Enzyme Plastics Broke Down in Deep Sea

Compostable plastics with enzymes baked into them degraded across marine environments from coastal sea water down to the deep-sea floor at 5,503 metres, a University of Tokyo-led team reports in a Nature paper published on 21 October.

The study, by QiuYuan Huang, Tadahisa Iwata and colleagues, embedded two enzymes into four widely used compostable polyesters and then sank samples at sites off Japan, recovering them months later to measure how much had broken down. A Nature research briefing summarising the work says the method achieves “rapid and complete biodegradation even in microbe-scarce environments” and “could therefore contribute towards solving the global plastic pollution problem”.

What the researchers actually did

The team took polyesters already marketed as compostable — PBS, PBSA, PCL and PBAT — and thermally embedded one of two enzymes, Candida antarctica lipase B (CaLB) or Humicola insolens cutinase (HiC), using twin-screw extrusion at 90 to 130 degrees Celsius. That produced films and microbeads with the enzyme dispersed inside the plastic rather than coated on the surface.

The samples were deployed from a coastal port at a few metres’ depth to the deep-sea floor, with recovery at depth carried out using the crewed submersible Shinkai 6500. Enzyme loadings were kept low: 0.1% by weight for the coastal site and 3% for the deeper sites, where colder water, higher pressure and fewer microbes slow natural breakdown.

The results are specific and worth stating plainly. At a 757-metre site, CaLB-embedded PBSA and PCL films lost 57.3% and 99.0% of their mass after 18 months, while enzyme-free controls of the same plastics barely changed. Even at 5,503 metres, the deepest site, the enzyme-embedded PBSA and PCL lost 30.5% and 7.7% of their mass, against 1.6% and 3.4% for the controls. In coastal sea water, a film carrying just 0.1% HiC reached 50.9% of its theoretical oxygen demand within a month, a biochemical-oxygen measurement the authors use as evidence that microbes were mineralising the broken-down material rather than simply fragmenting it.

A laboratory result, not a product

This is research, and it is worth being careful about what it does and does not show. The benefit on offer is real and the kind worth weighing: conventional “compostable” plastics often survive for years in cold, deep water, and a cheap way to make them actually disappear there would address one of the hardest corners of plastic pollution. The authors note the enzyme-embedded plastics kept mechanical properties similar to the enzyme-free versions, so the approach does not obviously trade durability for degradability, and the low enzyme loadings suggest the chemistry does not depend on flooding the material with additive.

The limits matter just as much. These are field and laboratory tests at a handful of sites off Japan, measured over months, not a manufacturing process or a commercial product; the paper offers no cost, no scale-up plan and no brand. Degradation was far from uniform — 99.0% for one plastic at one depth, 7.7% for another at the deepest site — so “the plastic dissolves in the ocean” would overstate it. The briefing itself frames the work as something that “could” contribute to the plastic problem, and the paper’s own language is that the strategy “represents a potential solution”. Earlier demonstrations of this idea had been confined to the lab or closed systems, so moving it into open deep-sea conditions is the advance here; turning it into materials people use is a separate, longer road.

The work also sits alongside a wider push to use designed enzymes and proteins for practical ends, from AI-designed enzymes that cut specific proteins to open models that generate new proteins and start-ups applying automation to specialty chemistry. Here there is no artificial intelligence involved; the enzymes are natural catalysts put to an environmental job, and the novelty is in the embedding and the deep-sea proving ground.