Plastic bites

In the hopefully second and last of my ‘bites’ headlines starting with the previous Featured Article, a story has recently made some buzz in recent news and probably a few content-generator sites. It’s about waxworms that are able to…well, eat plastic. Specifically, polyethylene (PE). This is an important thing since it’s the most produced type of plastic in the world, at about 80 million tons per year. If you’ve been to the grocery store lately, then you’ve got some on hand – this is shopping bag material. Anyway, these waxworms aren’t some lab-grown species that will someday invade us or at least provide the next summer blockbuster, these are larvae of Galleria mellonella – the wax moth.

galleria_mellonella_1
(Wikimedia Commons/Flickr, Author: Donald Hobern, 2009)

There have been studies over the years about how microorganisms like bacteria and fungi can degrade plastics. However, scientific progress means finding better ways of doing things (wouldn’t have smartphones otherwise), and perhaps there are faster ways to biodegrade plastics. At the microbial level, it can take days or even months to degrade bulk plastics like bottles into something smaller and perhaps easier to deal with, like liquid ethylene glycol (not that this is an entirely good thing – it is toxic). In addition, ‘better’ may also include easier ways of doing things, which in this case may have to do with perhaps not having to treat plastics with harsh chemicals or having to apply more energy before unleashing microbial fury (LOL, dramatics). The study’s background literature includes some examples of these chemical-workups, such as incubating PE with a species of Penicillium fungus (if it sounds familiar, it probably should) for three months after treating it with nitric acid. Anyone who’s ever taken chemistry in high school knows that this is nasty stuff, and even your teachers only let you use really diluted stuff (the higher up in university you go, the less diluted your reagents get). Also, all this treatment is highly good and well in the lab, but how are you going to apply this to something out in the field like, say plastics on the Great Pacific Garbage Patch?

Plastic pollution Pacific gyre garbage patch
(Author: Ryan Hagerty/US Fish and Wildlife Service)

(to the ecologically-inclined, I got the image from a WordPress blog run by the U.S. Fish and Wildlife Service – why not pop by?)

Anyway, is there a ‘better’ – i.e. faster and easier – way or biodegrading PE plastics? Back to the waxworms. I had a post last year about how silkworms (silk moth larva) can make stronger silk by feeding them some carbon nanotubes. The authors have an idea about how waxworms can biodegrade PE, and it’s similar to their diet as it is: they feed on beeswax, which is a mixture of stuff including carbon chains, which have similar chemical bonds to those in PE. But, they also state that it’s not clear whether this digestion comes from the waxworm itself or the stuff that’s in their digestive tract, which could include enzymes or microbes. Yes, even the tiniest things in nature have microbes involved.

They tested whether or not waxworms can actually degrade plastic through  a kind of infrared analysis, which is common for finding amounts (even trace amounts) of carbon compounds in materials. In their scan, the found signals that correspond to PE film, so the scanning method works. However, when they tested it on their PE sample after going through some worms, they found a signal that corresponds to ethylene glycol, which I mentioned earlier is a breakdown product of PE. These were seen when their infrared probe was pointed closer to the holes where the worms have been snacking out, but not when the probe was far from the holes. This was their proof that the worms were indeed, through digestion, biodegrading plastics. They also ran other tests, such as checking out the surfaces to show that the worms have been indeed eating and digesting the plastic. May be kind of obvious because you could just look at the holes in a plastic bag, but hey, due diligence.

There are still a few things that us humans are doing to curb the number of plastic bags that are being used, such as offering more paper shopping bags or all-out charging a tax on plastic bags, but research is there to show additional, better, easier ways of doing things. It’s not entirely clear if the plastic bag diet is harming the waxmoth larvae, but we’re going to need some entomologists on the issue. But at least for now, we’ve got some kind of solution to help with the plastic-bag problems.

Featured Article: Bombelli P, Howe CJ, Bertocchini F. (2017) Polyethylene bio-degredation by caterpillars of the wax moth Galleria mellonellaCurrent Biology 27, R283-R293. DOI: 10.1016/j.cub.2017.02.060

Featured Image: Public Domain (Author: Hans Braxmeier)

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1 Comment

  1. I had some pretty stark realizations while reading this. Informative and eye opening, while offering short term and long term paths of thought to move toward a solution. Thank you for bringing this knowledge to light!

    Liked by 1 person

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