New ‘magnet’ pulls pesky nonstick pollutants from drinking water
It targets toxic chemicals, which can themselves stick around in the environment — potentially forever
Making the chemical used in many nonstick frying pans, stain-resistant carpets and fire-fighting foams can pollute drinking water. Known as PFOA, this chemical can persist unchanged in the environment for years — perhaps for centuries or longer. And that can be troubling because studies have suggested that PFOA can harm the health of people and animals. But a new lab-made chemical can now remove PFOA from water.
Chemicals already existed to filter out PFOA. None, however, work as well as the new one appears to. William Dichtel is a chemist at Northwestern University in Evanston, Ill. He and his colleagues described their new PFOA “magnet” June 14 in the Journal of the American Chemical Society.
PFOA is short for perfluorooctanoic (Per-FLUOR-oh-OCK-teh-NO-ik) acid. It’s one of a family of related perfluorinated (Per-FLUOR-ih-NAY-ted) compounds, or PFCs, that toxicologists worry about. Each PFC has a backbone of carbon atoms to which a large number of fluorine atoms are strongly bound. Those fluorines make the chemicals stable. They are so stable, in fact, that some of these chemicals never want to break down.
Because of how long PFOA and some of its chemical cousins can pollute the environment, many companies have cut back on their use. But that hasn’t ended the problem. PFCs released even long ago still sit around, waiting to be picked up by plants and animals.
Already, low levels in all of us
“These compounds are very possibly some of the most persistent organic chemicals we’ve made to date,” says Christopher Higgins. He’s an environmental engineer at the Colorado School of Mines in Golden. Higgins wasn’t part of this new study. He has, however, been studying the problem of PFC pollution. In the natural environment, he says, these chemicals take practically forever to disappear.
And that’s a concern because the use of these chemicals has been so widespread. They now can be found nearly everywhere. For instance, studies found traces of PFOA and related PFCs in 98 percent of all Americans tested.
In rats and mice, exposure to PFOA raises the risk of certain tumors. But it’s unclear whether it also raises cancer risks in people. Studies in humans have linked the chemical to thyroid disease, to a weakened immune system and to problems for developing fetuses. There are even data linking PFOA and related PFCs to impaired vaccine effectiveness in kids.
PFOA will build up in a person’s body over time. So the U.S. Environmental Protection Agency advises keeping exposures very low — to just 0.07 parts per billion in drinking water. But water in many U.S. towns and cities have far higher levels, recent studies have shown.
Notes Dichtel: “We’re finding negative health effects from being exposed to [PFCs] even when they’re in trace concentrations.” As such, he says, “It’s becoming clear that we need to remove them almost completely.”
Designing a better PFC ‘magnet’
A common way to remove PFOA from water is with a filter that contains a material that acts like a PFC magnet. It will gather molecules of the pollutant onto the material’s surface. This makes the pollutant easy to remove.
Activated carbon is often used this way. But PFOA molecules are only somewhat attracted to it. This allows some PFOA molecules to remain in the water, Dichtel explains.
So his group designed a material to actually target PFCs. This material is a type of polymer. Such molecules are made of chains of repeating chemical units. The new polymer contains repeating units of two different molecules. One is a giant, ring-shaped molecule derived from cornstarch. It’s called beta-cyclodextrin (BAY-tuh SY-klo-DEX-trin). The other is a fluorine-rich molecule called DFB. (That’s short for decafluorobiphenyl.) Its fluorines help the polymer grab onto PFOA, Dichtel says.
Activated carbon grabs any contaminants that are nearby. The new polymer instead selectively attracts those hard-to-get fluorine-rich pollutants, says Karen Wooley. She’s a chemist at Texas A&M University in College Station and was not part of the study.
In tests, the new polymer grabbed 95 percent of PFOA from water. Activated carbon removed only a little more than half of it. Moreover, some common chemicals in water can make activated carbon less effective. But the polymer kept working even when those other chemicals were around.
Best of all, the new polymer is reusable. Washing it with methanol, a type of alcohol, removed the PFOA. This left the polymer ready to pull out more of the pollution.
Dichtel and his colleagues now are working to turn this polymer and others like it into products people can buy. Such materials might one day help homeowners and businesses filter their water.
Higgins at the Colorado School of Mines notes that other PFC pollutants also pose risks. He’s part of a group including Chinese researchers that has been focusing on how to clean up drinking water supplies that are polluted with PFC-based firefighting foams. They found PFOA and nearly 30 other PFCs in affected waters. Scientists only recently discovered nearly half of the PFCs they turned up.
Unlike Dichtel’s group, Higgins’ team found that activated carbon did a decent job of removing PFOA. But activated carbon did not work nearly as well for those other, under-the-radar molecules. Yet they might pose similar environmental and health risks.
His team reported its new findings June 6 in Environmental Science and Technology.
Concludes Higgens, when it comes to getting PFOA and its relatives out of drinking water, “we need all the help we can get.” And new filters could tackle that. This research, he says, “is an effort to do something quite new.”