Asbestos and metals as carcinogens

Our plain-English summary of Asbestos and metals as carcinogens, by T. Norseth (Journal of Toxicology and Environmental Health, 1980).

The study

• Author: T. Norseth
• Journal: Journal of Toxicology and Environmental Health
• Published: 1980;6(5-6):1021-8
• Read it: PubMed · Publisher

Abstract

Increased incidences of lung carcinoma and pleural mesothelioma in humans exposed to asbestos have been irrefutably established. Different forms of asbestos may have different tumorigenic activities, depending on surface properties, durability, and size of the fibers. A number of metals, such as nickel, chromium, and arsenic, are known to be carcinogenic to humans; for beryllium and cadmium the epidemiologic evidence is less extensive. All these metals also induce genetic toxicity in vitro. For chromium the molecular mechanism of metal tumorigenesis has been extensively investigated; the hexavalent form is generally a much more potent mutagen than is chromium (III). Solubility seems to be necessary for the genotoxicity of nickel. At present it cannot be concluded that all metals act by the same carcinogenic mechanism, even though direct modification of DNA seems to be the common experimental finding.

In plain English

This 1980 article was a review of published research, not a new study. It summarized what was then known about asbestos, other mineral fibers and certain metals as causes of cancer. The author wrote that increased lung carcinoma and pleural mesothelioma in people exposed to asbestos had been irrefutably established. Citing earlier work, the review said human studies made it hard to tell asbestos types apart. Animal experiments, by contrast, indicated that all commercial forms (chrysotile, amosite, anthophyllite and crocidolite) may cause lung carcinomas and mesotheliomas. It described animal studies in which glass fibers longer than 7 to 10 micrometres and thinner than 2 to 3 micrometres, injected into the pleura, had essentially the same effect as asbestos. It also stated that nickel, chromium and arsenic were known human carcinogens, with less extensive evidence for cadmium and beryllium. The author concluded that the most likely theory of how asbestos causes cancer involved fiber size, and found no reason to conclude that all metals act by the same mechanism.

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: Narrative review of previously published human, animal and laboratory studies; no original data
• Who was studied: No study population of its own; the article discussed earlier published research
• Exposure: Commercial asbestos (chrysotile, amosite, anthophyllite, crocidolite), other natural and manufactured mineral fibers (zeolite, glass fibers), and metals including nickel, chromium, arsenic, cadmium and beryllium
• Main results:
  • The author stated that increased lung carcinoma and pleural mesothelioma in humans exposed to asbestos had been irrefutably established
  • From human (epidemiologic) evidence, the review said it was difficult to tell asbestos types apart as causes of tumors, although anthophyllite did not seem to cause mesotheliomas and crocidolite may not cause lung cancer
  • Citing Selikoff and Lee (1978), the review said experimental evidence indicated that all commercial forms of asbestos may cause lung carcinomas and mesotheliomas
  • Citing earlier animal studies, the review said that glass fibers longer than 7 to 10 micrometres and thinner than 2 to 3 micrometres had essentially the same effect as asbestos after injection into the pleura
  • Citing earlier studies (Sincock 1977; Morgan et al. 1977), the review reported that extensive magnesium leaching of chrysotile decreased its genetic damage in hamster cells and the number of mesotheliomas after pleural injection in rats
  • The review stated that nickel, chromium and arsenic are known human carcinogens, and that the human evidence for beryllium and cadmium is less extensive
  • The review stated that every metal causing cancer in humans or tumors in experimental animals, except titanium, induces genetic toxicity in laboratory (in vitro) tests
  • Citing Nakamuro et al. (1978), the review reported that hexavalent chromium was 10 times as potent a mutagen as trivalent chromium
  • The author found no present reason to conclude that all metals cause cancer by the same mechanism
• The authors' conclusion: The author concluded that the most likely theory of how asbestos causes tumors involved a mechanism dependent on fiber size. Chemical constituents such as carcinogenic metals may influence this but did not seem to be absolutely required.
• Limitations the authors state:
  • The author noted that injecting fibers into the pleura in animals may be highly artificial compared with inhaling asbestos at work, and may be relevant only to mesothelioma, not lung carcinoma
  • The author noted that results from milling experiments are uncertain to interpret, because milling changes the chemistry of chrysotile as well as fiber length
  • The author stated that human evidence on whether manufactured mineral fibers cause tumors was inconclusive

Topics

Medical terms in this study, explained in our Lexicon: Carcinoma, Pleural Mesothelioma, Carcinogenic, Tumorigenesis, Genotoxicity.

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