Many people assume all bioplastics are made from plants and can break down completely in the environment. But that’s not the case.  The term “bioplastics” is actually used for two separate things: bio-based plastics (plastics made at least partly from biological matter) and biodegradable plastics (plastics that can be completely broken down by microbes in a reasonable timeframe, given specific conditions). Not all bio-based plastics are biodegradable, and not all biodegradable plastics are bio-based. And even biodegradable plastics might not biodegrade in every environment. Sounds confusing? It certainly is.

“There are a lot of bioplastics or materials that are called bioplastics that are not biodegradable,” says Constance Ißbrücker, head of environmental affairs at the industry association European Bioplastics.  For some plastics, the same polymer chains can be made from renewable sources. The resulting bioplastics are chemically identical to their fossil counterparts. PET, for example — short for polyethylene terephthalate, which is the stuff most bottles are made of — can be synthesized from fossil fuel products or plants like sugarcane. The resulting material is the exact same. Such non-biodegradable bioplastics behave in the environment just like conventional plastic and persist for an unknown but long amount of time.

Not only that, but none of the standards for plastics labeled as biodegradable or compostable today makes them suitable for disposal in the open environment. Given that, can bioplastics play a role in tackling environmental problems? Or are they merely greenwashing? The most accurate answer is, it depends.

Take polylactic acid (PLA), for example. This bioplastic is used to make shopping bags, transparent cups, 3-D printing material and other products. Because it can be derived from plant material like corn sugar, potato or sugarcane, it can reduce the demand for fossil fuels used to make conventional plastics. PLA is recyclable, biodegradable and compostable. But that doesn’t mean the ocean — or any other natural environment — can easily handle it.

To Frederik Wurm, a chemist at the Max Planck Institute for Polymer Research (MPIP), drinking straws made from PLA are “the perfect example for greenwashing.” They are more expensive than other plastic drinking straws, but don’t readily biodegrade on a beach or in the sea. “You put it on the package [that it] is biodegradable, but at the point where these materials are . . . fear[ed] to end up, they will not biodegrade,” Wurm says.

For biodegradation, PLA needs industrial composting conditions, including temperatures above 58 °C (136 °F). It needs to be properly managed and routed to specialized industrial composting or recycling facilities. Under the right circumstances, microbes can turn the material into carbon dioxide and water within a couple of weeks. However, if it becomes littered or dumped, PLA sticks around for much longer. When pure PLA ends up in seawater, it does not seem to biodegrade at all.

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