Skin penetration and kinetics of pristine fullerenes (C60) topically exposed in industrial organic solvents.

Pristine fullerenes (C60) in different solvents will be used in many industrial and pharmaceutical manufacturing and derivatizing processes. This report explores the impact of solvents on skin penetration of C60 from different types of industrial solvents (toluene, cyclohexane, chloroform and mineral oil). Yorkshire weanling pigs (n=3) were topically dosed with 500 microL of 200 microg/mL C60 in a given solvent for 24 h and re-dosed daily for 4 days to simulate the worst scenario in occupational exposures. The dose sites were tape-stripped and skin biopsies were taken after 26 tape-strips for quantitative analysis. When dosed in toluene, cyclohexane or chloroform, pristine fullerenes penetrated deeply into the stratum corneum, the primary barrier of skin. More C60 was detected in the stratum corneum when dosed in chloroform compared to toluene or cyclohexane. Fullerenes were not detected in the skin when dosed in mineral oil. This is the first direct evidence of solvent effects on the skin penetration of pristine fullerenes. The penetration of C60 into the stratum corneum was verified using isolated stratum corneum in vitro; the solvent effects on the stratum corneum absorption of C60 were consistent with those observed in vivo. In vitro flow-through diffusion cell experiments were conducted in pig skin and fullerenes were not detected in the receptor solutions by 24 h. The limit of detection was 0.001 microg/mL of fullerenes in 2 mL of the receptor solutions.