DURHAM, N.C. – In experiments reproducing the natural environment, Duke University researchers have demonstrated that silver nanoparticles, which are used in many consumer products, can have an adverse effect on plants and microorganisms.

These preliminary findings are important, the researchers said, because little is known about the environmental effects of these nanoparticles, and the only studies conducted to date involve high concentrations of the nanoparticles in a laboratory setting, which they point out, doesn’t represent “real-world” conditions.

Silver nanoparticles are used in a host of products, most commonly in textiles and clothing. These nanoparticles are used because one of their characteristics is the ability to kill bacteria, inhibiting unwanted odors. They work through different mechanisms, including generating oxygen free radicals which can cause DNA damage to microbial membranes without harming human cells. Other products with silver nanoparticles are children’s toys and pacifiers, disinfectants and toothpaste.

The main route by which these particles enter the environment is as a by-product of water and sewage treatment plants. The nanoparticles are too small to be filtered out, so they and other materials end up in the resulting “sludge,” which is then spread on the land surface as a fertilizer.

“Results from laboratory studies are difficult to extrapolate to ecosystems, where exposures will likely be at low concentrations and which are inhabited by a diversity of organisms,” said Benjamin Colman, a post-doctoral fellow in Duke’s biology department and a member of the Center for the Environmental Implications of Nanotechnology (CEINT), which is funded by the National Science Foundation and the Environmental Protection Agency.

“No one really knows what the effects of these particles are in the environment,” Colman said. “We’re trying to come up with the data that can be used to help regulators determine the risks to the environment from silver nanoparticle exposures.”

The results of the CEINT team’s experiments were published Feb. 27 in the online journal PLOS ONE .

“Our field studies show adverse responses of plants and microorganisms in a replicated long-term terrestrial environment following a single low dose of silver nanoparticles, applied by the likely route of exposure, sewage biosolid application,” Colman said. “An estimated 60 percent of the average 5.6 million tons of biosolids produced each year is applied to the land for various reasons, and this practice represents an important and understudied route of exposure of natural ecosystems to engineered nanoparticles.”

For their studies, the CEINT researchers created mesocosms, which are small, man-made structures containing different plants and microorganisms meant to represent the environment. They applied biosolids with low doses of silver nanoparticles in the mesocosms, then compared the effects of the nanoparticle-treated plants and microorganisms to the mesocosms receiving no nanoparticles.

“Our results show that silver nanoparticles in the biosolids added at concentrations that would be expected to a diverse terrestrial ecosystem caused ecosystem-level impacts,” Colman said. “Specifically, the nanoparticles led to an increase in nitrous oxide fluxes, changes in microbial community composition, biomass, and extracellular enzyme activity, as well as species-specific effects on the above ground vegetation.”

The researchers plan to continue their studies with another ubiquitous nanoparticle – titanium dioxide. Also, while the latest study of silver nanoparticles lasted 50 days, the researchers plan to study the long-term effects of such exposures.

The rest of the team, all members of CEINT, were Duke’s Christina Arnaout, Claudia Gunsch, Curtis Richardson, and Emily Bernhardt; Sarah Anciaux, Coe College, Iowa; Michael Hochella and Bojeong Kim, Virginia Tech University; Gregory Lowry and Brian C. Reinsch, Carnegie Mellon University, Pittsburgh; Jason Unrine, University of Kentucky; and Liyan Yin, Wuhan Botanical Garden, China. Bonnie McGill and Justin Wright from Duke, but not CEINT, were also members of the team.