The organic compounds produced by sunlight were analyzed at the National High Magnetic Field Laboratory, which designed and developed a mass spectrometer equipped with a 21 tesla magnet that achieves the highest mass resolution and accuracy in the world. Essentially, the instrument is the world’s fanciest scale, allowing the scientist to determine the composition of the sunlight-produced formulas.
Researchers found that under sunlight exposure, the four retailer bags produced between about 5,000 formulas (for the Target bag) to 15,000 formulas (for the Walmart bag), while the pure polyethylene film produced about 9,000 formulas. The scientist also found that the composition of the formulas produced was different between the pure and consumer plastics.
Many previous studies of marine plastics have generally used pure polymers, which are poor proxies for plastic in the marine environment. The paper calls for the research community "to embrace the diverse formulations and sunlight-driven transformations of plastics in the ocean" in order to gain a comprehensive and accurate understanding of the fate and impacts of marine plastic pollution.
"If the goal is to understand the fate and impacts of these materials, we need to study plastics that are representative of those that are actually leaked into the environment, as well as study the weathering processes acting on them," says Ward.
"I am excited about this work because it provides actionable and attainable approaches for making less persistent plastics in the future," says co-author Christopher Reddy, senior scientist in WHOI's Marine Chemistry and Geochemistry Department. ""By simply modifying the ingredients in their recipes, the plastic industry can make their products more susceptible to breakdown once the product reaches its useful lifespan".
"There is a lot of room for academia and industry to collaborate on this problem," adds Ward. "One logical way to solve the problem faster is to work with the people that develop the materials and understand their compositions. Ideally, we can figure out how plastic can be reformulated either to accelerate its degradation into products that are benign or to minimize the production of compounds that are not benign."
An earlier paper by Ward, Reddy, and lead author Taylor Nelson, a postdoctoral investigator in WHOI's Marine Chemistry and Geochemistry Department, shows that biofilms growing on plastic in the ocean screen light from reaching the plastic surface and may slow plastic degradation by sunlight. Like the paper led by Walsh, Nelson's paper also showed that the composition of the plastic, including the presence of additives, influenced the extent of this effect.