Are biodegradable bags better than plastic? It’s complicated.

Pedro_P

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Misleading labels and life cycle studies make for a messy story.

What's better: plastic bags or "biodegradable" ones?
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▼ In college, I drove a little electric truck around campus and picked up bins of fruit and vegetable waste, plant clippings, and coffee grounds, and hauled them to a 50-foot long, 5-foot-tall compost pile at the student farm. Although we asked that our pick-up sites didn’t put any post-consumer waste in the bins, “compostable” plates, cups, and bags inevitably found their way to our pile. And when they did, I’d pull them out and throw them in the trash.
That’s the problem with labels like “biodegradable” or “compostable.” These products—typically made from plant sources, often corn—biodegrade eventually, meaning that microbes and other organisms break the materials down into soil. But the environment the products are disposed in matters. As the banana peels and straw morphed into crumbly compost, the “compostable” bags and “biodegradable” cups hung around, full intact. They would have decayed if they were sent to a large-scale, industrial recycler, where workers manage the conditions and chemistry of materials, ensuring the frenzied action of millions of microbes capable of breaking down these tough materials. But here? Not for years, if at all.
On Sunday, scientists at the University of Plymouth published a  studyhighlighting the problem of confusing labelling. The researchers tested the degradability of several bioplastic bags—with labels like biodegradable and compostable—and conventional high-density polyethylene (read: plastic) bags in soil, outdoor air, and marine water. After three years in water and soil, all but the compostable bag were still able to tote a load of groceries. It was still around after 27 months underground, but easily tore apart.
“In day-to-day living, [these labels are] misleading,” says Imogen Napper, lead author and marine scientist. While the products are intended for an industrial composter, that’s not where most of them are going. Napper argues consumers are misled by the labels into thinking that the products do readily decay in natural environments like the ones she tested, when the reality is that the timeline from product to soil can be many years. “When it says biodegradable or compostable, what’s the time frame that you think of for a product in the natural environment?” she says. “For me, it would be days to months. As soon as you start to say two years to three years, does that have any meaningful advantage to the environment? I'd argue not.”
Headlines about the study have echoed that sentiment, such as Vice’s “ Biodegradable Plastic Bags  Aren’t Better For The Environment.” Most of the reports focused on the fact that the biodegradable bags could still carry groceries after three years underground. But, as alarming as that finding is, the reality is a bit more complex.
It starts with the difference between labels. In theory, “biodegradable” and “compostable” should mean the same thing (▪ ▪ ▪)

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