Asbestos and glass fibres in bacterial mutation tests

Our plain-English summary of Asbestos and glass fibres in bacterial mutation tests, by M. Chamberlain, E.M. Tarmy (Mutation Research, 1977).

The study

• Authors: M. Chamberlain, E.M. Tarmy
• Journal: Mutation Research
• Published: 1977;43(2):159-64
• Cited by: 95 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

Abstract

Asbestos fibres are carcinogenic in man and experimental animals but fine glass fibres are known, at present, only to be carcinogenic in experimental animals. Asbestos and glass fibres have been studied in mutation tests using auxotrophic strains of Escherichia coli and Salmonella typhimurium. The mutagenic activities of the positive control mutagens ultraviolet light, potassium chromate, ethyl methanesulphonate and benzo(a)pyrene were detected in the experiments. However, no mutagenic activity was found to be associted with any of the asbestos and glass fibres tested over a wide range of concentrations. The implications of these findings for the mode of action of asbestos and glass fibres as carcinogens are discussed.

In plain English

In this laboratory study, the authors tested whether asbestos and glass fibres cause mutations in bacteria. The samples were four reference asbestos types (Canadian chrysotile, crocidolite, amosite, anthophyllite), a superfine Canadian chrysotile, magnetite and "cleaned crocidolite" prepared from crocidolite, and two Johns-Manville glass fibres. All were tested at several amounts on agar plates with Escherichia coli WP2. The asbestos fibres were also tested with other E. coli and Salmonella typhimurium strains and with a rat liver extract (S-9). No significant increase in revertant colonies (the sign of mutation in these tests) was detected with any fibre sample under the conditions tested. Known mutagens used as checks did work. In E. coli WP2, potassium chromate gave a mean of 114 plus or minus 7 revertants per plate, against 26 plus or minus 2 with buffer alone. Benzo(a)pyrene with the extract gave a 5- to 6-fold increase. The authors concluded that the fibres could not be shown to be mutagenic in these tests. They noted that the fibres might still be mutagens these tests could not detect: the extract may have lacked needed enzymes, and fibres are not taken into bacteria.

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: Laboratory (in vitro) bacterial mutation tests using agar plate assays, with positive and negative controls
• Who was studied: No people or animals were tested directly. The test organisms were bacterial strains: Escherichia coli B/r WP2, WP2 uvrA and WP2 uvrA polA, and Salmonella typhimurium TA 1535 and TA 1538. The work was done at UK laboratories (MRC Pneumoconiosis Unit, Penarth; Institute of Cancer Research). The article was received in 1976.
• Exposure: U.I.C.C. reference samples of Canadian chrysotile, crocidolite, amosite and anthophyllite, plus SFA chrysotile (a superfine sample from a Canadian mine). Also tested were magnetite separated from U.I.C.C. crocidolite, the remaining "cleaned crocidolite", and Johns-Manville glass fibres code 100 and code 110. All of these were tabulated with E. coli WP2 at a range of amounts per plate. Asbestos fibres were also tested with other strains, and with rat liver supernatant (S-9) at 0.1 mg and 1.0 mg per plate.
• Main results:
  • The authors reported no mutagenesis with any of the glass fibre or asbestos samples in any of the bacterial strains studied, with or without microsomal (liver) enzymes. This means no significant increase in revertants was obtained in the presence of the fibres.
  • Positive control in E. coli WP2: buffer alone gave 26 plus or minus 2 revertants per plate and potassium chromate gave 114 plus or minus 7. Both figures are the mean and standard error of 5 separate experiments.
  • Positive control in E. coli: 5 seconds of ultraviolet irradiation gave more than 300 revertants per plate.
  • Positive control in E. coli WP2 uvrA and S. typhimurium TA 1535: ethyl methanesulphonate gave more than 1000 revertant colonies per plate.
  • With rat liver supernatant, the positive control benzo(a)pyrene gave a 5- to 6-fold increase in revertants. In Table II, the controls were 11.7 (TA 1538) and 21.7 (WP2 uvrA), and benzo(a)pyrene gave 58.5 and 92.7 respectively (means of 3 plates). The asbestos samples at 0.1 mg and 1.0 mg did not show this increase.
  • Results were also negative for TA 1535 and TA 1538 when the liver supernatant came from rats induced with 3-methylcholanthrene instead of Arochlor 1254.
• The authors' conclusion: The authors concluded that, in these bacterial tests, asbestos and glass fibres could not be shown to be mutagenic at any of the concentrations used.
• Limitations the authors state:
  • The authors stated that the fibres might still be mutagens not detectable in these tests. For example, the enzymes needed for metabolic activation may not have been present in the rat liver supernatants used.
  • The authors noted that, unlike macrophages, bacteria do not engulf fibres. Bacteria (prokaryotic organisms) may therefore not respond to any mutagenic activity of asbestos, whereas eukaryotic cells may do so.

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic.

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