Erionite Fibers Research Articles

Characterization and potential toxicity of asbestiform erionite from Gawler Downs, New Zealand

Abstract Erionite is the name for a zeolite mineral series originating from diagenesis or hydrothermal alteration of volcanic rocks. The particular erionite “species” is based on the dominant extra-framework cation, erionite-Ca, erionite-K, or erionite Na. Irrespective of the species, erionite can display a fibrous/asbestiform morphology and has been linked with cases of malignant mesothelioma, a disease typically associated with asbestos exposure. Characterization of new discoveries of erionite is therefore important to assess any potential exposure hazards. This study describes a new asbestiform erionite from vesicles within the Upper Cretaceous Mt. Somers Volcanics Group (MSVG), Canterbury, New Zealand. The erionite is within the Hinds River Dacite, the youngest unit within the MSVG at Gawler Downs, ~100 km west of Christchurch, in the foothills of the Southern Alps. A multi-analytical approach was taken to analyze the sample which included micro-Raman spectroscopy, thermogravimetric analysis, electron microscopy, electron microprobe analysis, and X-ray powder diffraction with the Rietveld method. Results confirmed the mineral as fibrous erionite-K. The chemical composition of the mineral is unique due to the presence of higher levels of Mg. While Fe was also identified, this was due to smectite flakes occurring on the surface of the erionite fibers. According to the World Health Organization (WHO) respirable mineral fiber definition, where length ≥5 μm, width ≤3 μm, and aspect ratio (L/w) ≥3:1, the Gawler Downs erionite fibers are respirable, while the fibers themselves exceed respirable thickness. In addition to morphology, a value for the potential toxicity model was computed to be 2.28 for the Gawler Downs erionite. This is similar to those of other carcinogenic erionites from Karain, Turkey (2.33), and Nevada, U.S.A. (2.28). Taken together, results indicate Gawler Downs erionite represents an environmental hazard. Nevertheless, further investigation is required to determine potential environmental exposure pathways by which erionite may become airborne and assess the actual environmental risk in the Gawler Downs area.

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).

Discerning Erionite from Other Zeolite Minerals During Analysis

ABSTRACT Erionite, a naturally occurring fibrous mineral that belongs to the zeolite group has been designated by the International Agency for Research on Cancer (IARC) as a Group 1 Carcinogen on the basis of mesothelioma, a disease also resulting from the inhalation of asbestos fibers. Significant outcrops of fibrous erionite have been reported in California, North Dakota, Nevada, Oregon, and other states. For geologists and industrial hygienists dealing with mining, construction, or various aspects of community protection, it is vital to understand the basics of detecting and handling erionite, since it is similar to asbestos and can cause similar disease. There are many fibrous zeolites, and discerning erionite from these other minerals requires modifications to current asbestos analysis methods. Without these modifications, identification and quantification are questionable and could increase the likelihood of both false negatives and false positives. There is currently no published method specific to erionite analysis; without guidance standards, each laboratory has approached erionite analysis independently. With a few small but significant changes to asbestos analysis methodologies, we developed a reproducible analytical procedure for rapid identification of erionite fibers in air, bulk, and soil samples by transmission electron microscopy (TEM). Using specialized preparation techniques, energy dispersive Spectrometry (EDS) calibrations, and a liquid nitrogen cryo-holder (cold stage), we were able to overcome the difficulties associated with erionite analysis. By incorporating these changes, commercial analytical laboratories can contribute reliable data to air-exposure studies and characterization guidelines, which may help in determining regulations and further understanding the health risks of erionite.

Pre-clinical Models for Malignant Mesothelioma Research: From Chemical-Induced to Patient-Derived Cancer Xenografts.

