The influence of cation exchange on the possible mechanism of erionite toxicity: A synchrotron-based micro-X-ray fluorescence study on THP-1-derived macrophages exposed to erionite-Na.

Fibrous erionite is the only zeolite classified as Group 1 carcinogen by the International Agency for Research on Cancer (IARC). Carcinogenesis induced by erionite is thought to involve several factors as biopersistence, the iron role and cation exchange processes. To better understand these mechanisms, a detailed investigation at the micro scale was performed, collecting elemental information on iron and cation release and their distribution in biological systems by synchrotron micro-X-ray fluorescence mapping (SR-micro-XRF) and synchrotron micro-X-ray absorption spectroscopy (SR-micro-XANES) at the TwinMic beamline (Elettra synchrotron) and at the ID21 beamline of the European Synchrotron Radiation Facility (ESRF). By microscopy and chemical mapping, highly detailed maps of the chemical and morphological interaction of biological systems with fibres could be produced. In detail, THP-1 cell line derived macrophages, used as in vitro model, were analysed during erionite-Na phagocytosis at different time intervals, after single dose exposure. For comparison, cellular fluorescent probes were also used to evaluate the intracellular free sodium and calcium concentrations. Synchrotron analyses visualised the spatial distribution of both fibre and mineral particle associated metals during the phagocytosis, describing the mechanism of internalisation of erionite-Na and its accessory mineral phases. The intracellular distribution of metals and other cations was mapped to evaluate metal release, speciation changes and/or cation exchange during phagocytosis. The fluorescent probes complemented microchemical data clarifying, and confirming, the cation distribution observed in the SR-micro-XRF maps. The significant cytoplasmic calcium decrease, and the concomitant sodium increase, after the fibre phagocytosis seemed due to activation of plasma membrane cations exchangers triggered by the internalisation while, surprisingly, the ion-exchange capacity of erionite-Na could play a minor role in the disruption of the two cations intracellular homeostasis. These results help to elucidate the role of cations in the toxicity of erionite-treated THP-1 macrophages and add knowledge to its carcinogenicity process.

The presence of erionite in North American geologies and the estimated mesothelioma potency by region.

OBJECTIVE: Erionite is a naturally occurring fibrous mineral found in soils in some geographical regions. Known for its potency for causing mesothelioma in the Cappadocia region of Turkey, the erionite fiber has attracted interest in the United States due to its presence in a band of rock that extends from Mexico to Montana. There are few toxicology studies of erionite, but all show it to have unusually high chronic toxicity. Despite its high potency compared to asbestos fibers, erionite has no occupational or environmental exposure limits. This paper takes what has been learned about the chemical and physical characteristics of the various forms of asbestos (chrysotile, amosite, anthophyllite, and crocidolite) and predicts the potency of North American erionite fibers. MATERIALS AND METHODS: Based on the fiber potency model in Korchevskiy et al. (2019) and the available published information on erionite, the estimated mesothelioma potency factors (the proportion of mesothelioma mortality per unit cumulative exposure (f/cc-year)) for erionites in the western United States were determined. RESULTS AND DISCUSSION: The model predicted potency factors ranged from 0.19 to 11.25 (average ∼3.5), depending on the region. For reference, crocidolite (the most potent commercial form of asbestos) is assigned a potency factor ∼0.5. CONCLUSION: The model predicted mesothelioma potency of Turkish erionite (4.53) falls in this same range of potencies as erionite found in North America. Although it can vary by region, a reasonable ratio of average mesothelioma potency based on this model is 3,000:500:100:1 comparing North American erionite, crocidolite, amosite, and chrysotile (from most potent to least potent).

[Erionite, an exposure factor linked to pleural mesothelioma]. / L'érionite, un facteur expositionnel lié au mésothéliome pleural.

Mesotheliomas are neoplasia developed from the mesothelium, a layer covering the viscera (visceral layer) and the cavity where the organs are (parietal layer). The best known, and the most frequently encountered is the pleural mesothelioma. This disease has a close link with exposure to asbestos, a mineral fibre now banned in several countries. However, other exposure factors have also been incriminated, including another one recognised as a certain carcinogenic agent for several years now : erionite. We present the case of a patient with pleural mesothelioma whose exposure to erionite could be demonstrated. The presentation of this clinical case will be complemented by a literature review on this less known and mostly environmental exposure, contrary to asbestos which is mostly professional.

