Enzymes that EAT polyester in drinks bottles and clothing could help reduce plastic waste in rivers and oceans
- An enzyme called PETase was found to break down polyester back in 2016
- Until now it’s been largely unusable because it breaks down at high temperature
- Scientists developed a polymer that protects the enzyme
- In a separate study, researchers discovered an enzyme that breaks down TPA – one of the chemical constituents in polyester
While the importance of recycling is regularly hammered home to us, plastic waste around the world is at an all-time high, with a whopping 353 million tonnes produced every year.
Now, scientists believe they may have the solution to reducing plastic waste, in the form of enzymes that eat polyester.
The first enzyme, called PETase, was discovered back in 2016, but until now it’s been largely unusable because it breaks down at high temperatures.
In a new study, researchers from Northwestern University designed a polymer that protects the enzyme, allowing it to break down polyester even at high temperatures.
Meanwhile, a second study, led by researchers from Montana State University and the University of Portsmouth, identified a second enzyme, called TPADO, that breaks down terephthalate (TPA) – one of the two chemicals produced when polyester breaks down.
Together, the researchers hope the enzymes could help engineers develop solutions for removing microplastics from rivers and oceans.
While the importance of recycling is regularly hammered home to us, plastic waste around the world is now at an all-time high, with a whopping 353 million tonnes produced every year
Polyester: The most widely used fiber in the world
Polyester is the most widely used fiber in the world, accounting for roughly half of the overall fiber market and around 80 per cent of synthetics fiber.
Polyester is a manufactured synthetic fiber, and is usually derived from petroleum.
Petroleum is a non-renewable resource and the petrochemicals industry has complicated social and political implications.
Polyester generally has significant negative environmental impact during production, use, and disposal.
‘Our idea was to build polymers capable of encapsulating the enzyme to protect its structure, so that it can continue to function outside of living cells and in the lab at sufficiently high temperatures to be able to break down PET,’ explained Professor Monica Olvera de la Cruz, senior author of the first study.
The polymer consists of a hydrophobic (water repelling) backbone, and highly specific concentrations of its three components.
To put it to the test, the team mixed the polymer with chemically synthesised PETase in the lab.
‘We found that if you put the complex of the polymer with the enzyme together, and close to a plastic, and then you heat it up slightly, the enzyme was able to break it down into small, monomeric units,’ Professor Olvera de la Cruz said.
‘In addition to operating in an environment like where it could clean microplastics, our method has protected against high temperature degradation, and one student was able to do the testing.’
When PETase does break down polyester, it leaves behind two chemicals – ethylene glycol (EG) and terephthalate (TPA).
In a separate study, researchers from 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 with many uses – it’s part of the antifreeze you put into your car, for example – TPA does not have many uses outside of PET, nor is it something that most bacteria can even digest.’
In their study, the researchers found that an enzyme from PET-consuming bacteria can recognise TPA ‘like a hand in a glove.’
The enzyme, called TPADO, is naturally occuring and breaks down TPA with amazing efficiency, according to the team.
Professor John McGeehan, who is the Director of the University’s Centre for Enzyme Innovation, said: ‘The last few years have seen incredible advances in the engineering of enzymes to break down PET plastic into its building blocks.
In the study, the researchers found that an enzyme from PET-consuming bacteria can recognise TPA ‘like a hand in a glove.’ The enzyme, called TPADO is naturally occuring, and breaks down TPA with amazing efficiency, according to the team
‘This work goes a stage further and looks at the first enzyme in a cascade that can deconstruct those building blocks into simpler molecules.
‘These can then be utilised by bacteria to generate sustainable chemicals and materials, essential making valuable products out of plastic waste.’
Using X-ray scanning, the researchers were also able to generate a detailed 3D structure of TPADO, revealing how it breakes down TPA.
‘This provides researchers with a blueprint for engineering faster and more efficient versions of this complex enzyme,’ Professor McGeehan added.
The studies come shortly after a report warned that plastic waste has more than doubled globally since 2000, with a whopping 353 million tonnes produced in 2019.
The report, by the Organisation for Economic Co-operation and Development, found that despite this surge in plastic waste, just nine per cent was successfully recycled.
‘After taking into account losses during recycling, only nine percent of plastic waste was ultimately recycled, while 19 percent was incinerated and almost 50 percent went to sanitary landfills,’ it said.
‘The remaining 22 percent was disposed of in uncontrolled dumpsites, burned in open pits or leaked into the environment.’
Eight million tonnes of plastics find their way into the ocean every year
Of 30 billion plastic bottles used by UK households each year, only 57 per cent are currently recycled.
With half of these going to landfill, half of all plastic bottles that are recycled go to waste.
Around 700,000 plastic bottles a day end up as litter.
This is largely due to plastic wrapping around bottles that are non-recyclable.
Bottles are a major contributor to the increasing amount of plastic waste in the world’s oceans.
Researchers warned eight million tonnes of plastics currently find their way into the ocean every year – the equivalent of one truckload every minute.
The amount of plastic rubbish in the world’s oceans will outweigh fish by 2050 unless the world takes drastic action to further recycle, a report released in 2016 revealed.
At current rates, this will worsen to four truckloads per minute in 2050 and outstrip native life to become the largest mass inhabiting the oceans.
An overwhelming 95 per cent of plastic packaging – worth £65 – £92billion – is lost to the economy after a single use, the Ellen MacArthur Foundation report stated.
And available research estimates that there are more than 150 million tonnes of plastics in the ocean today.
Plastic pollution is ruining the ecosystems of the world, both marine and terrestrial. It litters shorelines, snags animals and suffocates entire populations of animals
So much plastic is dumped into the sea each year that it would fill five carrier bags for every foot of coastline on the planet, scientists have warned.
More than half of the plastic waste that flows into the oceans comes from just five countries: China, Indonesia, Philippines, Vietnam and Sri Lanka.
The only industrialized western country on the list of top 20 plastic polluters is the United States at No. 20.
The US and Europe are not mismanaging their collected waste, so the plastic trash coming from those countries is due to litter, researchers said.
While China is responsible for 2.4 million tons of plastic that makes its way into the ocean, nearly 28 percent of the world total, the United States contributes just 77,000 tons, which is less than one percent, according to the study published in the journal Science.
Source: Read Full Article