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US study calls for cuts in cumulative CNT exposure

Cutting cumulative exposure to carbon nanotubes (CNTs) in the workplace is imperative for reducing the potential for adverse effects, according to a study by researchers from the US's National Institute for Occupational Safety and Health (Niosh).

A team, led by Aaron Erdely from NIOSH in Morgantown, West Virginia, points to a general failure to correlate animal study results to occupational exposures in workers, largely because of a lack of human exposure assessment data. The Niosh team addresses this gap by correlating workplace measurements of elemental carbon exposure to results of an inhalation study in mice.

The researchers pulled together exposure data collected from eight US-based multi-walled CNT (MWCNT) manufacturers. When extrapolated to the rodent results, the findings suggest that MWCNTs have a “limited” potential to cause inflammation in the lungs, at levels corresponding to the average inhalable elemental carbon concentrations observed in US CNT facilities, they write.

Toxicological evaluations suggest that MWCNTs have a relatively high hazard compared with other materials, including inflammation and promotion of lung tumours, say the researchers. Estimates suggest that considerable years of exposure are necessary for significant pathology to occur at that level, they add, concluding that limiting cumulative exposures is therefore imperative.

Writing in Particle and Fibre Toxicology, the researchers point to several study limitations, including the fact that elemental carbon concentrations do not distinguish between different types of carbon. The team is currently evaluating the toxicological endpoints of CNT materials in US manufacturing facilities.

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