Researchers have found that a polystyrene-eating beetle larva called a “supercook” can gain weight with a polystyrene-only diet.
They hope their findings can pave the way for technology to degrade and recycle plastic on a large scale, but others are skeptical of the approach.
Key points:
- Supercooks fed bran and polystyrene were much more active during the study period compared to the starvation diet group.
- Researchers hope to be able to develop a polystyrene foam recycling technology
- Many are skeptical that there is a safe recycling solution that can work on a scale and call for a ban on polystyrene foam.
Fed only polystyrene (also known as polystyrene foam) for three weeks, supercooks, the larvae of the dark beetle (Zophobas morio), survived at rates comparable to larvae fed a bran diet, according to the study published today in Microbial Genomics.
The fact that supercooks could gain a small amount of weight by eating only polystyrene is an indication that they are able to convert the material into energy, according to study co-author Christian Rinke of the University of Queensland’s School of Chemistry and Molecular Biosciences. .
“They have to get energy from somewhere,” Dr. Rinke said.
The supercook groups were fed bran, polystyrene, or no food during the three-week trial period.
Worm-fed worms doubled in weight over the three-week period, worms fed polystyrene foam added a small amount of weight, while those on the starvation diet maintained their initial weight approximately.
Worms fed bran or polyester were also much more active compared to worms on the hunger diet, according to Dr. Rinke.
“In terms of activity, the worms that had bran were super active, the polystyrene ones a little slower and the ones that were starving were basically still all the time.”
“Superworms” are not true worms, and are actually the larval stage of dark beetles. (Getty Images: Tomasz Klejdysz)
The pupation rate was also analyzed after the three-week test. The “worm” or larval stage of the superworm, is followed by the development of pupae, where the animal sinks and metamorphoses into a dark beetle.
As expected, the rate was higher in bran-fed beetles, with more than 90% becoming pupae.
But there was also a significantly higher pupation rate in polystyrene-fed beetles compared to hungry beetles, more than 60% compared to 10%, which again indicates that the polystyrene diet was at least higher than the hunger diet.
For each larva that entered the pupal phase of each diet group, they all successfully hatched as beetles.
Key enzymes in the microbiome
At the beginning and end of the study, a portion of the worms in each group were frozen and their intestinal contents and microbiome were analyzed.
Bacteria in the microbiome produce enzymes that, among other functions, can aid digestion.
The researchers identified several microbes that they believe are capable of degrading polystyrene in the intestines of worms. (Provided by: Christian Rinke / UQ)
Although the plastic diet was found to have an overall negative impact on the diversity and health of the intestinal microbiome of worms, the researchers identified several enzymes in the gut of the worm that they believe may degrade polystyrene.
Although it has long been known that some types of beetle larvae can consume polystyrene, this study goes a step further, according to Colin Jackson of the ANU School of Chemistry Research, who did not participate in this study.
“This study goes a long way in understanding how bacteria are introduced [the worms’] the gut does it on a molecular level, “said Professor Jackson.
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“[That’s] important for the translation and use of this type of approach in recycling “.
To obtain this information, the researchers used genetic analysis, according to Dr. Rinke.
“The novelty here is that we have used a technique called metagenomics, which allows us to identify all the genes in the microbiome,” he said.
Although researchers in this case inferred which enzymes were breaking down polystyrene, no experiment to date has been able to isolate critical enzymes and demonstrate the process in a test tube.
This means that while researchers believe they know which enzymes are responsible for breaking down plastic, there is still room for doubt.
Some researchers remain skeptical that polystyrene may be biologically degraded.
It is possible, according to some, that any weight gain associated with the consumption of the product is more likely to be related to other chemical elements in polystyrene foam, such as flame retardants or blowing agents.
Polystyrene is mainly made of styrene, a hydrocarbon.
Although it can be synthesized, styrene is also a naturally occurring, highly volatile chemical that is used to make plastics, rubber, and foam.
The idea, according to Dr. Rinke, would be to degrade polystyrene to styrene, and then use it to create new materials.
“It’s still the early days,” he said.
“The next step would be engineering [the enzymes]to increase this efficiency.
“In an ideal scenario … if everything works, you can add polystyrene-degrading enzymes or microbes to a bunch of chemical compounds and then use those compounds to form other products like bioplastics.”
Where from here?
While the findings are promising, it is not the first biological agent to be able to consume plastics.
It has previously been found that certain species of fungi, marine microbes and even bacteria found in the stomachs of cows have a potential to degrade plastic.
But if worms are able to consume and degrade polystyrene, there are still many difficulties in developing feasible recycling technology.
Many researchers are skeptical about a polystyrene recycling solution and have called for it to be banned. (ABC News: Amy Bainbridge)
The first is the ability to scale this type of technology to the point where it can have a significant impact on plastic pollution, Professor Jackson said.
“Expanding and translating research like this is always a challenge, which is magnified in the area of plastics by the incredible scale of the problem and the economy in terms of how cheap it is to produce new plastic.” he said.
Muxina Konarova of the University of Queensland School of Chemical Engineering, who did not participate in the study, said that even if the technology could be expanded, it would potentially create a number of new environmental and health problems.
“There are carcinogenic by-products that could come out of the polystyrene foam,” Dr. Konarova said.
Benzene is one of the chemicals used to make polystyrene foam and is listed as a carcinogen in the Australian National Pollutant Inventory.
“This is the main reason they don’t recycle polystyrene, because you end up with these compounds that you don’t want to touch,” Dr. Konarova said.
There are also greenhouse gas emissions associated with possible by-products of the process, he said.
“Even if we turn it into biodiesel, we will burn biodiesel, which will make CO2,” Dr. Konarova said.
“I do not want to give the impression that there is a solution [to styrofoam pollution] when there is none.
“Why don’t you ban this polystyrene? It’s a horrible plastic.”
In Australia this could happen soon, at least in part.
In 2021, the federal government launched a plan to phase out certain uses of polystyrene in packaging and packaging.
In July this year, the goal was to end the use of loose polystyrene foam packaging and molded consumer packaging, such as the type that includes televisions, computers, and household items.
By the end of this year, it is also assumed that polystyrene foam containers for food and beverages will be phased out.
Although he had great support at the time, the plan was also criticized for being voluntary and lacking legislated goals.
Gradual disposal does not include polystyrene in building and construction, in business-to-business packaging, or in medical applications.
In response to questions from the CBA about phasing out, a spokesman for Environment Minister Tanya Plibersek said she was currently receiving lectures from her department on her new portfolio.
“However, Australia should be ambitious in reducing waste and eliminating problematic plastics and polystyrene,” they said.
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