How quickly can plastics actually degrade?
A new research project is investigating new methods in which to quantify how quickly different plastics biodegrade after they enter the environment.
When plastics find their way into the natural world, do they biodegrade, and how long could it take for them to do so? Is there a special process for this to happen and what other things could contribute to this process?
How do plastics break down?
The rising amount of plastic polluting our environment shows how important it is to answer these questions. "Our knowledge is full of gaps, we don’t have the answers yet," said Stefan Mecking, a professor of chemical materials science from the University of Konstanz.
In a new research project, Mecking wants to establish if plastics such as polyethylene are biodegradable in different environments, how long it could take to break down, and if there is a way materials could be designed to biodegrade. The German Research Foundation (DFG) is funding the research by the Reinhart Koselleck Project, a programme for scientific work with contributions of up to 1.25 million euros.
Mecking wants to start with polyethylene (PE) which is the most widely produced plastic on the planet. "Polyethylene is what you would consider a non-biodegradable material. Polyethylene decomposes very slowly in the environment, via abiotic and biological steps, and there are controversial discussions about what role these steps play and how quickly they take place at all", said Mecking. They want to collect data to be able to clarify the matter. "Our aim is to develop a reliable method to quantify the biodegradation of this plastic".
Plastics in the environment are broken down by conversion to carbon dioxide, so theoretically you could follow the trace of carbon dioxide to investigate biodegradation of plastics in nature. One issue with this form of investigation is that carbon dioxide can be released by other things in nature, such as soil, making it difficult to know whether the carbon dioxide comes from plastics' biodegradation or from nature itself.
Mecking wishes to now make the carbon dioxide from plastics different, so it would have a chemical fingerprint. The team wants to develop a method that produces variants of polyethylene which are marked by stable isotopes. The variants would have the same properties as polyethylene but because of the marking, will be able to be traced as a source of carbon dioxide. Quantifying the amount of marked carbon dioxide released will inform the team of how long it takes for decomposition to happen.
Many questions to answer
One of the main questions the study has set out to answer is what factors can influence the biodegradability of plastics. It also includes the question of how plastic should be designed and produced so that it does not persist in the environment for decades. Mecking and the team will consider the molecular structure of the plastics to inform the answer to these questions. Plastics have very long, chain-like molecules, and this structure influences the biodegradability of the plastic alongside the size of its particles. The team will also focus on the functional groups within the chains, such as chemical break points.
"I am optimistic that we will be able to overcome the associated challenges. Among other things, because we are establishing all the methods that are essential for this project in our laboratory. This enables us to react quickly and design the next experiments" concluded Mecking.