Retailers are being urged to ditch making bottles and other items from brightly coloured plastics after a study found they degrade into microplastics quicker than plainer colours.
The findings of the study show. that the colourant used in the formulation of a plastic product can significantly affect the rate at which it degrades and breaks down.
This means that it potentially introduces harmful plastics into the environment more quickly.
The study marks the first time this effect has been proven and could be an important factor for retailers to consider when designing plastic and packaging, researchers said.
Researchers from the University of Leicester, UK and the University of Cape Town in South Africa undertook two complementary studies to show that plastics of the same composition degrade at different rates depending on what is added to colour them.
One study used bottle lids of various colours and placed them on top of the roof of a university building to be exposed to the sun and the elements for three years.
The second study used different coloured plastic items that were found on a remote beach in South Africa.
Samples were only analysed when the date of the manufacture of the plastic was known by a date stamp embossed into the plastic items.
The scientists measured how chemically degraded the samples were by looking at how much they had reacted with oxygen in the air using Fourier-transform infrared spectroscopy (FTIR).
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They also measured the structural integrity before and after, using a breaking strength test to measure how brittle and easy to break apart they were.
The findings across both studies showed that black, white and silver plastics were largely unaffected whereas blue, green and red samples became very brittle and fragmented over the same time period.
In fact, older samples in South Africa were all plain colours, with no brightly-coloured plastic items found. However, the surrounding sand was full of many coloured microplastics.
The microplastic research was led by Dr Sarah Key, who conducted the studies while a PhD student at the University of Leicester School of Chemistry.
She said: “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.
“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. Colourful plastics, such as red and green, degrade and form microplastics pretty quickly. When you look at more plain colours, such as black and white, they’re actually quite stable and remain intact.
“Next time you clean up some plastic litter, take note of the colour and think about how soon it would have otherwise broken down. Whatever the colour, always check the packaging for details of how to recycle plastic packaging.”
In March this year, a cross-party group of MPs came together to call for an end to the “toxic flow” of microplastics into UK rivers and waterways.
