If someone were to Google the term “microplastics,” they would be greeted by a page of findings from the National Oceanic and Atmospheric Administration, Harvard Medicine, the National Institutes of Health, and many other government agencies.
Other questions were suggested, including those related to health concerns related to microplastics.
Microplastics are generally visible to the human eye. Because of their size and with a fine enough sieve, a person could see them and remove them from soil, sand or other sources where they may be present.
But what about the plastic particles that cannot be seen with the naked eye but are still present, for example in drinking water or in the sea? How do you remove these nanoplastic particles?
Researchers at the University of Missouri have developed a method to remove these particles from water with almost 100 percent effectiveness. It uses a hydrophobic solvent made from natural ingredients, such as a mixture of a menthol compound and thymol, an extract from the thyme herb.
The findings, by nano and materials chemistry doctoral student Piyuni Ishtaweera and Gary Baker, an associate professor in MU’s Department of Chemistry, were published in June in the American Chemical Society’s journal Applied Engineering Materials. Other authors were Collen Ray, Wyland Filley and Garrett Cobb.
“Nanoplastics can disrupt aquatic ecosystems and enter the food chain, posing risks to both wildlife and humans,” said Ishtaweera, who graduated from college and now works at the U.S. Food and Drug Administration in St. Louis. “To put it simply, we are developing better ways to remove pollutants like nanoplastics from water.”
The method, which is still being used on a laboratory scale, is still in its infancy, Baker said, noting that the use of highly eutectic solvents is nothing new. Similar oily, water-repellent solvents are also used in the removal of metals and even radioactive materials from liquids such as water, he said.
“We’re at the beginning of something that I think is going to be pretty big and change things at some point. We’re at the beginning of a ‘green chemistry revolution,’ so to speak,” Baker said. “… We’re really the only group that’s looked at a variety of chemicals and looked at multiple sizes of nanoplastics. Everyone is suddenly using eutectic solvents for environmental remediation. We’re kind of in the right pole position in this area.”
Method for extracting nanoplastics from water
In their experiments with the hydrophobic, deep eutectic solvents on nanoplastics, Baker and his colleagues worked with plastic beads of different sizes. The sizes ranged from 0.1 micrometer to 1 micrometer or 1,000 nanometers.
“The largest size we looked at is just big enough to be considered microplastics, and the other sizes were even smaller. We were able to capture all sizes,” Baker said. “In some ways, it’s easier to capture microplastics than nanoplastics, so we focused on the smaller ones that are harder to extract.”
Samples of clear or salt water contained orange-colored nanoplastics emulsified in the water to which the solvent was added and mixed again. When the solvent separated from the water again, it had captured almost all of the nanoplastics. So after application, there is a defined line of orange nanoplastics trapped in the hydrophobic solvent and the clean water below, like those childhood science experiments trying to mix oil and water.
The average extraction of nanoplastics with the solvent in clear water was about 98%, while in salt water it was 99%.
“In salt water, these small nanoplastic particles tend to stick together more, so the particles get a little bigger because salt water has a higher ionic strength, so they kind of stick together. When they cling to each other, these larger chunks are easier to extract,” Baker said.
Expansion of the water treatment experiment
Expanding the experiment to practical applications, such as water treatment, will require more engineering, research, money and time, Baker said.
“We’re working at a lab scale because we’re pioneering the chemistry and proving it works. That’s what you need first,” he said. “Unless we scale up a company that does this commercially, we can’t do it at scale, but engineers could scale it up. There are no fundamental barriers to doing that.”
This technique and research could build on what Baker, Ishtaweera and the other study authors have already done. This could mean a different solvent, making what separates out easier to recover or even magnetically accessible.
“It’s going to be a race to the next best thing,” Baker said.
The use of eutectic solvents also needs further research to bring them into water treatment to remove insoluble chemicals known as PFAS. Baker has already begun researching this topic.
The future of nanoplastics and even PFAS lies in extraction. The next necessary step is destruction.
“We would really like to have eutectics that could extract things like microplastics, nanoplastics and PFAS and then use something harmless like light to photocatalytically convert them into something harmless. That’s the dream. Then you could really clean up water and not have a waste product to deal with,” Baker said. “As a society, we’re a long way from that.”
Medical applications to extract nano- and microplastics from human or animal blood or other body tissues are likely to be more difficult to achieve, Baker added. While it is not impossible, there are still questions about what effect micro- and nanoplastics have on human and animal biology.
“I think these things are being discussed and could be doable,” he said.
Charles Dunlap covers local politics, community stories and other general issues for the Tribune. Reach him at [email protected] or @CD_CDT on X, formerly Twitter. Subscribe to support important local journalism.
