Eating Away at Plastics Pollution

January/February 2016

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Eating Away at Plastics Pollution

DIET OF WORMS: They devour Styrofoam. Photo: Stanford News Service

Maybe nothing better captures the wild imbalance between plastic’s often fleeting useful life and its near immortality as trash than the satire of the Onion. “Child Entertained For 5 Minutes By Plastic Toy That Will Take 1,000 Years to Biodegrade,” one headline reads.

Our mounting plastic pollution is no joke, though. Each year, Americans toss away some 33 million tons of the stuff, recycling less than 10 percent of it. Much of the rest languishes in landfills for generations, contributing to a range of problems, from water contamination to animal poisoning.

But researchers at Stanford and Beihang University in China have uncovered hopeful signs that polystyrene, at least—a plastic widely known by the trademark name Styrofoam—isn’t as impenetrable to nature’s reapers as long thought. Traditionally regarded as nonbiodegradable, Styrofoam is nevertheless used for things like fast-food containers and other passing functions.

It turns out that tiny mealworms—the larvae of darkling beetles—have a taste for the foam. In experiments, the grubs, which are commonly sold as pet food, subsisted for 30 days on a diet made up exclusively of the petroleum-based polystyrene; its polymers promptly broke down in their guts.

The worms converted about half the plastic into carbon dioxide—as they would with any food—and excreted the rest as biodegraded fragments. The experimental mealworms stayed much smaller than those receiving a normal diet, but they remained healthy, and their waste appeared plastic-free and safe for agricultural use as soil.

The experiments are the first to provide detailed evidence of bacterial degradation of plastic in an animal’s intestine. “Our findings have opened a new door to solve the global plastic pollution problem,” says study co-author Wei-Min Wu, a senior research engineer in Stanford’s department of civil and environmental engineering.

Professor Craig Criddle, PhD ’89, who supervises Wu’s research, says the findings were unexpected. “Sometimes science surprises us. This is a shock.”

 The work raises important questions for more investigation, Criddle says, including whether the relevant microorganisms in the mealworms’ gut can be cultivated at high density and whether clues can be gleaned as to where else to look in nature for organisms and enzymes that degrade other plastics.

“I would not say solutions are ‘right around the corner,’ but this work lights a path.”

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