Junk food fit for the bugs

Plastic litter has become a major problem. Just as water runs to the ocean… plastic released in the environment is collecting in giant depositories in oceans around the world. Apart from being an eyesore, this plastic is being ingested by sea creatures, can damage coral, and can potentially serve as a carrier for other harmful chemicals or a source of dissolved organic carbon in the oceans. One of the reasons why plastic is such a big problem is that it doesn’t break down easily. There are some plastics designed to be biodegradable (you can read more  about them here), but most end up just breaking into smaller and smaller pieces, eventually becoming microplastics. But what if there was a way to digest commonly-used plastic using organisms found in the environment?

Bugs can eat plastic?

Some bugs can eat some plastic. There are recent findings of microbes (microorganisms) and insect larvae that can eat some commonly-used plastics! This research area is still in its infancy and there are a lot of things that need to be sorted out before it can become widely deployed. For example, there is a specific microbe that has been found to break down poly(ethylene terephthalate) or PET, which is used widely in plastic drink bottles and polyester clothing. However, it is a pretty rare microbe that isn’t found everywhere, and it takes a really long time to break the plastic down (more than six weeks for a very small, thin plastic film). You can read about more achievements and limitations here.

Mealworms and greater wax moth larvae, which are much more common, have also been shown to degrade polystyrene (PS) foam (styrofoam) and polyethylene (PE, the world’s most commonly used plastic). In addition to eating plastics being a slow process, the survival rate of these larvae is not very high. Although the larvae seem to be able to break down the plastic, they do not get much nutritional benefit from it and essentially starve. Talk about empty calories!

Developmental stages of the greater wax moth. Source

In order to address the problem of plastic diets leading to low survival rates, an international group of researchers led by Yu Lou at the Harbin Institute of Technology investigated the impacts of blending a diet of plastic with more nutritional food. In the case of greater wax moth larvae, nutritional food means beeswax and wheat bran.

In their experiments, the researchers exposed several groups of greater wax moth larvae to different feedstocks (with blends ranging from pure plastic to pure beeswax/bran) for 21 days. While plastic consumption was faster with a pure plastic feedstock (either PS or PE) than it was with a blended feedstock. This makes sense, since only plastic was available for the larvae to eat. However, the consumption slowed down with time as the larvae died. While plastic was consumed slower in blended feedstocks, larvae also lived longer. In fact, the researchers found that the maximum survival rate occurred with a feedstock that was 27% plastic and 73% beeswax. These experiments showed that a blended diet can increase the survival rate of these larvae, essentially elongating their plastic meal… even though they’ll eat plastic more slowly. More work is needed to figure out the best feedstock ratio of plastic to nutrition to maximize long-term plastic degradation by these larvae.

The scientists performed tests on the meal worm frass (excrement) to confirm that they were digesting the plastic, rather than just breaking it into smaller pieces, and it seemed that the plastic was at least partially digested, limiting microplastic generation. The researchers also observed that a diet of pure plastic can alter the mix of microbes that live in the gut of these larvae, reducing the diversity of microbes and the overall health of the gut and larvae.

What can you do to help?

Unfortunately, plastic-eating bugs aren’t at a stage where they can solve the plastic problem… yet. However, there are still things you can do to help solve the plastic right now. One of the biggest ways is by reducing the amount of plastic waste you generate. Consider using re-useable bags at the grocery store, buy in bulk to reduce packaging, look for ways to re-purpose plastic containers that you do have. Recycle all that you can and improve its efficiency by cleaning containers of food and paper scraps before putting them in the bin. You can even reduce plastic waste in the environment based on how you buy your clothes and do your laundry.

Source Article:  Lou, P. Ekaterina, S. Yang, B. Lu, B. Liu, N. Ren, P. F.-X. Corvini, D. Xing. Biodegradation of Polyethylene and Polystyrene by Greater Wax Moth Larvae (Galleria mellonellaL.) and the Effect of Co-diet Supplementation on the Core Gut Microbiome. Environ. Sci. Technol. 2020. https://pubs.acs.org/doi/abs/10.1021/acs.est.9b07044

Cover Image: https://pixabay.com/photos/garbage-waste-container-waste-2729608/

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Mary Davis

I earned my PhD in Chemical Engineering from Princeton University in 2018, where my research focused on nanoscale polymer systems and how their properties change with geometry. I am now applying my background in polymers to environmental systems as a postdoctoral research associate at the U.S. EPA. This involves studying the breakdown of plastics and the generation of microplastics in the environment, as well as their interactions with other pollutants. When I’m not working in the lab, I enjoy crafting, cooking, and being outside.

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