Review of published studies on gut penetration by ingested asbestos fibers

Our plain-English summary of Review of published studies on gut penetration by ingested asbestos fibers, by P.M. Cook (Environmental Health Perspectives, 1983).

The study

• Author: P.M. Cook
• Journal: Environmental Health Perspectives
• Published: 1983;53:121-30
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

During the 1970s, potential health risks associated with exposure to asbestos in drinking water became a national concern. One of the key questions that arose from debate over whether ingestion of mineral fibers could result in increased gastrointestinal cancer risk was whether fibers can penetrate the gastrointestinal mucosa and thus have some chance of residing in tissue. It is likely that such movement of a large number of fibers is a necessary precursor for carcinogenesis following ingestion of asbestos. Studies of the potential for fiber accumulation in tissues and body fluids following introduction of asbestos to the alimentary canal have provided seemingly contradictory observations. This review, which places particular emphasis on the impact of experimental and analytical limitations on the evidential strengths of each study, indicates the likelihood that a very small fraction of ingested microscopic asbestos fibers penetrates the gastrointestinal mucosa. A reliable estimate of the magnitude of long-term fiber retention in tissues as a consequence of chronic human ingestion of asbestos cannot be made at this time.

In plain English

This review examined more than 30 published reports on animals and humans exposed to asbestos by swallowing, not inhalation; excluding repeats left 19 studies. The author weighed each study's detection limits and contamination controls. Studies finding fibers generally reported the lowest detection limits; the fewer negative studies often lacked a defined detection limit or used less sensitive analysis. Chrysotile, the most studied fiber, was called a poorer marker because it leaches, splits apart and often contaminates samples. Amphibole fibers (including amosite and crocidolite) and attapulgite gave strong indications of penetration. One rat study estimated maximum daily passage into lymph fluid at 10 to the power of minus 4 to minus 7 times the fibers introduced to the stomach. In one human study, urine amphibole fiber levels were about 10 to the power of minus 3 of drinking-water levels. The author concluded these limited estimates indicated that a very small fraction of swallowed fibers likely penetrates, giving a low probability of significant tissue build-up and increased cancer risk. A reliable estimate of long-term tissue retention from chronic human ingestion could not yet be made.

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: Review of published studies examining tissues or body fluids for fibers after ingestion of asbestos and other mineral fibers
• Who was studied: 19 distinct published reports, reduced from more than 30 after excluding duplicate reports of the same observations, covering animals (many of them laboratory rodents) and human subjects exposed through ingestion
• Exposure: Ingestion of asbestos, mostly chrysotile. Amphibole fibers (including amosite and crocidolite asbestos) and attapulgite fibers were also studied.
• Main results:
  • The author judged it difficult to conclude, from the reviewed studies, that asbestos fibers do not cross the intestinal barrier
  • Studies reporting fibers in tissue or fluids generally reported the lowest detection limits, and most gave evidence that contamination was negligible
  • Studies reporting negative results were fewer, and either did not define the detection limit, gave incomplete information, or used less sensitive analysis
  • Chrysotile fibers were described as poorer indicators of penetration because of leaching, comminution (breaking into smaller pieces) and frequent contamination during sample preparation
  • Amphibole fibers (including amosite and crocidolite) and attapulgite fibers provided strong indications of fiber penetration
  • In one reviewed rat study, crocidolite fibers were found in the lymph fluid of rats fed crocidolite, and chrysotile fibers in the lymph fluid of rats fed chrysotile
  • Attapulgite fibers were found in high concentration in the urine of one human subject known to have ingested a large amount of that mineral
  • In reviewed human studies, amphibole fiber concentrations in urine and tissue were well associated with exposure or non-exposure to the same amphibole fibers (cummingtonite-grunerite and actinolite) in drinking water
  • One reviewed rat study (reference 35), of chrysotile or crocidolite given by ingestion or gavage, estimated maximum daily passage of fibers to lymph fluid at 10 to the power of minus 4 to 10 to the power of minus 7 times the number of fibers introduced to the stomach
  • In one reviewed human study (reference 31), amphibole fiber concentrations in urine were approximately 10 to the power of minus 3 of the concentration of the same fibers in drinking water consumed for up to 20 years
• The authors' conclusion: The author concluded that the limited available estimates indicate that a very small fraction of ingested fibers is likely to penetrate the gut, and therefore a low probability of significant tissue accumulation and increased cancer risk
• Limitations the authors state:
  • A reliable estimate of long-term fiber retention in tissues from chronic human ingestion of asbestos could not be made
  • Very little information exists for estimating what fraction of ingested fibers penetrates
  • The lymph fluid and urine measurements do not account for all fibers that may cross the gut lining
  • How fibers are transported and eliminated in the body is unknown
  • Many reviewed reports gave incomplete information on analytical sensitivity, sample contamination and fiber recovery
  • The summary table leaves out relevant details such as the time from exposure to tissue collection

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Carcinogenesis.

Related studies

• Transmigration of ingested asbestos — M.E. Meek (1983)
• Ingested mineral fibers: elimination in human urine — P.M. Cook, G.F. Olson (1979)
• An investigation of the penetration of ingested asbestos into the normal and abnormal intestinal mucosa of the rat — M.E. Meek, P. Grasso (1983)
• Accumulation of ingested asbestos fibers in rat tissues over time — K. Patel-Mandlik, J. Millette (1983)
• Penetration of cells by asbestos fibers — J.M. Davis, R.E. Bolton, et al. (1974)
• Effects of ingested chrysotile on DNA synthesis in the gastrointestinal tract and liver of the rat — D.E. Amacher, A. Alarif, et al. (1974)

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