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Shoes that are edible to sea creatures could help tackle plastic pollution, scientists claim

Scientists at the University of California, San Diego have created a shoe that begins to biodegrade after just four weeks underwater.

Leather can take 40 years to biodegrade and rubber soles take up to 80 years. Meanwhile, every piece of plastic you’ve ever used still exists on the planet.

That means the 600 million shoes thrown away every year in the UK could still be around thousands of years from now, but your next pair may not be that long.

That’s because scientists at the University of California, San Diego have created sneakers that begin to biodegrade after just four weeks underwater.

Its materials are designed to be broken down by sea creatures into their original chemicals, which they can then consume as nutrients.

The researchers say replacing plastic could tackle the pollution currently plaguing the world’s oceans.

Professor Stephen Mayfield said: “Improper disposal of plastic in the ocean breaks down into microplastics and has become a huge environmental problem.”

“We have shown that it is absolutely possible to make high-performance plastic products that can also degrade in the ocean.”

Scientists at the University of California, San Diego have created a shoe that begins to biodegrade after just four weeks underwater.

Scientists at the University of California, San Diego have created a shoe that begins to biodegrade after just four weeks underwater.

Its materials are designed to be broken down by sea creatures into their original chemicals, which they can then consume as nutrients.

Its materials are designed to be broken down by sea creatures into their original chemicals, which they can then consume as nutrients.

WHAT IS BIODEGRADABLE POLYURETHANE MADE OF?

About half of polyurethane foam is made from oils extracted from algae.

The other half is made from an isocyanate, which comes from petroleum.

The isocyanate remains biodegradable and edible for microorganisms.

“Some organisms can live on just our foam and some salts, so our foam is actually food for micro-organisms,” said Professor Mayfield.

A cube of polyurethane foam created with algae oil.

A cube of polyurethane foam created with algae oil.

Professor Mayfield added: “Plastics shouldn’t go into the ocean in the first place, but if they do, this material becomes food for micro-organisms and not plastic litter and microplastics that harm aquatic life.”

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In 2010, researchers estimated that 8 billion kilograms of plastic ends up in the ocean each year, with a steep increase predicted by 2025.

Footwear is a major contributor to this waste both in the water and in landfills, and plastic flip-flops are also the most popular shoes in the world.

When plastic debris enters the ocean, it disrupts marine ecosystems and migrates together to form giant mounds of garbage, like the 1.6 million square kilometer Great Pacific Garbage Patch.

The material never fully degrades in the sea, but instead breaks down into tiny microplastics that remain there for centuries.

For the last eight years, Professor Mayfield’s team have been developing polyurethane foams made from algae oil, which in 2020 they showed would break down rapidly in compost and soil.

The foam also meets commercial requirements for the insole of flip flops as well as the cushioning section of the midsole of shoes.

For their new study, published yesterday in Science of The Total Environment, they wanted to test whether submerging the material in seawater would give the same results.

They exposed foam samples to a natural nearshore ecosystem at the Ellen Browning Scripps Memorial Pier and Experimental Aquarium for up to 30 weeks.

Changes in molecular bonding of the samples were tracked using Fourier transform infrared spectroscopy and visualized with scanning electron microscopy.

Footwear is a major contributor to plastic waste in both water and landfills, and plastic flip-flops are also the most popular shoes in the world (stock image)

Footwear is a major contributor to plastic waste in both water and landfills, and plastic flip-flops are also the most popular shoes in the world (stock image)

The team exposed polyurethane foam samples to a natural nearshore ecosystem at the Ellen Browning Scripps Memorial Pier and Experimental Aquarium for up to 30 weeks.  Changes in molecular bonding of the samples were tracked by Fourier transform infrared spectroscopy and visualized by scanning electron microscopy.

The team exposed polyurethane foam samples to a natural nearshore ecosystem at the Ellen Browning Scripps Memorial Pier and Experimental Aquarium for up to 30 weeks. Changes in molecular bonding of the samples were tracked by Fourier transform infrared spectroscopy and visualized by scanning electron microscopy.

The polyurethane was found to begin to biodegrade after just four weeks, which was aided by a variety of marine organisms.

Professor Mayfield said: “I was surprised to see how many organisms colonize these foams in the ocean.” It becomes something like a microbial reef.

Bacteria and fungi broke down the long polyurethane molecules into their original starting chemical compounds, which they could then consume as nutrients.

The team then identified these microorganisms and located them at six sites in San Diego.

This suggests that the type of creatures capable of degrading the material are prevalent throughout the natural marine environment.

“No single discipline can tackle these universal environmental problems, but we have developed an integrated solution that works on land, and now we know it also biodegrades in the ocean,” said Professor Mayfield.

Left two panels: Photographs of foam samples adhered to Scripps Pier at week 0 and week 4. Right six panels: Scanning electron microscopy images of the polyurethane foam (top) and the control foam of ethylene and vinyl acetate (EVA) (bottom).  A, F: Foams before exposure to seawater;  D, G: after 4 weeks underwater;  E, H: After 12 weeks underwater

Left two panels: Photographs of foam samples adhered to Scripps Pier at week 0 and week 4. Right six panels: Scanning electron microscopy images of the polyurethane foam (top) and the control foam of ethylene and vinyl acetate (EVA) (bottom). A, F: Foams before exposure to seawater; D, G: after 4 weeks underwater; E, H: After 12 weeks underwater

Scanning electron microscopy images of polyurethane foam (top) and control ethylene vinyl acetate (EVA) foam (bottom).  A, D: Foams before exposure to seawater;  D, G: after 15 weeks underwater;  E, H: After 30 weeks underwater

Scanning electron microscopy images of polyurethane foam (top) and control ethylene vinyl acetate (EVA) foam (bottom). A, D: Foams before exposure to seawater; D, G: after 15 weeks underwater; E, H: After 30 weeks underwater

Eight million tons of plastic end up in the ocean every year

Of the 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.

Some 700,000 plastic bottles a day end up in the garbage.

This is largely due to the plastic wrap on the bottles which is not recyclable.

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Bottles are one of the main contributors to the increasing amount of plastic waste in the world’s oceans.

The researchers warned that eight million tons of plastics reach the ocean every year, the equivalent of one truck every minute.

The amount of plastic trash in the world’s oceans will outnumber fish by 2050 unless the world takes drastic action to recycle even more, a report published in 2016 revealed.

At the current rate, this will worsen to four truckloads per minute by 2050 and will overtake native life to become the largest mass inhabiting the oceans.

An overwhelming 95 per cent of plastic packaging, worth £65-£92 billion, is lost to the economy after just one use, according to the Ellen MacArthur Foundation report.

And available research estimates that there are more than 150 million tons of plastics in the ocean today.

It is estimated that around eight million metric tons of plastic enter the world's oceans each year.

Plastic pollution is ruining the world’s ecosystems, both marine and terrestrial. It litters shorelines, traps animals, and suffocates entire animal populations.

Every year so much plastic is dumped into the sea that it would fill five plastic bags for every foot of coastline on the planet, scientists have warned.

More than half of the plastic waste flowing into the oceans comes from just five countries: China, Indonesia, the Philippines, Vietnam and Sri Lanka.

The only Western industrialized country on the list of the top 20 plastic polluters is the United States in 20th place.

The United States and Europe aren’t mismanaging their collected waste, so the plastic trash coming from those countries is due to garbage, the researchers said.

While China is responsible for 2.4 million tons of plastic reaching the ocean, nearly 28 percent of the global total, the United States contributes just 77,000 tons, which is less than one percent, according to the study published in the journal Science. .

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