Nanotoxicology

Nanotoxicology is the study of the toxicity of nanomaterials. Because of the small size and large surface area of nanomaterials, these materials have unique properties compared with their larger counterparts. The nanomaterials, even when they are made of inert elements like gold, become very active at a nanometer range. Nanotoxicological studies are intended to determine whether and to what extent these may pose a threat to the environment and to human beings. For instance, Diesel nanoparticles have been found to damage the cardiovascular system in a mouse model.

Nanoparticles
Nanotoxicology is a sub-specialty of particle toxicology. It addresses the toxicology of nanoparticles (particles <100 nm diameter)which appear to have some toxic effects that are unusual and not seen with larger particles. Nanoparticles can be divided into combustion-derived nanoparticles (like diesel soot), manufactured nanoparticles like carbon nanotubes and naturally occurring nanoparticles from volcanic eruptions, atmospheric chemistry etc. Typical nanoparticles that have been studied are titanium dioxide, alumina, zinc oxide, carbon black, and carbon nanotubes, and "nano-C60". Nanoparticle seem to have some different properties from larger particles that are known to have pathogenic effects, like asbestos or quartz. These differences seem to be a result of their size. They have a larger surface area per unit mass and this means that in some cases they may have more pro-inflammatory effects in, e.g. the lungs. In addition, some seem to be able to translocate from their site of deposition to distant sites such as the blood and the brain. This has resulted in a sea-change in how particle toxicology is viewed- instead of being confined to the lungs, nanoparticle toxicologists study the brain, blood, liver, skin and gut. Nanotoxicology has revolutionised particle toxicology and rejuvenated it.

No Fullerene toxicity reported
Nanoparticles can also be made of C60, as is the case with almost any room temperature solid, and several groups have done this and studied toxicity of such particles. The results in the work of Oberdörster at Southern Methodist University, published in "Environmental Health Perspectives" in July 2004, in which questions were raised of potential cytotoxicity, has now been shown by several sources to be likely caused by the tetrahydrofuran used in preparing the 30 nm - 100 nm particles of C60 used in the research. Isakovic, et al., Biomaterials, 27, 5049-5058, 2006, who review this phenomenon, gives results showing that removal of THF from the C60 particles resulted in a loss of toxicity. Sayes, et al. Nanoletters, 2007. 7, (8), pp. 2399 - 2406, also show that particles prepared as in Oberdorster caused no detectable inflammatory response when instilled intratracheally in rats after observation for 3 months, suggesting that even the particles prepared by Oberdorster do not exhibit markers of toxicity in mammalian models. This work used as a benchmark quartz particles, which did give an inflammatory response.

A comprehensive and recent review of work on fullerene toxicity is available in "Toxicity Studies of Fullerenes and Derivatives," a chapter from the book "Bio-applications of Nanoparticles" (Chan ed., Landes Bioscience, 2007). In this work, the authors review the work on fullerene toxicity beginning in the early 1990's to present, and conclude that the evidence gathered since the discovery of fullerenes overwhelmingly points to C60 being non-toxic. As is the case for toxicity profile with any chemical modification of a structural moiety, the authors suggest that individual molecules be assessed individually.