The toxicity, in vitro, of silicon carbide whiskers

Our plain-English summary of The toxicity, in vitro, of silicon carbide whiskers, by G.L. Vaughan, J. Jordan, S. Karr (Environmental Research, 1991).

The study

• Authors: G.L. Vaughan, J. Jordan, S. Karr
• Journal: Environmental Research
• Published: 1991;56(1):57-67
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

To mouse cells in culture, SiC whiskers (SiCW) and asbestos are similarly cytotoxic, disrupting cell membranes and killing cells. Both shorten cell generation time, increase the rate of DNA synthesis, increase total cell DNA content, and cause a loss in growth control often associated with malignant cellular transformation. Within the narrow size range of materials examined, the amount of damage appeared to be more a function of the number of whiskers present than of their size. Silicon carbide whiskers, if mishandled, may pose a serious health hazard to humans.

In plain English

In this laboratory study of cells in culture, the authors exposed BALB/3T3 embryonic mouse cells to two silicon carbide whisker samples, about 0.8 micrometers wide (SiCW-1) and 1.5 micrometers wide (SiCW-2), and compared them with crocidolite asbestos and, in one test, silica dust. Within the first day, SiCW-1 and crocidolite damaged cell membranes to a similar degree; at 5.0 micrograms per square centimeter they caused 20-30% leakage of a radioactive label above controls, against approximately 8.0% for silica. By weight, SiCW-2 was less toxic to colony growth than SiCW-1 but not significantly different from asbestos; counted by number of whiskers, the two whisker samples did not differ significantly. Whiskers and crocidolite both produced cells that lost growth control, a laboratory sign of transformation, and raised cell DNA content (excess of 39% for SiCW-1, 42% for SiCW-2, 75% for asbestos). The authors concluded that silicon carbide is likely to pose a serious health hazard as a fine whisker, while noting that transformation in culture and the development of malignancy are not necessarily identical.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: In vitro laboratory experiment on cultured mouse cells
• Who was studied: BALB/3T3 embryonic mouse cells (clone A31) grown in culture, obtained from the American Type Culture Collection; work done at the Zoology Department, University of Tennessee, Knoxville
• Exposure: Two silicon carbide whisker samples: SiCW-1, 0.8 micrometer diameter (Tateho, Japan; mean length 18.1 micrometers), and SiCW-2, 1.5 micrometer diameter (American Matrix, Inc., Knoxville; mean length 19.0 micrometers). These were compared with crocidolite asbestos (mean diameter 0.4, length 4.3 micrometers) and, in the radiochromium test, silica (SiO2) dust. Doses ranged from 0.0 to 20.0 micrograms per square centimeter of plate surface. Several tests used 5.0 micrograms per square centimeter.
• Main results:
  • By trypan blue dye exclusion, crocidolite asbestos and SiCW-1 showed similar, dose-dependent cell killing within the first 24 hours.
  • In the radiochromium (51Cr) release test at 5.0 micrograms per square centimeter, cells exposed to SiCW-1 or crocidolite released 20-30% of the label in excess of controls. Silica dust caused an excess loss of approximately 8.0%.
  • In colony-forming tests, with dose measured by weight, SiCW-1 was slightly more toxic than crocidolite. The larger SiCW-2 was less cytotoxic than SiCW-1 (P < 0.01) but not significantly different from asbestos (P > 0.05).
  • When dose was recalculated as the number of whiskers rather than weight, the authors found no significant difference in cytotoxicity between the 0.8 and 1.5 micrometer whiskers.
  • SiCW-1, SiCW-2 and crocidolite induced, within eight generations, changes in cell growth (loss of contact inhibition) generally held to be characteristic of cellular transformation. Crocidolite produced a transformation frequency of 0.000069 (SD = 0.000046). Compared by number of particles, SiCW-1 and SiCW-2 differed little in transformation frequency.
  • Exposure to SiCW and asbestos increased the number of binucleate cells six to eight fold.
  • DNA synthesis rates in exposed cells were generally elevated, often by as much as 2.5 times, but the authors judged the results inconsistent and did not report them.
  • Total DNA per cell was significantly higher than in saline controls (2.49 x 10^-11 g, n = 45) 10-20 generations after treatment. Values were 3.48 for SiCW-1 (39% excess, n = 32), 3.54 for SiCW-2 (42% excess, n = 29) and 4.37 for asbestos (75% excess, n = 18); all P < 0.05 by ANOVA.
• The authors' conclusion: The authors concluded that silicon carbide, though relatively innocuous in non-fiber particulate form, is likely to pose a serious health hazard as a fine whisker. In their view, its cellular effects appear similar to those of crocidolite asbestos. They also concluded that, within the narrow size range examined, the cells' response probably depends more on the number of particles than on their size.
• Limitations the authors state:
  • Only a narrow range of whisker sizes was examined.
  • Cellular transformation in culture and the development of malignancy are not necessarily the same process.
  • The dye exclusion and radiochromium tests do not detect cells that survive the first 24 hours but die later.

Related studies

• In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems — N.F. Johnson, M.D. Hoover, et al. (1992)
• The immediate effects of silicon carbide whiskers upon ciliated tracheal epithelium — G.L. Vaughan, J.R. Kennedy, et al. (1991)
• Toxicity in vitro of some silicon carbides and silicon nitrides: whiskers and powders — I. Svensson, E. Artursson, et al. (1997)
• Pulmonary response, in vivo, to silicon carbide whiskers — G.L. Vaughan, S.A. Trently, et al. (1993)
• Carcinogenicity of fluoro-edenite, silicon carbide fibres and whiskers, and carbon nanotubes — Y. Grosse, D. Loomis, et al. (2014)
• The carcinogenicity of WHO fibers of silicon carbide: SiC whiskers compared to cleavage fragments of granular SiC — K. Rödelsperger, B. Brückel (2006)

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