Mealworms Can Safely Biodegrade Toxic Additive-Containing Plastic

Common mealworms, the larvae of the darkling beetle (Tenebrio molitor), can consume toxic additives in polystyrene with no ill effects; the worms can then be used as a safe, protein-rich feed supplement, according to new research from Stanford University.

Brandon et al investigated the fate of the flame retardant hexabromocyclododecane in polystyrene-degrading mealworms and in mealworm-fed shrimp. Image credit: Andrew Martin.

“This is definitely not what we expected to see. It’s amazing that mealworms can eat a chemical additive without it building up in their body over time,” said Anja Malawi Brandon, a Ph.D. candidate in the Department of Civil and Environmental Engineering at Stanford University.

In a previous study, Brandon and colleagues found that microorganisms in the guts of mealworms can biodegrade various types of plastic.

However, concern remained about whether it was safe to use the plastic-eating mealworms as feed for other animals given the possibility that harmful chemicals in plastic additives might accumulate in the worms over time.

“Our new work provides an answer to many people who asked us whether it is safe to feed animals with mealworms that ate Styrofoam,” said Dr. Wei-Min Wu, a senior research engineer in the Department of Civil and Environmental Engineering at Stanford University.

In the new study, the researchers used polystyrene containing the flame retardant hexabromocyclododecane (HBCD).

Mealworms in the experiment excreted about half of the polystyrene they consumed as tiny, partially degraded fragments and the other half as carbon dioxide.

With it, they excreted the HBCD — about 90% within 24 hours of consumption and essentially all of it after 48 hours.

Mealworms fed a steady diet of HBCD-laden polystyrene were as healthy as those eating a normal diet.

The same was true of the whiteleg shrimp (Litopenaeus vannamei) fed a steady diet of the HBCD-ingesting mealworms and their counterparts on a normal diet.

The plastic in the mealworms’ guts likely played an important role in concentrating and removing the HBCD.

“Mealworm-excreted HBCD still poses a hazard, and that other common plastic additives may have different fates within plastic-degrading mealworms,” the scientists noted.

“While hopeful for mealworm-derived solutions to the world’s plastic waste crisis, we caution that lasting answers will only come in the form of biodegradable plastic replacement materials and reduced reliance on single-use products.”

“This is a wake-up call. It reminds us that we need to think about what we’re adding to our plastics and how we deal with it,” Brandon said.

The study was published in the journal Environmental Science Technology.

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Anja Malawi Brandon et al. Fate of Hexabromocyclododecane (HBCD), a Common Flame Retardant, in Polystyrene-Degrading Mealworms: Elevated HBCD Levels in Egested Polymer but No Bioaccumulation. Environ. Sci. Technol, published online December 5, 2019; doi: 10.1021/acs.est.9b06501