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Bright colours make plastics break down faster, fuelling microplastic pollution

Colourful plastics break down faster according to new research.
Colourful plastics break down faster according to new research. Copyright Pexels
Copyright Pexels
By Rosie Frost
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The study’s authors say manufacturers should give more thought to what colour they make short-lived items.

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Plastics with bright colours degrade and form microplastics faster than those with plainer colours, according to new research.

Experts at the University of Leicester have demonstrated that colours like reds, blues and greens can significantly affect the rate at which plastics break down. This could potentially mean more harmful microplastics are introduced into the environment.

The study, published in the journal Environmental Pollution, is the first time this effect has been proved.

Which plastic colours break down faster?

The team from the University of Leicester in the UK and the University of Cape Town in South Africa used two complementary studies to show plastics degrade at different rates depending on what colour is added to them.

One used bottle caps of different colours placed on the roof of a university building, exposed to the sun and elements for three years. The second used different coloured plastic items found on a remote beach in South Africa.

Both showed that black, white and silver plastics were largely unaffected. Blue, green and red samples, however, became very brittle and fragmented over the same time period. In the South African study, the older samples found were all plain colours but the sand was full of brightly coloured fragments.

Researchers say it shows how black, white and silver colourants protect the plastic from damaging ultraviolet (UV) radiation which changes its polymer structure making it brittle.

Microplastic debris washed up on the shore.
Microplastic debris washed up on the shore. AP Photo/Andrew Selsky

“It’s amazing that samples left to weather on a rooftop in Leicester in the UK and those collected on a windswept beach at the southern tip of the African continent show similar results,” says Dr Sarah Key, who led the project.

“What the experiments showed is that even in a relatively cool and cloudy environment for only three years, huge differences can be seen in the formation of microplastics.”

“I’ve often wondered why microplastics in beach sand often appear to be all the colours of the rainbow,” adds co-author Professor Sarah Gabbott, from the University of Leicester School of Geography Geology and the Environment.

“Until our study I assumed that my eyes were being deceived and that I was just seeing the more colourful microplastics because they were easier to spot.”

But, Professor Gabbott says it turns out it really is likely more brightly coloured microplastics are in the environment because they are more susceptible to being fragmented into “millions of tiny, yet colourful microplastic particles”.

Could less colourful plastic reduce pollution?

Researchers say the study has significant implications for material design as not using bright colours could help reduce microplastic pollution. These tiny particles of decomposed plastic have made their way into clouds, ‘pristine’ prehistoric remains and were even found in human testicles.

“Manufacturers should consider both the recyclability of the material and the likelihood of it being littered when designing plastic items and packaging,” Dr Key says.

“For items that are used outdoors or extensively exposed to sunlight, such as plastic outdoor furniture, consider avoiding colours like red, green and blue to make them last as long as possible.”

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