These microscopic robots swim through the ocean and dissolve microplastics

By Adele Peters

May 25, 2021
 
Microplastics—tiny pieces of plastic smaller than five millimeters across—are everywhere, from snow in the Arctic and rain in the Rocky Mountains to bottled water and beer. On the ocean floor, there may be nearly 16 million metric tons of it. In the top 200 meters of the Atlantic Ocean, there may be 21 million more metric tons. It’s in lakes. It’s in rivers. It’s even on Mount Everest. And the smaller it gets, the harder it is to remove from water; technology attempting to clean up water usually focuses on catching larger pieces of plastic before they break down.

At a lab in the Czech Republic, researchers are developing tiny robots that could help. The microscopic robots “are moving machines the size of a red blood cell,” says Martin Pumera, a chemistry professor and director of the Center for the Advanced Functional Nanorobots at the University of Chemistry and Technology in Prague. “They don’t have wheels or flippers or engines,” he says. Instead, they’re made of material that is propelled forward when exposed to sunlight. And when material comes into contact with microplastic, it rapidly speeds up the  degradation of plastic that happens naturally in the sun. As the tiny robots move through water—several millimeters per second, fast for their size—they can continue encountering more plastic and help decompose it.

The robots “can decompose the microplastic much faster than it will decompose itself,” Pumera says. For some types of plastic, such as polyethylene glycol, the technology can fully break down the material. It also breaks down plastics like polylactic acid or PLA, a bioplastic that is designed to degrade in industrial composting facilities but doesn’t easily break down in cold ocean water. The scientists are studying ways to design the devices to target different types of plastic, since microplastic comes in forms ranging from synthetic fibers to tiny particles of old tires.

In the past, Pumera collaborated with an environmental remediation company to design microrobots to clean up other contaminants in groundwater; the basic concept can be tweaked to use for different purposes. “We construct the robots like Lego,” he says. “We have different layers and different functionalities.” In the case of microplastic, for example, it’s important that the robot can move by itself, not just break down the plastic, so that it can break down as much plastic as possible.

The technology is still in development, and the scientists need to do more work to make sure that the robots can also break down correctly themselves and not create new problems in the environment. But Pumera hopes to make it a reality, and as we spoke, he’d just gotten an email from a water treatment plant that wanted to begin using the robots. One recent study found that sewer overflow pipes from a wastewater plant could dump out millions of tiny particles of plastic in a day.

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