Compostable plastics are touted as a greener alternative to conventional petroleum-based plastics that can linger in the environment for centuries. But there’s a catch. Degradable plastics only break down in the right conditions typically found in a composting facility. The tons of compostable plastic that ends up in oceans can still float around for decades and threaten marine life and ecosystems.
Researchers have found a way for plastics to break down much faster in the ocean. They embedded tiny amounts of plastic-degrading enzymes in compostable polyester plastics. The enzyme-containing polyesters completely degraded in a relatively short time period even in microbe-scarce environments.
The method works at all depths from coastal waters to the deep open sea, the researchers report in the journal Nature.
There are many types of biodegradable plastics in commercial use today. These plastics are designed to decompose completely by microorganisms at certain temperatures and humidities. Those conditions are found in industrial composting facilities and with more care in backyard compost settings. But out in cold ocean water, biodegradable plastics can persist for a long time.
The research team from Japan took four types of compostable plastic—PBS, PBSA, PCL, and PBAT—and melted them. The heat of the melt would destroy plastic-degrading enzymes. So the researchers made freeze-dried forms of Candida antarctica lipase B and Humicola insolens cutinase enzymes. They added the enzymes to the melts at very low concentrations ranging from 0.1–3% by weight.
Then the researchers shaped the materials into films and microbeads. After sealing the samples in a polyethylene meshes, they placed the meshes at various locations off the coast of Tokyo, ranging in water depths from 2–6 m to 5,503 m. They monitored the samples over periods ranging from one month to 18 months.
At 757 m, PBS, PBSA and PCL films containing 3% cutinase nearly completely disappeared within five months. Films of those three plastics containing only 0.1 wt% cutinase lost 27.4%, 100% and 85.5% of their mass, respectively, in 1 month. But PBAT was more resistant, losing just over 12% under the same conditions.
Enzyme-free samples barely degraded. And enzyme-containing plastics also showed moderate biodegradation on the cold floor of the deepest test site. Meanwhile, microbeads embedded with 0.1 wt% cutinase formed visible pores and cracks within 2 weeks in coastal seawater.
“These results demonstrate enzyme embedding as a material-level strategy to enhance the environmental degradability of the compostable polyesters…across diverse marine environments without compromising their mechanical properties,” the researchers write.
Source: QiuYuan Huang et al. Enzyme-embedded polyesters for accelerated biodegradation in the deep sea. Nature, 2026.
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