Towards a quantitative model to predict the toxicity/pathogenicity potential of mineral fibers

Our plain-English summary of Towards a quantitative model to predict the toxicity/pathogenicity potential of mineral fibers, by A.F. Gualtieri (Toxicology and Applied Pharmacology, 2018).

The study

• Author: A.F. Gualtieri
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:89-98
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Some mineral fibers represent a health hazard because they are classified as cancer-causing chemical/physical toxicants upon (chronic) dust inhalation. Although in the last decades they have been the subject of intensive multidisciplinary investigations, the mechanisms by which mineral fibers induce toxic and pathogenic adverse effects on human health and environment are not yet fully understood. The major intricacy of the biological approach that prevents the design of a conclusive shared model of behavior of mineral fibers in a biological system stems from their very nature with intrinsic variability in chemical, molecular, structural and morphometric parameters, biodurability and surface reactivity. This paper presents the first attempt to devise a quantitative predictive model of toxicity/pathogenicity of minerals fibers based on their physical/chemical and morphological parameters. Although the author is aware that all parameters should be measured in comparable in vivo systems that accurately simulate the lung and or pleural environment, this preliminary model was conceived to deliver a fiber potential toxicity/pathogenicity index (FPTI) to be integrated with the biological approach so to create a quantitative predictive model of behavior of mineral fibers in a biological system. The FPTI model is thought to be a predictive tool aimed at ranking the toxicity and pathogenicity potential of fibers like asbestos or unregulated/unclassified mineral fibers. It may eventually be applied to other materials like man-made synthetic fibers and elongated mineral particles (EMP). Work is in progress to revise and validate the model in joint collaboration with international competent organizations, and to deliver a FPTI model-based user-friendly code.

Copyright © 2018 Elsevier Inc. All rights reserved.

In plain English

This single-author paper described a model meant to rank how likely mineral fibers are to be toxic and to cause disease. The model uses only the fibers' physical, chemical and shape properties. Called the fiber potential toxicity/pathogenicity index (FPTI), it scores 18 properties, such as length, diameter, iron content, dissolution speed and surface charge. Each score is weighted by the property's place in a hierarchy and by how uncertain its effect is. The author applied the model to 12 fiber samples, with estimated errors given in brackets. Scored on their actual dimensions (raw-fiber scores), UICC amosite ranked highest, at 3.17 (0.11), and fibrous sepiolite lowest, at 1.68 (0.11). Raw-fiber scores were above 2.50 for amphibole asbestos, 2.30 to 2.50 for fibrous erionite, and 2.00 to 2.30 for chrysotile. The four amphibole asbestos samples averaged 2.88 (0.19), against 2.18 (0.19) for the three chrysotile samples. The author concluded that amphibole fibers appeared to be the most harmful. The author noted that some properties were measured in artificial conditions quite different from the lung, and that validation work was in progress.

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: Development of a quantitative predictive index model based on fiber properties (a modeling paper), applied to a set of mineral fiber samples
• Who was studied: 12 mineral fiber samples: UICC amosite, UICC anthophyllite, UICC crocidolite, UICC chrysotile 'B', chrysotile from Balangero and from Valmalenco (Italy), tremolite asbestos from Val d'Ala (Italy), fibrous erionite-Na from Jersey, Nevada (USA), fibrous erionite-K from Karain, Cappadocia (Turkey), fibrous fluoro-edenite from Biancavilla (Italy), fibrous sepiolite from Vallecas (Spain) and wollastonite NYAD G
• Exposure: Fiber types listed above, each scored on 18 parameters grouped as morphometric (length, diameter, curvature, crystal habit, density, surface character, surface area), chemical (iron and other metal content), biodurability-related (dissolution time and release rates) and surface activity (zeta potential, aggregation, cation exchange)
• Main results:
  • On raw-fiber scores (actual fiber dimensions), UICC amosite had the highest FPTI, 3.17 (0.11)
  • When all fibers were assigned the same dimensions, tremolite from Val d'Ala scored 3.18 (0.43), slightly above amosite's 3.17 (0.11)
  • On raw-fiber scores, amphibole asbestos species had FPTI values above 2.50, fibrous erionite samples 2.30 to 2.50, and chrysotile samples 2.00 to 2.30
  • Raw-fiber values below 2.00 were for fibers used as negative standards (wollastonite 1.92, fibrous sepiolite 1.68)
  • The mean raw-fiber FPTI of the four amphibole asbestos samples (amosite, anthophyllite, crocidolite, tremolite) was 2.88 (0.19), which the author described as significantly higher than the mean of 2.18 (0.19) for the three chrysotile samples
  • Fibrous erionite had a mean FPTI of 2.34 (0.22), between amphibole asbestos and chrysotile. The author suggested that erionite's reported greater harm may lie in factors other than fiber characteristics, namely genetic susceptibility to malignant mesothelioma in the exposed population
  • When all fibers were assigned the same size parameters, the ranking did not appreciably change, except that wollastonite NYAD G rose from 1.92 to 2.42
• The authors' conclusion: The author concluded that applying the model established different classes of potential toxicity/pathogenicity, with amphibole fibers appearing as by far the most harmful fiber species
• Limitations the authors state:
  • The model is based in part on parameters measured in artificial conditions that are quite different from those in the lung
  • Surface chemical activity, such as iron activity, can be affected by the protein coating that forms around the fiber, and this needs further study
  • For some parameters there is not enough experimental evidence to assess how, and to what extent, they produce adverse effects
  • Measuring some parameters, such as dissolution rates, can take months to years
  • The model had not yet been optimized and validated; that work was in progress

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, STEM, Surface Reactivity.

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