These mushrooms eat plastic – that’s why they now raise high expectations

Polypropylene is hard plastic. It is used to make lids for PET bottles, food packaging such as yoghurt pots, foils or reusable containers such as thermo boxes. The problem: Polypropylene has one of the lowest recycling rates in the world.

Researchers from Australia have now found a possible way to solve this problem – with mushrooms.

Scientists at the University of Sydney used two fungal strains found in soil to break down lab samples of polypropylene in just 140 days. They fed them different types of plastic: plastic granules, plastic film and aluminum coated plastic film (composite).

The two mushrooms with the somewhat cumbersome names Aspergillus terreus And Engyodontium album fed on the plastic in the lab experiments: between 25 and 27 percent of the samples were eaten after 90 days. After 140 days, the plastic had completely broken down, the researchers report.

For this material, this is the fastest rate of degradation ever achieved, said Ali Abbas, a chemical engineering professor who led the research team. The findings are an important step in the development of practical biological processes for the treatment of plastic waste.

However: The mushrooms needed some prep work. The plastic was treated with UV light or heat before being “fed”. This is to weaken the waste so that the fungi can affect it. This step mimics the environmental conditions fungi need to attach to and break down plastics, and is believed to make the decomposition process more efficient.

Fungi are not the only microorganisms that can break down plastic. Until now, it has mainly been certain bacteria that have caused a stir with this ability in recent years. Some of them can break down plastic within 16 hours, as it turned out last year. However, it was PET and not hard plastic.

In total, more than 400 micro-organisms are known that can break down plastics naturally. However, fungi have received a lot of attention because of their versatility and their ability to break down all kinds of synthetic substrates with a powerful mixture of enzymes.

“Recent studies suggest that certain fungi can even break down some of the ‘forever chemicals’ like PFAS.” PFAS are a group of nearly 5,000 different man-made chemicals. They have been widely used for decades and in many products such as cosmetics, packaging, raincoats, kitchenware, etc. Over time, they accumulate in human tissues and the environment and can be harmful to health. “However, the process of PFAS degradation by fungi is slow and not well understood,” explains University of Sydney microbiologist Dee Carter.

Moreover, according to the research, no microbes have yet been found that can actually break down polypropylene. And after all, this plastic is one of the everyday plastics par excellence.

Nearly a third of the world’s plastic waste is made from polypropylene. It is a durable plastic that can take hundreds of years to break down without help.

Chemically speaking, all plastics are a chain of carbon atoms with different side chains that give each type of plastic its specific properties. Theoretically, recycling plastics is relatively easy. The problem, however, is that the different plastics are often mixed together – and it is not uncommon for other materials to be added. There are so many different types of plastic that it is virtually impossible to separate and recycle them when they are mixed together in bulk and mixed with other materials. This is another reason why most plastic waste is incinerated or sent to landfill.

Those are the two mushrooms Aspergillus terreus And Engyodontium album being able to break down polypropylene into various forms raises high expectations. But here too, as so often in science, a breakthrough in the laboratory does not mean a commercially usable product.

According to the head of the study, Abbas, their method can be scaled up like any other fermentation process, i.e. made possible on a larger scale. However, he adds that his team has not yet optimized the experimental conditions for industrial-scale work. The next steps for the researchers are therefore to build a prototype that also works under non-laboratory conditions, test the necessary changes to speed up the process and evaluate the economic feasibility on a commercial scale.