Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques

Our plain-English summary of Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques, by A. Morgan, J.C. Evans, R.J. Evans, et al (Environmental Research, 1975).

The study

• Authors: A. Morgan, J.C. Evans, R.J. Evans, R.F. Hounam, A. Holmes, S.G. Doyle
• Journal: Environmental Research
• Published: 1975;10(2):196-207
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The distribution of fibre deposited during 30 minute inhalation exposure of rats to the UICC standard reference samples was investigated. These samples were made radioactive by neutron irradiation, which enabled the amount of asbestos in various tissues to be determined radiometrically. The total amount of fibre deposited varied from 31 to 68% of that respired and, on average, 17% remained in the lower respiratory tract (alveoli and conducting airways up to and including the trachea) at the end of exposure. Activity median aerodynamic diameters (AMADs) of the materials used were measured with the cascade centripeter. Differences in the total deposition of inhaled fibre, and in the distribution of deposited material, were correlated with the AMADs of the various samples. Autoradiographs of lung sections showed that at the termination of exposure, fibre was present in the conducting airways, particularly at bifurcations, and also distributed relatively uniformly throughout the alveolated regions.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

In this rat experiment, the authors made the UICC standard reference samples of asbestos radioactive by neutron irradiation: amosite, anthophyllite, crocidolite, chrysotile A (one Rhodesian mine) and chrysotile B (eight Canadian mines), plus a synthetic fluoramphibole fibre. Groups of three or four male albino rats breathed the dust nose-only for 30 minutes at one of three concentrations. They were killed immediately, and the fibre in their tissues was measured by its radioactivity. Between 31 and 68% of the fibre breathed in was deposited. On average, 17% of the fibre breathed in remained in the lower respiratory tract (alveoli and airways up to and including the trachea). Samples of larger aerodynamic size were deposited more overall, but a smaller share of the deposited fibre stayed in the lower tract. Lower-tract deposition as a share of fibre breathed in appeared to rise from 11 to 20% as aerodynamic size rose from 1.2 to 2 micrometres. The authors said fibres covering a wider size range were needed to confirm this. Lung autoradiographs showed fibre at airway branch points and fairly evenly through the alveoli.

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 using radioactive (neutron-irradiated) fibres and autoradiography of lung sections
• Who was studied: Male albino rats about 5 months old, in groups of three or four, exposed nose-only. Table 4 lists 9 to 13 rats per fibre type (70 in total).
• Exposure: UICC standard reference samples (amosite, anthophyllite, crocidolite, chrysotile A from Rhodesia, chrysotile B from eight Canadian mines) and a synthetic nickel chromium fluoramphibole. Each was given for 30 minutes at nominal low, medium and high concentrations averaging about 4, 11 and 32 micrograms per litre.
• Main results:
  • Total deposition ranged from 31 to 68% of the fibre respired. On average, 17% of the fibre respired remained in the lower respiratory tract at the end of exposure.
  • The fibre found in the lower respiratory tract made up between 29 and 39% of the fibre deposited.
  • Average percentage total deposition was positively correlated with the samples' activity median aerodynamic diameter (AMAD), with r = 0.80. AMADs ranged from 1.2 to 2 micrometres.
  • Rats exposed to anthophyllite and the fluoramphibole had a smaller fraction of deposited fibre remaining in the lower respiratory tract.
  • Lower respiratory tract deposition, as a percentage of fibre respired, appeared to increase from 11 to 20 as AMAD increased from 1.2 to 2 micrometres.
  • Autoradiographs showed fibre concentrated at bifurcations of the smaller bronchi and bronchioles and spread relatively uniformly through the alveolar regions to the lung periphery. Amphibole fibres were seen in alveoli next to the pleura.
• The authors' conclusion: The authors concluded that as AMAD increased, total deposition increased while the fraction deposited in the lower respiratory tract fell.
• Limitations the authors state:
  • Confirming the increase in lower respiratory tract deposition with AMAD needs results from fibres covering a wider size range than the UICC samples.
  • Very brief exposure (to limit clearance) conflicts with the need to deposit enough fibre to measure, so a compromise was needed.

Topics

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

Medical terms in this study, explained in our Lexicon: Deposition, UICC, Alveoli.

Related studies

• Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques. 1. UICC crocidolite asbestos — J.C. Evans, R.J. Evans, et al. (1973)
• Deposition of inhaled asbestos and man-made mineral fibres in the respiratory tract — A. Morgan (1995)
• Kinetics of deposition and clearance of inhaled mineral dusts during chronic exposure — J.H. Vincent, A.M. Johnston, et al. (1985)
• Deposition pattern and clearance pathways of inhaled chrysotile asbestos — A.R. Brody, L.H. Hill (1981)
• Deposition, clearance, and translocation of chrysotile asbestos from peripheral and central regions of the rat lung — P.G. Coin, V.L. Roggli, et al. (1992)
• Deposition and cellular interaction of cancer-inducing particles in the human respiratory tract: Theoretical approaches and experimental data — R. Sturm (2010)

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