The United States National Institute for Occupational Safety and Health (NIOSH) has proposed a recommended exposure limit of seven micrograms per cubic meter of air for carbon nanotubes and nanofibers, which is the lowest concentration that can be reliably measured. These materials are used in many industries, including electronics, solar cell manufacturing, plastics and pharmaceuticals. NIOSH has observed pulmonary inflammation and fibrosis in animals resulting from exposure to certain nanoparticles. John Howard, NIOSH Director, said “[A]s nanotechnology becomes more widely used and as public awareness grows, employers, workers, and health and safety professionals all increasingly seek guidance on measures for controlling occupational exposures. These diverse stakeholders agree that the prudent stewardship of nanotechnology is essential for public acceptance and U.S. competitiveness in the global market.” NIOSH said, in the proposal, that employers should implement occupational health surveillance programs and take other steps to minimize risk, until researchers can better characterize the toxicity of carbon nanotubes and nanofibers. James Bonner, an associate professor at North Carolina State University’s Environmental and Molecular Toxicology Department, said that NIOSH chose a conservative recommended limit. “I think it’s a wise choice. Based on studies with exposure to animals, we and other folks at NIOSH see significant effects at carbon nanotube concentrations above that level,” Bonner said. “It’s a good place to start because there’s a lot of start-up companies dealing with carbon nanotubes.” NIOSH will accept public comments on its proposal until February 18, 2011, and will hold a public meeting on February 3, 2011, in Cincinnati, Ohio.