Today's KNOWLEDGE Share
Researchers led by the University of Leicester have demonstrated that plastics with bright colors such as red, blue, and green degrade and form microplastics quicker than those with plainer colors.
Their findings reveal that the colorant used in the formulation of a plastic product can significantly affect the rate at which it degrades and breaks down, potentially introducing harmful plastics into the environment more quickly.
Conducted Two Complementary Studies to Compare Degradation:
Published in the journal Environmental Pollution, it is the first time this effect has been proven in a field study and could be important for retailers to consider when designing plastics and packaging.
Researchers from the University of Leicester, UK and the University of Cape Town in South Africa used two complementary studies to show that plastics of the same composition degrade at different rates depending on what is added to color them.
One study used bottle lids of various colors 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 colored plastic items that were found on a remote beach in South Africa. Importantly, samples were only analyzed 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, 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 colors and not brightly colored plastic items were found. But the sand itself was full of many colored microplastics.
Black, White, and Silver Colorants Protect the Plastic from Damaging
This demonstrates that the black, white, and silver colorants protect the plastic from damaging ultraviolet (UV) radiation whereas other pigments do not. UV damage changes the plastic’s polymer structure, making it brittle and susceptible to fragmentation.
The research was led by Dr Sarah Key, who conducted the studies while a PhD student at the University of Leicester School of Chemistry and funded by CENTA – The Central England NERC Training Alliance and is now a senior research analyst with climate action NGO WRAP (Waste & Resources Action Program).
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. Colorful plastics, such as red and green, degrade and form microplastics pretty quickly. When you look at plainer colors, 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 color and think about how soon it would have otherwise broken down. Whatever the color, always check the packaging for details of how to recycle plastic packaging.”
Suggestion to Give More Consideration to Color of Short-lived Plastics:
Microplastics display different properties from their original bulk materials, and little is understood about their impact on the environment. We know that they can release toxic plastic additives into the environment, and they can potentially be transferred to humans, as well as toxic chemicals on their surfaces, through the food chain and water supplies.The study has significant implications for material design and suggests that manufacturers should give more consideration to the color of short-lived plastics.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 colors like red, green, and blue to make them last as long as possible. Where the plastic is designed to break down, such as by using pro-oxidant additives, consider the role that color could play in this.”
Co-author professor Sarah Gabbott, from the University of Leicester School of Geography Geology and the Environment, said, “I’ve often wondered why microplastics in beach sand often appear to be all the colors of the rainbow. Until our study I assumed that my eyes were being deceived and that I was just seeing the more colorful microplastics because they were easier to spot. Turns out there really are likely to be more brightly colored microplastics in the environment because those plastic items pigmented red, green, and blue are more susceptible to being fragmented into millions of tiny, yet colorful microplastic particles.”
Source: University of Leicester/polymer-additives.specialchem.com
