Inhalation Toxicity and Lung Toxicokinetics of C60 Fullerene Nanoparticles and Microparticles

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Abstract
While several recent reports have described the toxicity of water-soluble C60 fullerene nanoparticles, none have reported the toxicity resulting from the inhalation exposures to C60 fullerene nanoparticles or microparticles. To address this knowledge gap, we exposed male rats to C60 fullerene nanoparticles (2.22 mg/m3, 55 nm diameter) and microparticles (2.35 mg/m3, 0.93 μm diameter) for 3 h a day, for 10 consecutive days using a nose-only exposure system. Nanoparticles were created utilizing an aerosol vaporization and condensation process. Nanoparticles and microparticles were subjected to high-pressure liquid chromatography (HPLC), XRD, and scanning laser Raman spectroscopy, which cumulatively indicated no chemical modification of the C60 fullerenes occurred during the aerosol generation. At necropsy, no gross or microscopic lesions were observed in either group of C60 fullerene exposures rats. Hematology and serum chemistry results found statistically significant differences, although small in magnitude, in both exposure groups. Comparisons of bronchoalveolar (BAL) lavage fluid parameters identified a significant increase in protein concentration in rats exposed to C60 fullerene nanoparticles. BAL fluid macrophages from both exposure groups contained brown pigments, consistent with C60 fullerenes. C60 lung particle burdens were greater in nanoparticle-exposed rats than in microparticle-exposed rats. The calculated lung deposition rate and deposition fraction were 41 and 50% greater, respectively, in C60 fullerene nanoparticle–exposed group than the C60 fullerene microparticle–exposed group. Lung half-lives for C60 fullerene nanoparticles and microparticles were 26 and 29 days, respectively. In summary, this first in vivo assessment of the toxicity resulting from inhalation exposures to C60 fullerene nanoparticles and microparticles found minimal changes in the toxicological endpoints examined. Additional toxicological assessments involving longer duration inhalation exposures are needed to develop a better and more conclusive understanding of the potential toxicity of inhaled C60 fullerenes whether in nanoparticle or microparticle form.