'Biodegradable' Bags Can Still Carry Groceries After Three Years In The Ground, Study Finds

Three years after being in sea water, this bag could still hold some groceries. (Photo: Lloyd Russell, University of Plymouth)

I’m a cat owner, so cleaning up poop is a near daily occurrence. I buy special bags for my feline son, Mellow: the biodegradable type. If I’m going to dump his poop and pine litter into the trash, might as well use do so in something that decomposes, right?

Well, it turns out that those so-called biodegradable or compostable bags might not break down quite as easily as one would hope. A new study shows that many of these bags remain fully intact after three years of exposure to natural settings.

The research paper, published in Environmental Science and Technology Sunday, analyses five different type of plastic bags: a conventional plastic bag, two “oxo-biodegradable” bags, one biodegradable bag, and a compostable bag.

Each of these bags (outside the regular plastic one, which was used as a control) is supposed to degrade in the natural environment but only if it’s disposed of properly. For example, the oxo-biodegradable ones require oxygen, as the name entails. Others may need to head to an industrial composter.

The compostable bags were the only ones to see complete deterioration in the study—and that was only when exposed to water. The rest only fragmented a bit or stayed intact.

“Just because it’s labelled as biodegradable and compostable doesn’t mean it’s got an environmental advantage,” said author Imogen Napper, a research fellow at the University of Plymouth, to Earther.

The study authors from the University of Plymouth’s International Marine Litter Research Unit ran this experiment from July 2015 to August 2018. During those three years the samples were subjected to one of four environments: soil, air and sun, saltwater, and a dark box for control.

For soil, the scientists buried the samples in the university’s Skardon Garden, while they positioned the open-air samples along a garden in the wall. As for the marine samples, they sat in the Queen Anne’s Battery Marina not far from the university.

They used 16 samples of each bag cut into strips that measured about a half inch by an inch. This was to standardize the samples as the bags come in different shapes and sizes. However, the team also kept whole bags and exposed them to these environments, too.

By the end of the experiment, all the whole bags besides the compostable bag were able to carry nearly 2kg worth of groceries. So biodegradable? I don’t think so. The study wasn’t able to clarify how much the bags’ deterioration resulted in microplastics, but, well, most of the bags didn’t seem to break down enough for that to have been a concern.

The authors would like to study this topic over a longer period of time to find out how long it’d take to break these down, but this paper definitely sheds light on some of the greenwashing happening among these so-called “green” bag brands.

Still, they weren’t able to test every single brand and definitely not several of the specific types of bags. Napper is curious if other compostable bags would dissolve in a water environment.

The way Napper sees it, these bags would be better for the environment in more commercial settings where they can always be disposed of they way they are meant to. For instance, at a sports stadium where they’re all collected after use.

If you’re like me and prefer biodegradable bags to old fashioned plastic, this study is a bit of a rude awakening. Most bags, no matter what their marketing claims, won’t vanish over night. The key might be to use less of them entirely.  

Trending Stories Right Now