Do Bioplastics Actually Compost? Here’s What You Need to Know

“It’s almost the Wild West in terms of marketing phrases that consumers are exposed to,” said Judith Enck, who served as a senior official at the Environmental Protection Agency under President Barack Obama and now heads the advocacy group Beyond Plastics. “There’s real confusion about what’s truly biodegradable, what’s truly compostable, what’s environmentally friendly.”

Just the question of what bioplastic is can make your head spin.

In general, materials are called bioplastics if they are made partially or entirely from plants. Some of these plastics can be broken down through composting or natural processes such as biodegradation, according to a recent report on compostable plastics from Beyond Plastics.

But bioplastics don’t always break down in the environment or compost, said Kat Knauer, a polymer scientist and senior research scientist at the National Renewable Energy Laboratory. Compostable plastics aren’t all plant-based either, she said. They can be made from fossil fuels, but are designed to eventually break down.

“Bioplastics are quite diverse,” Knauer said. “They’re starting to become more than just the green compostable bag that we used to see.”

Here are some common types you may encounter:

• Biobased plastics are made partly or entirely from plant materials, such as sugar cane, sugar beets, molasses, corn and vegetable oils. Not all of them are compostable. Some examples are bio-polyethylene or bio-polypropylene, which are often used for food packaging and consumer goods.
• Biobased, compostable bioplastics are made in the same way from plants or other natural materials, such as fungi. Most can be broken down in industrial composting systems. The most common type is polylactic acid, or PLA, which is made from starches such as corn, cassava, beets and sugar cane. PLA is often used in compostable food products, cutlery and bags.
• Compostable plastics made from fossil fuels are made from petroleum products, but are designed to be biodegradable. PBAT is an example that you may encounter in the form of compostable garbage bags.

Because there are so many different types of bioplastic, it can often be difficult to read labels and determine whether the product you are purchasing will fully and safely break down in composting.

Knauer recommends looking for items that are certified compostable by the Biodegradable Products Institute, or BPI, or TUV Austria. BPI is the primary certifier of compostable packaging in the United States, and TUV Austria operates a certification program owned by the European Bioplastics Association. Some products sold in the United States have TUV Austria labels that say “OK Compost Industrial” or “OK Compost Home.”

But a recent report from Beyond Plastics raised concerns about bioplastics regulations and certifications. The report highlighted, in part, concerns that BPI-certified compostable products could retain some toxicity, and noted that the certification organization’s board of directors is made up of executives from U.S. petrochemical companies.

Beyond Plastics is urging the EPA to investigate bioplastics and the Federal Trade Commission to update and expand its guidelines for environmental marketing claims related to these types of plastics. In the meantime, Enck suggested people look for products with other verified, third-party eco-labels, such as GreenScreen Certified or Cradle to Cradle Certified.

BPI opposed the report. In a statement, the institute said its certified products must meet basic requirements and that the group “requires compostability testing, including strict limits for heavy metals, plant toxicity and biodegradation in compost.”

“Allegations that BPI’s certification poses a conflict of interest due to the composition of its board of directors are unfounded,” the institute said, adding that certification decisions are made entirely by DIN CERTCO, an independent group based in Germany.

Be wary if a product is labeled compostable but lacks certifications, Knauer said. You should also avoid putting these plastics in your backyard compost unless the label indicates it can be broken down in home composting setups.

According to Muhammad Rabnawaz, an associate professor in Michigan State University’s School of Packaging who researches sustainable materials, most compostable plastics can only break down in industrial systems that maintain high temperatures for extended periods of time.

But not all commercial composters accept these products. In Oregon, for example, local composters say they generally do not want compostable packaging or tableware because the “materials jeopardize our composting programs and reduce many of the environmental benefits of successful composting.” One reason they gave was that not all certified compostable items “will compost (break down) as completely or quickly as we need.”

“The result is a finished compost contaminated with bits of partially decomposed ‘compostable’ material,” they wrote in a public notice. They also raised concerns that some packaging could contain chemicals that leach into the finished compost.

However, the city of Berkeley, California does accept compostable products, including bags, cutlery, cups, and containers, as long as they are clearly labeled “compostable” and “BPI Certified.”

“It’s incredibly difficult to be an ‘ethical’ consumer and make the most sustainable choices,” Knauer said. “It’s so challenging, and especially in the plastics space where things are very confusing in terms of labeling.”

Learning about your local community’s waste collection system is crucial, Knauer said. What is and isn’t recyclable or compostable varies depending on where you are.

“Once you have that foundation, you can really start making informed decisions about what is the most effective, sustainable packaging for you and your family,” she said.

Just because a product is compostable or designed to break down naturally doesn’t necessarily mean it’s the most environmentally friendly option. Research hasn’t provided conclusive answers, and questions remain about long-term sustainability, experts say.

“There may be innovation in the future, but I don’t think it’s certain yet,” Enck said.

Compostable items also tend to be more expensive, Enck added, sometimes costing up to five times as much as non-compostable alternatives.

If you must purchase single-use products, such as disposable plates or cups, she advises opting for non-plastic materials, such as paper.

It’s also important to prioritize reducing and reusing waste, rather than focusing on the details of what type of material would be better for the planet, Knauer said.

Consumers have become dependent on plastic for its convenience and low cost, without considering its impact on the environment, Knauer said. Hopefully, she added, we can “move more toward a conscientious world where we try to reduce and reuse as much as possible.”