The crystal structure of the killer fibre erionite from Tuzköy (Cappadocia, Turkey)

Our plain-English summary of The crystal structure of the killer fibre erionite from Tuzköy (Cappadocia, Turkey), by C. Giacobbe, A. Moliterni, D. Di Giuseppe, et al (IUCrJ, 2023).

The study

• Authors: C. Giacobbe, A. Moliterni, D. Di Giuseppe, D. Malferrari, J.P. Wright, M. Mattioli, S. Raneri, C. Giannini, L. Fornasini, E. Mugnaioli, P. Ballirano, A.F. Gualtieri
• Journal: IUCrJ
• Published: 2023;10(Pt 4):397-410
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Erionite is a non-asbestos fibrous zeolite classified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen and is considered today similar to or even more carcinogenic than the six regulated asbestos minerals. Exposure to fibrous erionite has been unequivocally linked to cases of malignant mesothelioma (MM) and this killer fibre is assumed to be directly responsible for more than 50% of all deaths in the population of the villages of Karain and Tuzköy in central Anatolia (Turkey). Erionite usually occurs in bundles of thin fibres and very rarely as single acicular or needle-like fibres. For this reason, a crystal structure of this fibre has not been attempted to date although an accurate characterization of its crystal structure is of paramount importance for our understanding of the toxicity and carcinogenicity. In this work, we report on a combined approach of microscopic (SEM, TEM, electron diffraction), spectroscopic (micro-Raman) and chemical techniques with synchrotron nano-single-crystal diffraction that allowed us to obtain the first reliable ab initio crystal structure of this killer zeolite. The refined structure showed regular T-O distances (in the range 1.61-1.65 Å) and extra-framework content in line with the chemical formula (K2.63Ca1.57Mg0.76Na0.13Ba0.01)[Si28.62Al7.35]O72·28.3H2O. The synchrotron nano-diffraction data combined with three-dimensional electron diffraction (3DED) allowed us to unequivocally rule out the presence of offretite. These results are of paramount importance for understanding the mechanisms by which erionite induces toxic damage and for confirming the physical similarities with asbestos fibres.

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In plain English

This was a laboratory study of the mineral structure of fibrous erionite, a non-asbestos fibrous zeolite, taken from a tuff rock near Tuzköy village in Cappadocia, Turkey. It did not study people or disease. The authors combined microscopy, Raman spectroscopy, X-ray powder diffraction, chemical analysis, electron diffraction and synchrotron X-ray diffraction of a single fibre to work out the crystal structure. The tuff was 42.64 percent erionite by weight. What looks like an erionite fibre was a bundle of much thinner fibrils. Measured fibres were generally longer than 5.0 micrometres and 0.16 to 4.2 micrometres wide, and all had a length-to-width ratio above 3 to 1. Iron was not part of the crystal structure. It occurred as small iron-rich particles, mainly hematite, on the fibre surfaces. Several tests found no offretite, a closely related mineral, in the sample. The bulk chemical analysis pointed to erionite-K, while the single-fibre structure indicated an erionite-K/erionite-Ca term. The two differed mainly in calcium. The authors concluded that the Tuzköy erionite is not associated with offretite.

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: Laboratory mineralogical and crystallographic characterization of a rock sample. The methods were thermal analysis, micro-Raman spectroscopy, X-ray powder diffraction, scanning and transmission electron microscopy, electron probe microanalysis, three-dimensional electron diffraction, and synchrotron nano-single-crystal X-ray diffraction.
• Who was studied: A fibrous erionite sample extracted from a friable yellowish tuff near Tuzköy village, Nevşehir province, Cappadocia, Turkey. Length and width were measured on about 110 fibres from 30 SEM images. One fibre was used for synchrotron single-crystal diffraction. No human subjects were studied.
• Exposure: Fibrous erionite, a non-asbestos fibrous zeolite. No human or animal exposure was studied.
• Main results:
  • By weight, the Tuzköy tuff contained erionite 42.64 wt%, clinoptilolite 24.8, quartz 13.0 wt%, sanidine 7.59 wt%, hornblende 5.28 wt%, albite 5.05 wt% and mica 1.63 wt%.
  • The erionite fibres were generally longer than 5.0 micrometres and 0.16 to 4.2 micrometres wide. All observed fibres had a length-to-width ratio greater than 3:1.
  • All observed fibres had a length-to-width ratio greater than 3:1.
  • Electron microscopy showed that what is usually considered an erionite fibre is a bundle of fibrils only a few tens of nanometres thick.
  • Iron-containing compounds were found mixed with the fibres, mainly hematite, with goethite and magnetite rare. The authors reported that iron was not hosted in the erionite structure but occurred as surface particles.
  • Raman spectroscopy, electron diffraction and synchrotron diffraction tests found no offretite. This included a constant 210/211 diffraction intensity ratio measured at different heights along the fibre.
  • The bulk chemical analysis (EPMA) formula pointed to erionite-K. The single-fibre structure refinement indicated an erionite-K/erionite-Ca term. The two formulas differed mainly in calcium content.
• The authors' conclusion: The authors concluded that the erionite from Tuzköy is not associated with offretite. They stated that the findings are a starting point for in vivo and in vitro studies of its toxicity.
• Limitations the authors state:
  • The calcium content found by structure refinement was higher than in the chemical analysis. The authors attributed this possibly to cation migration during analysis, or to the difference between a bulk technique and a single-fibre technique.
  • Three-dimensional electron diffraction data were less sensitive than synchrotron nano-diffraction for the extra-framework content.

Topics

Medical terms in this study, explained in our Lexicon: Crystal Structure, erionite, Cappadocia, Zeolite, IARC, Carcinogenic, Asbestos, Mesothelioma.

Related studies

• Erionite bodies and fibres in bronchoalveolar lavage fluid (BALF) of residents from Tuzköy, Cappadocia, Turkey — P. Dumortier, L. Coplü, et al. (2001)
• Crystal structure determination of a lifelong biopersistent asbestos fibre using single-crystal synchrotron X-ray micro-diffraction — C. Giacobbe, D. Di Giuseppe, et al. (2021)
• The Cappadocia mesothelioma epidemic: its influence in Turkey and abroad — S.A. Emri (2017)
• Bridging the gap between toxicity and carcinogenicity of mineral fibres by connecting the fibre crystal-chemical and physical parameters to the key characteristics of cancer — A.F. Gualtieri (2021)
• Lung diseases due to environmental exposures to erionite and asbestos in Turkey — S. Emri, A. Demir, et al. (2002)
• Malignant pleural mesothelioma caused by environmental exposure to asbestos or erionite in rural Turkey: CT findings in 84 patients — A.A. Sahin, L. Cöplü, et al. (1993)

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