Plastic waste and the pandemic

Our use of plastic is changing worldwide – and not for the better. Many governments with bans or restrictions on the consumption of single-use plastics have withdrawn the bans and, during the COVID-19 pandemic, our consumption of them in the form of personal protective equipment (PPE) has escalated, with estimates as high as sixfold increases – much is unrecyclable, and domestic and small business users have no defined waste policy, with much of it ending up in recycling where, due to its medical nature, it cannot be processed. This causes bottlenecks in the recycling system, or illegal waste dumping.

Rubber trees.  松岡明芳 via WikiCommons.

Latex gloves are made from the rubber in rubber trees: a polymer of isoprene that is readily broken down in nature. However, not all plastics are so readily biodegradable. Some, such as nylon (also used in gloves), are a halfway house: they can decompose under warm, wet conditions, but are relatively sturdy; others, such as polypropylene (PP) (used in gowns and masks), which is a hydrocarbon with no oxygen nor nitrogen linkages to help make it compostable, may stick around for thousands of years.

Lifetime of a Plastic Bag

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?

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].