In recent years, “biodegradable” and “compostable” plastic bags have been heralded as a possible solution to the persistent global problem of plastic waste, but a new study found that these claims of sustainability don’t necessarily hold up.

When placed in different natural environments, various biodegradable and compostable bags failed to decompose over a three-year period, according to the study published in the journal Environmental Science and Technology.

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“Plastics are so common in our lifestyles and we've really gotten to this turning point where we’re trying to minimize it,” Imogen Napper, the lead author of the study, told Global Citizen.

“There’s lots of terms being thrown around, and I wanted to look at what these terms mean,” she added. “Will they degrade in an advantageous way?”

Napper and a team of researchers buried biodegradable plastic bags in soil, placed others in marine environments, and exposed another set to prolonged sunlight. They then monitored the bags over three years and found that the biodegradable bags failed to decompose in all cases.

In fact, the bags were even able to hold groceries after being subjected to these conditions.

My 3-year experiment is out today! This is a biodegradable plastic bag after 3-years in the marine environment, and it can hold a full bag of shopping. Biodegradable/compostable items do not necessarily break down quickly in natural environments like the ocean 🌊 pic.twitter.com/LDucC4NucJ

— Imogen Napper (@Imogennapper) April 29, 2019

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When exposed to sunlight, the bags fragmented into microplastics, an environmentally hazardous outcome, but did not decompose.

Napper said that the test conditions were meant to emulate what would happen to the bags in real-life situations — 95% of the more than 1 trillion plastic bags used annually get diverted into normal waste streams, where they aren’t recycled, and often end up contaminating environments.

Biodegradable bags are even harder to properly dispose of, she said, because of a general lack of support infrastructure. For these bags to actually biodegrade, they need to be collected and sent to dedicated facilities with the right combination of elements.

Napper said that these facilities are currently hard to come across, and most people who use these bags are not sending them to the right place. As a result, the bags are likely ending up in natural environments where they could be causing harm to wildlife.

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The researchers also studied “compostable” bags, which fared slightly better. These bags decomposed after three months when placed in marine environments, but researchers have to do further research to determine if the bags break down in a way that is safe for animals. If they’re merely breaking down into microplastics, for example, they would still pose a threat to marine life.

In both soil and sunlight, compostable bags similarly failed to decompose.

Ultimately, Napper said that the study highlighted areas for improvement.

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First, industry labeling standards need to be developed to more accurately describe plastic alternatives; current labels and product descriptions can be misleading.

Second, everyday people need to be better educated on how to properly dispose of these bags so they can biodegrade and compost as intended.

Finally, infrastructure needs to be set up to handle this waste or it will never be a viable alternative to conventional plastic.

“When you see anything that claims to be environmental advantageous, often they are, but keep asking questions and remain curious and think: Is this actually helping?” Napper said.

“Don’t think you need to change the world overnight, start small and proportionate to your lifestyle,” she added.