Updated: NIOSH empfiehlt Inhalationsgrenzwert für CNTs
Gegenwärtig sind in der Literatur zwar noch keine Studien zu finden über negative Gesundheitseffekte durch CNTs bei Arbeitern, dennoch hat das U.S. National Institute for Occupational Safety and Health (NIOSH) eine Empfehlung für einen Grenzwert für die Exposition gegenüber CNTs abgegeben. Er beträgt sieben Mikrogramm pro Kubikmeter Luft für Kohlenstoff-Nanoröhrchen und -Fasern. Dies entspricht der geringesten Konzentration, die noch zuverlässig gemessen werden kann.
NIOSH has observed pulmonary inflammation and fibrosis in animals resulting from exposure to certain nanoparticles. In addition, the long and thin structure of some CNT and Carbon Nanofibres dimensionally resemble asbestos fibers, and multi-walled carbon nanotubes (MWCNT) have been observed to migrate from pulmonary alveoli to the pleura tissue which is the same site in which malignant mesothelioma can develop due to asbestos exposure.
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. They also state that the dose-response data for CNT in animal studies provide a scientific basis for developing a recommended exposure limit (REL) to protect workers’ health.
The REL is based on the available subchronic and short-term animal dose-response data of early-stage fibrotic and inflammatory lung responses to CNT exposure. Benchmark dose (BMD) estimates from the animal data (and the 95% lower confidence limit estimates of the BMD) have been extrapolated to humans by accounting for species differences in alveolar lung surface area. Working lifetime exposure concentrations have been calculated based on estimates of either the deposited or retained alveolar lung dose of CNT assuming an 8-hour time-weighted average (TWA) work shift exposure during a 40-hour work week, 50 weeks per year, for 45 years.
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.
Update of 23.12.2010:
You may access the corresponding Federal Register Notice of December 23, 2010, via this link: http://www.federalregister.gov/articles/2010/12/23/2010-32328/draft-current-intelligence-bulletin-occupational-exposure-to-carbon-nanotubes-and-nanofibers.
Source: CDC / Nanodev