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Sorry, Compostable Plastic Isn’t Really Compostable (Or Recyclable). Here’s Why

Compostable plastic may seem a promising solution to waste management. But the reality is a bit more complicated.
Green plant grows among plastic garbage. Bottles and bags on blue background. Concept of environmental protection and waste sorting.

Every year, Canadians throw out over 3 million tonnes of plastic waste—only 9 percent of which is actually recycled. The majority ends up in landfills or natural environments, causing pollution and impacting the health of ecosystems.

Enter compostable plastic—a relatively new innovation that’s gaining widespread attention and use. The rise of compostable plastic seems, in theory, to be a promising solution to the global plastic problem. (If current plastic trends continue, by 2050 it’s estimated that ocean plastic pollution could reach a 1:1 weight ratio with fish). But will this promising solution actually pan out in practice?

To get the scoop, we spoke with two experts—Belinda Li, an environmental engineer and the Director of Innovation with the Food Systems Lab at Simon Fraser University, and Karen Storry, a senior engineer with Metro Vancouver—about whether compostable plastics truly are a greener option.

What are compostable plastics?

Compostable plastics are plastic items—cups, utensils, bags, takeout containers—that will break down, or compost, under specific conditions. "Products labelled compostable are very specific in terms of how they can break down safely—and they vary in terms of the specific conditions needed for them to break down completely, including pH, moisture levels, temperature and microbial activity," Storry says.

The use of the word “compostable” can be confusing because it sounds as though the material will simply decompose quickly on its own wherever you discard it, but that’s not the case. “A good example is a compostable bag,” Li says. “If you just throw it into the forest, it’s going to stay a compostable bag for a really long time. Whereas in a composting facility [under], it will break down.”

The most common type of compostable plastic is known as polylactic acid, or PLA, which is made of starches derived from sources like corn or sugarcane. “[Compostable] can be made from any kind of carbohydrate, as long as it has the basic building blocks to [create] plastic resin,” Storry says.

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To ensure durability—so that a takeout container filled with food doesn’t literally decompose as you’re eating out of it—compostable plastics are not made from plant sources alone. “There are synthetic compounds that need to be added to it so that you can turn it into plastic,” Li says. “So to make it durable enough, you sacrifice a little bit of it being able to break down.”

Are compostable plastics the same thing as biodegradable plastics?

Compostable plastics are often referred to interchangeably as “biodegradable plastics,” but these two terms have different technical meanings. While compostable plastics have set conditions for breaking down, biodegradable plastics do not.

“Biodegradable means it will break down under certain conditions, but it’s not specific about what the conditions are and it’s not specific about how long it will take—there’s no timeline attached to it. In my thinking, they’re no different than regular plastics other than that they have additives that make them break down faster,” Storry says.

To make matters more confusing, some plastics can also be considered “bio-based,” but this does not mean that the plastic is necessarily compostable or biodegradable. “A lot of companies might advertise that their plastics are made out of plants, but you can actually make plastics out of plants that are not biodegradable or compostable—in fact, they act more like regular plastics,” Li says.

Can compostable plastic go in a backyard or municipal compost?

Unless compostable plastic is labelled specifically as “home compostable,” it cannot go in a traditional backyard compost, because backyard composts do not meet the specific conditions required for the plastic to break down (such as the minimum temperature or moisture levels, which can vary by manufacturer). “There are some plastics that have been developed to be composted in smaller facilities, like a backyard, but those are less commercialized right now. The dominant [compostable] would only break down in an industrial facility,” Li says.

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But here’s the catch: the specific—and often narrow—conditions required for most compostable plastics to break down simply do not match with current infrastructure at most industrial composting facilities. As a result, most industrial composting facilities across Canada do not accept compostable plastics because they can’t process them, meaning you cannot compost these items through your municipal composting program.

One of the reasons for this is that there is a lack of across-the-board standards. “In Canada, there is no regulation that states how you can market these products,” Li says. “[Compost] processors almost need a guarantee that this plastic is actually compostable, and is not going to shatter into small pieces and stay in the compost, because then they can’t sell it.”

Some hope may be on the horizon. In July of 2022, the Government of Canada released a consultation paper towards creating nation-wide labelling regulations that will help improve the composting and recycling of plastic products. Storry says she’s hopeful that more accurate labelling will result in improvement, but for the time being, it’s best not to put these items in your municipal compost bin.

“Right now there's a big gap between how they test [compostable] and the realities of what happens at composting facilities. So at Metro Vancouver, we say no plastics in the green bin no matter how they’re labelled,” Storry says, noting that if these items do end up in a municipal compost bin, they are merely screened out at the compost facility and then discarded.

But a few businesses have found successful methods of composting their compostable plastic. In 2019, the National Arts Centre in Ottawa partnered with a waste processor facility called Tomlinson Group to source certified compostable plastic that could break down in the specific conditions of Tomlinson's facilities. So, while we may be far from composting plastic at a municipal level, the NAC's success is a good sign of what can be achieved.

Can compostable plastic be recycled?

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Recycling programs across Canada vary, but in most curbside recycling programs, compostable plastic cannot be recycled. “[Putting] would be considered contamination—it would be considered the same as a piece of food,” Li says. “Because chemically it’s not the same thing.”

When placed side-by-side, a compostable plastic cup and a regular plastic cup may look identical, which is why it’s important to check any labelling before tossing anything into your recycling bin. “I can’t tell the difference unless I see the labelling,” Storry says. “I think that’s one of the challenges—when those resins are turned into similar products, people can’t tell the difference and so they go with their default behaviour: if they see a clear plastic cup, they put it in the recycling.”

A clear, compostable plastic cup stands against a white background Photo: MPCA Photos

How do you dispose of compostable plastic properly?

Be sure to check with your municipality first to confirm which bin is the right one for compostable plastics. More often than not however, they have to be put in the garbage. “In a lot of municipalities across Canada, there’s not really a home for them because the market for these materials is not well controlled,” Li says.

If you’re holding out hope that a compostable cup may still break down on its own in the landfill, Storry notes this is typically not the case. “The timeline—and nobody really has clear data on this—but it wouldn’t break down like a banana peel. Between regular plastic and a banana peel, it would behave more similarly to regular plastic.”

Are compostable plastics really a greener option?

“It can be a greener option if [your] has the processing for it,” Li says. “If you keep this stuff completely separate and get it to an industrial composting facility that will mix it in and create compost, then yes, you have avoided putting all of that stuff in the landfill. But I think it’s just the difference in theory versus practice. In practice you’re not able to do that, so it’s going to the landfill.”

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Instead, Storry recommends sticking with reusables whenever possible. “If you can bring your coffee mug or your shopping bags to start, and then build from there, that’s the most sustainable [option]using what we already have over and over again.”

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