Where is iron in erionite? A multidisciplinary study on fibrous erionite-Na from Jersey (Nevada, USA).

Alessandro F. Gualtieri,Simone Pollastri,Nicola Bursi Gandolfi,Falko Langenhorst,Kilian Pollok

doi:10.1038/srep37981

Alessandro F. Gualtieri, Simone Pollastri + Show 3 more

Open Access

https://doi.org/10.1038/srep37981

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Abstract

Fibrous erionite is a mineral fibre of great concern but to date mechanisms by which it induces cyto- and geno-toxic damage, and especially the role of iron associated to this zeolite species, remain poorly understood. One of the reasons is that we still don’t know exactly where iron is in natural erionite. This work is focused on fibrous erionite-Na from Jersey (Nevada, USA) and attempts to draw a general model of occurrence of iron in erionite and relationship with toxicity mechanisms. It was found that iron is present as 6-fold coordinated Fe3+ not part of the zeolite structure. The heterogeneous nature of the sample was revealed as receptacle of different iron-bearing impurities (amorphous iron-rich nanoparticles, micro-particles of iron oxides/hydroxides, and flakes of nontronite). If iron is not part of the structure, its role should be considered irrelevant for erionite toxicity, and other factors like biopersistence should be invoked. An alternative perspective to the proposed model is that iron rich nano-particles and nontronite dissolve in the intracellular acidic environment, leaving a residue of iron atoms at specific surface sites anchored to the windows of the zeolite channels. These sites may be active later as low nuclearity groups.

Highlights

Natural fibrous erionite has recently gained great concern because its environmental exposure has been linked to the outbreak of malignant mesothelioma (MM) epidemics in several villages of Central Anatolia, Turkey12,13
The same sample has been selected for a BSE-EDS analysis combined with micro-Raman spectroscopy and iron has been identified as component of iron-bearing microcrystals of hematite (α-Fe2O3), goethite (α-FeOOH), and jarosite KFe3(SO4)2(OH)6 nucleated at the surface of the fibres30
The outcome of the structure refinement confirms the absence of structural iron in natural fibrous erionite ruling out both Fe2+/Fe3+ in place of Si4+/Al3+ in the zeolite framework and Fe3+/Fe2+ in the extraframework cavities as octahedral Fe(H2O)n clusters

Summary

Introduction

Natural fibrous erionite has recently gained great concern because its environmental exposure has been linked to the outbreak of malignant mesothelioma (MM) epidemics in several villages of Central Anatolia, Turkey. The EPMA analysis of several fibrous erionite-K (and offretite) samples from the Killdeer Mountains, Dunn County (North Dakota, USA) displays an extremely variable iron content (003–1.99 wt% Fe2O3) that was arbitrarily assigned as Fe3+ hosted in the zeolite framework. As far as model [3] is concerned, in erionite-K from Rome (Oregon, USA), 95% of iron was attributed to Fe3+-bearing, super-paramagnetic, oxide-like nanoparticles with dimensions between 1 and 9 nm, and the remaining 5% was attributed to hematite particles with size ≥10 nm, both located at the crystal surface. The same authors found that iron in fibrous erionite-K from Karlik (Cappadocia, Turkey) was as well present as iron-bearing sub-micrometric crystals of hematite and goethite coating the surface of the fibres, and not in the crystal structure

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