In one new experiment, Furgeson, a professor of pharmaceutical sciences, exposed zebrafish embryos to silver nanoparticles in a laboratory, and found that some died and others were left with dramatic mutations.

 “Some of the fish became extremely distorted, almost making a number nine or a comma instead of a linear fish,” he said.

The nanosilver caused malformations in their eyes, swim bladders, tails, and some embryos developed fluid around the heart that causes congestive heart failure, according to the study, which was published in August in the nanotechnology journal Small.

Furgeson tested concentrations until he found one that wasn’t lethal, about 0.01 grams per liter, to observe what nanosilver would do at doses that didn’t kill the embryos. 

Scientists do not yet understand what this toxicity means to humans and the environment. Testing silver nanoparticles on fish and other organisms is an important step toward understanding how they will interact in the human body.  It is unclear if these nanoparticles will accumulate in specific organs or what kind of damage they could cause.

“Zebrafish have similar tissues and organs to us,” Furgeson said. “They don’t have lungs, but they do have a liver, kidneys and heart – though it is only two chambered – and they have a blood-brain barrier.”

Raising concerns about potential harm to human health, other recent research has shown that some metal nanoparticles can damage DNA or kill cells. One new study found that nanoscale particles can cross into the womb through the placenta.

Different materials have different effects, according to the fish study. Both gold and silver nanoparticles were tested, but only the silver ones were toxic to the fish embryos in all sizes, according to the study. Gold particles did not have an effect. Other studies suggest that copper nanomaterials are toxic to rats.
 
“Chemical composition of the nanoparticle is as, if not more, important at inducing toxicity,” the authors said in their report.

Furgeson and his colleagues said that zebrafish could be used to identify “nanomaterial characteristics that afford minimal or no toxicity and guide more rational designs of materials on the nanoscale.”

Silver is one of the most toxic heavy metals.  In the 1970s, ionic silver from wastewater polluted San Francisco Bay at concentrations that prevented the mussels from reproducing. Changes in wastewater treatment have decreased the concentrations substantially.

“The silver that went into wastewaters when millions of people had their photographs developed taught us that small additions of silver to the environment make a big difference,” said Dr. Samuel Luoma, a former U.S. Geological Survey senior researcher who was lead author of a report by the Project on Emerging Nanotechnologies. The project is a partnership of industry, government and scientists established by the Woodrow Wilson International Center for Scholars and the Pew Charitable Trusts.

 “We have no means of detecting nanosilver in the environment once it is released, even if concentrations rise to levels that are toxic to aquatic ecosystems,” Luoma said in a statement when the report, “Nanoscale Silver: No Silver Lining?” was released last year.