Letter: Penetration of asbestos through the digestive tract of rats

Our plain-English summary of Letter: Penetration of asbestos through the digestive tract of rats, by R.D. Pontefract, H.M. Cunningham (Nature, 1973).

The study

• Authors: R.D. Pontefract, H.M. Cunningham
• Journal: Nature
• Published: 1973;243(5406):352-3
• Cited by: 55 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

In plain English

In this 1973 letter, the authors reported an experiment in rats. To rule out inhaled fibres, they opened the abdomen under anaesthesia and injected a water suspension of chrysotile asbestos directly into the stomach. Group 1 rats received 9.4 billion fibres and were killed 2 days later. Group 2 rats received 94 billion fibres and were killed 4 days later. Most fibres were 0.2 to 2.0 micrometres long. Blood and tissues were examined by electron microscope. No fibres were found in the blood of untreated control rats. Group 1 had 4.65 million fibres per gram of blood, which the authors reported as a statistically significant increase. Group 2 had 1.19 million per gram despite the tenfold dose, which the authors interpreted as the blood clearing itself. The omentum, tissue surrounding the small intestine, appeared to accumulate the most asbestos. Control rats' tissues held more asbestos than expected, and the authors did not know how much came from feed or air. Liver and kidney could not be examined. The authors concluded that fibres given into the stomach appear in the blood and accumulate in various tissues.

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: Animal experiment, reported as a letter
• Who was studied: Rats in two treated groups and an untreated control group. Results were averages of five rats per group except where noted (some values came from four rats). Food Research Laboratories, Health Protection Branch, Ottawa.
• Exposure: Chrysotile asbestos (Johns Manville No. 7RFO2) suspended in water. The top layer contained about 9.4 × 10^9 fibres (1 mg) per ml, most 0.2 to 2.0 μm long. It was injected directly into the stomach through the opened abdomen under anaesthesia. Group 1 got 9.4 × 10^9 fibres and was examined 2 days later. Group 2 got 94 × 10^9 fibres and was examined 4 days later.
• Main results:
  • No asbestos fibres were detected in the blood of control rats. Group 1 rats had 4.65 × 10^6 fibres per gram of blood, reported as a statistically significant increase.
  • Four days after treatment, blood asbestos in group 2 rats was 1.19 × 10^6 fibres per gram, although they received ten times as much asbestos. The authors took this to indicate that blood can clear itself of fibres.
  • Fibre counts in the spleen, heart and lung of group 2 rats were lower than in group 1, despite the larger dose. The authors attributed this to the tissues having longer to clear themselves.
  • The omentum (tissue surrounding the small intestine) appeared to accumulate the most asbestos.
  • Fibre counts in the brains of treated rats were about six times higher than in controls.
  • For group 1, the authors said the larger standard error in brain counts meant the values were not statistically significant.
  • Most fibres found were about 0.2 to 2.0 μm long, but some measured 15 μm. One fibre in the blood of a rat was 23.55 μm long.
• The authors' conclusion: The authors concluded that asbestos fibres of a size similar to those they had earlier found in air, snow, drinking water and beverages, when put into the stomach of rats, appear in the blood and accumulate in various tissues.
• Limitations the authors state:
  • Liver and kidney could not be examined under the electron microscope because too much ash remained in these organs, even after soluene treatment.
  • Asbestos levels in control rats' tissues were higher than expected, and the authors did not know how much came from the rats' feed or air.
  • The authors did not know how the fibres pass through the intestinal wall.

Related studies

• Light and electron microscope studies of the rat digestive tract following prolonged and short-term ingestion of chrysotile asbestos — R. Jacobs, J. Humphrys, et al. (1978)
• Digestive cancers and occupational asbestos exposure: incidence study in a cohort of asbestos plant workers — M. Boulanger, F. Morlais, et al. (2015)
• Effects of ingested chrysotile on DNA synthesis in the gastrointestinal tract and liver of the rat — D.E. Amacher, A. Alarif, et al. (1974)
• The dose-dependent effects of ingested chrysotile on DNA synthesis in the gastrointestinal tract, liver, and pancreas of the rat — D.E. Amacher, A. Alarif, et al. (1975)
• Asbestos fibers in human pulmonary and extrapulmonary tissues — J. Huang, N. Hisanaga, et al. (1988)
• An investigation of the penetration of ingested asbestos into the normal and abnormal intestinal mucosa of the rat — M.E. Meek, P. Grasso (1983)

Browse more research in Nature, or return to medical research.