University of Missouri Assistant Professor Zhiqiang Hu said he's found the silver nanoparticles might destroy benign bacteria that remove ammonia from wastewater treatment systems.

Several products containing silver nanoparticles are on the market, including high-tech, energy-efficient washing machines that disinfect clothes by generating the tiny particles.

"Because of the increasing use of silver nanoparticles in consumer products, the risk that this material will be released into sewage lines, wastewater treatment facilities and, eventually, to rivers, streams and lakes is of concern," he said.

Hu said silver nanoparticles generate chemicals known as highly reactive oxygen species. He noted the use of wastewater treatment "sludge" as a land fertilizer is a common practice, but if high levels of silver nanoparticles are present in the sludge, soil used to grow food crops might be harmed.

The study that included graduate student Okkyoung Choi appeared in the journal Water Research and Environmental Science & Technology.