Plastic Pollution From Polyethylene to CO₂: What Happens to Plastic in Nature?

How long do plastics like polyethylene take to biodegrade, and what factors influence the process? A pioneering research project led by Professor Stefan Mecking at the University of Konstanz aims to uncover the answers, developing innovative methods to track and quantify plastic decomposition in nature.

The increasing amounts of plastic polluting the environment show just how important these questions are. “Our knowledge is full of gaps, we don’t have the answers yet,” says Stefan Mecking, professor of chemical materials science at the University of Konstanz. In a new research project, the chemist now intends to clarify whether plastics such as polyethylene are biodegradable in different environments, how long this process takes, and how materials can be designed in order to be non-persistent. The German Research Foundation (DFG) funds this research with a Reinhart Koselleck Project, a funding programme for pioneering scientific work with funding of up to 1.25 million euros.

Stefan Mecking starts with polyethylene (PE) — the world's most widely produced plastic. “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”, explains Mecking. The chemist from Konstanz wants to collect data to clarify the matter. “Our aim is to develop a reliable method to quantify the biodegradation of this plastic”.

But how do you investigate this? Plastics in the environment are ultimately broken down by conversion to carbon dioxide. Theoretically, you could simply follow the trace of carbon dioxide. The only problem is that carbon dioxide is also released from, for example, soil as a background. This makes it difficult to determine whether the CO₂ comes from the plastic or from the natural environment.

Mecking's approach now is to make the carbon dioxide from the plastic distinguishable, like a chemical fingerprint. His research team aims to develop methods that produce special variants of polyethylene, marked with stable isotopes. These variants will have the same properties as ordinary polyethylene, but, because of the marking, it can be traced whether they are the CO₂ source. The amount of marked carbon dioxide released indicates how quickly the decomposition process takes place.

A key question of the project will be which factors influence the biodegradability of a plastic. This also touches on the question of how a plastic should be designed so that it does not persist for decades or centuries if it is released into the environment. To this end, Stefan Mecking and his team consider its molecular structure. Plastics consist of characteristic, sometimes very long chain-like molecules. This structure will influence the biodegradability of a plastic, as will the size of the plastic particles. The researchers will also focus on functional groups in the chains, which are created by preceding degradation steps. Such chemical break points can significantly influence biodegradation. A central part of the research project will be to elucidate the roles of all these factors with the help of customized molecules. “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”, says Mecking.

(ID:50266509)