A study published by researchers from the Woods Hole Oceanographic Institution (WHOI) shows that polystyrene can be broken down into one of the world's most ubiquitous plastics that can be mined in decades or centuries instead of thousands of years, as previously thought. The study was published on October 10, 2019 in the journal Environmental Science and Technology Letters .
"Currently, policymakers generally believe that polystyrene is durable in the environment," says Collin Ward, a WHOI marine chemist and lead author of the study. "This is part of the justification for drafting policies that prohibit this." One of our motivations for this study was to understand whether polystyrene really does last forever. We do not say that the plastic pollution is not bad, only that the persistence of polystyrene in the environment can be shorter and probably more complicated than we have understood so far. The danger of environmental damage for decades remains. "
Polystyrene has been routinely detected in the world's oceans since the 1970s. The idea that sunlight breaks down plastics is nothing new, Ward says. "Just look at toys made of plastic, park benches, or lawn chairs that can be sun-bleached quickly." The WHOI study shows that sunlight does not just cause plastics Degradation, however, also leads to their being chemically degraded into dissolved organic carbon and traces of carbon dioxide far too low to affect climate change. Once the plastic undergoes this transformation, its original form disappears from the environment and it becomes completely new by-products that are invisible to the naked eye. Given how this transformation works, it is important to estimate how much plastic is actually present in the environment.
Earlier estimates of how quickly polystyrene is broken down were based on other assumptions, Ward said. Previous studies have focused largely on the role that microbes play in degradation rather than other factors such as sunlight. That's not surprising, says Chris Reddy, marine chemist at WHOI and co-author of the paper. Plastic is just another form of organic carbon and microbes probably would "eat" it – but it warns that microbes are also smart and selective. The chemical structure of polystyrene is complex and bulky and has an annular backbone that inhibits microbes or makes the plastic unsightly.
The WHOI study shows that sunlight not only physically disintegrates the plastic. however, it also leads to chemical degradation to dissolved organic carbon and trace amounts of carbon dioxide far too low to affect climate change.
"Although the ring-based backbone of polystyrene is a challenging target for microbes, it's the perfect shape and size to capture specific frequencies of sunlight," adds Ward. By absorbing this energy, the carbon bonds can be broken.
In the lab, researchers tested whether sunlight can transform polystyrene by exposing five different samples of commercial polystyrene. The group dipped each of them in sealed glass containers of water and lit them from a solar simulator, a lamp that mimics the frequencies of sunlight. The scientists then collected CO2 and compounds that dissolved in the water.
With a variety of chemical tools, including a room-size accelerometer mass spectrometer, Ward and colleagues tracked the origins of carbon atoms found in both CO2 and filtered water. "We used several methods that all pointed to the same result: sunlight can convert the polystyrene to CO2. However, we need to look more closely at what happens to the other products that dissolve in water, "says Ward.
The study also found that additives to polystyrene, which can determine color, flexibility and other physical properties, play an important role in collapse. "Different additives seem to absorb different frequencies of sunlight, which affects how quickly the plastic decays," says Reddy.
The paper was also edited by WHOI's Cassia J. Armstrong and Julia H. Jackson, WHOI's Anna N. Walsh, and the Massachusetts Institute of Technology. The research was funded by the Frank and Lisina High Endowment Fund, the Andrew W. Mellon Foundation, the Stanley Watson Chair of Oceanography, and a National Science Foundation Graduate Research Fellowship.
The Woods Hole Oceanographic Institution is a private, non-profit organization based in Cape Cod, Massachusetts dedicated to marine science, engineering and higher education. Founded in 1930 on the recommendation of the National Academy of Sciences, its main mission is to understand the oceans and their interaction with the Earth as a whole and to provide a basic understanding of the role of the oceans in the changing global environment] Reference: "Sunlight converts polystyrene in Carbon Dioxide and Dissolved Organic Carbon "by Collin P. Ward, Cassia J. Armstrong, Anna N. Walsh, Julia H. Jackson, and Christopher M. Reddy, October 10, 2019, Environmental Science and Technology Letters ,
DOI: 10.1021 / acs.estlett.9b00532