Bright-coloured plastics degrade and form microplastics quicker than plainer-coloured plastics, a study from researchers led by the University of Leicester showed.
According to the study, the colourant used in the formulation of a plastic product can significantly affect the rate at which it degrades and breaks down, which could potentially introduce harmful plastics into the environment more quickly.
Published in the journal Environmental Pollution, the University of Leicester said this is the first time this effect has been proven in a field study.
Researchers from the University of Leicester and the University of Cape Town in South Africa used two complementary studies to measure if plastics of the same composition degrade at different rates depending on what is added to colour them.
As part of one study, researchers placed used bottle lids of various colours on top of a university building’s roof for three years.
The second study used different coloured plastic items that were found on a remote beach in South Africa.
The research was led by Dr Sarah Key, who conducted the studies while a PhD student at the University of Leicester School of Chemistry funded by CENTA, The Central England NERC Training Alliance.
Key is now a senior research analyst with climate action non-governmental organisation WRAP (Waste & Resources Action Programme).
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.
Commenting on the study, Dr Key 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.”
The University of Leicester said 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).
They also measured the structural integrity before and after the experiment 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 timeframe.
Older samples in South Africa were all plain colours and no brightly coloured plastic items were found. However, the sand where the items were collected from was full of many coloured microplastics, the University said.
Dr Key added: “Manufacturers should consider both the recyclability of the material and the likelihood of it being littered when designing plastic items and packaging.
“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.”