Les mésothéliomes sont des néoplasies se développant à partir du mésothélium, feuillet recouvrant, d'une part, les viscères (feuillet viscéral) et, d'autre part, la cavité où se trouvent les organes (feuillet pariétal). Le plus connu, et le plus fréquemment rencontré, est le mésothéliome pleural. Cette maladie a un lien étroit avec l'exposition à l'amiante, fibre minérale maintenant interdite dans plusieurs pays. Cependant, d'autres facteurs expositionnels ont également été incriminés, dont un autre reconnu comme cancérogène certain depuis plusieurs années : l'érionite. Nous présentons le cas d'un patient atteint d'un mésothéliome pleural pour lequel une exposition à l'érionite a pu être étayée. La présentation du cas clinique sera complétée d'une revue de la littérature sur cette exposition particulière moins connue et majoritairement environnementale, contrairement à l'amiante dont l'exposition est majoritairement professionnelle.

Mechanistic in vitro studies: What they have told us about carcinogenic properties of elongated mineral particles (EMPs).

In vitro studies using target and effecter cells of mineral-induced cancers have been critical in determining the mechanisms of pathogenesis as well as the properties of elongated mineral particles (EMPs) important in eliciting these responses. Historically, in vitro models of 'mutagenesis' and immortalized cell lines were first used to test the theory that EMPs were mutagenic to cells, and 'genotoxicity', as defined as damage to DNA often culminating in cell death, was observed in a dose-dependent fashion as responses of many cell types to a number of EMPs. As two-stage and multi-step models of cancer development emerged in the 1970s and 1980s, differentiated 3D organ cultures and monolayers of lung epithelial and mesothelial cells were used to probe the mechanisms of cancer development. These studies demonstrated a spectrum of pre-neoplastic changes, including hyperplasia and squamous metaplasia, in response to long (>5 µm in length) needlelike EMPs whereas long, curly chrysotile fibers caused acute cytotoxicity. Shorter fibers of many types were taken up by cells and encompassed in phagolysosomes. Comparative studies using chemical carcinogens showed that chemical agents interacted directly with DNA whereas long EMPs appeared to be promoters of cancers via a number of mechanisms such as inflammation, generation of oxidants, and instigation of cell division. The multitude of these signaling cascades and epigenetic mechanisms of both lung cancers and mesotheliomas have been most recently studied in normal or telomerase immortalized human cells. Importantly, many of these pathways are elicited by long, straight amphibole asbestos fibers or carbon nanotubes in rodents and not by short (<5 µm) EMPs, fragments, or nonfibrous particles. However, the chemistry and surface properties of long fibers are also critical in cell responses to minerals.

Assessing occupational erionite and respirable crystalline silica exposure among outdoor workers in Wyoming, South Dakota, and Montana.

Erionite is a naturally occurring fibrous mineral found in many parts of the world, including the western United States. Inhalational exposure to erionite fibers in some localities is associated with health effects similar to those caused by asbestos exposure, including malignant mesothelioma. Therefore, there is concern regarding occupational exposures in the western United States. Currently, there are no standard sampling and analytical methods for airborne erionite fibers, as well as no established occupational exposure limits. Due to the potential adverse health effects, characterizing and minimizing exposures is prudent. Crystalline silica also occurs naturally in areas where erionite is found, principally as the mineral quartz. Work activities involving rocks containing quartz and soils derived from those rocks can lead to exposure to respirable crystalline silica (RCS). The typically dry and dusty environment of the western United States can increase the likelihood of exposures to aerosolized rocks and soils, but inhalation exposure is also possible in more humid conditions. In this case study, we describe several outdoor occupational environments with potential exposures to erionite and RCS. We describe our method for evaluating those exposures and demonstrate: (1) the occurrence of occupational exposures to airborne erionite and RCS, (2) that the chemical make-up of the erionite mineral can be determined, and (3) that effective dust control practices are needed to reduce employee exposures to these minerals.

The role of key genes and pathways involved in the tumorigenesis of Malignant Mesothelioma.

Malignant Mesothelioma (MM) is a very aggressive cancer with low survival rates and often diagnosed at an advanced stage. Several players have been implicated in the development of this cancer, such as asbestos, erionite and the simian virus 40 (SV40). Here, we have reviewed the involvement of erionite, SV40, as well as, the role of several genes (p16(INK4a), p14(ARF), NF2, LATS2, SAV, CTNNB1 and among others), the pathways (RAS, PI3K, Wnt, BCL and Hippo), and their respective roles in the development of MM.

