It can take 40 years for leather to biodegrade, and rubber soles up to 80 years. Meanwhile, every piece of plastic you’ve ever worn still exists on the planet.
That means the 600 million shoes thrown away in the UK every year will still be there thousands of years from now – but your next pair may not last as long.
This is because scientists at the University of California San Diego have created a sneaker that starts to break down underwater after just four weeks.
The materials are designed to be broken down by marine animals into their original chemicals, which they can then consume as nutrients.
The researchers say plastic replacement could address the pollution currently plaguing the world’s oceans.
Professor Stephen Mayfield said: ‘Incorrect 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-quality plastic products that can also break down in the ocean.’
Scientists at the University of California at San Diego have created a sneaker that biodegrades after just four weeks underwater
The materials are designed to be broken down by marine animals into their original chemicals, which they can then consume as nutrients
WHAT IS THE BIODEGRADABLE POLYURETHANE MADE OF?
About half of the polyurethane foam is made from oils extracted from algae.
The other half is made from an isocyanate, which comes from petroleum.
The isocyanate is still biodegradable and edible for microorganisms.
“Some organisms can only live on our foam and some salts, so our foam is actually food for microorganisms,” said Professor Mayfield.
A polyurethane foam cube made with algae oil
Professor Mayfield added: ‘Plastics shouldn’t go into the ocean in the first place, but when they do, this material becomes food for microorganisms and not plastic waste and microplastics that harm aquatic life.’
In 2010, researchers estimated that 8 billion kilograms of plastic ends up in the ocean every year and a sharp increase is predicted by 2025.
Footwear is a major contributor to this waste, both in the water and in the landfill, and plastic-based flip flops are also the world’s most popular footwear.
When plastic waste ends up in the ocean, it disrupts marine ecosystems and migrates together to form giant mounds of waste, such as the 1.6 million square kilometer Great Pacific Garbage Patch.
The material never completely degrades in the sea, but instead breaks down into tiny microplastics that remain there for centuries.
Over the past eight years, Professor Mayfield’s team has been developing polyurethane foams based on algae oil, which in 2020 proved to degrade quickly in compost and soil.
The foam also meets commercial requirements for the footbed of slippers and the cushioning midsole of shoes.
For their new study, published yesterday in Science of the total environmentthey wanted to test whether immersing the material in seawater would produce the same results.
They exposed foam samples to a natural nearshore ecosystem at the Ellen Browning Scripps Memorial Pier and Experimental Aquarium over a period of up to 30 weeks.
Changes in the molecular binding of the samples were monitored by Fourier transform infrared spectroscopy and visualized by scanning electron microscopy.
Footwear is a major contributor to plastic waste in both water and landfills, and plastic-based flip flops are also the world’s most popular footwear (stock image)
The team exposed polyurethane foam samples over a period of up to 30 weeks to a natural nearshore ecosystem at the Ellen Browning Scripps Memorial Pier and Experimental Aquarium. Changes in the molecular binding of the samples were monitored by Fourier transform infrared spectroscopy and visualized by scanning electron microscopy
The researchers studied polyurethane foam submerged in the Scripps Institution of Oceanography Pier
The polyurethane was found to biodegrade after just four weeks, aided by an assortment of marine organisms.
Professor Mayfield said: ‘I was surprised to see how many organisms colonize these foams in the ocean. It’s going to be like a microbial reef.’
The bacteria and fungi broke down the long polyurethane molecules into their original starting chemicals, which they could then consume as nutrients themselves.
The team then identified these microorganisms and located them at six locations in San Diego.
This suggests that the types of creatures capable of breaking down the material are widespread in the natural marine environment.
“No discipline can address these universal environmental problems, but we have developed an integrated solution that works on land – and now we know biodegradation in the ocean as well,” said Professor Mayfield.
Left two panels: photographs of foam samples attached to the Scripps muscle at week 0 and week 4. Right six panels: scanning electron microscopy images of the polyurethane foam (top) and control ethylene vinyl acetate (EVA) foam (bottom). A, F: Foams before being exposed to seawater; D, G: After 4 weeks underwater; E, H: After 12 weeks underwater
Scanning electron microscopy images of the polyurethane foam (top) and control ethylene vinyl acetate (EVA) foam (bottom). A, D: Foams before being exposed to seawater; D, G: After 15 weeks underwater; E, H: After 30 weeks underwater
Eight million tons of plastic ends up in the ocean every year
Of the 30 billion plastic bottles used by UK households each year, only 57 percent are currently recycled.
With half of this going to landfill, half of all recycled plastic bottles are thrown away.
About 700,000 plastic bottles a day end up as litter.
This is largely due to plastic packaging around bottles that are not recyclable.
Bottles are an important contributor to the increasing amount of plastic waste in the world’s oceans.
Researchers warned that eight million tons of plastic currently end up in the ocean each year — the equivalent of one truckload per minute.
The amount of plastic waste in the world’s oceans will exceed that of fish by 2050 unless the world takes drastic measures to further recycle, a 2016 report found.
At the current rate, this will deteriorate to four truckloads per minute by 2050 and outnumber native life to become the largest mass in the oceans.
An overwhelming 95 percent of plastic packaging – worth £65-£92 billion – is lost to the economy after a single use, according to the Ellen MacArthur Foundation report.
And available 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 at sea and on land. It pollutes coastlines, traps animals and suffocates entire populations of animals
So much plastic is dumped into the sea every year that it would fill five carrier bags for every meter of coastline on Earth, scientists warn.
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 industrialized western country on the list of the top 20 plastic polluters is the United States at number 20.
The US and Europe don’t mismanage their collected waste, so the plastic waste coming from those countries is due to litter, researchers say.
While China is responsible for 2.4 million tons of plastic that ends up in the ocean, nearly 28 percent of the world’s total, the United States contributes just 77,000 tons, which is less than one percent, according to the study published in the journal Science.