly than conventional bags. But, after three years at least, our research shows that might not be the case.”

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The compostable bag in the marine environment did completely disappear within three months. The compostable bag in the soil also showed some signs of deterioration but was , according to a news release about the study.

All the bags in the open air disintegrated into fragments or were too brittle to be tested after nine months of exposure. More work is needed to understand what researchers told The Guardian.

The study said none of the bags could be relied upon to show any substantial deterioration over a three-year period in all of the environments, and therefore, it's not clear if oxo-biodegradable or biodegradable bags are any better for the marine environment than regular plastic bags.

Professor Richard Thompson, head of the university's International Marine Litter Research Unit, said, “This research raises a number of questions about what the public might expect when they see something labelled as biodegradable. We demonstrate here that the materials tested did not present any consistent, reliable and relevant advantage in the context of marine litter. It concerns me that these novel materials also present challenges in recycling. Our study emphasizes the need for standards relating to degradable materials, clearly outlining the appropriate disposal pathway and rates of degradation that can be expected."

The European Union is estimated to use about 100 billion bags every year. In 2018, the , National Geographic reports. The United Nations has said biodegradable plastics are not the solution to marine plastic pollution.

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A spokesperson for the manufacturer of the compostable bags used in the study, Vegware, told The Guardian the bags can only be recycled in the proper facility.

“It’s important to understand the differences between terms like compostable, biodegradable and (oxo)-degradable,” the spokesperson said. “Discarding a product in the environment is still littering, compostable or otherwise. Burying isn’t composting. Compostable materials can compost with five key conditions – microbes, oxygen, moisture, warmth and time.”

Symphony, which produces oxo-biodegradable bags, told National Geographic the bags are not intended to degrade in landfills or beneath the ocean surface.

Michael Stephen, Symphony's deputy chairman, told the magazine that oxo-biodegradable bags are "intended to degrade if they become litter on the open landscape or ocean surface.

Thompson said instead of being an indictment of biodegradables or compostables, the study shows we should rethink which products work best as biodegradables.

Napper, who led the study, said it should "teach people like you and me to have a look at the label and think 'Is this doing what it says it will do? Is it actually biodegradable? Is it compostable?' "