Malignant mesothelioma (MM) is a rare disease often associated with environmental exposure to asbestos and other erionite fibers. MM has a long latency period prior to manifestation and a poor prognosis. The survival post-diagnosis is often less than a year. Although use of asbestos has been banned in the United States and many European countries, asbestos is still being used and extracted in many developing countries. Occupational exposure to asbestos, mining, and migration are reasons that we expect to continue to see growing incidence of mesothelioma in the coming decades. Despite improvements in survival achieved with multimodal therapies and cytoreductive surgeries, less morbid, more effective interventions are needed. Thus, identifying prognostic and predictive biomarkers for MM, and developing novel agents for targeted therapy, are key unmet needs in mesothelioma research and treatment. In this review, we discuss the evolution of pre-clinical model systems developed to study MM and emphasize the remarkable capability of patient-derived xenograft (PDX) MM models in expediting the pre-clinical development of novel therapeutic approaches. PDX disease model systems retain major characteristics of original malignancies with high fidelity, including molecular, histopathological and functional heterogeneities, and as such play major roles in translational research, drug development, and precision medicine.

EPR, TEM and cell viability study of asbestiform zeolite fibers in cell media

Human monocyte U937 cell line was used as a model to verify the toxicity of erionite and offretite asbestiform zeolite fibers. As a presumed non-toxic reference, a fibrous scolecite zeolite was also used. To analyze the process of fiber ingestion into cells and the cells-fibers interactions, a spin-probe electron paramagnetic resonance (EPR) analysis was performed supported by transmission electron microscopy (TEM) and cell viability measurements as a function of the incubation time. Erionite fibers were fast internalized in the membrane mainly as aggregates with radical-solution drops trapped inside, and were found in the cytosol and at the nucleus. In 24h, first erionite fibers rich in sodium and potassium, and then calcium-rich erionite fibers, induced cell necrosis. The offretite fibers formed rounding electron-dense filaments which transformed in curved filaments, initially perturbing the cell structure and interacting at the external surface more than erionite fibers. Such interactions probably diminished the toxic effect of offretite on cells. Interestingly, the presumed non-toxic scolecite fibers were partially internalized, inducing formation of swollen mitochondria and squared cells. Overall, the toxic effect of the fibrous zeolites was related to fiber morphology, chemical distribution of sites, structural variations and formation of aggregates.

Diagnostic and prognostic biomarkers for malignant mesothelioma: an update.

Malignant mesothelioma (MM) is an aggressive and lethal cancer, mostly related to inhalation of asbestos and erionite fibers. MM is associated with poor prognosis, because of its resistance to current therapies, even if higher survival occurs in patients diagnosed and treated when at stage I of the disease. However, these do not exceed 5% of the total number of cases, due to the inadequacy of the existing biomarkers for early and accurate diagnosis. Therefore, new effective biomarkers are needed for MM detection at earlier stages and to develop tailored therapies. Here we review the most promising biomarkers in MM to date: mesothelin, soluble mesothelin-related peptides (SMRPs), megakaryocyte potentiating factor (MPF), Osteopontin (OPN), Fibulin-3, high mobility group B1 (HMGB1), microRNAs (miRNAs), multiplex protein signatures. The validation of these biomarkers will allow their use, alone or in combination, for monitoring individuals from cohorts at risk of MM and attaining early detection of MM that is instrumental in improving patient survival.

