The biological effects of crocidolite asbestos and silicon carbide fibers on mammalian cells in culture

To study the mechanisms associated with the carcinogenicity of natural and man- made fibers/whiskers at the cellular level, mouse fibroblast cultures were exposed to 5 µg/cm2 crocidolite asbestos (0.36 µM in diameter) and two different sizes of silicon carbide whiskers (0.8 and 1.5 µM in diameter). After 48 hours of exposure, 60 to 90 percent of metaphase spreads had chromosomes that were entangled with, attached to, or lying adjacent to fibers. Over 40 percent of isolated nuclei contained fibers, and were seen inside of, or attached to various parts of the nucleus (i.e. nuclear membrane, nuclear matrix, DNA, chromatin). Total DNA and chromosomal content were also determined up to 20 generations post exposure to test materials. After 10-12 generations postexposure (6-8 passages), all fibers/whiskers induced a 40 to 75 percent increase in cellular DNA. There was also a significant increase in chromosome number per cell 18 generations post exposure to fibers/whiskers, as compared to control. This increase in DNA and chromosome content could possibly provide information on the cellular mechanism of toxicity associated with the exposure to fibrous materials. These quantitative in vitro tests may also be useful as a tool to suggest the long-term genetic effects of a potential carcinogen.