The first direct in vivo comparison of nanoparticles with their equivalent bulk materials shows little difference in their toxic effects
The rapid advance of nanotechnology has raised concerns that substances known to be harmless in bulk might turn out toxic or carcinogenic in certain fibrous or nanoparticle forms. Some scientists have pointed to the case of serpentine minerals, where the fibrous form, chrysotile asbestos, is highly carcinogenic, while other, chemically identical forms are harmless.
But those fears may be somewhat allayed by Torsten Hansen and his coworkers at the University of Mainz, Germany, who have now performed the first in vivo tests for carcinogenic effects that allows a direct comparison between nanoparticles and their corresponding bulk materials.1 They used five different materials including cobalt, nickel, SiO2, TiO2, and PVC, building on an earlier study in which they had tested the toxicity of these nanoparticles in vitro and found cytotoxic effects only in cobalt nanoparticles.2
In their new analysis, the researchers studied the carcinogenic effects of these substances in rats by implanting samples of nanoparticles and their corresponding bulk materials in the same animal, and observing them for a duration between four and 12 months. ’Our data show that nanoparticles show a broad variety of biological effects extending from inflammation to malignant tumours, depending on their different chemical properties,’ Hansen told Chemistry World.
Not good. The researchers observed the strongest carcinogenic effect in the animals that had received nickel implants, who all developed tumours within six months. But crucially, there was no significant difference between the implantation sites with bulk metal or nanoparticles.
The only group of animals that did show a difference between bulk and nanoparticles was the ones exposed to cobalt. In this case, cancer-related phenomena occurred earlier at the sites of the nanoparticle implants than at the bulk site. With the other three materials, no carcinogenic effect was observed, and the team point out that in their tests, no harmless substances were turned into carcinogens merely by reformulating them as nanoparticles.
However, Hansen cautioned that ’there is still no relevant animal model which is able to predict possible neoplastic effects of nanoparticles in humans,’ and added that the results could not be extrapolated to humans.
et al.J. R. Soc. Interfaceet al. J. Mat. Sci.15, 321.