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

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

Garbage dump biodegradable compostable bag
What's better: plastic bags or "biodegradable" ones?Deposit Photos

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 study highlighting 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—that organisms in the soil can break down a product. But the truth is that “biodegradable” gives you the same amount of information as the label “natural” on a food item does, says Kate Bailey, policy and research director at Eco-Cycle, a nonprofit recycling organization. Biodegradable simply means that at some unspecified time in the future—months, years, decades, who knows!—the product will break down.

To continue the food analogy, the term “compostable” is more like “organic,” in that regulators are trying to ensure it meets certain standards, though what exactly those standards are is still a work-in-progress. When a product carries the label of “certified compostable,” that means when you send it to an industrial facility, it becomes compost in about the same amount of time as other things in the pile like food waste and yard clippings—usually between 90 and 180 days. There are a few third-party verifications of this, including one by the ASTM International, an organization that develops standards for thousands of products and services. “We are definitely seeing some movement toward ‘this [label] needs to mean something,’ and it can’t just be getting thrown out there and confusing consumers,” says Bailey.

But biodegradable remains a stress-inducing word for composters, Bailey adds. “There’s a lot of concern about the labelling,” she adds. “Composters want it to be certified compostable—biodegradable doesn’t work for them.” Really, biodegradable is just another greenwashed phrase, one companies use to make us feel good about a pricey purchase, even though its environmental benefit isn’t actually clear.

Some agencies are taking action. The Federal Trade Commision in its most recent "Green Guides" says that "degradable claims" need to backed up by "competent and reliable scientific evidence that the entire item will completely... decompose into elements found in nature within a reasonably short period of time after customary disposal." California is also cracking down on decomposition deception. The state has banned sales of products marketed as "biodegradable", "compostable," etc. unless they have evidence to prove it. The Golden State has a $1.5 million settlement coming its way after district attorneys sued Amazon for selling products with misleading labels, including "biodegradable."

By now, you might be questioning the little green bags you use to line the compost bin on your kitchen counter or the eco-friendly foodware at your office, wondering if it’s all a waste of money. If your city does partner with a composter, like San Francisco, Seattle, and Portland do, great! There’s a dedicated place where these products can go to become soil. Just double check the label. “Look for the certified compostable label,” says Bailey.

But what if you’re among the roughly 95 percent of households that don’t have such a service available? Even if a product is “certified compostable,” it might not be preferable to plastic. Right now, a lot of compostable bags, cups, and foodware are made from corn, and that process has all sorts of environmental impacts, from the pesticides that leach into rivers to the greenhouse gases emitted from plants manufacturing the products. “There’s a lot of hope that we can make compostable plastic out of things like mushrooms, algae, or hemp—things that could be much more beneficial than plastic,” says Bailey, “But right now … with most things coming from corn, it’s not clear that there really is much of a benefit [compared to plastic].”

Research from the Oregon Department of Environment Quality underscores this point. Scientists reviewed previous life cycle assessments of different "packing attributes"—labels like "recycled content," "biobased," and our friend "compostable." Each study analyzed the product's environmental impacts across its "life," from manufacture to disposal. The analysis concluded that compostable products aren't an easy answer to plastics. "Many compostable packages are made of biobased materials and inherit the significant environmental burdens from their production," the authors wrote. "These burdens are often much greater that the offset benefits that composting provides."

Much of the environment impacts of these greenwashed products arise from their production. As a factsheet for the study states, “39 percent of our domestic greenhouse gas emissions take place before a product even reaches a consumer, and only 2 percent of GHG emissions occurs from disposal (landfill, compost and incineration).”

Still, these life cycle assessments largely ignore what happens when an item doesn't stick to its ideal disposal route, whether that's a landfill, recycler, or compost pile. But plenty of plastic veers off course each year. In 2010, one study found that 4.8 to 12.7 million metric tons of plastic debris wound up in the ocean. And plastic in the environment doesn't decompose—it just breaks into smaller and smaller pieces with the same chemical structure. These microplastics are a problem because they're near-impossible to clean up and are eaten by marine life, even ending up in the fish we eat—and, as a result, inside our own bodies.

Compostable products could have an edge when it comes to curbing this ocean plastic disaster. In the study from University of Plymouth, compostable bags dissolved in marine water within three months. So, while they might not be beneficial from a life cycle perspective, they’re perhaps less harmful to marine organisms.

While there are many ways to weigh the impacts of conventional plastic versus biodegradable alternatives, there is one clear route to win on all environmental fronts. It’s the one you’ve heard before: cut back on plastic, especially single-use items, and you’ll create less litter and use fewer resources. But for those situations when you can’t avoid disposable bags, cups, or plates, “more clear labelling standards [for compostable products] are a great first step,” says Bailey.