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Mizzou Engineering researcher studying environmental impact of popular nanotechnology

The microscopic image above shows silver nanoparticles attaching themselves to bacteria used across the country to remove ammonia from the wastewater treatment system. Chemicals released by the nanosilver probably inhibit the bacteria's growth. Image courtesy of Zhiqiang Hu

A University of Missouri researcher has found an increasingly popular nanomaterial kills bacteria used to clean the nation’s wastewater, and is launching a follow-up study to determine the levels at which it becomes toxic.

Zhiqiang Hu, an MU civil and environmental engineering assistant professor, found in a National Science Foundation-sponsored study that silver nanoparticles destroy benign bacteria employed across the country to remove ammonia from the wastewater treatment system. Several products containing silver nanoparticles already are on the market, including nanosilver socks designed to inhibit odor-causing bacteria and wash machines that disinfect clothes with the tiny particles.

“We found that silver nanoparticles are extremely toxic,” Hu said.

Hu said nanosilver particles generate more unique chemicals—known as highly reactive oxygen species—than do larger forms of silver. Those chemicals likely inhibit bacterial growth, he said.

The Water Environment Research Foundation recently awarded Hu $150,000 to determine more precisely when silver nanoparticles start to impair wastewater treatment. Work on the follow-up research is slated to start May 1 and be completed by 2010, Hu said.

In that project, Hu will determine how silver nanoparticles affect representative wastewater treatment processes by gradually releasing as well as injecting a shock load of the nanomaterial into wastewater and sludge. Measuring subsequent microbial growth will allow MU researchers to determine the nanosilver levels that will harm wastewater treatment and sludge digestion, Hu said.

With that knowledge, nanoparticles in wastewater can be better managed and regulated, he said.

Hu’s silver nanoparticle research has been published in Water Research and Environmental Science & Technology.