What’s the problem?
In 2019, global plastic production reached almost 370 million tonnes (PlasticsEurope, 2020).
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 (World Economic Forum, 2016).
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 (PlasticsEurope, 2020).
Most plastic in use today is made from petroleum. When items made from this kind of plastic end up in the , they will stay there for hundreds or even thousands of years without breaking down. This is harmful to wildlife, which can become entangled or suffocated by plastic items, or mistake plastic for food and suffer indigestion or starvation.
As plastics are exposed to frost and UV radiation, they slowly degrade, breaking down 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.
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
Another possibility is to switch to biodegradable plastic for some uses. ‘Biodegradable’ means that microbes (bacteria, archaea, fungi and microalgae) can completely degrade the plastic, by 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 the solution to combat plastic pollution. 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.
So, for some specific applications, we may be able to reduce the accumulation of plastics in the environment by using biodegradable plastics . But our main priority must be to get better at systematically collecting, recycling and re-using plastics.
Developing biodegradable plastics
Biodegradable plastics can be produced from fossil-based building blocks (petroleum) or bio-based building blocks (for instance, from plants or other renewable organic sources). One type of bio-based plastics is even made by bacteria!
But there are challenges. Firstly, products that are made from biodegradable plastics usually contain additives to make sure they have the right shape, functionality and durability. This can make the products harder for the microbes to biodegrade. Also, these additives may be toxic to living organisms in the environment. So researchers are also working on developing additives that are themselves biodegradable and non-toxic.
Biodegradation is a “system property”
Calling a plastic product ‘biodegradable’ means that it can be completely broken down by microbes and converted to CO2 (and methane at anoxic conditions) 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 degrade at the same rate in all environments. In fact, biodegradation in a “system property”, which means that it depends on many other factors apart from the plastic itself, including:
- type of environment: sea water, fresh water, soil, etc.
- 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
- several other factors that influence microbial activity in general
So, you can imagine that the speed of degradation for a biodegradable plastic product varies considerably depending on the environment it ends up in.
The first step in the process of certifying plastics as biodegradable in a certain environment involves testing of the pure plastic before any products are made. This is done in the laboratory under controlled conditions in a closed flask. The next step is field testing at environmental conditions. During this test, the plastic is carried in a meshed container exposing the plastic to the elements and organisms, while at the same time protecting the plastic from mechanical impact and keeping it in place.