behind the experiment
What’s the problem?
In 2019, global plastic production reached almost 370 million tonnes. Estimates suggest that the equivalent of one garbage truck of plastic is dumped into the ocean every minute, and this will increase to two trucks per minute by 2030 if we don’t act now.
Since 2006, the amount of plastic that is collected and sent to recycling has doubled in Europe — but still, by 2018, a quarter of all post-consumer plastic waste was sent to landfill, from where it can enter open environments such as rivers, oceans and soil. This problematic waste management needs to be reduced — or better, eliminated — as quickly as possible.
But even if waste is properly managed and littering is reduced, there will still be some areas where we can’t avoid plastics reaching the open environment. This includes examples of intentional use (e.g. fireworks, agricultural applications); plastic items that are likely to be lost (e.g. fishing gear); and input due to use (e.g. abrasion of textiles, tyres, paint).
Most plastic in use today is made from petroleum. Often, when these plastics end up in the open environment, they will stay there for hundreds or even thousands of years without breaking down — or else break up into microplastics and stay in the environment. Both macro- and microplastics are harmful to wildlife, which can become entangled or suffocated, or suffer toxic effects, or starvation after indigestion.
Biodegradable, ‘bio-based/ and ‘bioplastic’ do not mean the same thing! Biodegradable plastics can be either fossil-based (made from petroleum) or bio-based (made from renewable organic matter). And some ‘bioplastics’ are not biodegradable even though they are made from organic sources.
As plastics are exposed to frost and UV radiation, they slowly degrade, breaking up into smaller pieces known as microplastics and nanoplastics. We know that these smaller pieces can already be found in all types of natural environments, and that they travel through food chains and may eventually end up at our dinner table.
We don’t yet know exactly how microplastics and nanoplastics affect human health, but we already know that plastics of all sizes are harmful to living creatures and their environments, and negative effects have been identified for many different organisms.
But we depend on plastic products for a range of different applications. And plastic is a good material if the waste is collected and managed properly, and damage to the environment is prevented.
So we need to stop the littering of plastics into the open environment, by continually improving the way we handle waste and recycling. It is down to all of us – governments, industries and individual citizens – to make a difference here.
The role of biodegradable plastics
Biodegradable plastics may be an alternative to conventional plastics for some specific purposes. ‘Biodegradable’ means that microbes (bacteria, archaea, fungi and microalgae) can completely eat the plastic, converting it to gas and new microbes!
Biodegradable plastics are useful when we manufacture products that are likely to be lost to the environment and would be too difficult to retrieve — for instance, fishing gear which gets worn away during use — or products that are intended for a narrow environmental application, such as agricultural plastics. Other examples of useful applications are the plastics used in fireworks, which can’t easily be retrieved after use, and tobacco filters, which are the second most frequently found single-use plastic item on beaches in the EU (Official Journal of the European Union, 2019).
However, it is important to stress that biodegradable plastics are not a silver bullet to combat plastic pollution in the environment. If they are released into the environment in the same way as conventional plastics, they pose many of the same harms to wildlife and the environment, and there are some potential new harms too.
For the majority of applications, including most single-use packaging and plastic bags, it would be better to reduce the amount of plastic we use, and to promote reuse and recycling.
Biodegradation is a “system property”
Calling a plastic product ‘biodegradable’ means that it can be completely broken down by microbes and converted to carbon dioxide (CO2) and methane (CH4) in conditions without oxygen, and new microbial biomass.
Even though biodegradable plastics are broken down by microbes as a source of food, this does not mean that biodegradable plastics always biodegrade at the same rate in all environments. In fact, biodegradation is a “system property”, which means that it depends on many other factors apart from the plastic itself.
For instance, the type of environment (river, sea or soil) where the plastic ends up will determine:
- which microorganisms are present: microbes that live in soil are different to the ones living in the ocean, and it generally takes longer to biodegrade plastic in the sea compared to soil
- temperature: biodegradation rates generally speeds up with increasing temperature
- humidity: microbes needs water just like we do
- nutrients: microbes need nitrogen, phosphorus and other compounds, so if these are limited, biodegradation will be slower
- several other factors that influence microbial activity in general (e.g. oxygen level, pH).
So, you can imagine that the speed of biodegradation for a biodegradable plastic product varies considerably depending on the environment it ends up in.
The rate at which a plastic item biodegrades is not just down to the material it is made of — it also depends on the conditions in the environment where it ends up.