Mesothelioma in Relation to Asbestos - Terminal Progress Report, Grant No. 3301.EC-00226-04S1

Our plain-English summary of Mesothelioma in Relation to Asbestos - Terminal Progress Report, Grant No. 3301.EC-00226-04S1, by William E. Smith (1970).

The study

• Author: William E. Smith
• Published: Health Research Institute, Fairleigh Dickinson University, Madison, N.J.; grant period 03/01/66 - 08/31/70 (1970)
• Type of article: Report
• 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

This is a final progress report on a grant-funded animal experiment at the Health Research Institute, Fairleigh Dickinson University, Madison, New Jersey. The authors tested 23 preparations of asbestos and other minerals by injecting each once into the chest (pleural) cavity of hamsters, with 50 animals per group and two untreated control groups. Results were mostly reported up to 650 days. At the highest dose tested (25 mg), three long-fiber chrysotile samples produced mesotheliomas in 8, 9 and 10 of the 50 hamsters in each group. When these chrysotiles were ground so that most fibers were shorter than 5 microns, no mesotheliomas arose. Lower doses of chrysotile, amosite and crocidolite gave fewer tumors. At 1 mg, only crocidolite produced mesotheliomas. Talc containing tremolite, nemalite and glass fibers produced no mesotheliomas, and serpentine rock dust produced one. Untreated controls had no mesotheliomas. The authors concluded that asbestos hazards should be controllable by reducing exposure. They added that the fiber-length findings bear on mask design and dust monitoring. The available copy of the text is heavily corrupted by OCR errors, so some table values could not be read.

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 (single intrapleural injection in hamsters); final grant progress report
• Who was studied: LVG:LAK hamsters from the Lakeview Hamster Colony, Newfield, N.J., 50 per test group, plus 2 untreated control groups; Health Research Institute, Fairleigh Dickinson University, Madison, N.J.; grant period ending 08/31/70 (start date unreadable in the text)
• Exposure: 23 preparations given as a single intrapleural injection: soft, harsh and heat-treated chrysotile (long- and short-fiber), amosite, UICC crocidolite, long and short anthophyllite, serpentine rock dust (antigorite), nemalite, talc containing tremolite, diatomaceous earth (natural and calcined), microquartz fibers, fiberglass with phenol-formaldehyde binder, glass fibers and nickel powder, at doses including 25, 10 and 1 mg
• Main results:
  • At 25 mg, three chrysotile samples with mean fiber lengths around 32 to 39 microns (Groups 1, 2, 3) yielded 8, 9 and 10 mesothelioma-bearing hamsters (of 50 per group)
  • When fiber length of these chrysotiles was reduced so that the large majority of fibers were under 5 microns (Groups 4, 5, 6), fibrogenicity was reduced and no mesotheliomas occurred. Electron microscopy gave a mean fiber length of 0.75 micron for sample 4.
  • With reduced dose, fibrogenic and carcinogenic responses to chrysotile, amosite and crocidolite fell. At the lowest dose (1 mg), the authors reported no tumors with chrysotile or amosite but tumors with crocidolite. In Table 1, the 1-mg chrysotile group (Group 8) shows 0 mesotheliomas.
  • Chrysotile, amosite and anthophyllite appeared less carcinogenic than crocidolite
  • At 10 mg, long-fiber anthophyllite induced 3 mesotheliomas (Group 20) and short-fiber anthophyllite induced 1 (Group 21). The authors said this was consistent with shorter fibers being less carcinogenic, but the difference was not statistically significant.
  • Native harsh chrysotile induced tumors more rapidly than soft chrysotile. Heat treatment of soft chrysotile increased fibrogenicity but not carcinogenicity.
  • Mesotheliomas followed injection of diatomaceous earth, calcined diatomaceous earth, nickel powder and microquartz fibers. No mesotheliomas followed talc (which contained a large amount of tremolite), nemalite, or glass fibers with or without binder. Serpentine rock dust (antigorite) induced a single case.
  • No mesotheliomas were found in the untreated control groups
  • Lymphoid tumors occurred in 14 of the 23 treated groups and in 1 of the 2 untreated control groups; the authors regarded them as spontaneous and unrelated to treatment
  • In fractionated long-fiber chrysotile samples, chromium and nickel were detected in the fractions shorter than 10 microns but not in the longer fractions. Because the short-fiber preparations were essentially non-carcinogenic, the authors argued against these trace elements being important in carcinogenesis.
• The authors' conclusion: The authors concluded that hazards from asbestos exposure should be controllable by measures that reduce the amount of exposure. They also stated that the fiber-length findings give information relevant to the design of masks and to dust monitoring for industrial hygiene.
• Limitations the authors state:
  • The long and short anthophyllite samples were not tested at the 25 mg level
  • Mean fiber lengths differed considerably depending on the measurement method. In electron microscopy, fibers extending beyond the field were excluded, so reported mean lengths for samples 1 and 2 were much smaller than by optical microscopy.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Amosite, Crocidolite, Talc, Tremolite, Serpentine Group.

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