Consensus Report of the 2015 Weinman International Conference on Mesothelioma

On November 9 and 10, 2015, the International Conference on Mesothelioma in Populations Exposed to Naturally Occurring Asbestiform Fibers was held at the University of Hawaii Cancer Center in Honolulu, Hawaii. The meeting was cosponsored by the International Association for the Study of Lung Cancer, and the agenda was designed with significant input from staff at the U.S. National Cancer Institute and National Institute of Environmental Health Sciences. A multidisciplinary group of participants presented updates reflecting a range of disciplinary perspectives, including mineralogy, geology, epidemiology, toxicology, biochemistry, molecular biology, genetics, public health, and clinical oncology. The group identified knowledge gaps that are barriers to preventing and treating malignant mesothelioma (MM) and the required next steps to address barriers. This manuscript reports the group’s efforts and focus on strategies to limit risk to the population and reduce the incidence of MM. Four main topics were explored: genetic risk, environmental exposure, biomarkers, and clinical interventions. Genetics plays a critical role in MM when the disease occurs in carriers of germline BRCA1 associated protein 1 mutations. Moreover, it appears likely that, in addition to BRCA1 associated protein 1, other yet unknown genetic variants may also influence the individual risk for development of MM, especially after exposure to asbestos and related mineral fibers. MM is an almost entirely preventable malignancy as it is most often caused by exposure to commercial asbestos or mineral fibers with asbestos-like health effects, such as erionite. In the past in North America and in Europe, the most prominent source of exposure was related to occupation. Present regulations have reduced occupational exposure in these countries; however, some people continue to be exposed to previously installed asbestos in older construction and other settings. Moreover, an increasing number of people are being exposed in rural areas that contain noncommercial asbestos, erionite, and other mineral fibers in soil or rock (termed naturally occurring asbestos [NOA]) and are being developed. Public health authorities, scientists, residents, and other affected groups must work together in the areas where exposure to asbestos, including NOA, has been documented in the environment to mitigate or reduce this exposure. Although a blood biomarker validated to be effective for use in screening and identifying MM at an early stage in asbestos/NOA-exposed populations is not currently available, novel biomarkers presented at the meeting, such as high mobility group box 1 and fibulin-3, are promising. There was general agreement that current treatment for MM, which is based on surgery and standard chemotherapy, has a modest effect on the overall survival (OS), which remains dismal. Additionally, although much needed novel therapeutic approaches for MM are being developed and explored in clinical trials, there is a critical need to invest in prevention research, in which there is a great opportunity to reduce the incidence and mortality from 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 hematite—Fe2O3, goethite—FeO(OH), or jarosite—KFe3(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.

Crystal chemical and structural modifications of erionite fibers leached with simulated lung fluids

Inhalation of erionite has been proven to be the cause of the extended epidemic of malignant mesothelioma occurring in Central Anatolia, Turkey, and of cases of lung diseases in the U.S.A. Its carcinogenicity is three orders of magnitude greater than that of regulated asbestos. Here we report the results of the investigation of the structural and crystal chemical modifications occurring in erionite leached with artificial lysosomal fluid (ALF) and Gamble’s solution. ALF leaching produces a migration of Na+ ions from Ca1 to Ca2 extraframework cationic site, without the occurrence of any significant modification of the chemical composition of the fibers. In contrast, leaching with Gamble’s solution induces a complex ionic-exchange process resulting in a temporary partial replacement of Na+ by Ca2+, coming from the fluid, which is fixed at a third Ca3 cationic site. Subsequently, the exchange process reverses. In fact, Ca2+ is removed from Ca3 and Na+ migrates back to Ca1, the structure being indistinguishable from the starting, unleached material. Such processes seem to be accompanied by a progressive amorphization of fibers. Present data could provide valuable background for a more detailed comprehension of the morphostructural/biological activity relationships inducing pathogenicity.

Abstract 446: BAP1 mutation in mesothelioma and “BAP1 Cancer Syndrome”

