Australian researchers find PP-eating fungi

As a popular choice for producing a wide range of everyday products, PP is one of the most commonly used plastics. But at the same time, it is one of the least recycled. It has been estimated that PP accounts for roughly 28 percent of the world's plastic waste, while only 1 percent of it is recycled.

The reason, say researchers at the University of Sydney, is because of its short life as a packaging material and because it often becomes contaminated by other materials and plastics. Addressing this requires the development of new recycling methods  - that have minimal environmental impact. A study conducted by the researchers published today in npj: Materials Degradation identifies two common strains of fungi found in soil and plants, Aspergillus terreus and Engyodontium album, that could contribute to solving the problem of the overrepresentation of PP in plastic waste and pollution globally and lead to a greater understanding of how plastic pollution might biodegrade naturally under certain conditions.

“Plastic pollution is by far one of the biggest waste issues of our time. The vast majority of it isn’t adequately recycled, which means it often ends up in our oceans, rivers and in landfill. It’s been estimated that 109 million tonnes of plastic pollution have accumulated in the world’s rivers and 30 million tonnes now sit in the world’s oceans – with sources estimating this will soon surpass the total mass of fish,” said the study’s lead author from the University of Sydney’s School of Chemical and Biomolecular Engineering, PhD student Amira Farzana Samat.

The research team first pre-treated PP in various forms 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.Both fungi types were found to be able to break down polypropylene, reducing the plastic by 21 percent over 30 days of incubation, and by 25-27 percent over 90 days. 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 and to explore enhancing the overall efficiency in degrading PP.

“One big question our result has raised is – what are the naturally occurring conditions which can fast track the degradation of plastics? We seek to further explore the role of biological processes offered by fungi and other microorganisms,” said Ms Samat’s PhD supervisor, Professor Ali Abbas from the School of Chemical and Molecular Engineering and Chief Circular Engineer at Circular Australia.

Professor Dee Carter, an expert in mycology in the School of Life and Environmental Sciences and co-author of the study said that 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. Often, these fungi have evolved to break down woody materials, but this ability can be repurposed to attack other substrates - this is why we find fungi growing on all sorts of man-made materials like carpets, painted furniture, grout around tiles, shower curtains, upholstery and even car headlights.” 

She continued: “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.”

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 rates.