17 November 23
One way to help tackle the growing plastic pollution problem could be all around us: microscopic bacteria and fungi.
A growing body of research has identified a host of microorganisms, some of which can be found in the bellies of certain larvae and other insects, that contain enzymes capable of breaking down common types of plastic.
“In no small part because of just how much plastic we’ve polluted across the planet, in nearly every environmental type, microorganisms are starting to interact with plastic more,” said Anja Brandon, a plastics expert with Ocean Conservancy, a nonprofit group. “We’re finding some that are starting to either evolve and be able to handle this material or, fortuitously, we’re able to get to actually start breaking this down.”
Research is still in the early stages, and it remains unclear how much plastic microorganisms could break down. But given the scale of plastic pollution, some experts say, it’s necessary to explore a variety of strategies.
There are more than 170 trillion pieces of plastics in the world’s oceans — an amount that is doubling about every six years, according to a major study released in March.
The most obvious way to curb plastic pollution, advocates say, is to stop producing the material. But that’s challenging for many reasons, including that it’s difficult to find plastic substitutes that are as cheap and effective.
The world’s nations have moved to create a global treaty on plastic pollution, but they have struggled to agree on how to address the problem.
Bacteria and fungi capable of breaking down plastics could help support traditional recycling efforts — if scientists can figure out a way for the microorganisms to do it at scale.
“To even make a small dent in managing our plastic waste, we really need to be able to scale up and speed up these systems, which also comes with its own potential complications,” Brandon said. “Scaling up is never quite as simple as like, ‘Oh, I’ll just make more of it.’”
Plastic eaters
There is a strong incentive for microorganisms to evolve to eat plastics, said Brandon, who studied biodegradation using mealworms.
Research suggests a number of these organisms appear to have figured out that plastics could be a valuable food source. In 2015, researchers from Stanford University found mealworms could live off polystyrene, or what’s widely known as plastic foam. Soon after that, Japanese scientists documented bacteria that could eat plastic bottles. More recently, a team from the University of Texas created an enzyme that can digest polyethylene terephthalate, a common plastic resin found in clothes, liquid and food containers. Meanwhile, researchers in Australia showed that the larvae of a darkling beetle can survive solely on plastic foam.
How these organisms degrade the durable material can lead to different results. Most bacteria, for instance, secrete certain enzymes that allow them to break large molecules into smaller ones, Brandon said. In some cases, these enzymes can chop up a big molecule into its building blocks. Those simple monomers could be recovered and used to make new plastic, effectively recycling the material, she said.
It’s also possible for microorganisms to break down plastics into water, carbon dioxide and organic material known as biomass, other experts say.
Picky and slow
But many of the known life forms that want to munch on plastics are picky about what they eat. Most of the microorganisms identified by researchers will only eat certain kinds of plastic, experts said. That means if recycling centers want to use this approach, they would still need to sort trash by material, a complicated process that limits the kinds of plastics they can recycle today.
“There are too many different types of plastic resins, thousands of different chemical additives and different colorants,” said Judith Enck, a former senior Environmental Protection Agency official under President Barack Obama who now heads the Beyond Plastics advocacy organization. “One size does not fit all.”
These organisms also need time to break down plastics. Brandon’s research into mealworms that eat polystyrene showed that on average, 100 of the critters could consume 20 to 30 milligrams of plastic per day. That means it would take 3,000 to 4,000 mealworms to process a single Styrofoam coffee cup. At this rate, more than a quadrillion mealworms would be needed to eat just one day’s worth of the world’s plastic production.
“Even the fastest microorganisms that we found really just pale in comparison to the amount of plastics we’re making and using in a single day,” Brandon said.
Researchers at Harvard’s Wyss Institute for Biologically Inspired Engineering say they’re developing a solution to these obstacles by not only identifying organisms that can naturally degrade plastic, but also using genetic engineering to boost their ability to efficiently break down the material.
The Harvard team is starting by looking for these plastic-eating microorganisms, said Sukanya Punthambaker, one of the project’s lead researchers. Then, they plan to isolate the enzymes and work on ways to speed up their functions.
“It’s a natural solution, so we’re just trying to work with what nature has already figured out millions of years ago and we’re trying to expedite that process,” Punthambaker said.
Still at the lab stage
Much of the research into the ability of microorganisms to biodegrade plastics remains at the laboratory stage. But some experts say if the approach is scaled up and made to be more efficient, it could have some use in the real world.
The organisms could help supplement the existing recycling system, Brandon said, particularly for trash recovered from the environment. These plastics are often degraded and not suitable to go through most recycling facilities, so they often end up in landfills.
Still, Brandon and other experts emphasized there is a way to go before these types of solutions can be readily deployed.
Bacteria and enzymes “are incredibly cool and very innovative, and I can see value for them in the future,” she said. “But in terms of being the solution or the get out of jail free card from our plastic pollution crisis, it is simply not the case.”
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