Magnetic ‘rusty’ nanoparticles pull estrogen out of water

Iron oxide particles trap estrogen hormones, possibly limiting harm to aquatic life

An illustration of a clump of iron oxide nanoparticles, illustrated in orange, coated with phosphonic acid, illustrated in gray. While a collection of green estrogen bits are scattered around.

Iron oxide nanoparticles (one illustrated, orange) coated with phosphonic acid molecules (gray) can capture estrogen hormones (green) from water samples.

Dustin Vivod and Dirk Zahn/Computer Chemistry Center/Friedrich-Alexander-Universität Erlangen-Nürnberg

A new “smart rust” could one day help pull pollutants out of waterways, leaving cleaner water behind.

Researchers adorned tiny particles of iron oxide, better known as rust, with “sticky” molecules that grab on to estrogen and similar hormones in water samples. A magnet can then remove both the particles and the trapped pollutants from the water, materials scientist Lukas Müller reports August 16 in San Francisco at a meeting of the American Chemical Society.

The new technology could potentially limit excess estrogen’s harmful effects on animals, especially those that live in waterways.

With the nanoparticles, “we are able … to clean very different kinds of environmental pollutants,” says Müller, of Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany.

Estrogen hormones typically enter waterways through humans’ and other animals’ waste (SN: 1/2/02). Even low concentrations can have harmful chronic effects on aquatic life, like higher instances of cancer or reproductive issues, says Konrad Wojnarowski, a biologist at Ludwig-Maximilians-Universität München who was not involved in the study. Wastewater treatment plants can remove some estrogen hormones, he says, but the process isn’t cheap or energy efficient.

For now, “we still don’t have an ideal way of dealing with estrogen pollution in the environment,” but nanoparticles could help, Wojnarowski says.

To build the estrogen-catching particles, Müller and Marcus Halik, a chemist also at Friedrich-Alexander-Universität, drew on prior experience designing iron oxide nanoparticles that can catch other kinds of pollutants like oil or herbicides (SN: 7/25/08). The tiny iron oxide cores are each about 10 nanometers in diameter. Each core is then covered in phosphonic acid molecules, which act like sticky hairs that scoop up contaminants.

The new version of the nanoparticles specifically targets estrogen by including two types of phosphonic acid. One kind is long, repels water and attaches to the neutrally charged part of the estrogen molecule. The other is positively charged to attract parts of estrogen hormones that carry a slight negative charge.

The smart rust removed much of the estrogen from small water samples prepared in the lab, the researchers found. Their next step is to test the nanoparticles on samples from actual waterways.

And the team is investigating exactly how the molecules on the nanoparticle surfaces grab and hold on to estrogen at the atomic scale. With this information, Halik says, they can improve the estrogen binding even more.

Skyler Ware was the 2023 AAAS Mass Media Fellow with Foogue. She has a Ph.D. in chemistry from Caltech, where she studied chemical reactions that use or create electricity.

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