Clearance of chrysotile asbestos from human lung

Our plain-English summary of Clearance of chrysotile asbestos from human lung, by A. Churg, L. DePaoli (Experimental Lung Research, 1988).

The study

• Authors: A. Churg, L. DePaoli
• Journal: Experimental Lung Research
• Published: 1988;14(5):567-74
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 003647).

Abstract

In contrast to amphibole asbestos, chrysotile asbestos fails to accumulate in human lungs. The reason for this phenomenon is not known. To examine this problem, we extracted chrysotile and tremolite fibers from the lungs of 11 chrysotile miners and millers whose last exposure was within 2 years of death and 12 chrysotile miners and millers whose last exposure was greater than 12 years (7 with last exposure 12-15 years and 5 with last exposure 22-25 years) before death. Fibers were extracted by bleach digestion, and concentrations, compositions, and sizes were determined by analytical electron microscopy. Native UICC Canadian chrysotile was used as a composition standard. Compared to the standard, there was minor loss of magnesium at 2 years and additional very slight loss after 12 years. The ratio of chrysotile to tremolite concentration did not change with time. There was also no evidence of increasing fiber length with time from last exposure. These data indicate that accumulation of amphibole compared to chrysotile in human lungs does not reflect either long-term dissolution of chrysotile or long-term preferential clearance of chrysotile compared to amphibole. Contrary to results of animal studies, fiber length in humans does not increase with time since last exposure. These findings imply that the failure of chrysotile to accumulate in human lungs reflects events that occur early after exposure rather than long-term clearance mechanisms.

In plain English

This study asked why chrysotile asbestos, unlike amphibole asbestos, does not build up in human lungs. The authors analyzed autopsy lungs from 23 Quebec chrysotile miners and millers, whose ore also contained a small amount of the amphibole tremolite. Eleven died within 2 years of last exposure, 7 after 12 to 15 years, and 5 after 22 to 25 years. Fibers were extracted from lung tissue and analyzed by electron microscopy. Chrysotile from the lungs had lost a small but statistically significant amount of magnesium compared with a standard sample. The magnesium-to-silicon ratio was 1.20 in the standard and 1.08, 0.94 and 0.95 in the three groups, with no further loss between the 12 to 15 year and 22 to 25 year groups. Fiber lengths and widths of chrysotile and tremolite did not differ significantly between groups. Neither did the ratio of chrysotile to tremolite concentration. In every group, tremolite concentrations were much higher than chrysotile. The authors concluded that long-term dissolution plays a very minimal role in chrysotile clearance. They also concluded that differences in fiber retention must reflect events relatively early after inhalation.

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: Autopsy lung fiber analysis comparing groups of workers by time since last exposure (bleach digestion of lung tissue, analytical electron microscopy)
• Who was studied: 23 chrysotile miners and millers from Quebec, studied at autopsy. 11 died within 2 years of last exposure: 10 at 1 to 2 years and 1 at about 6 months ('recent'). 7 died 12 to 15 years after last exposure ('intermediate'). 5 died 22 to 25 years after last exposure ('remote'). Mean ages were 66, 72 and 66 years. Mean years of exposure were 42, 34 and 23. Dates of death are not given.
• Exposure: Occupational exposure to Quebec chrysotile ore, which contains chrysotile with a minor contaminant of the amphibole tremolite
• Main results:
  • Chrysotile magnesium:silicon ratios (mean plus or minus SD) were: UICC standard 1.20 plus or minus 0.22 (100 fibers); recent group 1.08 plus or minus 0.32 (880 fibers); intermediate group 0.94 plus or minus 0.30 (537 fibers); remote group 0.95 plus or minus 0.34 (397 fibers). Each test group differed from the standard (p less than 0.001). The recent group differed from the intermediate or remote group (p less than 0.001). The intermediate and remote groups did not differ significantly.
  • Short chrysotile fibers (under 2 micrometers) showed slightly more magnesium loss than long fibers (over 5 micrometers) at each time period. The difference was significant only in the recent exposure group (1.05 versus 1.13, p less than 0.01).
  • Fiber size did not differ significantly by time since last exposure. Geometric mean chrysotile length was 2.7, 2.8 and 2.6 micrometers in the recent, intermediate and remote groups. Tremolite length was 2.2, 2.2 and 2.0 micrometers.
  • Median chrysotile:tremolite concentration ratios were 0.22 (range 0.09 to 0.84) in the recent group, 0.11 (0.05 to 0.23) in the intermediate group and 0.15 (0.10 to 1.17) in the remote group, with no significant differences.
  • In all groups, tremolite fiber concentration in the lungs was much greater than chrysotile, although the ore contained only a few percent tremolite.
  • The authors interpreted the magnesium findings as showing that long-term dissolution plays a very minimal role in chrysotile clearance in humans.
• The authors' conclusion: The authors concluded that the failure of chrysotile to accumulate, compared with amphibole, does not reflect long-term dissolution or long-term preferential clearance of chrysotile. They concluded that differences in fiber retention must reflect events relatively early after inhalation.
• Limitations the authors state:
  • The authors noted that their results reflect only events occurring more than about 1 to 2 years after last exposure.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amphibole Asbestos, Tremolite, UICC, Fiber Length, Amphibole Group.

Related studies

• Rapid short-term clearance of chrysotile compared with amosite asbestos in the guinea pig — A. Churg, J.L. Wright, et al. (1989)
• Deposition and clearance of chrysotile asbestos — A. Churg (1994)
• 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)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)
• Lung proliferative and clearance responses to inhaled para-aramid RFP in exposed hamsters and rats: comparisons with chrysotile asbestos fibers — D.B. Warheit, S.I. Snajdr, et al. (1997)
• The effect of amostie and chrysotile asbestos on the clearance of TiO2 particles from the lung — J. Ferin, L.J. Leach (1976)

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