Previous estimates of how quickly polystyrene breaks down were based on a different set of assumptions.
A study published by researchers at Woods Hole Oceanographic Institution (WHOI) shows that polystyrene, one of the world’s most ubiquitous plastics, may degrade in decades or centuries when exposed to sunlight, rather than thousands of years as previously thought. The study published October 10, 2019, in the journal Environmental Science and Technology Letters.
“Right now, policy makers generally assume that polystyrene lasts forever in the environment,” says Collin Ward, a marine chemist at WHOI and lead author of the study. “That’s part of justification for writing policy that bans it. One of our motivations for this study was to understand if polystyrene actually 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.”
Polystyrene has been routinely detected in the world’s oceans since the 1970s. The idea that sunlight degrades plastics is nothing new, Ward says: “Just look at plastic playground toys, park benches, or lawn chairs, which can rapidly become sun-bleached.” The WHOI study shows that sunlight doesn’t just cause the plastics to physically break down, however—it also causes them to degrade chemically into dissolved organic carbon and trace amounts of carbon dioxide, at levels far too low to impact climate change. Once the plastic undergoes this transformation, its original form disappears from the environment, and it becomes entirely new byproducts that cannot be seen by the naked eye. Considering how this transformation happens will be an important part of estimating how much plastic is actually out in the environment, he adds.
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