Biodegradable plastic bags could still carry a full load of groceries after being buried in soil for three years, a new study has found.
University of Plymouth researchers in the UK tested five different types of commonly used plastic bags to see how well they broke down. They discovered that brands labelled “biodegradable” and “compostable” didn’t break down quickly—in soil and even the seas, they remained intact, just like regular plastic.
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While compostable bags stayed in one piece after being buried in soil, they couldn’t hold a significant amount of weight without tearing. They were also noticeably better in a marine environment, where they disintegrated into confetti-like plastic fragments after three months. However, lead researcher Imogen Napper told VICE this is a problem too because it can contribute to the creation of a “plastic soup” in the ocean, which can easily be ingested by marine animals.
Conventional plastic bags showed very little change in their physical or chemical structure in both water and soil over the 27 months of testing. In fact, the study corroborates what previous research has suggested—that saltwater slows down the decomposition of plastic.
The report states that none of the bags showed “a substantial deterioration” in all three of the scenarios—open-air, marine and soil.
“Our studies show that biodegradable and compostable really offer no meaningful advantage to the environment at the moment,” said Napper.
“Biodegradable” means something that can be broken down by living organisms, usually bacteria. “Compostable,” on the other hand, refers to things that break down with the help of existing processes, such as a municipal green bin program.
All the bags put to the test deteriorated after nine months outside, exposed to oxygen and sunlight.
Napper says there’s value in figuring out whether the current manufacturers’ definitions of “biodegradable” and “compostable” make sense based on consumer behaviour and expectations.
According to Brandon Gilroyed, an associate professor at the University of Guelph’s School of Environmental Sciences, the bar for being able to use these designations is pretty low. A product can be marketed as “biodegradable” as long as it breaks down over some unspecified period of time. “Compostable” means that under perfectly engineered industrial composting conditions, where products are subjected to several days of high heat, materials will break down.
“There’s a disconnect between the definition that manufacturers have to meet to [label] that product, how it’s marketed, and what the consumer expects from that product based on how those terms are used in pop culture,” he told VICE.
Gilroyed says there’s a level of public education that’s missing; most consumers don’t know that these products break down under very narrow circumstances.
He says the danger is that these labels can encourage people to be complacent, while making them feel like they’re doing something good for the environment. “People think it’s OK just to throw it away, because it’s biodegradable, and they don’t feel bad about it.”
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