Abstract Malignant mesothelioma (MM) is a lethal cancer whose pathogenesis results from complex interactions between host genetics and environmental carcinogens, such as asbestos and erionite fibers. Recently, BAP1 (BRCA associated protein 1) has been identified as a novel MM tumor suppressor gene located at 3p21, a region frequently deleted in MM, which encodes for a deubiquitinase enzyme known to target histones and other proteins. We discovered that germline BAP1 mutations cause a novel cancer syndrome characterized by a significant excess of both pleural and peritoneal MM, uveal and cutaneous melanoma and possibly other tumors. In the same study, we reported that 22% sporadic MM tumors, among the Caucasian population, harbored somatic BAP1 mutations. Several other studies supported a relevant role of BAP1 in MM. However, a significant variation in the frequency of BAP1 mutation was found across different studies and populations. In fact, one research group found BAP1 gene altered in 61% of tumor samples from a Japanese cohort, pointing out to a possible influence of ethnicity on the prevalence of BAP-1 alterations among MM patients. However, the limitations in tumor sample sizes and methodological differences across studies do not allow for conclusive associations. We are now further analyzing BAP1 status and possible clinicopathological associations using different and more sensitive methods, such as MPLA, DNA and RNA sequencing, DNA copy number and methylation. Our preliminary results indicate that, regardless of ethnicity, BAP1 plays a crucial role in MM pathogenesis. More experiments are urgently needed to see whether BAP1 expression could be used in diagnostic, prognostic, or therapeutic settings. The impact of this work will extend to other cancers with BAP1 mutations. Citation Format: Masaki Nasu, Andrea Napolitano, Sandra Pastorino, Mika Tanji, Erin Flores, Francine Baumann, Amy Powers, Giovanni Gaudino, Harvey I. Pass, Haining Yang, Michele Carbone. BAP1 mutation in mesothelioma and “BAP1 Cancer Syndrome”. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 446. doi:10.1158/1538-7445.AM2014-446

Toxicological and epidemiological studies on effects of airborne fibers: Coherence and public 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.

Micro‐Raman spectroscopy identifies crocidolite and erionite fibers in tissue sections

Exposure to asbestos or erionite is associated with malignant mesothelioma (MM) and other diseases. Micro‐Raman spectroscopy and Variable Pressure Scanning Electron Microscopy/Energy Dispersive Spectroscopy were used to identify mineral fibers in histological sections of various tissues taken from mice injected with crocidolite asbestos and erionite fibers. Routine diagnostic histopathological slides of biopsies from erionite‐exposed MM patients from Turkey were also analyzed. We show here that micro‐Raman spectroscopy easily permits the recording of distinct Raman patterns of both crocidolite and erionite fibers, in both murine tissues and in human biopsies. The described findings provide a new powerful and non‐destructive tool to determine the type of fiber exposure in patients with MM and other mineral fiber‐associated diseases. Copyright © 2013 John Wiley & Sons, Ltd.

Analysis of fibrous zeolites in the volcanic deposits of the Viterbo Province, Italy

Since Etrurian age, the Viterbo Province (Central Italy) is famous for its ancient towns carved out of local ignimbrite deposits which geologically represent the sedimentation of pumice-rich, volcano-related pyroclastic flows. Almost the entire study area is geologically characterized by a thick succession of ignimbrites, tephra fallouts and lava flow deposits locally subjected to zeolitization. Among zeolites, fibrous erionite represents a well-known health hazard and so this work aims at locating and quantifying the presence of fibrous zeolites in volcanic deposits of the Viterbo area, suggesting at the same time a standard operational procedure useful in other areas showing the same possible hazard. 41 samples collected in the Viterbo area were analyzed by X-ray powder diffraction, optical and electron microscopy. Fibrous zeolites were detected in five samples and quantified in amounts ranging from 0.35 to 1.66% vol. They generally occur in tetragonal or orthorhombic prismatic habit and showed chemical composition mainly consistent with K-phillipsite. Fibrous zeolites occurred with aspect ratios (mean = 6.3), comparable or lower than those of erionite fibers reported in previous studies and mean diameters >3 μm.

