Iron from a geochemical viewpoint. Understanding toxicity/pathogenicity mechanisms in iron-bearing minerals with a special attention to mineral fibers

Our plain-English summary of Iron from a geochemical viewpoint. Understanding toxicity/pathogenicity mechanisms in iron-bearing minerals with a special attention to mineral fibers, by A.F. Gualtieri, G.B. Andreozzi, M. Tomatis, et al (Free Radical Biology & Medicine, 2019).

The study

• Authors: A.F. Gualtieri, G.B. Andreozzi, M. Tomatis, F. Turci
• Journal: Free Radical Biology & Medicine
• Published: 2019;133:21-37
• Type of article: Review
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Iron and its role as soul of life on Earth is addressed in this review as iron is one of the most abundant elements of our universe, forms the core of our planet and that of telluric (i.e., Earth-like) planets, is a major element of the Earth's crust and is hosted in an endless number of mineral phases, both crystalline and amorphous. To study iron at an atomic level inside the bulk of mineral phases or at its surface, where it is more reactive, both spectroscopy and diffraction experimental methods can be used, taking advantage of nearly the whole spectrum of electromagnetic waves. These methods can be successfully combined to microscopy to simultaneously provide chemical (e.g. iron mapping) and morphological information on mineral particles, and shed light on the interaction of mineral surfaces with organic matter. This review describes the crystal chemistry of iron-bearing minerals of importance for the environment and human health, with special attention to iron in toxic minerals, and the experimental methods used for their study. Special attention is devoted to the Fenton-like chain reaction involving Fe2+ in the formation of highly reactive hydroxyl radicals. The final part of this review deals with release and adsorption of iron in biological fluids, coordinative and oxidative state of iron and in vitro reactivity. To disclose the very mechanisms of carcinogenesis induced by iron-bearing toxic mineral particles, crystal chemistry and surface chemistry are fundamental for a multidisciplinary approach which should involve geo-bio-scientists, toxicologists and medical doctors.

Copyright © 2018 Elsevier Inc. All rights reserved.

In plain English

This article is a review, not a new study. Writing as geoscientists, the authors described how iron sits in the crystal structures of minerals, the techniques used to study it, and how iron in mineral fibers such as asbestos and fibrous erionite may contribute to harmful effects. Drawing on earlier work, the review explained that Fe2+ (ferrous iron) on asbestos is recognized to promote the formation of highly reactive hydroxyl radicals, and that not all iron in a fiber takes part. It summarized cited estimates for a fiber 0.1 micrometers wide at pH 4, assuming a zero-order reaction: about 239 days to dissolve for chrysotile, versus 2500, 5000 and 18500 days for amosite, crocidolite and tremolite. It also noted that the role of iron in erionite's toxicity is controversial. The authors stated that a general model of how iron leads to adverse effects is still missing. They concluded that the crystal chemistry and surface chemistry of iron-bearing toxic minerals should underpin a multidisciplinary approach to understanding how these minerals cause cancer. They said the review could not cover the whole literature on this topic.

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: narrative review
• Who was studied: No study population. The review covers iron-bearing minerals, with a focus on toxic minerals such as asbestos, drawing on previously published research.
• Exposure: Iron in mineral fibers: chrysotile (serpentine asbestos); the amphibole asbestos types actinolite asbestos, amosite, anthophyllite asbestos, crocidolite and tremolite asbestos; and fibrous erionite (a zeolite)
• Main results:
  • Citing earlier work, the review stated that Fe2+ associated with asbestos is recognized to promote the formation of highly reactive hydroxyl radicals through a Fenton-like chain reaction.
  • The review stated that not all iron in a mineral can take part in these radical-forming reactions. Only iron at specific surface sites can do so.
  • The review cited earlier estimates for a fiber 0.1 micrometers in diameter at pH 4, assuming a zero-order reaction. Under those conditions, the estimated dissolution time was about 239 days for chrysotile, 2500 days for amosite, 5000 days for crocidolite and 18500 days for tremolite.
  • The review described the role of iron in fibrous erionite's toxicity as controversial. Earlier work showed that in natural erionite, iron is not part of the crystal structure but is found in impurities on the fiber surface.
  • The review summarized a cited cell-culture study. After 96 hours in contact with cells, iron was still present within chrysotile and crocidolite fibers and was retained at the surface of erionite fibers.
  • The review cited an animal study in which peritoneal mesothelioma developed in rats after repeated injections of iron (ferric saccharate) into the abdomen.
  • The review stated that ferruginous (asbestos) bodies form on all varieties of asbestos but more often on amphiboles than on chrysotile.
• The authors' conclusion: The authors concluded that a general model of how iron leads to adverse effects is missing. In their view, knowledge of the crystallography and crystal chemistry of iron-bearing toxic substances should be the foundation of a multidisciplinary effort to uncover the mechanisms of carcinogenesis.
• Limitations the authors state:
  • The authors stated that describing the vast literature on the role of iron in asbestos toxicity, even partially, was beyond the scope of the review. They focused only on key toxicological concepts.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Crystalline, Hydroxyl Radical, Carcinogenesis, Multidisciplinary Team.

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