Numerous Iron-Rich Particles Lie on the Surface of Erionite Fibers from Rome (Oregon, USA) and Karlik (Cappadocia, Turkey).

Erionite samples from Rome, Oregon (USA) and Karlik, Cappadocia (Turkey) were analyzed by environmental scanning electron microscopy (E-SEM) coupled with energy-dispersive spectroscopy (EDS) to verify the chemical composition of this mineral phase, and the presence of iron in particular. By means of backscattered electron images, a large number of particles/grains were observed on the surface of the erionite fibers from both locations. The particles were found to be micrometric on samples from Rome and submicrometric on samples from Karlik, and always lighter than the hosting crystal in appearance. In different areas of the same fiber or bundle of fibers, several EDS spectra were recorded. Iron was detected only when a light particle was lying in the path of the electron beam. Iron was never identified in the EDS spectra acquired on the flat erionite surface. The results from E-SEM/EDS were confirmed by micro-Raman spectroscopy, showing bands ascribing to hematite­Fe2O3, goethite­FeO(OH), or jarosite­KFe3(3+)(SO4)2(OH)6 when the laser beam was addressed on the light particles observed on the fiber surface. The evidence that iron is on the surface of erionite fibers, rather than being part of the crystalline structure, may be relevant for the carcinogenic potential of these fibers.

Erionite induces production of autoantibodies and IL-17 in C57BL/6 mice.

BACKGROUND: Erionite has similar chemical and physical properties to amphibole asbestos, which induces autoantibodies in mice. Current exposures are occurring in North Dakota due to the use of erionite-contaminated gravel. While erionite is known to cause mesothelioma and other diseases associated with asbestos, there is little known about its effects on the immune system. OBJECTIVES: We performed this study to determine whether erionite evokes autoimmune reactions in mice. METHODS: Bone marrow derived macrophages (BMDM) were used to measure toxicity induced by erionite. Cytokine production by BMDM and splenocytes of C57BL/6 mice was examined by bead arrays and ELISA following exposure to erionite, amphiboles and chrysotile. Wild type C57BL/6 mice were exposed to saline, erionite, amphibole asbestos (Libby 6-Mix) or chrysotile through intratracheal instillations at equal mass (60µg/mouse). Seven months after exposure, sera were examined for anti-nuclear antibodies (ANA) and IL-17. Immunohistochemistry was used to detect immune complex deposition in the kidneys. RESULTS: Erionite and tremolite caused increased cytokine production belonging to the TH17 profile including IL-17, IL-6, TGF-ß, and TNF-α. The frequency of ANA was increased in mice treated with erionite or amphibole compared to saline-treated mice. IL-17 and TNF-α were elevated in the sera of mice treated with erionite. The frequency of immune complex deposition in the kidneys increased from 33% in saline-treated mice to 90% with erionite. CONCLUSIONS: These data demonstrate that both erionite and amphibole asbestos induce autoimmune responses in mice, suggesting a potential for adverse effects in exposed communities.

Toxicological and epidemiological studies on effects of airborne fibers: coherence and public [corrected] health implications.

Airborne fibers, when sufficiently biopersistent, can cause chronic pleural diseases, as well as excess pulmonary fibrosis and lung cancers. Mesothelioma and pleural plaques are caused by biopersistent fibers thinner than ∼0.1 µm and longer than ∼5 µm. Excess lung cancer and pulmonary fibrosis are caused by biopersistent fibers that are longer than ∼20 µm. While biopersistence varies with fiber type, all amphibole and erionite fibers are sufficiently biopersistent to cause pathogenic effects, while the greater in vivo solubility of chrysotile fibers makes them somewhat less causal for the lung diseases, and much less causal for the pleural diseases. Most synthetic vitreous fibers are more soluble in vivo than chrysotile, and pose little, if any, health pulmonary or pleural health risk, but some specialty SVFs were sufficiently biopersistent to cause pathogenic effects in animal studies. My conclusions are based on the following: 1) epidemiologic studies that specified the origin of the fibers by type, and especially those that identified their fiber length and diameter distributions; 2) laboratory-based toxicologic studies involving fiber size characterization and/or dissolution rates and long-term observation of biological responses; and 3) the largely coherent findings of the epidemiology and the toxicology. The strong dependence of effects on fiber diameter, length, and biopersistence makes reliable routine quantitative exposure and risk assessment impractical in some cases, since it would require transmission electronic microscopic examination, of representative membrane filter samples, for determining statistically sufficient numbers of fibers longer than 5 and 20 µm, and those thinner than 0.1 µm, based on the fiber types.