Erionite series minerals: mineralogical and carcinogenic properties

Erionite is a human and animal carcinogen and one of the most toxic minerals known. Erionite deposits have been reported in many countries; however, it is only in the area of three villages of Cappadocia, Turkey, that environmental exposure to erionite has been demonstrated to be the cause of an epidemic of the disease mesothelioma. In the USA, no cases of mesothelioma have been reliably proven to be the result of erionite exposure, though the possibility exists. Erionite samples from three villages of the Cappadocia region were characterized mineralogically and compared with three different standards from the USA. Micro morphological details of erionite minerals using a high-resolution field-emission SEM showed that microstructures of "bundles", "fibers", and "fibrils" are important physical properties of fibrous erionite minerals. Typical lung burden of erionite and asbestos fibers were compared in terms of number of fibers. Assuming the lung burden of fibers in a human mesothelioma victim is about 1 mg, and the hazardous fibers are approximately 1 mum in diameter and 10 mum long, that milligram contains approximately 40 million asbestos and 50 million erionite fibers. These microstructures of erionite minerals draw attention to the concepts of surface area or surface-area-to-volume ratio and their relationship to the carcinogenicity of the mineral. The larger surface area creates a wider platform for mineral-cell interaction and thus more possibilities of proliferative transformation of mesothelial cells. Consequently, understanding the exact mineralogical properties will help determination of the true carcinogenic mechanism(s) of the mineral for prevention and possibly treatment of malignant mesothelioma.

Spotlight

Bertino et al., pp. 12–20 Like asbestos, the mineral erionite can transform human mesothelial cells, leading to malignant mesothelioma (MM). Unlike asbestos, erionite can do its damage without the aid of SV40, according to this study by Bertino et al. The findings could explain the high rate of MM in the Cappadocia region of Turkey, where SV40 has not been isolated. They also suggest that the hazard of exposure to similar fibers should be carefully evaluated. Erionite, a ubiquitous zeolite, is a strong mutagen and induces a high incidence of MM in rats who inhale it. Exposure to erionite fibers leads to the creation of reactive oxygen metabolites from macrophages and turns up transcription of early response proto-oncogenes. Earlier work has shown that asbestos fibers-induced transformation of cells was enhanced by SV40 infection acting through the PI3K/Akt signaling pathway. In the current study, the authors looked at how efficiently erionite transformed human mesothelial cells in the absence of SV40, compared with two varieties of asbestos – amosite and chrysotile. They also investigated signal transduction in the transformed cells to better understand the mechanism by which the mineral fibers spur transformation. Cells exposed to erionite began proliferating faster within 24 hours. The erionite fibers were less toxic to cells than the amosite, allowing a high proliferation rate. Chrysotile asbestos, although not as toxic to cells as amosite, could not promote proliferation. The cells showed the morphologic changes associated with full transformation. Obviously, erionite transforms cells in the absence of SV40. Gorlova et al., pp. 111–118 Relatives of people who have had lung cancer but have never smoked appear to have a higher risk for cancer, particularly young-onset cancers, according to a new case-control study from Gorlova et al. The study, which included nearly 5,000 people, contradicts some earlier reports and could indicate that shared genetic factors could predispose individuals to lung cancer and several other cancers. Several previous studies have reported no increased risk of lung cancer in immediate relatives of lung cancer patients who have not smoked. One study, based on a small number of participants, reported a 6-fold increase in lung cancer patients. Because individuals who have never smoked and who develop lung cancer may represent a distinct, genetically susceptible population, identifying familial aggregation of cancers could help illuminate genetic factors that contribute to lung cancer susceptibility. Gorlova et al. analyzed data from 2,465 relatives of 316 nonsmoking lung cancer patients and 2,441 relatives or 318 never-smoking controls to compare the groups' risk of lung cancer and other cancers. The authors identified a 25% increase in risk of any type of cancer among first-degree relatives of lung cancer patients and a 44% increase in risk of cancer occurring before age 50, compared with relatives of controls. Certainly, shared environmental factors, such as secondhand smoke from parental smoking, could cause multiple family members to develop cancer with no shared genetic vulnerability. In this study, there was a slightly higher number of smokers among relatives of controls than lung cancer cases, and parental smoking does not seem to influence the conclusions. The authors controlled for smoking status and conducted analyses stratified by smoking status, and therefore conclude that genetic factors remain the more likely explanation for the familial aggregation of cancers that they observed. Wang et al., pp. 157–164 The one-two punch of rapamycin and herceptin administered together fights breast cancer better than rapamycin alone, says a new study from Wang et al. The results, which confirm earlier work showing increased susceptibility of certain breast cancer cells to inhibitors of the PI3 kinase signaling pathway – such as rapamycin – could improve breast cancer treatment strategies. About a third of breast cancers overexpress ErbB2, a member of the epidermal growth factor receptor (EGFR) family. Overexpression of ErbB2 is associated with a high relapse rate and poor clinical prognosis, and ErbB2 plays a functional role in cell transformation and mammary cell carcinogenesis. Breast cancer cells that overexpress ErbB2 are particularly sensitive to rapamycin, which interferes with cell cycle progression and halts tumor growth. Rapamycin and its analogs are being developed as anticancer drugs alone and in combination with other agents. In this study, the authors investigated rapamycin's effectiveness when paired with herceptin, a monoclonal antibody against ErbB2. In clinical trials, herceptin achieves a 15-30% response rate in breast cancers overexpressing ErbB2. The new results demonstrate that rapamycin and herceptin together inhibit the growth of ErbB2-overexpressing cancer cells in culture and in mouse xenograft and transgenic models more effectively than each component by itself.

