Experimental Demonstration of the Penetration of Asbestos Fibres into the Gas intestinal Tract

Our plain-English summary of Experimental Demonstration of the Penetration of Asbestos Fibres into the Gas intestinal Tract, by R. Masse, P. Sebastien, G. Monchaux, et al (1980).

The study

• Authors: R. Masse, P. Sebastien, G. Monchaux, J. Bigon
• Published: BIOLOGICAL EFFECTS OF MINERAL FIBRES (J.C. WAGNER, EDITOR), LYON: IARC SCIENTIFIC PUBLICATIONS, VOLUME 30., PP 321-328 (1980)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

In this animal experiment, the authors collected intestinal lymph through a catheter in 70 rats fed fibres, by gavage or sometimes in a diet, to see whether swallowed fibres cross the gut wall. A single asbestos dose was given in a gelatin capsule pushed down the oesophagus with a plastic rod. Afterwards, eight of ten treated rats, and no control rats, had fibres in their lymph. With the chrysotile diet, fibres were found in 27 of 33 treated rats. Fibres appeared in abdominal lymph 2 to 24 hours after feeding; about half the absorbed amount appeared within the first six hours. Passage was greatest for long asbestos fibres. Comparing lymph with diet showed selection of the longest fibres, with a bimodal size distribution. Unfinished attapulgite work found no fibres with certainty in lymph and suggested much less transfer than asbestos, if transmission electron microscopy could reliably identify such fibres. Transfer varied over three orders of magnitude, which the authors said made extrapolation to people difficult. They concluded that lymph collection was the most appropriate method for detecting intestinal absorption.

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: intestinal lymph was collected by catheter (method of Bollman et al., 1948) from rats given fibres by gavage or in the diet
• Who was studied: 70 rats with lymph-vessel catheters fed different types of fibres. These included 10 treated rats in the single-gavage asbestos experiment, 33 treated rats in the chrysotile-diet experiment, and untreated control rats. Attapulgite was tested in groups of 20 and 10 rats; the article does not say whether these are counted among the 70.
• Exposure: A single gavage of UICC asbestos in a gelatin capsule, forced down the lubricated oesophagus with a plastic rod. The garbled table key appears to list UICC chrysotile A and UICC crocidolite. Other rats were fed diets containing short-range or intermediate-range chrysotile fibres for periods from hours up to about 12 days. Attapulgite was given by gavage at about 10 mg (20 rats) or 100 mg (10 rats).
• Main results:
  • Single gavage: fibres were detected in the lymph of 8 of 10 treated rats. No fibres were found in the lymph of control rats.
  • Chrysotile diet: fibres were detected in the lymph of 27 of 33 treated rats
  • Fibres crossed the gut wall and were present in abdominal lymph 2 to 24 hours after feeding
  • About half of the total absorbed load appeared in the lymph within the first six hours. The scan prints this as '507', evidently 50%.
  • The greatest fibre passage was seen with long asbestos fibres. The fraction of the ingested load this reached is printed as 2.1 times 10 to a power, but the exponent is lost in the scan, so the value cannot be read.
  • Comparing fibre sizes in lymph and diet showed selection of the longest fibres. The size histogram of fibres in lymph appeared bimodal.
  • Attapulgite (preliminary, many samples not yet measured): no attapulgite fibres had yet been detected with certainty in lymph. Transfer to the blood appeared much less than for asbestos, provided transmission electron microscopy reliably identifies such fibres.
  • Transfer coefficients for asbestos varied over three orders of magnitude
  • In their discussion, the authors estimated that any cancer risk from directly ingested fibres would be a small fraction of the risk from the same number of inhaled fibres; the exact figures are unreadable. They wrote that such an excess would most probably be diluted by spontaneous human tumours.
• The authors' conclusion: The authors concluded that lymph collection was the most appropriate method for detecting intestinal absorption of fibres
• Limitations the authors state:
  • Extrapolating the asbestos results to humans is difficult because transfer coefficients varied over three orders of magnitude
  • Attapulgite measurements were still in progress, and the result depends on transmission electron microscopy reliably identifying such fibres
  • The recovery rate in the diet experiments was estimated by assuming that the rate of fibre passage did not change over time; the authors describe this assumption as partly substantiated

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Palygorskite (Attapulgite), Transmission Electron Microscopy (TEM).

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