Biodegradable plastic is a spanner in the works for sustainability

It sounds appealing when a plastic product has ‘bio’, ‘degradable’ or ‘compostable’ on it. But if you want to make the most environmentally sound choice, you should not choose biodegradable plastic. Learn more about what bioplastic, biodegradable and compostable plastic is really all about.

Admittedly, it’s not easy for consumers when words like ’bio’ or ’compostable’ adorn products on the supermarket shelves. Of course, we are led to believe that we’re doing our bit for the environment by choosing such products. There is great confusion about what the various terms actually cover, and they are often used inaccurately and incorrectly – by the consumer, the retail industry and the companies – which only adds to the confusion, and unfortunately creates misguided green, but good, intentions.

The key difference between the ‘bio’ product types

So, what are the ins and outs of bio-based plastic and compostable plastic? The short answer is that bio-based plastic is about what the plastic is made from (the raw material), whereas compostable/biodegradable plastic is about whether the plastic can be biodegraded under controlled conditions. The confusion occurs because the word ‘bio’ is included in both types of plastic and because the naked eye cannot tell them apart. Lastly, the word ‘bioplastic’ is also often mistakenly used for ‘biodegradable plastic’.

These two aspects (the raw material and degradability) can be combined – thus providing four different overall types of plastic. In practice, plastic products can also be compound products, which means they are partly bio-based and partly fossil fuel-based.

1.Bio-based plastic is about raw materials and the climate

We’ll start with bio-based plastic, and – nerd alert – we need to include the technical bits too to get a good understanding of this topic.

‘Regular’ plastic is produced using oil or natural gas as the raw material, while bio-based plastic is made from biological material, i.e. plants (corn, sugar cane, hemp, etc.) and bio-waste. Because plastic is artificially manufactured by chemical manipulation, nature’s microorganisms (bacteria, fungi) are not able to break it down. A few special bacteria and fungi species that are capable of degrading plastics have been found, but they are very sparsely found in nature and will therefore never be able to tackle the plastic pollution we are facing.

Regardless of what the plastic is made from (when it comes to non-compostable plastic) there is no fundamental chemical difference between the plastic polymers produced. That means you end up with the same plastic product whether it is made from oil or plants. Therefore, you can safely sort bio-based (non-compostable) plastic and regular plastic in the same way.

Bio-based plastic has a climate benefit – but is far from climate neutral

And you might be wondering why bio-based plastic was ever invented. There has long been a need to find solutions to our unsustainable use of fossil fuels. It is estimated that 90% of the plastic produced today is made up of fossil fuels. The bio-based plastic has the clear advantage of being better for the environment in a climate perspective because it is made from plant-based resources. When the plastic ends up at the incineration plant instead of being recycled, it means that the raw material in the bio-based plastic does not contribute to greenhouse gas emissions provided that the same amount of biomass is restored to the earth. By contrast, the raw material for oil-based plastic cannot be recreated naturally within a relevant timeframe (it takes several million years) and so therefore contributes to anthropogenic climate change. 

However, bio-based plastic is – in terms of how it is made and used today – far from being climate-neutral, since (a considerable amount of) fossil fuels are still used, e.g. in the extraction of raw materials, in the manufacturing process, for transportation and if/when it is recycled. In addition, the production of bio-based plastic risks taking up agricultural land that could otherwise be used for food production. Industrial agriculture for new bioplastic production can contribute to an increase in monoculture, drought and the use of pesticides, which threaten nature and ecosystems, as well as directly harm biodiversity by removing and fragmenting natural wildlife habitats. Bio-based plastic made from bio-waste is more sustainable compared to plastic made from new plant material.

2. Compostable plastic is about how it breaks down

Compostable/biodegradable plastic can be made from fossil fuels and from biological material, but the common element is that during production, special substances are added that allow the plastic to be broken down by nature’s microorganisms. However, for this biological degradation process to take place within a reasonable timeframe, it requires some very special conditions, including high temperatures and humidity, oxygen, and high concentrations of microorganisms that can only be achieved jointly in an industrial plant. In nature, where the physical conditions vary between environments and over time, we are not able to control these conditions, which is why there’s no guarantee that compostable plastic can disappear into the ground.

The same is true for home composting, for which some compostable plastic claims it is suitable because the temperature requirements are lower: Here too, it is extremely difficult to control the conditions precisely enough to ensure a quick and complete degradation process. In a worst case scenario, there is a risk that the the plastic is fragmented into smaller pieces and is spread to other environments, where the degradation process stops or slows down significantly.

Biodegradable plastic is not a good solution for sustainable green plastic

There has been so much focus on plastic in nature that there’s been a desire to invent the ‘perfect’ plastic, which disappears in a blink of an eye as soon as it comes into contact with the soil. But, in practice, this is utopian because we want (and should) have products that can last a long time and be reused and recycled..

Whether or not the product is compostable has a decisive influence on how the individual product should be discarded and treated. Because compostable plastic only makes sense when it is sent for industrial composting, it is extremely limited in terms of what it can actually be used for. In ordinary households [in Denmark, but also many other countries], we have to throw compostable plastic products into residual waste, after which it is incinerated – including the compostable dog poop bags! Therefore, compostable plastic must never be sorted as plastic waste because, in terms of the added substances, it degrades or destroys the quality of the recycled plastic.

The solution is less plastic and more recycling

Therefore, the invention of compostable plastic has little use in practice but has contributed an awful lot of confusion in the retail industry and among consumers – as it is extremely difficult as a consumer to figure out what kind of plastic should go into which waste system. At the same time, we are led to believe that compostable plastic disappears easily and quickly in nature, and we therefore risk dumping a load of plastic into the ground. This is by no means beneficial to sustainability. The solution should be far fewer types of plastic in circulation. Our main focus should be, first and foremost, on waste prevention, reduction and reuse of plastic, rather than developing plastic products that ‘can break down in nature’ – because no waste should end up there.

If we had the opportunity to collect compostable plastic in a closed system, that solution could make sense. One of the few examples that does make sense is compostable biobags that are sent out for the purpose of sorting food waste. However, we currently only have one large industrial composting plant in Denmark (near Holbæk on Zealand). This means that most compostable food waste biobags are still removed   prior to composting the biowaste because they cannot be composted in the biogas plants – and are sent for incineration. Therefore, nothing is really gained from compostable plastic.

About biologist Claudia Sick 

Worked for Plastic Change since the association was established in 2014 and started sailing with Ekspedition Plastik to document plastic pollution in seas around the world.
Works within biological, environmental and technical areas relating to plastic.

(1) Zimmermann et al. (2019): Benchmarking the in Vitro Toxicity and Chemical Composition of Plastic Consumer Products. Environmental Science & Technology