Worm Spit Can Digest the World's Most-Polluting Plastic

A molecule found in wax-worm saliva has been found to break down one of the most-polluting forms of plastic without the need for high energy inputs.

The study, published in Nature Communications and led by a team from the Spanish National Research Council (CSIC), has important implications for the future of sustainable plastic disposal and the health of our planet.

Plastic pollution is one of the biggest threats to marine life, and up to 12.7 million metric tons (28 billion pounds) of plastic end up in the ocean every year. As plastic production continues to increase, the toxins they contain will likely spread into human communities as well.

"[Polyethylene] accounts for around 30 percent of plastic production," Clemente Fernández Arias, a co-author on the study, told Newsweek.

"It's mostly used for single-use objects such as food packaging...[and] plastic bags." Polyethylene is also one of the most difficult plastics to recycle and dispose of.

Previous research has shown how certain species of bacteria and fungi are able to break down disposable plastic bottles using specialized enzymes, biological molecules that increase the rate of chemical reactions.

For example, the bacterium Ideonella sakaiensis is able to digest PET, the plastic used to make water bottles, and the fungus Aspergillus tubingensis has been shown to break down polyurethane (PU), which is used to make adhesives, foam and clothing.

However, until now, no biological organisms have been able to digest the most widely produced form of plastic.

"There are a few microorganisms that can grow on polyethylene [too] but...the polyethylene has to be oxidized first," Arias said. In other words, oxygen needs to be introduced into the plastic's molecular structure before it can be broken down.

"This can happen in the natural environment after years of exposure or it can happen in the lab using heat or radiation." Either way, the process uses a lot of time and energy.

The latest research has found that enzymes isolated from wax-worms, the larvae of the greater wax moth, are able to perform this oxidization step at room temperature in less than an hour.

This essentially bypasses the slowest, most energy-intensive step of the degradation process.

"We would need lower temperatures and we would spend less energy on breaking down the plastic," Federica Bertocchini, another of the paper's co-authors, told Newsweek.

Bertocchini first came across the phenomenon five years ago, after seeing how polyethylene film broke down when it was left in contact with newly formed wax-worm cocoons.

The larvae make their cocoons out of silk, which is just hardened saliva. Bertocchini found that it was this saliva that contained the plastic-degrading enzymes.

In 2022, she and her team have isolated the compounds responsible for this digestion.

In nature, plastics break down slowly into smaller and smaller fragments that eventually cannot be seen by the naked eye. These microplastics are often ingested by animals and can end up in human food and in our water supply.

Although most of these fragments pass through our bodies quickly, they contain a range of toxic chemicals that, after repeated exposure, could pose a risk to our health.

"We have to reduce plastic use sharply, otherwise there will be no solution," Arias said. "But we sometimes have to use this type of plastic because we have nothing else like it."

The discovery of these wax-worm enzymes opens up a range of possibilities for plastic-waste management and low-cost recycling in the future.