There is no doubt that the rapid development of nanotechnologies requires a clear understanding about the safety of the developed nanomaterials, both for humans and for the environment. And the biological properties of nanoparticles depend not only on their composition, but mainly on their size, form, physical and chemical properties of their surface, determined by the peculiarities of their synthesis method. All of this also holds true for fullerenes – most simple representatives of nano-objects – for which we already knew dozens of ways to obtain their nanoparticles, especially as water dispersions. Nevertheless, one can often face a rather simplified and superficial approach to understanding the definite physical and chemical properties of fullerene nanoparticles synthesised in different ways. In turn, it is well known from scientific literature that this approach has produced many contradicting results during toxicological trials of fullerene nanoparticles.

 

As a consequence of the above, if you enter the key words “toxicity, fullerene” in an Internet search, you can see a long list of fearful denominations and phrases connected with two works carried out in the USA in 2004: an article by V. Colvin with his co-workers from Rice University, and one by E. Oberd?rster from Dallas University [1]. As a “toxic” fullerene, water dispersions of nano-C60 (nC60, THF/nC60) were used for the purposes of this research, prepared with one and the same method, where rather toxic tetrahydrofuran (THF) was used as an intermediate solvent. We reproduced this method and thoroughly analysed the resultant water dispersion of C60. We obtained evidence that standard manipulations with such a dispersion had no desired result in terms of getting rid of THF and that gas chromatography analysis always detects THF and products of its degradation that are integral and prevailing components of nano-C60 particles. It is THF and products of its oxidising modification and their further polymerisation that stipulate the negative biological effects of nano-C60 particles. Our critical remarks as for the pseudo-sensation about fullerenes’ toxicity can be found in the English-language article [2] or its Russian variant, written as an open letter to the scientific community.

 

Considering our criticism, E. Oberd?rster repeated her experiments with aquarian fish and water flea (Daphnias) in 2005. But this time she used fullerene water solution, obtained via 2-month mixing of fullerene powder in water. In this case, any influence of harmful impurities of organic solvents was excluded, but she received water dispersions of fullerene particles of 10–200 nm, whose surfaces consisted of modified hydroxylated (oxidised) fullerenes. However, there was no significant toxicity of fullerenes to any extent, as there had been in previous research work. It was only at very high concentrations (~35 mg/l) of oxidised fullerene particles that any adverse and unreliable effects were observed, which were mainly connected with the very high level of turbidity of the medium, where the water organisms lived and were tested.

 

At the same time, scientists from France [3] demonstrated that the use of water dispersions of fullerene C60 during experiments on rats had no toxic effects, even in very high doses of C60 (? 2.5 g/kg). Moreover, pure fullerene C60 perfectly protected the animal’s organism from the influence of strong toxicant and proved to have powerful antioxidant and hepatoprotective properties.

 

In spite of this, the idea that fullerenes can be toxic gave occasion for theorists from Vanderbilt University to “play” with computer modelling with fullerene C60 molecules and DNA. However, the real physical and chemical properties of fullerene and DNA molecules in water systems were not considered; speculative conclusions were received as to the possible genotoxicity of fullerenes. You can see our critical remarks (in Russian) on this issue on the Internet-site “Elements”.

 

Then, in spite of the fact that, back in 1997, Russian scientists clearly demonstrated the absence of any mutagenic, DNA-disturbing action on the part of pure fullerenes (Genetica, 1997, vol. 33, pp. 405-409), two works from American groups appeared in 2006-07 (V. Tarabara et al. from Michigan State University, and S. Pacheco, K. Arcaro et al. from the University of Massachusetts), which included high-sounding statements to the effect that they had established the genotoxicity of fullerene C60 dispersions in water. In addition, in testing done by the second group of researchers, they apparently discovered that colloidal particles of silica (the main component of usual sand!) had DNA-disturbing effects and that they were similar in their extent to those of fullerenes!

 

A detailed analysis of the results provided by American research works have revealed the scientific incorrectness and fallibility of further conclusions, which were connected with the fundamental non-applicability of the chosen method – the Single-Cell Gel Electrophoresis Assay or Comet assay with Olive Tail Moments (OTM) observation – for an analysis of the genotoxicity of nanoparticles and nanomaterials. The conclusion of our critical analysis (in Russian) can be expressed by the following way: “Pure fullerenes are no more dangerous than regular sand”!

 

Before these publications appeared, for the previous 20 years, nobody from many laboratories of the world had noticed any toxicity of fullerenes; and fullerenes in their toxicological characteristics have always been equated and continue to be equated to amorphous technical carbon, to carbon black (carbon black, U.S. Department of Labour, OSHA's Hazard Communication Standard, 29 CFR 1910.1000 and 29 CFR 1910.1200).

 

Numerous biological experiments with our molecular colloidal solutions of hydrated fullerenes (FWS) virtually always start with the testing of their probable toxic effects. And none of the in vitro and in vivo tests have revealed any signs of their toxicity.

 

Thus, we can fully confidently answer the question about fullerenes’ toxicity: fullerene molecules are not toxic and cannot be more toxic than coal, graphite, diamond or usual sand. What can be toxic are both the chemical derivatives of fullerenes (which is determined by the properties of the chemical groups attached to the fullerene core) and nanoparticles in the form of crystalline solvates (or clathrates) of fullerene molecules with other toxic molecules. In contrast with that, FWS contain only pure fullerenes and water; therefore, one cannot expect any toxic effects upon applying hydrated fullerenes and their aqueous solutions.

 

Incidentally, at the end of 2005, we gave E. Oberd?rster a sample of our FWS and suggested that he carry out comparative biological testing, but there has been no answer as of yet. Moreover, this is probably due to the fact that the myth of fullerenes’ toxicity, which appeared with much fuss in 2004, is being constantly shattered under pressure from reliable and unquestionable scientific findings. Water dispersions, known as nano-C60 or nC60, or THF/nC60, or nC60/THF, which scientists in the West like to work with, are absolutely unsuitable objects for the objective assessment of pure fullerenes’ toxicity. That is exactly why conclusions on the toxicity of fullerene C60, obtained on the basis of such objects, should be considered false ones and they should not be taken into consideration in future.

[1] Oberdorster E. Manufactured nanomaterials (fullerenes, C60) induce oxidative stress in brain of Juvenile Largemouth bass. Environ Health Perspect., 112(10), (2004) 1058–1062.

[2]. G.V. Andrievsky, V.K. Klochkov, L.I. Derevyanchenko. IS C60 FULLERENE MOLECULE TOXIC?! Fullerenes, Nanotubes and Carbon Nanostructures, 13 (4), (2005) 363-376.

[3] Najla Gharbi, Monique Pressac, Michelle Hadchouel, Henri Szwarc, Stephen R. Wilson and Fathi Moussa. [60]Fullerene is an in vivo Powerful Antioxidant With no Acute or Sub-acute Toxicity. Nano Letters, 5 (12) (2005) 2578-2585.