Misconceptions regarding the pathogenicity of silicas and silicates

Our plain-English summary of Misconceptions regarding the pathogenicity of silicas and silicates, by D.S. Feigin (Journal of Thoracic Imaging, 1989).

The study

• Author: D.S. Feigin
• Journal: Journal of Thoracic Imaging
• Published: 1989;4(1):68-80
• Type of article: Review
• Cited by: 15 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. 002546).

Abstract

Several inhaled substances, from occupational or other environmental exposure, produce significant pulmonary disease and abnormalities demonstrated by pulmonary imaging. Areas of controversy and misconception relate principally to the extent and nature of both the clinical disease and the imaging abnormalities specific to each substance. The size and shape of the inhaled particles is an important determinant of the nature and severity of the disease produced, with fibrous shapes usually being the most pathogenetic. Fibrogenicity is another important pathogenetic characteristic of talc and kaolin, as well as asbestos. Talc produces four distinct forms of pulmonary disease, depending not only on the other substances with which it is inhaled, but also whether it is inhaled or injected intravenously. When inhaled alone, talc does not appear to produce significant pulmonary fibrosis or malignancy. Kaolin, mica, fuller's earth, zeolite, and fiberglass all vary in disease production according to their shape and fibrogenicity. Silica, diatomaceous earth, and other forms of silica are all highly fibrogenic and thus produce clinically obvious disease with sufficient inhalation. The largest particles usually produce nodular patterns in the upper pulmonary fields, as is typical of silicosis. The fibrous particles are more likely to manifest themselves as interstitial patterns in the lower pulmonary fields.

In plain English

This 1989 article was a narrative review, not an original study. The author described the published evidence on lung disease from inhaling talc and other silicates, with an emphasis on exposure outside mining. The author described four forms of talc-related lung disease: talcosilicosis, talcoasbestosis, pure talcosis, and disease from injecting talc intravenously. Talcoasbestosis, from talc containing asbestiform fibers (the text names tremolite and anthophyllite), was described as appearing to be associated with bronchogenic carcinoma and malignant mesothelioma. Diaphragm calcification from talc had been described only in this form. Pure talc might be fibrogenic, but not all reports agreed. For mica, pleural calcification and thickening had never been shown without asbestos inhalation. Exposure to erionite, a fibrous zeolite from central Turkey, was described as well documented to be related to pleural thickening, diaphragmatic plaques, bronchogenic carcinoma and pleural mesothelioma. No distinct radiographic changes had been attributed to synthetic fibers. The author concluded that particle size and shape are an important determinant of disease, with fibrous shapes usually the most pathogenetic. The author noted that mixed-dust exposures make it hard to link findings to a single dust.

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 of published literature (no original data)
• Who was studied: No study population. The author reviewed published reports on talc, kaolin, mica, fuller's earth, zeolites, synthetic vitreous fibers, other silicates, and free silica, emphasizing nonmining exposure settings.
• Exposure: Inhaled talc (pure, mixed with silica, or mixed with asbestiform fibers such as tremolite and anthophyllite) and intravenously injected talc; kaolin; mica (especially muscovite); fuller's earth; zeolites including erionite; synthetic vitreous fibers (fiberglass, rock wool, ceramic fibers); wollastonite; vermiculite; cement; free silica in nonmining work; diatomaceous earth; nepheline; alunite
• Main results:
  • The author described talc as producing four distinct forms of lung disease, depending on what else is inhaled with it and whether it is inhaled or injected intravenously.
  • Talcoasbestosis was described as appearing to be associated with malignancies, including bronchogenic carcinoma and malignant mesothelioma. The author noted that the incidence may vary with the type of asbestos inhaled with the talc.
  • Diaphragmatic calcification from talc exposure had been described only in talcoasbestosis, not in the other three forms of talc-related disease.
  • Pure talc (free of silica and asbestiform minerals) may be fibrogenic, but reports disagreed.
  • For mica, pleural calcifications and thickening had never been shown to occur without asbestos inhalation.
  • Exposure to erionite, a fibrous zeolite from central Turkey, was described as well documented to be related to pleural thickening, diaphragmatic plaques, bronchogenic carcinoma and pleural mesothelioma.
  • No distinct radiographic changes had been attributed to exposure to any synthetic fibrous material.
  • Exposure to free silica outside mines was described as at least as common as exposure in mines in recent years.
• The authors' conclusion: The author concluded that the size and shape of inhaled particles are an important determinant of the nature and severity of disease, with fibrous shapes usually the most pathogenetic.
• Limitations the authors state:
  • The author noted that people commonly inhale fibrogenic and nonfibrogenic dusts together, which makes it impossible to determine which findings are specifically related to which dust.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Silicate, Environmental Exposure, Talc, Pulmonary Fibrosis, Mica, Zeolite, Fibrogenic, Silicosis.

Related studies

• One agent, many diseases: exposure-response data and comparative risks of different outcomes following silica exposure — K. Steenland (2005)
• Silicosis and smoking strongly increase lung cancer risk in silica-exposed workers — N. Kurihara, O. Wada (2004)
• Silica exposure and altered regulation of autoimmunity — S. Lee, H. Matsuzaki, et al. (2014)
• Silica and asbestos exposure in ANCA-associated vasculitis with pulmonary involvement — Z. Rihova, D. Maixnerova, et al. (2005)
• Silica and asbestos: contrasts in tissue response — A.G. Heppleston (1979)
• Expression of the T cell receptor Vbeta repertoire in a human T cell resistant to asbestos-induced apoptosis and peripheral blood T cells from patients with silica and asbestos-related diseases — Y. Nishimura, Y. Miura, et al. (2006)

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