Once the subject of sci-fi flicks and techno-thrillers, nanomaterials are now mainstream. These tiny particles can be found in hundreds of consumer products from camping gear to anti-stink socks, while helping medical researchers deliver drugs by fooling the body's defense mechanisms. Nano-silver particles, for example, have become common in both wound dressings and sunscreens.
But experts say the rise of nanomaterials is a concern. Compounds at the nano-scale (from 1 to 100 nanometers, or down to 1/100,000 the width of a human hair) often behave differently than at normal size. Metals change color or conduct electricity differently, and may interact with human cells in unusual ways. Scientists worry that not enough testing has been done yet to understand the effects on the environment -- how will tiny particles affect plants and animals that we eat, for example?
A study published last week in the journal PNAS by researchers at the University of California, Santa Barbara, found that the presence of two nanomaterials used in exhaust gases and fertilizers stunt the growth of soybean plants.
The researchers used high doses of zinc oxide (used in cosmetics and ultimately found in waste fertilizers) -- and cerium oxide (used to improve engine performance) in soybean plants grown hydroponically or without soil. The cerium oxide slowed the soybean plant growth rates by blocking a bacteria's ability to fix nitrogen. Plants treated with zinc oxide grew faster, but the zinc built up in leaves and stems.
"What this report shows is we have a lot more to learn," said Jennifer Sass, senior scientist at the Natural Resources Defense Council. "They are not well tested. We don't know before these things are already being used."
But Andrew Maynard, director of the Risk Science Center at the University of Michigan, says the results muddy the waters when it comes to nanotech safety. "There isn't enough information to say there's a plausible or definite risk associated with a release of these nanomaterials to the environment," he said.
The soybeans weren't grown in normal conditions for the experiment, Maynard said. He adds that each nano-particle has to be studied anew, meaning that existing risk assessments drawn from years of chemical studies may not be a good guidepost as to the fate of these compounds. "Almost every kind of nano-particle that comes along is different from others," he said.
Researchers at the Woodrow Wilson Center in Washington have been compiling an inventory of nano-materials used in consumer products. It now includes 1,317 items and has grown five-fold since 2006. The most common nano-material is silver, followed by carbon, titanium, silica and zinc.
While the federal government has been funding nanotechnology research at about $1.3 billion per year, there haven't been enough tests about the risks to health and the environment, according to Todd Kuiken, senior research associate at the Wilson Center's Project on Emerging Nanotechnologies.
Nutritional supplements are the worst offenders, Kuiken said. Companies are putting out claims of health benefits from drinking nano-silver laced water to artichoke "nano-clusters" that claim to improve digestion, but no federal agency regulates the supplement industry.
Maybe the best advice is following the old saying of "the dose makes the poison."
"The real question is what is your exposure?" Kuiken said. "A textile that may have nanosilver embedded into the materials, but can it cross into your skin, does it leave the fabric? Those are the questions that are outstanding."
The U.S. Food and Drug Administration recently put out draft rules for the use of nanomaterials in both cosmetics and food that are not binding on manufacturers.