MINERALS IN THE HUMAN BODY: Erionite and offretite from the Killdeer Mountains, Dunn County, North Dakota, U.S.A.

The carcinogenic potential of erionite has sparked concern about human exposure in areas where it is present in regional bedrock. The Arikaree Formation in western North Dakota contains altered tuffaceous units with authigenic zeolites. We sampled stratigraphic profiles in the Killdeer Mountains, Dunn County, North Dakota, to determine the distribution and chemical composition of zeolites. Powder X-ray diffraction, SEM/EDS and electron microprobe analyses were carried out on sample concentrates. Only samples stratigraphically in or below the distinctive burrowed marker unit were found to contain zeolites. Erionite and offretite were the most common zeolites identified, with offretite being more abundant based on frequency of measured Mg/(Ca+Na) ratios. Intermediate chemical compositions could be natural or due to intimate intergrowths of the two minerals. A better understanding is needed of the potential toxicity across the range of erionite and offretite compositions.

Environmental asbestos exposure and lung cancer.

Apart from living near an asbestos industry site, mine, or in an asbestos-contaminated house, environmental asbestos exposure is observed in certain regions where the (natural) soil is 'contaminated' with asbestos (fibers). In this essay, we review the association between environmental asbestos exposure and lung cancer in Turkey. Other studies have also suggested that environmental asbestos exposure is able to increase the risk of lung cancer. Lung cancer associated with environmental asbestos exposure seems to be diagnosed at a younger age, and the risk for women is in the same range as that for men. Our data indicate that the relationship between exposure dose and risk is linear and that a safe threshold cannot be established. Therefore, people living in areas with increased chances of environmental asbestos exposure should be mentored to take part in smoking cessation programs and considered candidates for inclusion in lung cancer screening programs. There is an obvious need for additional studies on this topic.

One-Pot Synthesis of CHA/ERI-Type Zeolite Intergrowth from a Single Multiselective Organic Structure-Directing Agent.

We report the one-pot synthesis of a chabazite (CHA)/erionite (ERI)-type zeolite intergrowth structure characterized by adjustable extents of intergrowth enrichment and Si/Al molar ratios. This method utilizes readily synthesizable 6-azaspiro[5.6]dodecan-6-ium as the exclusive organic structure-directing agent (OSDA) within a potassium-dominant environment. High-throughput simulations were used to accurately determine the templating energy and molecular shape, facilitating the selection of an optimally biselective OSDA from among thousands of prospective candidates. The coexistence of the crystal phases, forming a distinct structure comprising disk-like CHA regions bridged by ERI-rich pillars, was corroborated via rigorous powder X-ray diffraction and integrated differential-phase contrast scanning transmission electron microscopy (iDPC S/TEM) analyses. iDPC S/TEM imaging further revealed the presence of single offretite layers dispersed within the ERI phase. The ratio of crystal phases between CHA and ERI in this type of intergrowth could be varied systematically by changing both the OSDA/Si and K/Si ratios. Two intergrown zeolite samples with different Si/Al molar ratios were tested for the selective catalytic reduction (SCR) of NOx with NH3, showing competitive catalytic performance and hydrothermal stability compared to that of the industry-standard commercial NH3-SCR catalyst, Cu-SSZ-13, prevalent in automotive applications. Collectively, this work underscores the potential of our approach for the synthesis and optimization of adjustable intergrown zeolite structures, offering competitive alternatives for key industrial processes.

Journey to the centre of the lung. The perspective of a mineralogist on the carcinogenic effects of mineral fibres in the lungs.

This work reviews the bio-chemical mechanisms leading to adverse effects produced when mineral fibres are inhaled and transported in the lungs from the perspective of a mineralogist. The behaviour of three known carcinogenic mineral fibres (crocidolite, chrysotile, and fibrous-asbestiform erionite) during their journey through the upper respiratory tract, the deep respiratory tract and the pleural cavity is discussed. These three fibres have been selected as they are the most socially and economically relevant mineral fibres representative of the classes of chain silicates (amphiboles), layer silicates (serpentine), and framework silicates (zeolites), respectively. Comparison of the behaviour of these fibres is made according to their specific crystal-chemical assemblages and properties. Known biological and subsequent pathologic effects which lead and contribute to carcinogenesis are critically reviewed under the mineralogical perspective and in relation to recent progress in this multidisciplinary field of research. Special attention is given to the understanding of the cause-effect relationships for lung cancer and malignant mesothelioma. Comparison with interstitial pulmonary fibrosis, or "asbestosis", will also be made here. This overview highlights open issues, data gaps, and conflicts in the literature for these topics, especially as regards relative potencies of the three mineral fibres under consideration for lung cancer and mesothelioma. Finally, an attempt is made to identify future research lines suitable for a general comprehensive model of the carcinogenicity of mineral fibres.

