en.Wedoany.com Reported - Engineers at Northwestern University have discovered that salt and organic matter in natural waters significantly slow down the decomposition process of plastics, explaining why plastic products can persist in rivers, lakes, and oceans for decades or even centuries. The findings have been published in the Nature journal Materials Degradation.
It was previously known that ultraviolet rays from sunlight can promote plastic decomposition through photodegradation, yet the degradation rate of plastics in natural water bodies is exceptionally slow. The research team simulated various real-world water environments in the laboratory, placing thin strips of polystyrene plastic in pure water, freshwater simulation fluid, and seawater simulation fluid, and exposing them to full-spectrum sunlight for approximately three months. The results showed that plastics degraded the most in pure water, less in freshwater, and the least in seawater.
The study indicates that salts in seawater, such as chlorides, bromides, bicarbonates, and sulfates, inhibit sunlight-induced chemical reactions. When natural organic matter from decaying plants and microorganisms was added, the degradation process was further hindered. This is because dissolved ions and organic matter in the water compete with plastics for sunlight-driven reactions, preventing sunlight from effectively initiating the degradation process.
The research team further introduced environmental bacteria known to degrade plastics into each water sample. They found that plastics pre-exposed to sunlight in freshwater solutions showed more microbial decomposition than those exposed in seawater solutions. This suggests that because seawater inhibits the initial damage to plastics by sunlight, fewer decomposition products are available for microorganisms to utilize.
The study was led by Ludmilla Aristilde, a professor of civil and environmental engineering at Northwestern University's McCormick School of Engineering, who is also a member of the Center for Synthetic Biology, the International Institute for Nanotechnology, and the Paula M. Trienens Institute for Sustainability and Energy. Postdoctoral researcher Nasrin Naderi Beni and doctoral student Cara Flynn led the research work. The study was funded by the National Science Foundation. The team stated that these findings help understand the behavior of plastics in real environments and provide new insights for designing novel plastic materials that degrade more easily under natural conditions.
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