Lung diseases due to environmental exposures to erionite and asbestos in Turkey

Asbestos deposits have been used locally by the rural inhabitants of Central and Southeastern Anatolia for domestic purposes for many years. Mineralogical analysis revealed that tremolite is the most prominent asbestos type found in the region. There is in addition another mineral fiber found particularly in three villages located in the Cappadocian region of Central Anatolia (zeolite villages). This is a non-asbestos mineral, which has been identified as the fibrous zeolite, erionite. This fiber is present in the volcanic tuffs, which are used as building stone. Hence, exposure to erionite fibers is always possible in the houses, annexes, and streets of the villages. It has been demonstrated that both asbestos and erionite cause a variety of benign and malignant chest diseases. Among the diseases, calcified pleural plaques (CPP) are the most frequently seen and may be used as an indicator of mineral fiber exposure. Asbestos and erionite exposure are the main causes of malignant mesotheliomas in Turkey. In zeolite villages malignant mesothelioma is responsible for more than 50% of the total deaths. A recent study showed that simian virus 40 is not a cofactor in the pathogenesis of environmental malignant mesothelioma in Turkey. An additional recent genetic–epidemiological study showed that there are some families, which are genetically predisposed to mesothelioma.

Patterns of c-fosand c-junProto-oncogene Expression, Apoptosis, and Proliferation in Rat Pleural Mesothelial Cells Exposed to Erionite or Asbestos Fibers

Erionite, a naturally occurring fibrous zeolite, is associated with the development of nonmalignant and malignant lung diseases and is more carcinogenic than asbestos fibers in man and rodent inhalation models of disease. To investigate the possible molecular mechanisms of erionite-induced toxicity and carcinogenesis and whether cationic content of erionite fibers was important, we examined c-fosand c-junmRNA levels, activator protein-1 (AP-1) binding to DNA, and changes in cell proliferation and apoptosis in rat pleural mesothelial (RPM) cells exposed to different cation-substituted erionite fibers or crocidolite asbestos at various concentrations (1, 5, or 10 μg/cm2dish) at time periods from 8 to 48 h after addition of minerals. c-fosmRNA levels in cells exposed to equal weight concentrations of various erionites and crocidolite fibers were increased comparably. When compared to other fibers, Na-erionite caused significantly increased levels of c-junmRNA at lower mass concentrations (1 and 5 μg/cm2) than crocidolite asbestos, but comparable AP-1 binding to DNA. In comparison to untreated controls, numbers of RPM cells incorporating 5′-bromodeoxyuridine (BrdU) were increased dramatically after exposure to asbestos or Na-erionite at 5 and 10 μg/cm2. Significant dose-dependent increases in apoptosis were observed with asbestos at all time points, whereas erionites failed to induce apoptosis at 8 or 24 h, with minimal induction at higher concentrations than asbestos at 48 h. These data suggest that erionite increases the balance between cell proliferation (and/or abnormal DNA repair) and apoptosis, a normal mechanism of elimination of transformed or proliferating cells.

