PORTLAND, Ore. — Scientists at the University of California at San Diego and the nearby Veterans Affairs Medical Healthcare System in La Jolla recently concluded that magnetic nanoparticles may be hazardous to your health.

Experiments revealed that iron oxide particles less than 10 nanometers in diameter stunt the growth of nerve cells. Separate in vitro experiments at the National Institute of Standards and Technology (NIST) have also concluded that nanotubes shorter than 200 nanometers interfere with human lung cells.

Both groups called for animal testing that would not only quantify the toxic effects of nanomaterials on living organisms but also characterize the most toxic types of nanomaterials. Currently the National Science Foundation (NSF) spends almost 10 times more on developing nanomaterials than on engineering to prevent their toxic effects.

"NSF is spending a lot more money on developing nanomaterials than [on] measuring their toxicity or characterizing what makes certain kinds of nanomaterials toxic," said Shunho Jin, a professor of materials science at UCSD. "We want to see increases in funding for studies like ours, which try to determine what types of nanomaterials are most toxic and how that toxicity can be avoided."

In 2007, NSF's National Nanotechnology Initiative will spend $273 million, but only $28 million is earmarked for "societal dimension" studies, including testing and safety issues. The $28 million is divided among its Nanoscale Science and Engineering Centers, which are studying nanoparticle manufacturing wet environments, occupational safety during nanomanufacturing and the interaction between nanomaterials and cells. Studies are also underway to characterize nanomaterials. At UCSD scientists studied the toxicity of iron oxide nanoparticles, which are being developed worldwide for such applications as enhancing magnetic resonance images to killing cancer cells. By injecting magnetic iron oxide nanoparticles into humans before an MRI, image contrast can be enhanced. For cancer treatment, injected nanoparticles would be heated by an external magnetic field—the theory being that cancer cells can be killed more easily with heat than normal cells.

"There are thousands of groups around the world looking to use magnetic nanoparticles for all kinds of bio- and nanotechnologies," said Jin. "But they tend to just assume that iron oxide nanoparticles are a biocompatible material, which our study shows they are not."

Jin's group has found that iron oxide nanoparticles smaller than 10 nanometers in diameter can stunt the growth of nerve cells. Instead of responding to the natural chemical signals from nerves by extending neurites that facilitate communications, nerve cells tend to go dormant in the presence of iron oxide nanoparticles, they found.

"We have found that even moderate levels adversely affect neural cell-to-cell interaction and signal transmission," said Jin. "Instead of sprouting out neurites to facilitate communications, they tend to stay put."