Fullerene (carbon sixty [C(60)]) has potential industrial and medical applications. In the future, people working in or residing near manufacturing facilities may be exposed to C(60). Therefore, quantitative data on long-term C(60) clearance from the lungs are required. To estimate the clearance rate and deposition fraction of C(60) from inhalation exposure, the C(60) burden in the lungs, liver, and brain of rats was determined after intratracheal instillation and inhalation. Male Wistar rats were intratracheally instilled with different concentrations of a C(60) suspension prepared with Tween 80 (geometric mean [GM] of particle diameter based on number, 18-29 nm; geometric standard deviation [GSD] of particle diameter, 1.5; and doses, 100, 200, and 1000 micrograms per body) or exposed to a C(60) aerosol prepared with nebulizer (GM of particle diameter based on number, 96 nm; GSD of particle diameter, 2.0; and exposure level, 120 μg/m(3)). C(60) burden in the lungs, liver, and brain was determined at various time points (1 h to 6 months) by a newly developed sensitive high-performance liquid chromatography-ultraviolet absorptiometry combined with extraction and concentration of C(60) from the organs. C(60) clearance was evaluated using a 2-compartment model: fast clearance after deposition on lung surface and slow clearance after retention in the epithelium. The detection limit of our analysis method was 8.9 ng/g tissue. Pulmonary C(60) burden decreased with time and depended on the C(60) concentration administered. The concentration of C(60) in the liver and brain was below the detection limit: 8.9 ng/g tissue. The half-life of intratracheally instilled C(60) was 15-28 days. The deposition mass fraction of inhaled C(60) was 0.14. Mode evaluation revealed that most instilled particles could be eliminated by the fast clearance pathway. This finding is consistent with the transmission electron microscopy finding that many particles were present in alveolar macrophages.

As a result of the growing potential industrial and medical applications of multi‐walled carbon nanotubes (MWCNTs), people working in or residing near facilities that manufacture them may be exposed to airborne MWCNTs in the future. Because of concerns regarding their toxicity, quantitative data on the long‐term clearance of pristine MWCNTs from the lungs are required. We administered pristine MWCNTs well dispersed in 0.5 mg ml−1 Triton‐X solution to rats at doses of 0.20 or 0.55 mg via intratracheal instillation and investigated clearance over a 12‐month observation period. The pristine MWCNTs pulmonary burden was determined 1, 3, 7, 28, 91, 175 and 364 days after instillation using a method involving combustive oxidation and infrared analysis, combined with acid digestion and heat pretreatment. As 0.15‐ and 0.38‐mg MWCNTs were detected 1 day after administration of 0.20 and 0.55 mg MWCNTs, respectively, approximately 30% of administrated MWCNTs may have been cleared by bronchial ciliary motion within 24 h of administration. After that, the pulmonary MWCNT burden did not decrease significantly over time for up to 364 days after instillation, suggesting that MWCNTs were not readily cleared from the lung. Transmission electron microscopy (TEM) showed that alveolar macrophages internalized the MWCNTs and retained in the lung for at least 364 days after instillation. MWCNTs were not detected in the liver or brain within the 364‐day study period (<0.04 mg per liver, < 0.006 mg per brain). Copyright © 2015 The Authors Journal of Applied Toxicology Published by John Wiley & Sons Ltd.

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