Many of us have heard the statistics by now: 8 million metric tons of plastic enter the oceans each year. What happens to these plastics in salty, sunny seas? To find out, researchers at the Pennsylvania State University turned to artificial intelligence.
Using a machine-learning algorithm, the researchers analyzed how 110 different types of plastic, including commercial and experimental varieties, will degrade in the ocean. The results, published in Nature Communications, show that certain types of plastics break down quicker than others when subjected to the conditions found in the oceans.
There are already over 150 million metric tons of plastics in the ocean, according the Ocean Conservancy. These plastics can break down under conditions found in the ocean, such as the sun’s ultraviolet radiation, wind, waves, seawater, water temperature, and bacteria.
But there is a wide variety of plastics used to make products. These plastics have different molecular structures, chemical groups, additives, and other traits. Both the physical breakdown as well as bacteria-driven biodegradation of plastics depends on these molecular and physical features.
The team gathered data on the molecular structure and physical properties of over 110 types of plastics found in the ocean. The physical properties include things such as molecular weights, the glass transition temperature, and crystallinity. “We figured out how to translate molecular structure into a metric that we called hydrophobicity, which is how much is the material likely to absorb water or want to be in contact with water,” said Penn State chemistry professor Robert Mathers.
Using computational models to analyze polymer structure, composition, physical properties, and degradation data, the team was able to predict features that control degradation. They classified ocean plastics into fast, medium, and slow degradation categories.
Strategies such as making plastics water-soluble, adding weak links that breaks more easily, or additives that trigger breakdown under light, could accelerate the degradation of plastics under environmental conditions. But it is not economically feasible to produce such plastics at scale.
“It’s just hard to economically compete with polyethylene and polypropylene, which are the most-used plastics in the world,” Mathers said. “So, we probably want to keep focusing on recycling because that offers the most immediate help.”
Source: Min, K., Cuiffi, J.D. & Mathers, R.T. Ranking environmental degradation trends of plastic marine debris based on physical properties and molecular structure. Nat Commun, 2020.