Review of published studies of orally administered asbestos

Our plain-English summary of Review of published studies of orally administered asbestos, by L.W. Condie (Environmental Health Perspectives, 1983).

The study

• Author: L.W. Condie
• Journal: Environmental Health Perspectives
• Published: 1983;53:3-9
• Type of article: Review
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

There has been great public concern about the adverse health effects resulting from the presence of asbestos fibers in municipal drinking water supplies. This article reviews and summarizes the experimental findings of 11 published papers that have evaluated the carcinogenic potential of asbestos following its ingestion. The long-term, high-level ingestion of various types of asbestos fibers in more than one animal species failed to produce any definite, reproducible, organ-specific carcinogenic effect.

In plain English

This 1983 article was a review, not a new experiment. It summarized 11 published animal studies that tested whether swallowed asbestos causes cancer, prompted by concern about asbestos fibers in drinking water. The studies used rats, hamsters and, in one case, baboons, given chrysotile, crocidolite, amosite or taconite tailings in food, drinking water or other ways. The baboon study found no peritoneal or gastrointestinal tumors. In the hamster study, a few tumors in exposed groups were not attributed to asbestos because none occurred at the highest doses. A study of Duluth tapwater and related materials found no significant increase in malignant tumors. In one rat study, differences in colon tumors were not statistically significant, though those researchers argued that ingested asbestos was not inert in the colon. Another rat study reported a 14% rate of Zymbal gland tumors in rats given only amosite. The author suggested that accidental exposure to azoxymethane, a chemical that causes cancer, might explain it. The author concluded that the vast majority of studies were negative or equivocal. Many studies used too few animals or too short exposures.

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 11 published experimental (animal) studies of orally administered asbestos
• Who was studied: Laboratory animals in the 11 reviewed studies: mainly rats (several strains), plus hamsters in one study and baboons in one study (the only primate study)
• Exposure: Asbestos given by mouth: chrysotile, crocidolite and amosite, as well as taconite tailings, Duluth tapwater, Lake Superior water sediment and chrysotile-containing filter material. Delivery was in feed, drinking water, butter or margarine, malted milk, or by gavage. Some studies used talc, cellulose fiber or diatomaceous earth as comparison materials. In one study, hamsters drank water containing amosite or taconite tailings at three dose levels.
• Main results:
  • In the first ingestion study (Bonser and Clayson), rats were fed asbestos at 0.15% of their feed. No malignant tumors were seen in the exposed rats. High mortality from pulmonary infection seriously compromised that study.
  • In the only primate study (Webster), baboons ate 'heavy' concentrations of asbestos in food and water for up to 5 years. They showed no peritoneal or gastrointestinal tumors.
  • Gibel et al. fed rats asbestos filter material containing 53% chrysotile. Twelve malignant tumors were noted in the exposed rats, and their survival was shorter. However, those authors stated that no conclusions could be drawn, and other substances in the filter material confounded the study.
  • In Cunningham and co-workers' first, small study of rats fed 1% chrysotile, 6 of 7 autopsied exposed rats had tumors. Only one malignancy was seen in the controls.
  • In Cunningham and co-workers' larger study of 80 rats, exposed and control groups had equal numbers of malignant tumors.
  • In Smith's hamster drinking-water study, a small number of malignant tumors occurred in exposed groups. They were not specifically attributed to asbestos because no cancers occurred in the high dose groups.
  • In Donham et al.'s study of F344 rats fed 10% asbestos, differences in colon tumors between asbestos-fed and control rats were not statistically significant.
  • Donham et al. nonetheless presented observations that they said suggest ingested asbestos is not inert in the colon.
  • In Ward et al.'s first experiment, intestinal carcinomas occurred only in rats given azoxymethane (an intestinal carcinogen), either alone or with asbestos.
  • Ward et al. reported a 14% incidence of Zymbal gland tumors in rats exposed only to amosite. The historical rate in the National Cancer Institute program was 0.34%. The reviewing author suggested that accidental exposure to azoxymethane might explain this and the intestinal tumors, and noted that the second experiment had no controls.
  • Hilding et al. tested unfiltered Duluth tapwater, reservoir sediments, taconite tailings, amosite and diatomaceous earth in rats. They found no significant increases in malignant tumors in any group compared with controls.
  • In Bolton and co-workers' study, rats were fed amosite, crocidolite and chrysotile in margarine for up to 25 months. Those researchers concluded there were no significant adverse health effects.
  • The author wrote that these studies cast some doubt on the idea that peritoneal mesotheliomas and gastrointestinal cancers come from swallowing asbestos fibers cleared from the lungs after inhalation.
• The authors' conclusion: The author concluded that long-term, high-level ingestion of various asbestos fiber types failed to produce any definite, reproducible, organ-specific cancer effect. The vast majority of ingestion studies were negative or equivocal. The one apparent cancer response, to amosite, may have been due to accidental azoxymethane exposure.
• Limitations the authors state:
  • Many of the reviewed studies used too few animals and had inadequate exposure times.
  • Many of the reviewed studies were not lifetime studies.
  • Comparing studies is difficult because they differed in rat strain, dose, exposure conditions and asbestos type.
  • It is questionable whether animal models suit the human response to swallowed asbestos, since animals may not live long enough for cancers to develop.

Topics

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

Related studies

• Orally ingested chrysotile asbestos affects rat lungs and pleura — H.C. Hasanoglu, E. Bayram, et al. (2008)
• Animal models of malignant mesothelioma — A.B. Kane (2006)
• Chronic effects of dietary exposure to amosite and chrysotile asbestos in Syrian golden hamsters — E.E. McConnell, A.M. Shefner, et al. (1983)
• Chronic effects of dietary exposure to amosite asbestos and tremolite in F344 rats — E.E. McConnell, H.A. Rutter, et al. (1983)
• Use of protamine to augment adenovirus-mediated cancer gene therapy — M. Lanuti, C.E. Kouri, et al. (1999)
• Chrysotile asbestos fibers mediate homologous recombination in Rat2 lambda fibroblasts: implications for carcinogenesis — K. Lezon-Geyda, C.M. Jaime, et al. (1996)

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