Every year, Americans throw away 2.5 billion plastic foam cups. Though the number sounds huge, it is only a small fraction of the 33 million tons of plastic waste discarded every year.
Less than 10 percent of this plastic gets recycled. The remainder ends up in landfills or the environment, presenting challenges ranging from water contamination to toxicity in wildlife.
Research engineers at Stanford University believe they have discovered a potential solution to managing all this foam waste.
They found that the mealworm, the larvae from of the darkling beetle, can subsist on a diet of Styrofoam and other forms of polystyrene. Microorganisms in the worms’ guts biodegrade the plastic during the digestion process.
Dinner Time
In a lab setting, the mealworms ate between 34 and 39 milligrams of Styrofoam per day, about the weight of a small pill. The worms converted about half the Styrofoam into carbon dioxide, as they would with any other food source.
Within 24 hours, the worms excreted the bulk of the remaining plastic as biodegraded fragments that look similar to tiny rabbit droppings.
Mealworms fed a steady diet of Styrofoam were as healthy as those eating a normal diet, said lead researcher Wei-Min Wu, and their waste appeared to be safe to use as soil for crops.
Researchers, including Wu, have shown in earlier research that waxworms, the larvae of Indian mealmoths, have microorganisms in their guts that can biodegrade polyethylene, a plastic used in filmy products such as trash bags.
Styrofoam was previously thought to have been non-biodegradable and thus, dangerous for the environment.
"Our findings have opened a new door to solving the global plastic pollution problem," Wu said.
Understanding how the bacteria within mealworms carry out this feat could potentially enable new options for safe management of plastic waste.
Is There a Buffet?
Researchers led by Craig Criddle, a professor of civil and environmental engineering who supervises plastics research by Wu and others at Stanford, are collaborating in ongoing studies with researchers at Beihang University in China and other Chinese researchers.
Together, they plan to study whether microorganisms within mealworms and other insects can biodegrade plastics such as polypropylene (used in products ranging from textiles to automotive components), microbeads (tiny spheres used as exfoliants) and bioplastics (derived from renewable biomass sources such as corn or biogas methane).
Another area of research could involve searching for a marine equivalent of the mealworm to digest plastics, Criddle said. Plastic waste is a particular concern in the ocean, where it pollutes habitats and kills countless seabirds, fish, turtles and other marine life.
More research is needed, however, to understand conditions favorable to plastic degradation and the enzymes that break down polymers. This, in turn, could help scientists engineer more powerful enzymes for plastic degradation and guide manufacturers in the design of polymers that do not accumulate in the environment or in food chains.
"There's a possibility of really important research coming out of bizarre places," said Criddle. "Sometimes, science surprises us. This is a shock."
Papers describing the mealworm research are published in Environmental Science and Technology.