The term ‘plastic’ encompasses many different materials (PET, Bisphenol A, PVC, Styrofoam, and more), but most of them share the same problem of slow breakdown in nature (referring to synthetic plastic products, not the natural alternatives).
Moreover, some of those materials’ degradation involves the emission of dangerous gases.
Under normal conditions in nature, plastic bottles (usually made of polyethylene, also known as PET, or polyethylene terephthalate) will begin to break down only after 500-700 years and even then, the process will be very slow. Plastic bags will begin the process only after a thousand years.
Clearly, as plastic in its current form (bottles and bags) has been around for little over 50 years, no actual experiment has involved the burial of plastic materials for a 1,000 years; these figures were obtained from experiments in which different types of plastic were buried in nature and the time for breakdown was estimated according to the effects tested.
As a comparison, if the crusaders and Salah a-Din had used plastic bags at their battle at the Horns of Hattin (1187 AD), the remnants would still be around for archaeologists to examine.
The reason for the slow degradation is a simple one. These materials do not exist in nature, and therefore, there are no naturally occurring organisms that can break them down effectively or at all. The chemical bonds in plastic materials are not accessible or “familiar” to bacteria in nature. These materials are called “xenobiotic.”
Today, there are various methods – heat, pressure, chemical additives, and biological techniques (some under development) that can accelerate the degradation pace and prevent the emission of dangerous material during this process.
Another approach is to make biodegradable plastic bags from natural organic materials (such as corn). Over the past year, different organizations in Israel have started using them.
There is also a plastic material called polyhydroxyalkanoate (PHA), which is made naturally by microorganisms – and therefore, is more biodegradable.
Molecular structure of PHA and similar molecules
Pictures are from Wikipedia.
By Dr. Meir Barak
Department of Structural Biology
Weizmann Institute of Science
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