A popular ‘compostable’ bioplastic isn’t as biodegradable as it seems

The use of plastic across all facets of human life has grown more and more pervasive in the last few decades, resulting in a surge in global environmental pollution. More than half of the amount of plastic produced from 1950 to 2017 became plastic waste, which harms ecosystems, livelihoods, and food security around the globe. In the United States alone, about 35.7 million tons of plastic were generated in 2018. Exploring potential alternatives to conventional petroleum-based plastics, like bioplastics, is necessary to mitigate pollution and reduce the waste stream.

Bioplastics are usually made from extracted starches, oils, and sugars from renewable sources such as corn and sugarcane—like poly(lactic acids) or PLAs. Others are made from polymers produced by microorganisms, like polyhydroxyalkanoates or PHAs. PLA, one of the most commonly used bioplastics, has similar functionalities to conventional plastic and is considered to be recyclable, biodegradable, and compostable. “Biodegradable” means that it can be degraded naturally by microorganisms, while “compostable” means it is biodegradable in industrial composting operations. However, new research shows that PLA might not be as environmentally friendly as initially thought.

[Related: Why the recycling symbol is part of a ‘misinformation campaign’.]

Because PLA is applied extensively in single-use items and often touted as an alternative to conventional plastics, the authors of a recent PLOS One study looked into the biodegradability of textiles made of PLA in marine waters. The authors found that PLA showed no sign of environmental degradation even after spending 428 days under natural marine conditions. If consumers are buying PLA thinking it’s an ecological solution to plastic items since it biodegrades under normal conditions, they are being misled, says Sarah-Jeanne Royer, visiting scholar at the UC San Diego Scripps Institution of Oceanography who was involved in the study.

She adds that PLA is only compostable under specific high-temperature conditions that “cannot be found in nature.” Therefore, the material needs to be properly disposed of and composted to be biodegradable. PLA may be industrially compostable, but since it doesn’t degrade easily in the environment, it demonstrates the potential to be a marine pollutant. The authors conclude that the common practice of referring to industrially compostable materials as “biodegradable plastic” could mislead consumers and increase the amount of plastic waste in the environment.

There is a tendency to assume that bioplastics are biodegradable since they are made from biological materials. However, if they are designed to mimic the structure of conventional plastics, they can last in the environment just as long. In fact, the International Union of Pure and Applied Chemistry (IUPAC) discourages the use of “bioplastic” and instead pushes for “bio-based polymer” to avoid misleading individuals that any polymer derived from biomass is inherently environmentally friendly.

Royer says potentially misleading terminology about what is biodegradable or not can affect the environment. Some consumers may think of “biodegradable” and “compostable” as interchangeable, but these materials can often end up in the waste stream just like conventional plastic items. To avoid misconceptions, companies promoting PLA can inform consumers how to use and dispose of their products and let them know the conditions under which the material will biodegrade. “This information should not be hidden and hard to find,” says Royer. “The right labeling is important as it is counterproductive to buy PLA and then discard it in the wrong way.”

In general, a material should be tested under different conditions and scenarios to assess its biodegradability, says Royer. More importantly, it must be tested “under realistic scenarios, such as the natural environment, where these types of materials might end up.” For instance, PLA can be biodegradable under composting facilities, while cellulose-based textile fibers can biodegrade under normal oceanic conditions, she adds.

[Related: Earthworms can break down bioplastic, for better or for worse.]

While the idea of bioplastics can be promising, they’re not the end-all solution. Addressing plastic pollution does not mean using more biodegradable and compostable plastics, but rather, generating less waste in general. Royer says PLA is used for single-use items most of the time, something consumers should avoid using at all costs. 

“Creating a product needs a lot of energy and resources, and using it only a few minutes and then discarding it does not make any sense,” she adds. “If consumers really need to buy a biodegradable bioplastic, then they should make sure to have access to composting facilities, which is not always easy.”