One Small Step in the War on Plastic

“I want to say one word to you. Just one word. Plastics.” Maybe some of you remember those prophetic lines from the 1976 movie “The Graduate”. Since that time plastics have become both the boon and the bane of our modern world. They are a cheap and easily adapted material used in nearly everything from food packaging to electronics. Without plastics, almost nothing in our daily lives would be as simple and efficient as it is now, so this versatile material is inextricably embedded in our society. Unfortunately, we’ve discovered significant downsides in our plastic-dominated world. Plastic is a useful material because it is tough and stable, but these properties also make it very difficult to break down in the environment. Instead, plastic just accumulates and accumulates in our oceans, our landfills, and even into plants and animals, including humans. One of the newest concerns is plastic nanoparticles that may collect in our bodies with unknown health risks. This pervasive use and continued manufacturing of plastics have altered the global environment over the last 50 years and we desperately need to reduce plastic contamination.

One of the major approaches to reduce the plastic burden has been an emphasis on recycling. Instead of continuing to produce more and more new plastic, we try to collect and repurpose already existing plastics via recycling. While recycling should reduce new plastic production, it won’t solve all the inherent problems. First, recycling has not been widely adopted and not all plastics can be recycled. Because of these issues, many estimates indicate that less than 20% of all plastics are recycled. Second, reusing recycled plastic for new manufacturing is problematic. Because of its chemical structure, plastics are difficult to break down into their original chemical components. Instead, they are mostly melted down and reformed, and a significant portion of the plastic is unreclaimed in the process and is discarded as waste. Additionally, much of the reclaimed material only produces a low-grade plastic that is used in making carpets and clothing that often end up back in landfills. Ideally, it would be most effective if the chemical bonds of plastic could be broken apart to regenerate the original starting compounds. This would allow cleaner and more efficient reuse of plastics over and over again instead of constantly manufacturing more new plastic.

Even during the human tragedy and economic devastation of COVID-19, science continues to bring us advances that help improve the world such as a recent report in Nature on a plastic dissolving enzyme. Polyethylene terephthalate (PET) is a commonly used plastic manufacturing material for many types of food packaging. PET is a polymer made from two chemicals: ethylene glycol and terephthalic acid which can be heated to form a molten liquid that is molded into the finished products. Unfortunately, once made, remelting weakens the structural integrity and limits the use of recycled PET products. This new work presents an enzyme that can cleave gently heated PET polymer back into its component compounds: ethylene glycol and terephthalic acid.  These starting compounds can be reused in the manufacturing process to produce structurally sound plastic.  Originally isolated from a bacterium known as Ideonella sakaiensis, the weak native enzyme was mutated and screened repeatedly to find a more active version.   The final mutated enzyme was not only 10,000 times more efficient at breaking down PET, but also active at 72⁰C where PET plastic is soft enough for easier enzymatic digestion. Plans are already underway to build a demonstration plant, and if successful this approach should dramatically improve PET recycling and reduce the environmental plastic burden. Hopefully, similar approaches will be developed for other types of common plastics in our lives.

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