450 years into the future - that’s the agreed lifetime of a uniform piece of plastic like a bag. But who’s arguing? Man-made plastics have only been around for about 50 years: we don’t know for sure how long it takes a plastic bag to decompose: so where does this number come from?
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| A floating plastic bag. Like so many, it has ended up in the ocean. Image credit: Andrew (Flickr). |
Plastic readily breaks down into smaller and smaller pieces (microplastics) under environmental conditions: it can now be found anywhere, a splash of colour amongst sand particles viewed beneath a microscope. But this isn’t the same as biodegradation, defined as the bacteria-driven chemical transformation of a material into other compounds.
Natural plastics do exist and do biodegrade: rubber and cellulose, for example. But these don’t make a good comparison with man-made plastics: cellulose is eaten by many animals, and enzymes and microorganisms exist in nature to catalyse its break down, which normally happens by about 6 months[1]. There are some man-made plastic-eating bacteria, but these have only recently been discovered: how fast they act or what products the plastics are broken down into (and whether they are safe and useful) is still a mystery[2].