The Real Meaning of Biodegradable

Rita Steyn

So, yesterday we dispelled a few myths about ‘biodegradable’ plastics. But what does biodegradable actually mean? It’s been thrown around so much that a lot of us have been left feeling very confused. How can we tell if companies are using this label to greenwash their products? Can plastics actually biodegrade? Read on to find out…

Definitions are simple, standards are not

To put a few things straight, here are a few definitions for you:

  • Degradable: Material that will undergo a process of deterioration or breaking-up by the action of natural forces (air, light, water) or by the addition of certain chemicals. 

  • Biodegradable: Capable of being broken down (decomposed) rapidly by the action of living organisms, producing water, carbon dioxide, and biomass.

  • Photodegradable: Substances that can be degraded (broken-up) by the action of ultraviolet rays (e.g. from sunlight).

  • Compostable: Something which will decompose into, or become part of, usable compost or mulch (decayed organic material) which is non-toxic. This definition is further split into materials which can be home composted, and those which need to be commercially composted.

The key difference between these definitions is ‘breaking up’ and ‘breaking down’. Whilst biodegradable and compostable materials break DOWN into constituent molecules (think CO2, H2O), degradable and photodegradable materials break UP into smaller pieces. 

And just because something can biodegrade, doesn’t mean it will. 

Organisms that help biodegrade materials typically require light, water, and oxygen to work. And warmer temperatures are a vital factor determining how quickly a material will biodegrade. So many environments (landfill, oceans) won’t be suitable for the biodegradation of materials. Even natural items such as food waste have been shown to break down very slowly in landfill. 

Photodegradation, as the name suggests, requires light in order to occur. Think about the depths of a landfill site, or anywhere in the ocean below 200m (i.e. 90% of it), and you will realise there is very little (if any) light there. So even this process can’t lend a helping hand.

Many brands and companies are labelling their products ‘biodegradable’, after doing their own ‘tests’ (or no tests at all) and there is absolutely no regulation of this, meaning the word can be thrown around willy nilly. 

The conditions in landfill sites are typically not favourable for degradation. Photo: Pixabay

The conditions in landfill sites are typically not favourable for degradation. Photo: Pixabay

Using the biodegradable label to greenwash

Companies have the single goal of convincing you to buy the thing that they sell. Sometimes this means that they might make claims or say things that sound good, but are so vague that you aren’t exactly sure what they mean. Using eco-friendly promises and terms to market and sell products is called greenwashing, and often hides environmental harms. 

Whenever you’re looking at labels, or on a company website, look for proof of what they claim. Critical thinking skills are your new best friend. If there is no proof, write to them and ask for it! If they have nothing to hide they should have no problem supplying you with evidence of what they’re saying. If you get a vague reply, with no concrete or detailed answer, or they say ‘all the information is on our website’ they’re most definitely greenwashing. 

Companies may claim their packaging is ‘biodegradable’ or ‘compostable’ without giving any evidence. Photo: The Terramar Project. ** Disclaimer ** We are not implying the brand pictured is greenwashing.

Companies may claim their packaging is ‘biodegradable’ or ‘compostable’ without giving any evidence. Photo: The Terramar Project. ** Disclaimer ** We are not implying the brand pictured is greenwashing.

So, is there such a thing as a biodegradable plastic?

Technically, when people talk about plastic ‘breaking down’ what they mean is the action of UV light and physical forces (wind, waves etc) breaking the polymer bonds and allowing the plastic to fragment into ever smaller pieces (photodegradation). 

We have no good measure for how long conventional plastics take to degrade, because we only started making them around 50 years ago, and they still haven’t gone away. And conventional tests (respirometry) won’t work with plastics. So the estimates of how long say, a plastic bottle, carrier bag, or straw will ‘last’ actually estimate the time taken for these products to photodegrade. 

Some estimates give around 50-100 years, some give a 1000 years or more. Basically, a really, really long time. So, that single-use plastic cup you use once and throw away, will surpass the lives of your children’s grandchildren’s grandchildren (and beyond). 

A few species of organisms have been found to be capable of breaking down plastic, including a caterpillar, mealworms, a fungi, and a bacterium. But before you get excited, they are only found in precise locations, and can only target specific types of plastic. 

Now for the confusing bit, compostable plastics. 

Technically, compostable plastics are biodegradable. But only under the conditions in a commercial composting facility. Even then, these plastics can take up to 6 months to compost. The time it takes largely depends on the type and size of the plastic, the composting conditions. Compostable products need to meet 3 criteria 

  1. Biodegrade - break down into carbon dioxide, water, biomass at the same rate as cellulose (paper)

  2. Disintegrate - the material is indistinguishable from other material in the final compost

  3. Eco-toxicity - the biodegradation does not produce any toxic material and the compost can support plant growth

There are various tests and standards for compostability, and companies can get the Biodegradable Products Institute logo, which certifies that their product is compostable. But as we discovered yesterday, this can feed into our consumerist, throw-away lifestyles.

The degradation products from compostable products must be able to support plant growth. Photo: Pixabay

The degradation products from compostable products must be able to support plant growth. Photo: Pixabay

There are many great biodegradable materials out here already

Basically anything that is a natural substance, that hasn’t been significantly altered chemically in manufacturing is inherently biodegradable. Think paper, cardboard, wood, bamboo, cotton, hemp. Look out for our article tomorrow for more alternatives to plastic, that actually are biodegradable, and some cool innovations that are breaking into the market.

Still a bit confused? We don’t blame you! The best solution is to avoid all plastics, whether they’re claiming to be biodegradable, compostable, or eco-friendly. 


For more information on definitions check out this site

This month, The Marine Diaries will be sharing our knowledge on plastic pollution to help educate the public about the impact of our actions on marine life, in the hope of promoting change. Together we can fight plastic.

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