Introduction
Though there is general agreement that plastic takes a very long time to degrade, it might be worth thinking about what the degradation process is and the products generated by it. Plastic is a catch-all term for a diverse suite of materials, so understanding the degradation of plastic is extremely complicated and difficult to observe.
What is degradation?
It could be classified as mechanical or chemical. These do not occur in isolation and likely interact to generate a spectrum of differently sized and shaped fragments, and with different chemical properties. It is rare, more likely nonexistent, to understand the complete timeline of degradation starting with a “pristine” plastic.
Consider an empty water bottle. Has there ever been a water bottle exposed to the forces of nature, monitored until it was “completely” degraded? What does that mean? What does it look like? It remains a mystery. However, it is known that plastic that gets into the environment, and then into human bodies, can wreak biological havoc.
Amount of Degredation
Large plastics, still in the form that they were manufactured, can interact with large animals when mistaken for a food source, for example.
At the smaller end of the size range (which is much harder to detect), plastic can cross biological membranes and, for example, affect the endocrine system in humans by interacting with and disrupting our natural hormones. This is especially concerning considering that microplastics have been found in human blood and even fetuses.
Understanding the Degredation Process & Spectrum
To better understand how plastic harms wildlife and humans, we must understand how plastic degrades and how the spectrum of materials generated from this degradation process can affect organisms at every step, from a single cell to a whale whose digestive system is stuffed full of plastic. Plastics break down through a number of processes, including:
- Photodegradation: UV light can interact with oxygen to create free radicals which affect the plastic surface and cause structural chemical changes leading to disintegration.
- Thermooxidative degradation: High temperatures can cause similar changes as photodegradation but these effects penetrate beneath the surface layers.
- Hydrolytic degradation: Incorporation of a water molecule can break apart molecules of the polymer into its simpler constituent compounds.
- Biodegradation: Though generally resistant, microorganisms may, at some stages, be capable of metabolizing the carbon or additives in plastic.
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