Fungi could consume hard-to-recycle plastic

Polypropylene is a common plastic that is used for a wide variety of products from packaging and toys to furnishing and fashion, accounting for about 28% of the world’s plastic waste. Only 1% of it is recycled.

Researchers at the University of Sydney have discovered a potential solution to the problem, with two common strains of fungi used to successfully biodegrade polypropylene in a laboratory experiment. The study was published in npj: Materials Degradation.

Typically found in soil and plants, Aspergillus terreus and Engyodontium album were able to break down polypropylene after it had been pre-treated with either UV light or heat, reducing the plastic by 21% over 30 days of incubation, and by 25–27% over 90 days.

“Polypropylene is a common plastic used to make a huge variety of everyday products like food containers, coat hangers and cling film, but it only has a recycling rate of only 1%, meaning it is overrepresented in plastic waste and pollution globally,” said the study’s lead author, PhD student Amira Farzana Samat.

The researchers hope their method could reduce the amount of plastic polluting the environment and lead to a greater understanding of how plastic pollution might biodegrade naturally under certain conditions.

According to Samat, plastic pollution is one of the biggest waste issues due to inadequate recycling leading to waste ending up in landfill, rivers and the ocean. It has been estimated that 109 million tonnes of plastic pollution are in the world’s rivers and 30 million tonnes in the world’s oceans.

Polypropylene is so infrequently recycled because of its short life as a packaging material and because it is often contaminated by other materials and plastics, necessitating new recycling methods that have minimal environmental impact.

Samat’s PhD supervisor, Ali Abbas from the School of Chemical and Molecular Engineering and Chief Circular Engineer at Circular Australia, said, “Despite the massive scale of plastic production and consumption, there has been very little attention paid to plastics degradation under environmental conditions, and our understanding of how plastics can be degraded is limited.”

According to Abbas, a question the research has raised is which naturally occurring conditions can fast-track plastic degradation? The researchers aim to further explore the role of biological processes offered by fungi and other microorganisms.

Dee Carter, an expert in mycology — the study of fungi — in the School of Life and Environmental Sciences and co-author of the study, said, “Fungi are incredibly versatile and are known to be able to break down pretty much all substrates. This superpower is due to their production of powerful enzymes, which are excreted and used to break down substrates into simpler molecules that the fungal cells can then absorb.”

Fungi have evolved to break down woody materials. This can be repurposed to attack other substrates, which is why fungi tends to grow on various man-made materials.

“Recent studies suggest some fungi may even degrade some of the ‘forever chemicals’ like PFAS, but the process is slow and not yet well understood. There is also evidence that the amount of plastic accumulated in the ocean is less than what might be expected based on production and disposal levels, and there is speculation that some of this ‘missing’ plastic may have been degraded by marine fungi,” Carter said.

Polypropylene in various forms was initially treated with one of three separate methods: ultraviolet light, heat and Fenton’s reagent — an acidic solution of hydrogen peroxide and ferrous iron often used to oxidise contaminants.

In a petri dish, the fungi were applied separately as single cultures to treated polypropylene. The validity of the biodeterioration was then confirmed through microscopy techniques. While the research didn’t evaluate how the plastic was degraded by the fungi or whether it was metabolised, the researchers hope to conduct further research to determine the type of bio-chemical processes taking place.

Abbas believes the low rate of plastics recycling creates a circularity gap, and that the development of disruptive recycling technologies must be supported to improve circularity. He says the study did not carry out optimisation of the experimental conditions, so there is room for improvement.

The researchers will explore enhancing the overall efficiency in degrading polypropylene before seeking investment to scale the technology and develop a small-scale pilot prototype for commercialisation.

Since completing the study, the team has isolated other microorganisms from the marine environment and used a similar process to degrade marine plastic waste, with preliminary results showing even higher degradation.

Samat said, “We are quite excited about this and have started looking at different ways to improve the degradation process using these microorganisms. Watch this space.”

Image credit: iStock.com/Mario De Moya F