Experimental Studies Of Asbestosis

Our plain-English summary of Experimental Studies Of Asbestosis, by A.J. Vorwald, T.M. Durkin, P.C. Pratt (1951).

The study

• Authors: A.J. Vorwald, T.M. Durkin, P.C. Pratt
• Published: Archives Of Industrial Hygiene 3(1):1-43, January (1951)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library, J-M no. 001922. The article is still under copyright, so we describe it here rather than post it.

In plain English

This paper reported animal experiments on asbestosis done at the Saranac Laboratory in Saranac Lake, New York, over more than twenty years. Guinea pigs, rabbits, cats, rats, mice and dogs either inhaled asbestos dust or had dust injected into the windpipe, abdomen or veins. Four inhalation experiments used different dusts: King's floats, short fiber, 100 per cent ball-milled and long fiber. Short fiber and ball-milled dusts caused slower, less extensive reactions than King's floats. In guinea pigs, the reaction to long fiber dust developed in about half the time needed with ball-milled dust. Injected long fibers of chrysotile, amosite, crocidolite and brucite (a mineral that is not a silicate) caused fibrosis. Anthophyllite, glass wool, nonfibrous serpentine and fibers ground to 20 microns or less did not cause typical fibrosis. Mice and dogs did not develop fibrosis. After exposure stopped, mature lesions partly cleared. The authors concluded that long, flexible fibers were essential and that asbestos acted mainly mechanically rather than chemically. They called their tuberculosis findings tentative. They noted that the animals breathed higher dust concentrations than are ordinarily found in industry.

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: Series of animal experiments (long-term inhalation in a dust room, and injection by intratracheal, intraperitoneal, intravenous and subcutaneous routes), begun in 1928 and reported here as a complete survey
• Who was studied: Laboratory animals at the Saranac Laboratory, Saranac Lake, N.Y.: guinea pigs, rabbits, cats, rats, mice and dogs. More than 160 animals were used in each of four inhalation experiments, which ran from two to more than five years.
• Exposure: Inhalation of four chrysotile-based dusts: King's floats (only 14 per cent fibrous chrysotile, from Thetford, Quebec), short fiber, 100 per cent ball-milled, and long fiber. Injection of long and short fibers of chrysotile, amosite, crocidolite and anthophyllite, plus brucite, glass wool, serpentine, heated (ignited) chrysotile and asbestosis bodies taken from a worker's lung.
• Main results:
  • King's floats dust produced peribronchiolar fibrosis in guinea pigs but not in rabbits or rats.
  • The short fiber dust caused a slower and less extensive reaction than King's floats dust.
  • The ball-milled dust caused a reaction that was slower and less extensive than with short fiber dust, even though more dust built up in the lungs.
  • In the ball-milled experiment, 39 of the 100 guinea pigs died accidentally, 32 of them from pneumonia in an epidemic.
  • Ball-milled dust, in which 0.6 per cent of the airborne material was fibers longer than 10 microns, still produced typical fibrosis in guinea pigs. The authors calculated this as less than 1 million such long fibers per cubic foot of air.
  • In guinea pigs inhaling long fiber dust, lung lesions were seen after 8 months, and definite fibrosis by the 16th month.
  • The authors estimated about 2.7 million long fibers per cubic foot of air in the long fiber experiment, against 0.8 million in the ball-milled experiment. The lung reaction developed in about half the exposure time with long fiber dust.
  • Injected into the trachea, all long fiber asbestos minerals tested caused typical fibrosis except anthophyllite.
  • Brucite, a fibrous magnesium hydroxide containing only 0.90 per cent silica, caused fibrosis like that from asbestos.
  • Injected glass wool fibers caused no fibrosis.
  • Nonfibrous serpentine, with the same chemical composition as chrysotile, caused only an inert type of tissue reaction.
  • Fibers ground to 20 microns or less, or to 3 microns or less, caused no fibrosis. The authors placed the minimum effective fiber length between 20 and 50 microns.
  • Injected into the abdominal cavity, long fiber dusts caused a fibrous reaction; particles 3 microns or less caused only an inert response.
  • Injected into veins, asbestos minerals generally caused only an inert type of reaction.
  • Mice and dogs did not develop fibrosis.
  • After exposure stopped, mature lesions partly cleared as the fibrous tissue contracted. Immature lesions continued to progress.
  • Aluminum hydroxide added to long fiber chrysotile did not prevent tissue irritation in rats.
  • Asbestosis bodies injected into the trachea of guinea pigs did not produce the typical reaction.
  • Pneumonia occurred in 16 to 39 per cent of guinea pigs across the four inhalation experiments. The authors nonetheless felt asbestos dust did not significantly affect susceptibility to nontuberculous lung infection.
  • In guinea pigs infected with low-virulence tubercle bacilli and exposed to King's floats dust, the authors interpreted asbestos as having no more than a mildly unfavorable effect on tuberculosis.
• The authors' conclusion: The authors concluded that long fibers are essential to experimental asbestosis. In their view, the action of the fibers is mainly mechanical, tied to their flexible, filamented structure, rather than chemical.
• Limitations the authors state:
  • Animals were exposed to higher dust concentrations than ordinarily found in industry, to speed up the reaction within their short life span.
  • The tuberculosis findings are tentative: they rest on two series of guinea pigs exposed only to King's floats.
  • Infection studies could not be done in the later inhalation experiments.
  • The lowest concentration of long fibers that can cause asbestosis in animals could not be established.
  • The upper limit of effective fiber length was not studied.

Topics

Medical terms in this study, explained in our Lexicon: Saranac Laboratory, Chrysotile, Amosite, Crocidolite, Brucite, Silicate, Fibrosis, Anthophyllite.

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