When exposed to sunlight, polystyrene can break down in as little as decades or centuries, rather than thousands of years, a study from the US reveals.
The ubiquitous plastic — which is used for assorted applications from takeaway boxes to packaging materials — is often considered to last ‘forever’.
However experts using a sun-simulating lamp found they could chemically degrade polystyrene slowly, releasing organic carbon and trace amounts of carbon dioxide.
Governments writing policies banning or limiting the use of the plastic may be working without knowing the full facts, the researchers argue.
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When exposed to sunlight, polystyrene can break down in as little as decades or centuries, rather than thousands of years, a study from the US reveals
‘Policymakers generally assume that polystyrene lasts forever in the environment,’ said paper author and marine chemist Collin Ward of the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, in the US.
‘That’s part of justification for writing policy that bans it.’
Dr Ward and his colleagues, however, set out to determine whether or not polystyrene really does last forever.
‘We’re not saying that plastic pollution isn’t bad, just that the persistence of polystyrene in the environment may be shorter and likely more complicated than we previously understood’
‘The chance for injury to the environment over decades is still available.’
The ubiquitous plastic — which can be made solid or as the foamed variety often used for packing chips, fast food containers and disposable cups — was first found littering the world’s oceans in the 1970s and has fallen into lawmakers’ cross-hairs.
Like many polymer-based plastics, polystyrene slowly turns yellowed and brittle when exposed to the ultraviolet (UV) component of sunlight.
‘Just look at plastic playground toys, park benches, or lawn chairs, which can rapidly become sun-bleached,’ said Dr Ward.
According to the researchers, however, sunlight does not only cause the plastics to physically break down, but also causes them to degrade chemically.
This process forms both dissolved organic carbon and trace amounts of carbon dioxide, albeit at levels far too low to impact climate change.
According to Dr Ward, understanding exactly how this transformation happens will be vital for future estimations of how much plastic waste is actually out in the environment.
The ubiquitous plastic — which is used for assorted applications from takeaway boxes to packaging materials — is often considered to last ‘forever’
Previous estimates of the rate at which polystyrene breaks down, he added, used a different set of assumptions — and often focused on the impact of plastic-eating microbes, rather than other factors like sunlight.
Paper co-author and marine chemist Chris Reddy, also of the WHOI, noted that plastic is just another form of organic carbon.
While microbes would eat plastic, they can also be smart and selective, he noted, with the complex and bulky structure of polystyrene not making it the most appealing fodder for bacteria.
‘Although the ring-based backbone of polystyrene makes it a difficult target for microbes, it’s the perfect shape and size to catch certain frequencies of sunlight,’ said Dr Reddy.
However experts using a sun-simulating lamp found they could chemically degrade polystyrene slowly, releasing organic carbon and trace amounts of carbon dioxide
To test whether sunlight could break down polystyrene, the researchers placed five of the most commonly-used types in water and under a sun-simulating lamp.
They then collected the CO2 and other compounds that they found had been dissolved into the water.
‘We used multiple methods to do this, and they all pointed to the same outcome: sunlight can transform the polystyrene into CO2,’ said Dr Ward.
‘But we need more research to understand what happens to the other products that dissolve into water.’
The team also found that chemicals often added to polystyrene in order to change its colour or levels of flexibility have a key impact on the plastic’s breakdown.
‘Different additives seem to absorb different frequencies of sunlight, which influences how fast the plastic breaks down,’ Dr Reddy said.
The full findings of the study were published in the journal Environmental Science and Technology Letters.
