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Thursday, Aug 22, 2019

Can caterpillars rescue the planet from plastic pollution?

Caterpillars can mow through plastic waste by biodegrading polyethylene, one of the toughest and most used plastics that frequently clogs landfill sites.

world Updated: Apr 25, 2017 17:42 IST
Prasun Sonwalkar
Prasun Sonwalkar
Hindustan Times, London
File photo of the wax worm, a type of caterpillar that researchers says has the ability to biodegrade polyethylene, one of the toughest and most used plastics.
File photo of the wax worm, a type of caterpillar that researchers says has the ability to biodegrade polyethylene, one of the toughest and most used plastics.(University of Cambridge)

The humble caterpillar can be the answer to dealing with the growing mountains of plastic waste around the world, according to new research that shows it breaks down chemical bonds in plastic used for bags and packaging at unusually high speeds.

Scientists from the University of Cambridge and Spain say the discovery could lead to a biotechnological approach to polyethylene waste that chokes oceans and landfills. Plastic is usually highly resistant to breaking down, but nature may provide the answer. 

The researchers found a caterpillar commercially bred for fishing bait has the ability to biodegrade polyethylene, one of the toughest and most used plastics, frequently found clogging landfill sites in the form of shopping bags.

The discovery is based on the wax worm, the larvae of the common insect Galleria mellonella, or greater wax moth, considered a scourge of beehives across Europe. In the wild, the worms live as parasites in bee colonies. Wax moths lay their eggs inside hives, where the worms hatch and grow on beeswax.

The chance discovery occurred when a member of the scientific team, Federica Bertocchini, an amateur bee-keeper, was removing the parasitic pests from honeycombs in her hives. The worms were temporarily kept in a typical plastic shopping bag that became riddled with holes.

Bertocchini, from the Institute of Biomedicine and Biotechnology of Cantabria, Spain, collaborated with colleagues Paolo Bombelli and Christopher Howe at the University of Cambridge’s department of biochemistry to conduct a timed experiment.

File photo of a wax worm caterpillar.
File photo of a wax worm caterpillar. ( University of Cambridge )

Around 100 wax worms were exposed to a plastic bag from a UK supermarket. Holes started to appear after just 40 minutes, and after 12 hours, there was a reduction in plastic mass of 92 mg from the bag.

Scientists believe the degradation rate is extremely fast, compared to other recent discoveries, such as bacteria reported last year to biodegrade some plastics at a rate of 0.13 mg a day, a release from the University of Cambridge said.

"If a single enzyme is responsible for this chemical process, its reproduction on a large scale using biotechnological methods should be achievable," said Bombelli, first author of the study published in the journal Current Biology.

"This discovery could be an important tool for helping to get rid of the polyethylene plastic waste accumulated in landfill sites and oceans."

Polyethylene is largely used in packaging, and accounts for 40% of total demand for plastic products across Europe – where up to 38% of plastic is discarded in landfills. People around the world use around a trillion plastic bags every year.

While the molecular detail of wax biodegradation requires further investigation, researchers said it is likely that digesting beeswax and polyethylene involves breaking similar types of chemical bonds.

“Wax is a polymer, a sort of ‘natural plastic’, and has a chemical structure not dissimilar to polyethylene,” said Bertocchini, the study’s lead author.

The researchers conducted spectroscopic analysis to show the chemical bonds in the plastic were breaking. The analysis showed the worms transformed the polyethylene into ethylene glycol, representing un-bonded “monomer” molecules. 

To confirm it wasn’t just the chewing mechanism of the caterpillars degrading the plastic, the team mashed up some of the worms and smeared them on polyethylene bags, with similar results.

 “The caterpillars are not just eating the plastic without modifying its chemical make-up. We showed that the polymer chains in polyethylene plastic are actually broken by the wax worms,” said Bombelli.

First Published: Apr 25, 2017 16:15 IST

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