Mutant Enzymes are Cool, But Not Likely to Solve Our Ocean Plastics Problem

A newly discovered mutant enzyme can break down plastics in just a few days

There’s a lot of awe-inspiring stuff that happens in our natural world, and if there’s one thing I’ve learned about science over the years it’s this: never say never. That’s why I was optimistic when I read the headlines about the discovery of mutant enzymes that can solve our ocean plastic problem; with eight million metric tons of plastics entering the ocean annually, the oceans need all the help they can get and we need to consider all potential solutions that are brought forward.

Scientists at the University of Portsmouth, UK, accidentally created a new mutant enzyme that breaks down plastic drink bottles (which are made of a specific plastic resin called PET). The research was prompted by a 2016 discovery in Japan that revealed a bacterium had evolved the ability to eat plastics at waste dumps. The newly discovered mutant enzyme takes this further; it can start breaking down plastics in just a few days, which is far faster than the decades or centuries it takes for PET to break down in the oceans.

This sounds awesome, but as an ocean scientist, neither complex enzymatic processes nor plastics chemical properties are my expertise. As I read through the findings published in the Proceedings of the National Academy of Science (PNAS), I quickly realized I needed to seek the counsel of a bona fide expert. At Ocean Conservancy, we work closely with a range of academic scientists with expertise on a variety of topics including plastics; and one of our most trusted is my friend and colleague, Dr. Ramani Narayan, University Distinguished Professor in the Department of Chemical Engineering & Materials Science at Michigan State University. Could these mutant enzymes be a silver bullet to the ocean plastic crisis?

Dr. Narayan shared this perspective:

“The problem is not in the “technology” to reuse PET or dismantle into its constituents but recovery and economics of the processes used. Semi-crystalline PET bottles are already fully recyclable within our current systems. PET can also be readily depolymerized into the constituent building blocks using water in 30 min or less and very scalable.  They do not need further help from a new, genetically engineered enzyme.

It needs to be re-emphasized that the barrier to recycling PET and other plastic wastes is in recovery and reducing/eliminating “mismanaged wastes” through responsible waste management infrastructures that includes material design for recycling and composting – in line with the circular economy concepts.”

To summarize Dr. Narayan’s expert judgment: Though these findings are promising, they are far from being a solution and offer only minimal utility at present to address the waste PET problem, not to mention all the other plastic resins out there.  And the big problem is making sure these bottles make their way to a recovery facility, which enzymes cannot help overcome. Current processes exist to “break down” the PET but the big missing link that remains is the actual collection and recovery of PET (and other plastics) in the first place.

In short, plastic-eating enzymes are mostly scientifically intriguing, not commercially applicable. To truly get a handle on our global plastic pollution problem, we must address both the explosive production/consumption of single-use products as well as the lack of collection capacity in much of the world to reuse materials. We have the technology to do so already but, at present, only a very small percentage of plastics are actually recycled. We need to do much better.

The media attention to this week’s study on the mutant enzymes shows there is a growing global movement committed to solving this problem. Let’s harness that energy to keep plastics out of the ocean in the first place, invest in new materials that minimize or eliminate harm and scale up the solutions we already have that work.

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