Dosimetry of inhaled elongate mineral particles in the respiratory tract: The impact of shape factor

Our plain-English summary of Dosimetry of inhaled elongate mineral particles in the respiratory tract: The impact of shape factor, by B. Asgharian, T.P. Owen, E.D. Kuempel, et al (Toxicology and Applied Pharmacology, 2018).

The study

• Authors: B. Asgharian, T.P. Owen, E.D. Kuempel, A.M. Jarabek
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:27-35
• Type of article: Review
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Inhalation exposure to some types of fibers (e.g., asbestos) is well known to be associated with respiratory diseases and conditions such as pleural plaques, fibrosis, asbestosis, lung cancer, and mesothelioma. In recent years, attention has expanded to other types of elongate mineral particles (EMPs) that may share similar geometry with asbestos fibers but which may differ in mineralogy. Inhalability, dimensions and orientation, and density are major determinants of the aerodynamic behavior for fibers and other EMPs; and the resultant internal dose is recognized as being the critical link between exposure and pathogenesis. Insufficient data are available to fully understand the role of specific physicochemical properties on the potential toxicity across various types of fiber materials. While additional information is required to assess the potential health hazards of EMPs, dosimetry models are currently available to estimate the initially deposited internal dose, which is an essential step in linking airborne exposures to potential health risks. Based on dosimetry model simulations, the inhalability and internal dose of EMPs were found to be greater than that of spherical particles having the same mass or volume. However, the complexity of the dependence of internal dose on EMPs dimensions prevented a straightforward formulation of the deposition-dimension (length or diameter) relationship. Because health outcome is generally related to internal dose, consideration of the factors that influence internal dose is important in assessing the potential health hazards of airborne EMPs.

Copyright © 2018 Elsevier Inc. All rights reserved.

In plain English

This article was an overview of a computer model, the multi-path particle dosimetry (MPPD) model version 3.04, with example simulations of how elongate mineral particles (EMPs), a group that includes asbestos fibers, are breathed in and deposited in the respiratory tract. No people or animals were studied, and no specific fiber type was modeled. The authors simulated theoretical particle aerosols in a model adult human breathing through the nose while sitting, and compared inhalability in humans and rats. In the model, EMPs were more inhalable than spherical particles of the same volume or mass. Inhalability fell for larger particles, fell more with nasal than with oral breathing, and was much lower in rats. The authors could not find a simple relationship between EMP dimensions and how much deposited in each lung region. Compared with spheres of equal volume, modeled EMPs deposited more in the airways (tracheobronchial region) and less in the deep lung (pulmonary region). The authors concluded that dosimetry models can predict internal dose. The article's own summary statements contradict each other on whether EMPs are more or less inhalable, and deposit more or less, than spheres.

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: Overview of a mechanistic computer dosimetry model (MPPD v. 3.04), with example model simulations; no human or animal subjects
• Who was studied: Simulated (modeled) human respiratory tract: tidal volume 625 cm3, 12 breaths per minute, functional residual capacity 3,300 cm3, nasal breathing, no wind. Inhalability was also simulated for rats (0.62 m3 per day) and humans (20 m3 per day).
• Exposure: Theoretical EMP aerosols of varying minor diameter and aspect ratio (length to diameter ratios of 10 and 50), compared with spherical particles. In one comparison, 1 µm spheres were set against equal-volume EMPs with minor diameters of 0.33 µm (aspect ratio 10) and 0.2 µm (aspect ratio 50).
• Main results:
  • In the human model, EMPs were predicted to be more inhalable than spherical particles of the same volume or mass.
  • In humans, inhalability decreased for larger-diameter EMPs, and more so for nasal than for oral breathing. With nasal breathing, EMPs longer than 20 micrometres were predicted not to be inhaled.
  • Predicted inhalability in rats was much lower than in humans.
  • No simple relationship could be drawn between EMP dimensions and deposition fraction in the different respiratory tract regions.
  • Compared with volume-equivalent spherical particles, modeled EMPs had higher tracheobronchial and lower pulmonary deposition fractions. Overall, spherical particles deposited more in the lower respiratory tract.
  • Predicted pulmonary (deep lung) deposition with nasal breathing was about 8 to 10% for EMPs and about 10% for volume-equivalent spherical particles.
  • With filtering by the upper respiratory tract included, a smaller fraction of longer, thinner EMPs reached the tracheobronchial and pulmonary regions than of shorter, thicker EMPs.
• The authors' conclusion: The authors concluded that dosimetry models can predict internal dose of inhaled particles including EMPs. They stated that their predictions showed that, because of their elongated shape, EMPs have higher inhalability and higher deposition on lung airway surfaces than spherical particles.
• Limitations the authors state:
  • The authors stated that there are no experimental or modeling studies on the inhalability of non-spherical particles and EMPs.
  • The authors stated that a lack of mechanistic information limits analysis of how much of the EMPs is retained in the respiratory tract as a function of their dimensions.
  • The authors stated that dosimetry models are not available for elongate shapes other than those with a circular cross-section.
  • The regional deposition simulations left out inhalability.

Topics

Medical terms in this study, explained in our Lexicon: elongate mineral particles (EMPs), Pleural Plaques, Fibrosis, Lung Cancer, Mesothelioma, Mineralogy, Deposition.

Related studies

• A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans — D.H. Garabrant, S.T. Pastula (2018)
• Measurement of elongate mineral particles: What we should measure and how do we do it? — E.J. Chatfield (2018)
• The epidemiologic evidence for elongate mineral particle (EMP)-related human cancer risk — P. Boffetta, K.A. Mundt, et al. (2018)
• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, et al. (2014)
• Predicting EMP hazard: Lessons from studies with inhaled fibrous and non-fibrous nano- and micro-particles — G. Oberdörster, U. Graham (2018)
• Elongate mineral particles in the natural environment — M.E. Gunter (2018)

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