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

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.

Acute cytotoxicity of mineral fibres observed by time-lapse video microscopy.

Inhalation of mineral fibres is associated with the onset of an inflammatory activity in the lungs and the pleura responsible for the development of fatal malignancies. It is known that cell damage is a necessary step for triggering the inflammatory response. However, the mechanisms by which mineral fibres exert cytotoxic activity are not fully understood. In this work, the kinetics of the early cytotoxicity mechanisms of three mineral fibres (i.e., chrysotile, crocidolite and fibrous erionite) classified as carcinogenic by the International Agency for Research on Cancer, was determined for the first time in a comparative manner using time-lapse video microscopy coupled with in vitro assays. All tests were performed using the THP-1 cell line, differentiated into M0 macrophages (M0-THP-1) and exposed for short times (8 h) to 25 µg/mL aliquots of chrysotile, crocidolite and fibrous erionite. The toxic action of fibrous erionite on M0-THP-1 cells is manifested since the early steps (2 h) of the experiment while the cytotoxicity of crocidolite and chrysotile gradually increases during the time span of the experiment. Chrysotile and crocidolite prompt cell death mainly via apoptosis, while erionite exposure is also probably associated to a necrotic-like effect. The potential mechanisms underlying these different toxicity behaviours are discussed in the light of the different morphological, and chemical-physical properties of the three fibres.

Degradation of dye containing in textile wastewater by sequential process: photocatalytic and biological treatment.

In this research, a combined photocatalytic and biological treatment is proposed for the elimination of pollutants present in textile wastewater using a natural erionite zeolite (PE) and aluminum oxide (PA) synthesized by the sol-gel method as photocatalysts, and solar radiation. Both catalysts were characterized by XRD, SEM, and EDS. For biological treatment two bacterial consortium were used: BC1 (Escherichia coli N16, Serratia k120, Pseudomonas putida B03 and Enterobacter hormaechei), and consortium BC2 (Escherichia coli N16, Serratia Mc107, Enterobacter N9, Enterobacter hormaechei Mc9). The photocatalytic and microbiological treatments were carried out initially separately and subsequently in a sequential manner, first the photocatalytic followed by the microbiological to determine if a synergistic effect was achieved. Comparing the photocatalytic performance, erionite showed higher performance of dyes degradation (54.75%) than alumina (28.62%). While in the biological process, BC1 decreased the dye concentration to 56.93% and BC2 to 53.56%. Finally, the best combined process was PA+BC1 reaching pollutants degradation 64.62%, showing that the application of both processes promotes a decolorization in textile wastewater. The water resulting from the combined photocatalysis-microbiological degradation processes was tested for toxicity using Daphnia magna, obtaining that none of the effluents shows toxicity.

Global geological occurrence and character of the carcinogenic zeolite mineral, erionite: A review.

As with the six regulated asbestos minerals (chrysotile, amosite, crocidolite, anthophyllite, tremolite, and actinolite), the zeolite mineral, erionite, can exhibit a fibrous morphology. When fibrous erionite is aerosolized and inhaled, it has been linked to cases of lung cancers, such as malignant mesothelioma. Importantly, fibrous erionite appears to be more carcinogenic than the six regulated asbestos minerals. The first health issues regarding erionite exposure were reported in Cappadocia (Turkey), and more recently, occupational exposure issues have emerged in the United States. Erionite is now classified as a Group 1 carcinogen. Thus, identifying the geological occurrence of erionite is a prudent step in determining possible exposure pathways, but a global review of the geological occurrence of erionite is currently lacking. Here, we provide a review of the >100 global locations where erionite has been reported, including: 1) geological setting of host rocks; 2) paragenetic sequence of erionite formation, including associated zeolite minerals; 3) fiber morphological properties and erionite mineral series (i.e., Ca, K, Na); and 4) a brief overview of the techniques that have been used to identify and characterize erionite. Accordingly, erionite has been found to commonly occur within two major rock types: felsic and mafic. Within felsic rocks (in particular, tuffaceous layers within lacustrine paleoenvironments), erionite is disseminated through the layer as a cementing matrix. In contrast, within mafic (i.e., basaltic) rocks, erionite is typically found within vesicles. Nevertheless, aside from detailed studies in Italy and the United States, there is a paucity of specific information on erionite geological provenance or fiber morphology. The latter issue is a significant drawback given its impact on erionite toxicity. Future erionite studies should aim to provide more detailed information, including variables such as rock type and lithological properties, quantitative geochemistry, and fiber morphology.

