While the importance of recycling is regularly brought to our attention, the amount of plastic waste worldwide is at an all-time high, with a whopping 353 million tons being produced annually.
Scientists now believe they may have a solution to reduce plastic waste in the form of enzymes that absorb polyester.
The first enzyme, called PETase, was discovered back in 2016, but so far it is practically unusable because it is destroyed at high temperatures.
In a new study, researchers at Northwestern University have developed a polymer that protects the enzyme, allowing it to break down polyester even at high temperatures.
Meanwhile, a second study by scientists at Montana State University and the University of Portsmouth has identified a second enzyme, called TPADO, that breaks down terephthalate (TPA), one of two chemicals formed when polyester breaks down.
Together, the researchers hope the enzymes will help engineers develop solutions to remove microplastics from rivers and oceans.
While the importance of recycling is brought to our attention regularly, plastic waste worldwide is now at an all-time high, with a whopping 353 million tons being produced annually.
Polyester: the most widely used fiber in the world
Polyester is the most widely used fiber in the world, accounting for about half of the total fiber market and about 80 percent of synthetic fibers.
Polyester is a man-made synthetic fiber usually derived from petroleum.
Oil is a non-renewable resource and the petrochemical industry has complex social and political implications.
Polyester generally has a significant negative environmental impact during production, use and disposal.
Source: CFDA.
“Our idea was to create polymers capable of encapsulating the enzyme to protect its structure so that it can continue to function outside of living cells and in the laboratory at temperatures high enough to be able to degrade PET,” explained Professor Monica Olvera de. La Cruz, senior author of the first study.
The polymer consists of a hydrophobic (water-repellent) base and three highly concentrated components.
To test this, the team mixed the polymer with chemically synthesized PETase in the lab.
“We found that if you put the polymer-enzyme complex together and close to the plastic and then heat it up a bit, the enzyme can break it down into small monomeric units,” Professor Olvera de la. Cruz said.
“In addition to working in an environment where it can purify microplastics, our method protected against degradation at high temperatures, and one student was able to test it.”
When PETase breaks down polyester, it leaves behind two chemicals, ethylene glycol (EG) and terephthalate (TFA).
In a separate study, researchers at Montana State University and the University of Portsmouth looked at the next steps for these chemicals.
Professor Jen Dubois, who led the study, said: “While EG is a chemical that can be used in many applications — like the antifreeze you put in your car — TPA doesn’t have a wide range of uses outside of PET, and is not something that most bacteria can even digest.”
In their study, the researchers found that an enzyme from PET-consuming bacteria can recognize TPA “like a hand in a glove.”
The enzyme, called TPADO, is naturally occurring and breaks down TPA with amazing efficiency, the team says.
Professor John McGeehan, director of the University’s Center for Enzyme Innovation, said: “The last few years have seen incredible advances in the development of enzymes to break down PET plastic into building blocks.
In the course of the study, the researchers found that an enzyme from PET-consuming bacteria can recognize TPA “like a hand in a glove.” The enzyme, called TPADO, is naturally occurring and breaks down TPA with amazing efficiency, the team says.
“This work goes even further and looks at the first enzyme in the cascade that can break down these building blocks into simpler molecules.
“They can then be used by bacteria to produce sustainable chemicals and materials needed to make valuable products from plastic waste.”
Using X-ray scanning, the researchers were also able to create a detailed 3D structure of TPADO, showing how it breaks down TPA.
“This gives researchers a blueprint for making faster and more efficient versions of this complex enzyme,” Professor McGeehan added.
The study comes shortly after a report warned that plastic waste worldwide has more than doubled since 2000, with a whopping 353 million tons produced in 2019.
A report by the Organization for Economic Co-operation and Development says that despite the surge in plastic waste, only nine percent have been successfully recycled.
“Including recycling losses, only nine percent of plastic waste was ultimately recycled, 19 percent was incinerated, and almost 50 percent ended up in sanitary landfills,” the report said.
“The other 22 percent was thrown into uncontrolled landfills, burned in quarries or leaked into the environment.”
Eight million tons of plastic end up in the ocean every year
Of the 30 billion plastic bottles used annually by UK households, only 57 percent are currently recycled.
Half of them go to landfill, and half of all plastic bottles that are recycled are thrown away.
Approximately 700,000 plastic bottles a day become garbage.
This is largely due to the plastic wrapping of the bottles, which are not recyclable.
Bottles are one of the main sources of the growing amount of plastic waste in the oceans.
The researchers have warned that eight million tons of plastic are now being dumped into the ocean each year, the equivalent of loading one truck every minute.
According to a report published in 2016, by 2050 the amount of plastic waste in the oceans will exceed the weight of fish if the world does not take drastic measures for further recycling.
At current rates, this will degrade to four trucks per minute in 2050 and surpass local life to become the largest mass inhabiting the oceans.
According to a report by the Ellen MacArthur Foundation, the vast majority of 95% of £65bn to £92bn worth of plastic packaging is lost to the economy after a single use.
Research estimates that there are more than 150 million tons of plastic in the ocean today.
Plastic pollution is destroying the world’s ecosystems, both marine and terrestrial. It litters coastlines, traps animals, and suffocates entire animal populations.
Scientists warn that so much plastic is dumped into the sea every year that there are five carry bags for every foot of coastline on the planet.
More than half of the plastic waste that ends up in the oceans comes from just five countries: China, Indonesia, the Philippines, Vietnam and Sri Lanka.
The only industrialized western country on the list of the top 20 plastic polluters is the US in 20th place.
The researchers argue that the US and Europe are handling their collected waste properly, which is why plastic trash coming from these countries is associated with garbage.
While China is responsible for 2.4 million tons of plastic entering the ocean, nearly 28 percent of the global total, the United States contributes just 77,000 tons, less than one percent, according to a study published in the journal Science. .