Fluorescence imaging of reactive oxygen metabolites generated in single macrophage cells (NR8383) upon phagocytosis of natural zeolite (erionite) fibers.

In this paper we address the phenomenon of reactive oxygen metabolite generation subsequent to phagocytosis of mineral fibers by macrophages. Natural erionite fibers were chosen because of their established toxicity. Macrophages (cell line NR8383) were loaded with the dye 5-(and 6)-carboxy-2',7'-dichlorodihydrofluorescein diacetate and exposed to erionite particles by centrifuging cells and fibers together to effect adherence. Reactive oxygen metabolite generation was examined by monitoring the fluorescence of oxidized dye formed via the reaction with oxygen species produced during phagocytosis. Individual cells were repeatedly scanned for up to 2 hr to monitor the evolution of this fluorescence. It was found that erionite-exposed cells had a mean total fluorescence of three times that of controls during the first 35 min, declining to two times that of controls at 35-60 min and about the same level as that of controls at 60-80 min. Ultrastructural studies of similarly treated aliquots of cells showed marked variation in size and numbers of the phagocytized particles. This study demonstrates that intracellular oxidation can be monitored on a single cell basis over a period of time. Quantitative studies are in progress to establish the relationship between the phagocytized particulate load and the extent of fluorescence.

Fluorescence Imaging of Reactive Oxygen Metabolites Generated in Single Macrophage Cells (NR8383) upon Phagocytosis of Natural Zeolite (Erionite) Fibers

In this paper we address the phenomenon of reactive oxygen metabolite generation subsequent to phagocytosis of mineral fibers by macrophages. Natural erionite fibers were chosen because of their established toxicity. Macrophages (cell line NR8383) were loaded with the dye 5-(and 6)-carboxy-2',7'-dichlorodihydrofluorescein diacetate and exposed to erionite particles by centrifuging cells and fibers together to effect adherence. Reactive oxygen metabolite generation was examined by monitoring the fluorescence of oxidized dye formed via the reaction with oxygen species produced during phagocytosis. Individual cells were repeatedly scanned for up to 2 hr to monitor the evolution of this fluorescence. It was found that erionite-exposed cells had a mean total fluorescence of three times that of controls during the first 35 min, declining to two times that of controls at 35-60 min and about the same level as that of controls at 60-80 min. Ultrastructural studies of similarly treated aliquots of cells showed marked variation in size and numbers of the phagocytized particles. This study demonstrates that intracellular oxidation can be monitored on a single cell basis over a period of time. Quantitative studies are in progress to establish the relationship between the phagocytized particulate load and the extent of fluorescence.

A Proposed Control Limit for Exposure to Airborne Erionite Fibers

Abstract The unique physical and chemical properties of the zeolite minerals have resulted in their use in many industrial processes. Environmental exposures to erionite, a commonly fibrous zeolite, have been linked to elevated incidence of malignant pleural mesotheliomas and associated pleural disorders through epidemiological investigations. The presence of erionite in the workplace, with its documented relationship to elevated rates of pleural malignancies in environmentally exposed populations, requires that individuals exposed to the mineral during the course of their work take precautions to avoid excessive airborne exposures to the mineral. A review of relevant environmental, toxicological, and epidemiological literature was undertaken to quantify the effects of erionite exposure. This review identified erionite as a potent mesothelioma risk agent. The risks were compared to those accepted by the U.S. Department of Labor Occupational Safety and Health Administration in the promulgation of the current asbestos permissible exposure limit. We recommend an 8-hour exposure limit of 0.0007 fibers of erionite per cubic centimeter of air based on comparison of the mortality data from an environmentally exposed population with the excess mortality risk accepted by the Occupational Safety and Health Administration in the 1994 asbestos permissible exposure limit. The proposed control limit is readily measured by current analytical techniques and may be used to assess the adequacy of respiratory protective equipment and other control measures supplied to exposed worker populations.