ACS Meeting News: Tiny iron particles pose new concern for drinking water

When it comes to drinking water, where there’s lead, there’s usually iron. Researchers have established a correlation between the two metal contaminants but lack a clear understanding of how iron influences the release of toxic lead from pipes into water.

And that relationship may be more complex than water experts anticipated, according to Graham Gagnon, director of the Center for Water Resources Studies at Dalhousie University. Iron mineral nanoparticles may play a hitherto unconsidered role in helping lead leach into tap water, Gagnon said Wednesday morning at the American Chemical Society national meeting in Philadelphia.

Researchers who study drinking water currently consider metals in two forms: dissolved or particulate, which means metallic bits larger than about 450 nm, Gagnon explained in a session sponsored by the Division of Colloid & Surface Chemistry.

Colloidal nanoparticles don’t fit squarely into either category. Yet these particles, which are roughly 10 nm in diameter, accounted for more than 30% of the lead content in simulated drinking water samples analyzed by Gagnon and his colleague, Benjamin F. Trueman.

The team analyzed water from a model pipeline system representing a common construction in North America, where cast iron main pipelines carry water over long distances. Shorter lead distribution lines then connect the main to residences and businesses.

Although the model system fit on a benchtop, the duo built and operated it using authentic materials and practices. The researchers collected water that spent months in their system and used a combination of size exclusion chromatography and inductively-coupled mass spectrometry to reveal nanoscopic iron minerals, including goethite and magnetite (Environ. Sci. Technol. 2016, DOI: 10.1021/acs.est.6b01153).

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It remains unclear exactly how the iron particles and lead pipes interact, but Gagnon posited that the nanoparticles release lead electrochemically and absorb it.

Now that researchers know the nanoparticles are in water, they can start asking more specific questions about them, said Irina Chernyshova, a physical chemist in the environmental engineering department at Columbia University. For instance, scientists can now examine iron particle-lead pipe interactions, considering variables such as a water’s pH and salinity, along with nanoparticle size and geometry.

For his part, Gagnon is interested in exploring how corrosion inhibitors for pipes, primarily orthophosphate, affect the nanoparticles. That understanding could help better protect people as long as lead pipes remain in water systems, he said.

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