Asbestos and Other Hazardous Fibrous Minerals: Potential Exposure Pathways and Associated Health Risks.

There are six elongate mineral particles (EMPs) corresponding to specific dimensional and morphological criteria, known as asbestos. Responsible for health issues including asbestosis, and malignant mesothelioma, asbestos has been well researched. Despite this, significant exposure continues to occur throughout the world, potentially affecting 125 million people in the workplace and causing thousands of deaths annually from exposure in homes. However, there are other EMPS, such as fibrous/asbestiform erionite, that are classified as carcinogens and have been linked to cancers in areas where it has been incorporated into local building materials or released into the environment through earthmoving activities. Erionite is a more potent carcinogen than asbestos but as it is seldom used for commercial purposes, exposure pathways have been less well studied. Despite the apparent similarities between asbestos and fibrous erionite, their health risks and exposure pathways are quite different. This article examines the hazards presented by EMPs with a particular focus on fibrous erionite. It includes a discussion of the global locations of erionite and similar hazardous minerals, a comparison of the multiple exposure pathways for asbestos and fibrous erionite, a brief discussion of the confusing nomenclature associated with EMPs, and considerations of increasing global mesothelioma cases.

Characterisation of potentially toxic natural fibrous zeolites by means of electron paramagnetic resonance spectroscopy and morphological-mineralogical studies.

This study explored the morphological, mineralogical, and physico-chemical features of carcinogenic erionite and other possibly hazardous zeolites, such as mesolite and thomsonite, while also investigating the interacting capability of the mineral surface at the liquid/solid interface. Extremely fibrous erionite is K+ and Ca2+-rich and shows the highest Si/Al ratio (3.38) and specific surface area (8.14 m2/g). Fibrous mesolite is Na+ and Ca2+-rich and displays both a lower Si/Al ratio (1.56) and a smaller specific surface area (1.56 m2/g). The thomsonite composition shows the lowest values of Si/Al ratio (1.23) and specific surface area (0.38 m2/g). Electron paramagnetic resonance data from selected spin probes reveal that erionite has a homogeneous site distribution and interacts well with all spin probes. The surfaces of mesolite and thomsonite are less homogeneous and closer polar sites were found through consequent interaction with the probes. The mesolite surface can also clearly interact but with a lower strength and may represent a potential health hazard for humans, though with a lower degree if compared to erionite. The thomsonite surface is not inert and interacts with the probes with a low-grade capability. We can expect small fragments of thomsonite to interact with the biological environment, though with a low-grade intensity.

Reanalysis of historic elemental speciation filters to investigate the presence of fibrous mineral particles using microscopy techniques.

A case is presented for the value of archiving air quality filters to allow for retrospective analysis of emerging contaminants, that is filter constituents not considered to be harmful (and thus not identified or quantified specifically) at the time of collection but subsequently considered to be of interest. As an example, filters from a 20-year historical archive consisting of 16,000 filters from three sites across Auckland are re-examined for the presence of elongated mineral fibres known to be present in rock across the city. Originally collected for the purpose of the source apportionment of particulate matter, 10 filters from each of the three sites were chosen for reanalysis based on their high silica and aluminium content, and thus considered more likely to contain fibre-like particles (FLP). These filters were analysed using various microscopic methods, including phase contrast microscopy (PCM), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). The results show that although the commonly used fibrous polytetrafluoroethylene (PTFE) material of the filters may hamper the visual identification of any fibre-like particles under a certain length, their key components are able to be identified using a combination of PCM and SEM when they are of a suitable dimension and have settled in a certain orientation on the filter. In this case, the use of EDS confirmed the silicon content of the fibres and also revealed elemental spectra. Although the exact identification of the mineral fibre is uncertain, the EDS scan is consistent with hazardous zeolites such as erionite, known to be present in the rock found in Auckland. This study highlights the value in maintaining filter archives for the purpose of investigating the historical evolution of emerging atmospheric pollutants.