Chronic inhalation of short asbestos: lung fiber burdens and histopathology for monkeys maintained for 11.5 years after exposure

Our plain-English summary of Chronic inhalation of short asbestos: lung fiber burdens and histopathology for monkeys maintained for 11.5 years after exposure, by L.E. Stettler, D.D. Sharpnack, E.F. Krieg (Inhalation Toxicology, 2008).

The study

• Authors: L.E. Stettler, D.D. Sharpnack, E.F. Krieg
• Journal: Inhalation Toxicology
• Published: 2008;20(1):63-73
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In an earlier report, Platek et al. (1985) presented the results of an 18-month inhalation exposure of rats and monkeys to short chrysotile asbestos. The mean chamber exposure level was 1.0 mg/m(3) with an average of 0.79 fibers/ml > 5 microm in length. Gross and histopathological examination of exposed and control rats indicated no treatment-related lesions. Asbestos bodies adjacent to the terminal bronchioles, but no fibrosis, were found in lung biopsy tissue taken from the exposed monkeys at 10 months post-exposure. Fifteen monkeys (9 exposed and 6 controls) from this study were maintained for 11.5 years following exposure. Lung fiber burdens were determined by transmission electron microscopy. The mean lung burden (+/- standard deviation) for 59 samples from exposed monkeys was 63 +/- 30 x 10(6) fibers/g dry lung (range, 18-139 x 10(6)). The geometric mean fiber length was 3.5 microm with 35% of the fibers being > 5 microm in length. These data indicate some chrysotile fibers are durable in vivo for a significant period of time. Lungs were examined grossly and microscopically. No lesions attributable to the inhalation exposure were noted. Asbestos bodies were seen in the lungs of treated monkeys, primarily in the interstitium near bronchioles or small pulmonary blood vessels (which also may have been near to bronchioles just out of the plane of section).

In plain English

This animal experiment followed male Cynomolgus monkeys from an earlier inhalation study run for the National Institute for Occupational Safety and Health. The monkeys had breathed short chrysotile asbestos, prepared by ball milling, for 18 months (7 hours a day, 5 days a week). The average level was 1.0 mg/m3, including 0.79 fibers/ml longer than 5 micrometers. Nine exposed and six unexposed control monkeys were kept for 11.5 years after exposure ended and then examined. No treatment-related lesions were found. The only treatment-related lung finding was minimal numbers of asbestos bodies, seen in 9 of 9 exposed and 0 of 6 control monkeys. The 59 lung samples from exposed monkeys held a mean of 63 million fibers per gram of dry lung (standard deviation 30 million). The fibers had a geometric mean length of 3.5 micrometers, and 35% were longer than 5 micrometers. An older preparation method, ashing, gave higher counts and shorter fibers than digestion. The authors concluded that, at this dose, short chrysotile was non-toxic in these 9 monkeys. They noted that the small number of animals and the low exposure limit what can be inferred.

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 inhalation experiment with long-term follow-up (lung pathology and lung fiber burden measured 11.5 years after exposure ended)
• Who was studied: Male Cynomolgus monkeys: 9 exposed and 6 controls, the survivors of the original 20 (10 exposed, 10 controls). They were necropsied in 1991, and were held at the NIOSH animal facility from 1986 to 1991.
• Exposure: Short chrysotile asbestos (type 7TF1), prepared by ball milling, inhaled for 18 months, 7 hours/day, 5 days/week. The mean chamber concentration was 1.0 (plus or minus 0.28) mg/m3, with 0.79 (plus or minus 0.41) fibers/ml longer than 5 micrometers.
• Main results:
  • No treatment-related lesions were seen in the 9 exposed monkeys 11.5 years after exposure.
  • The only treatment-related lung effect was minimal numbers of asbestos bodies, found in 9 of 9 exposed monkeys and 0 of 6 controls.
  • Pigment suggestive of asbestos body fragments was found in macrophages in the tracheobronchial lymph nodes of 6 of 9 exposed monkeys and 0 of 6 controls.
  • Across 59 digested lung samples from the exposed monkeys, the mean chrysotile concentration (plus or minus standard deviation) was 63 plus or minus 30 million fibers per gram of dry lung.
  • Mean chrysotile concentrations for the individual exposed monkeys ranged from 27 to 95 million fibers per gram of dry lung.
  • In the exposed monkeys' lungs, the geometric mean chrysotile fiber length was 3.5 micrometers, and 35% of fibers were longer than 5 micrometers.
  • In the exposed monkeys, asbestos bodies made up 4.0% of the total chrysotile lung burden.
  • Most fibers from the exposed monkeys had an irregular surface coating.
  • Non-chrysotile fibers made up 1.7% of the exposed monkeys' total lung fiber burden.
  • In five ashed samples from exposed monkeys, the mean chrysotile concentration was 202 million fibers per gram. This was significantly greater (p = 0.0087) than the 43 million per gram in five adjacent digested samples. The authors attributed the difference to fiber breakage during ashing.
  • Among exposed monkeys, fiber burdens in samples with pleura were significantly greater than in subpleural samples (p = .0183). There were no statistically significant differences between upper, middle and lower lobes in samples with pleura.
• The authors' conclusion: The authors concluded that, despite a significant lung fiber burden, short chrysotile fibers at the dose used were non-toxic 11.5 years after an 18-month exposure in the 9 monkeys evaluated. They also concluded that some chrysotile fibers were durable in the body for 11.5 years or longer.
• Limitations the authors state:
  • The study used only a small number of animals, and exposure levels and duration were low relative to human exposures, so the ability to draw inferences is limited.
  • Fiber burdens at 10 months and at 11.5 years after exposure cannot be reliably compared, because different sample preparation methods were used at the two times.
  • No biopsy tissue remained for re-analysis with the digestion method.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Fiber Burden, Histopathology, Chrysotile, Asbestos Bodies, Fibrosis, Biopsy, Transmission Electron Microscopy (TEM), Fiber Length.

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