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CINCINNATI--Protective guidance for workers exposed to carbon nanotubes and nanofibers “will be a living document,” responsive to emerging research, National Institute for Occupational Safety and Health (NIOSH) scientists said Feb. 3.
Current scientific literature on possible adverse health impacts from working with nanomaterials, to date, has been spotty, and animal studies “seem to justify a cautious approach,” Charles Geraci, coordinator of NIOSH's Nanotechnology Research Center, told a public forum discussing the draft document, Current Intelligence Bulletin: Occupational Exposure to Carbon Nanotubes and Nanofibers.
The final document, expected later this year, will contain a recommended exposure limit (REL) that is based on a review of relevant research and in-house risk assessments, as well as guidelines for good work practices, Geraci said, noting the bulletin is “a high priority” for the agency and has been fast-tracked since NIOSH was given approval to proceed by the Centers for Disease Control in March 2009.
Last month NIOSH Director John Howard said the final bulletin is “a big deal” because it will mark the first time that a government agency will recommend a REL for these materials, an action that will move the nanotechnology field ahead.
Carbon nanotubes and nanofibers are used in numerous industrial and biomedical applications, according to the draft document. As such, employees who work in a wide range of facilities, such as research laboratories, electronics production plants, or facilities where these nanomaterials are processed, used, disposed, or recycled, can be exposed to them.
Various animal studies using different exposure routes have shown a consistent toxicological response to these carbon nanomaterials, primarily adverse respiratory reactions, such as pulmonary inflammation and interstitial fibrosis, Vincent Castranova, chief of pathology research within NIOSH's Health Effects Laboratory Division, said.
Pulmonary inflammation appears to come on rapidly following exposure, he said, and several studies in rodents have shown an equal or greater potency of carbon nanotubes compared to other inhaled particles known to be hazardous to workers, such as asbestos.
Animal studies have shown that carbon nanotubes can reach and remain in sub-plural tissue, reduce oxygen-availability for cells after one day of exposure, disrupt mitosis and set off uncontrolled cell proliferation, produce cardiac dysfunction, and trigger mesothelioma, said Castranova.
NIOSH has an “active agenda of research” into the health effects of carbon nanotubes and nanofibers, he said, and is taking a multi-metric approach to its investigation.
The pulmonary inflammation and interstitial fibrosis observed in animal studies “are relevant to occupational lung diseases associated with worker exposure to inhaled particles and fibers in the workplace,” the draft document said, adding that the extent of worker exposure to these engineered nanoparticles is poorly understood right now.
Using dose-response data from animal studies and extrapolating exposure concentrations to humans, taking into account species differences, NIOSH is recommending a REL of seven micrograms per cubic meter as an eight-hour time-weighted average respirable air mass concentration, Eileen Kuempel, senior research health scientist for NIOSH”s Nanotechnology Research Center, said.
NIOSH proposed the REL in December (34 CRR 1169, 12/6/10).
The recommended limit is set at the lowest airborne concentration that NIOSH Method 5040 can measure, but excess risk of adverse lung effects is predicted below this level, since these particles persist in the lungs, Kuempel said. Thus, employers should try to reduce airborne concentrations of carbon nanotubes and nanofibers as much as possible below the REL, he said.
Any risk assessment always carries a certain amount of uncertainty, prompting the need for more research regarding worker exposures, physical-chemical properties of the two nanomaterials, and more sensitive dose metrics, Kuempel said.
As work progresses to understand the health risks, NIOSH recommends employers identify and characterize processes that expose workers to carbon nanotubes and carbon nanofibers and use “best practices” for containment and control of these airborne particles.
Respiratory equipment, exhaust ventilation, and containment chambers are part of NIOSH's workplace recommendations, he said, as well as protective gloves and clothing, since dermal exposure to these nanomaterials may pose a health risk.
Employee training is a key recommendation, Geraci said, but this is proving “a big challenge” since it is difficult to communicate possible dangers to workers and industry “when we're trying to understand the hazards ourselves.”
NIOSH has worked with its partners to advance strategic research on the occupational health and safety aspects of nanotechnology for more than six years, and has published numerous studies, recommendations, and scientific methods in this pioneering area. The NIOSH web page provides a portal to these and other resources.
Written comments on the draft document will be accepted through Feb. 18.
By Bebe Raupe
The 149-page draft document, as well as instructions for submitting comments, is available online at http://op.bna.com/env.nsf/r?Open=sbra-8dutk5.
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