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Smaller than a virus and used in more than 200 consumer products, silver nanoparticles can kill and mutate fish embryos, new research shows.
Tiny particles of silver – potent anti-microbial agents that can kill bacteria on contact – are becoming increasingly popular in consumer goods, including washing machines, refrigerators, clothing and toys.
But as use of these microscopic silver particles grows, some scientists now are raising concerns about potential effects on the environment and human health.
Many nanoparticles, including nanosilver, wash down drains and are not removed by sewage treatment, so they are discharged into lakes and rivers, where fish and other aquatic life are exposed. Research into the environmental implications of these silver nanoparticles has begun, but there are no answers yet about what happens when they enter ecosystems.
“I think we jumped the gun” by creating such large volumes of nanoparticles, said University of Utah researcher Darin Furgeson. “We should take more time and really look at these new nano-systems before we start to throw them into personal products and shoot them into these ecosystems.”
Nanotechnology is projected to be a trillion dollar industry by 2015, with some saying it will be the focus of the next industrial revolution. The number of products – including sunscreens, paints, vitamins, food additives, electronics, vehicles and appliances – that use nanomaterials has increased almost 380 percent since 2006, according to the Project on Emerging Nanotechnologies, a Washington, D.C.-based non-profit group that tracks nanotechnology.
Nanoparticles are pieces of metal or other substances that are engineered to measure less than 100 nanometers in length. A nanometer is one-billionth of a meter. In comparison, a human blood cell is about 8,000 nanometers and the HIV virus is about 130.
The U.S. Environmental Protection Agency recently announced a new research strategy to better understand the environmental effects of these microscopic particles. In addition, last year, the EPA and the National Science Foundation established two new centers, led by UCLA and Duke University, to examine the environmental implications of nanotechnology.
“The same special properties that make nanoscale materials useful are also properties that may cause some nanoscale materials to pose potential risks to humans and the environment, under specific conditions. At this point not enough information exists to fully assess these risks,” said an EPA report released in January. The report summarized the EPA’s Nanoscale Materials Stewardship Program, which collected voluntary information from companies that manufacture or use nanoparticles.
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.
An industry group, the Silver Nanotechnology Working Group, said that there has been a long history of safe, regulated use of ionic silver, which “suggests that the EPA is adequately managing the risks of silver nanoparticles.”
Ionic silver has been used over the last six decades for a variety of anti-microbial uses, including algaecides, water filters and disinfectants approved by the EPA. The industry group says there is no difference between it and the newer nanosilver – other than the new name – so there are “no significant new risks.”
But Todd Kuiken, a research associate at the Project on Emerging Nanotechnologies, said that unlike ionic silver, the particles used in consumer products are “intentionally engineered at the nanoscale for its properties” and that they may react differently with whatever they come in contact with. “There are a few studies out there that show that nanosilver reacts differently than conventional ionic or colloidal silver,” he said.
Dale Kemery, an EPA spokesman, said that the field of nanotechnology is “relatively new and the scientific information on the potential environmental and human health risks is limited.”
As a result, he said the EPA is consulting with a panel of scientists to figure out how to assess the potential risks. In September, the agency announced a research strategy to identify what happens to nanomaterials used in products such as sunscreens, paints, automobiles and electronics and how to avoid potential health or ecological problems.
Eric Hoek, a UCLA professor of environmental engineering and a member of the University of California Center for Environmental Implications of Nanotechnology, said the prevailing wisdom is that silver isn’t toxic to humans. But he added that there hasn’t been much human exposure to silver nanoparticles until recent years, when use of them has increased. They are now used in 259 products on the market today, according to the Project for Emerging Nanotechnologies.
“These materials have tremendous potential, but we need to proceed with cautious optimism,” Hoek said. “We need people to be skeptics, but not to be unjustly fearful and inciting fear unnecessarily.”
Mark Wiesner, director of the Center for the Environmental Implications of Nanotechnology at Duke University, is researching the effects that nanomaterials have on ecosystems rather than individual animals. His center is constructing 30 different aquatic mesocosms – experimental, miniature ecosystems – where small amounts of nanoparticles will be released.
“We’re looking at things that you wouldn’t be able to predict if you look from a molecular to organization level,” Wiesner said. “For example, if you take DDT and you predict its effects from organism to organism, you never would have guessed it would bioaccumulate. There are ecosystem-level effects that only become apparent when you look at the compete system.”
Hoek explained that silver particles are dynamic in the environment so they “are going to take different forms, react and form new particles.”
“To be able to say conclusively that they are good or bad is wrong from the beginning,” he said.
There are still many questions that need to be answered about toxicity of silver nanoparticles, said Kuiken at the Project on Emerging Nanotechnologies.
“The products are already out there, but we’re still waiting to see if they are really safe,” he said.
This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.