Back in August 2007, we ran a short article on an in vivo study published in Nanotoxicology regarding the potential toxicity of carbon-based nanohorns on mice which was conducted by researchers at the Oak Ridge National Laboratory and the University of Tennessee.  The scientists concluded the "combined results [of the experiments] suggest that SWCNH is a relatively innocuous nanomaterial when delivery to mice in vivo using aspiration as a delivery mechanism.”  In a recent article in the monthly trade newsletter "Nanoparticle News," one of the original researchers theorized that the largely benign results might be attributable to a lack of metal contaminants in the nanohorns because they are manufactured "through simple ablation of a pure carbon target without the use of transitional metal catalysts."  Metal catalyst contaminants are thought to cause the inflammatory responses and oxidative stress found in prior toxicology studies of single-walled carbon nanotubes.