Effects of fiber characteristics on lung deposition, retention, and disease

Our plain-English summary of Effects of fiber characteristics on lung deposition, retention, and disease, by M. Lippmann (Environmental Health Perspectives, 1990).

The study

• Author: M. Lippmann
• Journal: Environmental Health Perspectives
• Published: 1990;88:311-7
• Type of article: Review
• Cited by: 133 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004998).

Abstract

There is abundant epidemiologic evidence that asbestos fibers can cause lung fibrosis (asbestosis), bronchial cancer, and mesothelioma in humans, as well as limited evidence for such effects in workers exposed to slag and rockwool fibers. Epidemiological evidence for human disease from inhalation exposures to conventional fibrous glass is negative. While health concerns based on the morphological and toxicological similarities between man-made fibers and asbestos are warranted, it is important to note that most of the toxicological evidence for glass fiber toxicity in laboratory animals is based on nonphysiological exposures such as intratracheal instillation or intraperitoneal injection of fiber suspensions. Man-made fibers have produced lung fibrosis and mesotheliomas in such tests, albeit at much lower yields than asbestos. For all durable mineral fibers, critical length limits must be exceeded to warrant concern about chronic toxicity; i.e., 2 microns for asbestosis, 5 microns for mesothelioma, and 10 microns for lung cancer. Fiber width must be less than 0.1 microns for mesothelioma, and larger than this limit for asbestosis and lung cancer. The human health risks for most fibrous glass products are either low or negligible for a variety of reasons. First, most commercial fibrous glass products have mean fiber diameters of approximately 7.5 microns, which results in mean aero-dynamic diameters approximately 22 microns. Thus, most glass fibers, even if dispersed into the air, do not penetrate into the lung to any great extent. Second, the small fraction of smaller diameter fibers that do penetrate into the lungs are not persistent within the lungs for most fibrous glass products due to mechanical breakage into shorter lengths and overall dissolution.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This article reviewed how fiber features affect lung deposition, retention and disease. It covered others' work on asbestos, including chrysotile and crocidolite, and man-made mineral fibers such as glass, rockwool and slag wool. Citing an earlier review, the author reported asbestosis was most closely related to the surface area of fibers longer than about 2 and thicker than about 0.15 micrometers. Mesothelioma was related to the number of fibers longer than about 5 and thinner than about 0.1 micrometers; lung cancer, to the number longer than about 10 and thicker than about 0.15 micrometers. In a reviewed rat study, crocidolite fibers longer than 5 micrometers did not decrease in number for over a year; glass fibers that long declined with a 55-day halftime from dissolution. The author described epidemiological evidence of human disease from conventional fibrous glass as negative. The author concluded that slag and rockwools' greater hazards than glass appeared related to smaller diameters and greater lung durability. Most animal toxicity evidence for glass fibers, the author noted, came from nonphysiological exposures such as intratracheal instillation or intraperitoneal injection.

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 published studies on fiber deposition, retention, dissolution and disease
• Who was studied: No new population studied. The review covered other researchers' studies in casts of human airways, in rats and other laboratory animals, and in exposed workers.
• Exposure: Asbestos (amphiboles, chrysotile, crocidolite, anthophyllite), erionite, and man-made mineral fibers (glass fibers, glass microfiber, rockwool, slag wool, ceramic wool), with attention to fiber length, diameter and durability
• Main results:
  • Citing the author's earlier review: asbestosis was most closely related to the surface area of fibers longer than about 2 micrometers and thicker than about 0.15 micrometers. Mesothelioma was related to the number of fibers longer than about 5 micrometers and thinner than about 0.1 micrometers. Lung cancer was related to the number of fibers longer than about 10 micrometers and thicker than about 0.15 micrometers.
  • Most commercial fibrous glass products have mean fiber diameters of about 7.5 micrometers. The author stated that this gives mean aerodynamic diameters of about 22 micrometers, so most glass fibers do not penetrate far into the lung.
  • In rat studies by Morgan et al., glass fibers 1.5 micrometers in diameter were placed in the lungs by intratracheal instillation. Retention at 1 year was 10% for 5-micrometer-long fibers and 20% for 10-micrometer-long fibers. Fibers 30 or 60 micrometers long showed no measurable clearance during the first 9 months.
  • In rat lung studies by Bellmann et al., crocidolite fibers longer than 5 micrometers did not decrease in number for over 1 year. Chrysotile fibers longer than 5 micrometers doubled in number, probably from longitudinal splitting. Glass fibers longer than 5 micrometers were reduced with a halftime of 55 days, due to dissolution. All fibers shorter than 5 micrometers were cleared with halftimes of 100 to 150 days.
  • In rats exposed by inhalation to chrysotile (Brody et al.), fibers were found at relatively high concentrations on the alveolar duct bifurcations nearest the terminal bronchioles.
  • The author stated that conventional glass fibers appear to dissolve much more rapidly than other man-made mineral fibers and asbestos.
  • In humans, the author reported negative epidemiological evidence for disease from conventional fibrous glass. The only evidence of chronic disease from man-made mineral fibers was among workers handling rock or slag wool or ultrafine glass fibers during periods of very high exposure.
• The authors' conclusion: The author concluded that the greater hazards of slag and rockwools compared with glass appear to be related to their smaller diameters and greater durability within the lungs. The author also concluded that conventional fibrous glass, which has fewer fibers of critical dimensions and lower durability, has not been associated with excess cancer in workers.
• Limitations the authors state:
  • Most of the toxicological evidence for glass fiber toxicity in laboratory animals comes from nonphysiological exposures such as intratracheal instillation or intraperitoneal injection.
  • The role of diffusion in fiber deposition is poorly understood.
  • Little is known about electrical charge levels on man-made mineral fibers in the workplace.

Topics

Medical terms in this study, explained in our Lexicon: Deposition, Fibrosis, Mesothelioma, Mineral Fiber, Lung Cancer.

Related studies

• Asbestos dust deposition and retention in rats — J.C. Wagner, J.W. Skidmore (1965)
• Human disease consequences of fiber exposures: a review of human lung pathology and fiber burden data — V.L. Roggli (1990)
• Solubility of asbestos and man-made mineral fibers in vitro and in vivo: its significance in lung disease — A. Morgan, A. Holmes (1986)
• Biopersistence of respirable synthetic fibers and minerals: point of view of the chest physician — P. De Vuyst (1994)
• Review of the significance of fibre size in fibre-related lung disease: a centrifuge cell for preparing accurate microscope-evaluation specimens from slurries used in inoculation studies — V. Timbrell (1989)
• Metsovo lung: pleural calcification and restrictive lung function in northwestern Greece. Environmental exposure to mineral fiber as etiology — S.H. Constantopoulos, J.A. Goudevenos, et al. (1985)

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