Mineral-fluid interaction in the lungs: insights from reaction-path modeling

Our plain-English summary of Mineral-fluid interaction in the lungs: insights from reaction-path modeling, by S.A. Wood, A.E. Taunton, C. Normand, et al (Inhalation Toxicology, 2006).

The study

• Authors: S.A. Wood, A.E. Taunton, C. Normand, M.E. Gunter
• Journal: Inhalation Toxicology
• Published: 2006;18(12):975-84
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Thermodynamic modeling, in conjunction with available kinetic information, has been employed to investigate the fate of chrysotile and tremolite in the human lung. In particular, we focus on mineral-fluid reactions using techniques borrowed from geochemistry, including calculation of saturation indices, activity-ratio phase diagrams, and reaction-path modeling. Saturation index calculations show that fresh lung fluid is undersaturated with respect to both tremolite and chrysotile and these minerals should dissolve, in accordance with conclusions from previous work described in the literature. Modeling of reaction paths in both closed and open systems confirms previous suggestions that chrysotile dissolves faster than tremolite in lung fluid, which offers an explanation for the apparent increase in tremolite/chrysotile ratios in lungs of miners and millers over time. However, examination of activity-ratio phase diagrams and reaction-path model calculations raises the possibility not only that minerals dissolve congruently in lung fluid, but that secondary minerals such as talc or various Ca-Mg carbonates might potentially form in lung fluid as asbestiform minerals dissolve.

In plain English

This was a geochemical computer modeling study of what might happen to chrysotile and tremolite fibers in the human lung. No people or animals were studied. The authors calculated whether a model lung fluid based on blood plasma would dissolve the minerals. They then simulated 50 years of reaction with the fluid either replaced daily (an open system) or never replaced (a closed system). Fiber sizes were chosen from earlier data on lungs of Quebec miners and millers. Both minerals were undersaturated in the model fluid, meaning they should dissolve. In the open model, chrysotile was gone after about 50 days. Tremolite only began to decrease substantially after 1000 days at pH 6.8 and after 100 days at pH 4.5. In the closed model at pH 6.8, new minerals, talc and magnesite, formed. No calculation predicted tremolite forming from chrysotile. The authors concluded that minerals might leave residues or be replaced by other minerals rather than simply dissolving. They said much more research is needed to check whether this happens in living lungs, and noted that the models left out organic components of lung fluid.

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: Computer modeling study using geochemical methods (saturation index calculations, activity-ratio diagrams, and reaction-path modeling in open 'flush' and closed systems over 50 years)
• Who was studied: No human or animal subjects. A simulated lung fluid based on Gamble's solution and blood plasma was used. Fiber dimensions and masses were chosen from published data on lungs of former miners and millers in Quebec (Nayebzadeh et al., 2001).
• Exposure: Pure chrysotile (5 µm long, 0.075 µm diameter) and tremolite (3 µm long, 0.3 µm diameter), with quartz included in the starting mineral mix; modeled at pH 4.5 (inside a macrophage) and pH 6.8 (closer to blood plasma)
• Main results:
  • Both chrysotile and tremolite were undersaturated in the model lung fluid, meaning they should dissolve. Scaled saturation indices were −1.37 at pH 4 and −0.19 at pH 7.34 for chrysotile, and −1.47 and −0.23 for tremolite.
  • In the open (flush) model at both pH 4.5 and 6.8, chrysotile was completely removed after about 50 days
  • In the open (flush) model, tremolite only began to decrease in abundance significantly after 1000 days at pH 6.8 and after 100 days at pH 4.5
  • At pH 4.5 in the open model, no secondary (new) minerals appeared
  • In the closed-system model, chrysotile disappeared completely by 60 days
  • In the closed-system model at pH 6.8, talc appeared at about day 5, decreased steeply after about 3200 days and disappeared after 5000 days; magnesite also formed
  • None of the reaction-path calculations predicted tremolite forming from chrysotile or any other mineral
• The authors' conclusion: The authors concluded that chrysotile and tremolite should dissolve in lung fluid, with chrysotile dissolving much faster. They said their modeling raises the possibility that minerals may dissolve incongruently, leaving residues, or be replaced by more stable minerals, but that much more research is needed to verify whether this occurs in living people.
• Limitations the authors state:
  • The models ignored organic components of lung fluid
  • Kinetic information was not included for any precipitation reactions or for many dissolution reactions; macrophage effects and other components such as iron and fluoride were not considered
  • The calculations did not account for minerals added after the modeled process began
  • Calculations at pH 7.35, the pH of blood plasma, did not converge
  • The authors stated it is premature to say with certainty that any particular mineral transformation takes place under lung conditions
  • More research is needed to verify whether these processes actually occur in the body

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Tremolite, Talc, Asbestiform.

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