Engineers at the Woods Hole Oceanographic Institution are developing a tool that could autonomously scan the earth's waterways to separate and identify tiny plastic shards and other pollutants that are notoriously difficult to track.

The new technology was detailed in an ACS Sensors article on Jan. 9 and in a subsequent patent application published March 11 by the U.S. Patent and Trademark Office.

Researchers today can easily spot the vast array of abandoned fishing nets and patches of manmade trash that occupy the earth's major water systems. What's harder to see, though, are the estimated 14 million tons of microplastics, classified as being less than five millimeters in length, that lie on the ocean floor. 

Microplastics can come from manufacturing sources and clothing fibers or from larger pollutants that become battered by ocean waves, sand and sunlight. And although their environmental impact is still being investigated, microplastics have been located in the tissue of many living organisms and can contaminate food and drinking water.

Until recently, researchers had to collect and identify microplastic particles manually. This proved to be an often long and arduous process — one that made it difficult to assess which regions of the world are most affected by microplastic contamination or the extent to which microplastics pose a threat to humans and animals.

"People will put a filter paper of microplastics into really fancy, expensive machines, and they'll wait a whole day for it to analyze," Beckett Colson, a doctoral candidate at MIT and Woods Hole who was a coauthor of the January study and who developed the candidate invention, told The Academic Times. "And you get all of this rich data, but it's just one sample."

Colson, whose work centers on oceanographic engineering, set out to create a machine that would more efficiently detect and remove microplastics from the water in a continuous and automatic process. In order to differentiate native organic compounds in the water from foreign, man-made objects, he took cues from the spectrometer techniques biomedical researchers use to determine whether red blood cells are living or dead.

In particular, Colson's technology can analyze a stream of water and detect subtle changes in electrical resistance to identify its contents as either plastic or organic in nature. 

"The neat trick here is that biological things are constructed in a very different way than plastics," Colson said. "And so you can work out the material properties of the particle that's going through based off of that." 

Colson first built a prototype with affordable hobby components and capacitors and used everyday objects such as spinach and blades of grass to test against minuscule plastic compounds. Next, he sent tiny crustaceans and bottom-dwellers through the device to see if it could recognize them as living creatures. An exciting milestone, Colson said, was the point at which his device could detect plastic fragments that were impossible to see with the naked eye, without mistaking them for organic compounds. 

So far, Colson's experiments have taken place solely in a lab, with computer monitors transmitting the data to him. But later this year, he will venture out into the field to test his device in storm drains and other aquatic habitats to see how it functions in a less-controlled environment. This will be difficult, Colson admits, since even tiny fragments from one's own clothes can contaminate water samples.

Eventually, Colson hopes to scale his microplastic detection technology to a more commercial enterprise. That might mean attaching the filtration device to large research vessels or locating sources of micropollutants in the water at the mouth of a river, a contaminated runoff or a wastewater treatment plant. It could also one day be possible to send microplastics into separate streams of water for further processing and collection.

"You could imagine setting up 100 of these at once and doing some sort of microplastic filter," said Colson. "But that's definitely way in the future."

The application for the patent, "System and method of use for electrically differentiating particles in a liquid," was filed on Sept. 11, 2020, to the U.S. Patent and Trademark Office. It was published on March 11, 2021 with the application number 17/018626. The earliest priority date was Sept. 11, 2019. The inventors of the pending patent are Anna Pauline Miranda Michel and Beckett Colson. The assignee is Woods Hole Oceanographic Institution.

Parola Analytics provided technical research for this story.

The study, "Flow-Through Quantification of Microplastics Using Impedance Spectroscopy," published January 9 in ACS Sensors, was authored by Anna P.M. Michel, Woods Hole Oceanographic Institution; and Beckett C. Colson, Woods Hole Oceanographic Institution and Massachusetts Institute of Technology.