Are plastics biodegradable?

Photo: Outagamie County Recycling & Solid Waste, 2018.

We’ve all heard the stats – every piece of plastic that has ever been created still remains today. Plastics are designed to have a long life span. Many of the advantageous properties of plastics, such as their toughness and durability, present challenges when they are released into the environment. So what happens to them when our use for them ends? Can they be recycled? And are any plastics truly biodegradable?
 
Plastics contain a complex mix of stabilisers that prevent them from degrading too rapidly (1). While this is great for some things – think of dear Liza and the hole in her bucket – it’s not so great when we are finished with them and want to dispose of them. These stabilisers mean that many common plastics including polypropylene (denoted as PP – found in bottle caps, straws, fabrics) polyethylene (PE – bottles, food wrap, toys), polystyrene (PS – takeaway food containers, disposable cups) and polyethylene terephthalate (PET – water and soft drink bottles, jars) are extremely persistent in the environment (1). They undergo very slow fragmentation where they break down into ever smaller particles eventually becoming microplastics that never go away. Out of sight, out of mind, right?
 
So now we know what plastics are and why they are grade-A clingers to the Earth, what can we do about it? And are biodegradable plastics the way to go?
 
Degradable or biodegradable?
In recent years, the word “biodegradable” has become a powerful and appealing marketing term that is very misleading. While biodegradability refers to any organic substance that can be broken down by living microorganisms such as bacteria and fungi into carbon dioxide, water and biomass (2), in most cases, product biodegradability is tested under very specific conditions (2,3). Although suggesting that products break down in this natural and environmentally friendly way, these materials in fact may take far longer to fully break down and still generate large quantities of potentially harmful small particles (4). What’s more, these little micro powerhouses are powerless against many conventional plastics which are resistant against complete microbial attack (5). Add to that the fact that many biodegradable plastics contain metal salts that speed up the break-down process resulting in micro-fragments of plastics AND metals which remain in the environment (2) and we realise that maybe these plastics aren’t so eco-friendly. While some of these products are in fact biodegradable under natural conditions, be wary that this may not be the case for all.
 
Now, a tip for young players – biodegradable is not to be confused with degradable products. While the addition of bio- to the front of this word seems like an insignificant detail, the two are actually very different. Degradability refers to any physical or chemical change in a polymer’s properties. It relates to compounds that break down into simpler compounds by stages. That is, a large piece of degradable plastic can breakdown into ever smaller pieces of plastic.
 
But what is bioplastic? And is it any better?
Research has been focusing on the development of novel plastics that are derived from biological or renewable resources, rather than petroleum (6), that can be biodegraded (are compostable) in the environment (4). These are known as bio-plastics. Two of the most common materials used to create bioplastics are starch and cellulose which are derived from either corn or sugar cane. While bio-plastics may be the way of the future, we still have a way to go. Some companies will market their products as bioplastics made from plant-based materials however also state that these can only be composed in a commercial facility. Some are also heat sensitive and must be stored out of direct sun and away from heat sources. And contrary to popular belief, while bioplastics may be composed (*see previous sentence regarding this), they cannot be recycled. Those that can be are done so chemically and the method at this stage is not yet commercially viable. Know those clear disposable cups and packaging that look and feel like plastic but have eco-friendly logos? Just sayin’.
 
Confused yet? So are we!
But don’t fear! Put simply, compostable is the way to go. This refers to any organic material that can truly biodegrade, disintegrate and is non eco-toxic. That is, it can break down into the goodness of carbon dioxide, water and biomass, it does so rapidly so that after three months of composting no more than 10% remains, the breakdown process does not produce any toxic material and the compost can sustain plant growth (2). Just think, if natural goodies are going in, natural goodies will come out. But remember, if you decide to go compostable, ensure you follow through on your good intentions and dispose of correctly. Your compost bin and garden will love you. And so will the world.
 
What you can do:

• Ditch the single-use plastics
• Go for more sustainable and longer-lasting natural alternatives
• Opt for items made of compostable materials such as plant-based cellulose or corn starch
• Ensure compostable products DON’T end up in your recycling and DO end up in your compost
• If you can’t avoid it (plastic), repurpose and reuse items rather than throwing them away
• If you can no longer reuse it, check to see if it’s recyclable – check your local recycling guidelines, a great place to start is the RecycleSmart App which provides details for everything from food and household, to construction and automotive waste.
• Scrunchable plastics can also be recycled at many REDcycle participating outlets. Check out for details

1. Kubowicz, S., Booth, A.M. 2017. Biodegradability of plastics: challenges and misconceptions. Environ. Sci. Technol. 51, 12058-12060.2. Philp, J.C., Bartsev,
2. A., Ritchie, R.J., Baucher, M.A., Guy, K. 2013. Bioplastic science from a policy vantage point. New Biotech. 30, 635-646.
3. Shah, A.A., Hasan, F., Hameed, A., Ahmed, S. 2008. Biological degradation of plastics: a comprehensive review. Biotech. Adv. 26, 246-265.
4. Karamanlioglu, M., Robson, G.D. 2013. The influence of biotic and abiotic factors on the rate of degradation of poly(lactic) acid (PLA) coupons buried in compost and soil.
5. Mueller, R.J. 2006. Biological degradation of synthetic polyesters – enzymes as potential catalysts for polyester recycling. Process Biochem. 41, 2124-2128.
6. Tokiwa, Y., Calabia, B.P., Ugwu, C., Aiba, S. 2009. Biodegradability of plastics. Int. J. Mol. Sci. 10, 3722-3742.