Assessment of the pathogenic potential of asbestiform vs. nonasbestiform particulates (cleavage fragments) in in vitro (cell or organ culture) models and bioassays

A review of the mesotheliogenic potency of cleavage fragments found in talc

It has long been recognized that amphibole minerals, such as cleavage fragments of tremolite and anthophyllite, may exist in some talc deposits. We reviewed the current state of the science regarding the factors influencing mesotheliogenic potency of cleavage fragments, with emphasis on those that may co-occur in talc deposits, including dimensional and structural characteristics, animal toxicology, and the most well-studied cohort exposed to talc-associated cleavage fragments. Based on our review, multiple lines of scientific evidence demonstrate that inhaled cleavage fragments associated with talc do not pose a mesothelioma hazard.

Environmental asbestos exposure from nephrite jade mining and lung cancer

BACKGROUND

Nephrite is an asbestos mineral composed of tremolite and actinolite. Fengtian is a community where nephrite was mined between 1970 and 1980 and asbestos was mined between 1960 and 1985. The lung cancer risk to the surrounding community is unknown.

AIMS

To analyse the trend of lung cancer caused by environmental contamination from nephrite mining.

METHODS

We conducted a field survey of nephrite mines and tracked new cases of lung cancer from 1980 to 2019. We calculated the age-standardized incidence rates (ASIRs) and applied join-point regression to examine the lung cancer trend. We assessed the age effect, period effect, and birth cohort effect on lung cancer risk.

RESULTS

The nephrite mines were contaminated with chrysotile and tremolite/actinolite asbestos. A total of 278 new cases of lung cancer were reported during the study period. There was an apparent age effect and a slight period effect for lung cancer. After adjustment for the age and period effects, the birth cohort born between 1970 and 1980 during the period of nephrite mass production had the highest relative risk compared with other birth cohorts. The ASIR of lung cancer increased significantly from 1980 to 2010 (the annual percentage change = 6.8 %, 95 % CI: 4.0-9.7 %, P < 0.01) and then decreased 30 years after the cessation of nephrite jade mining.

CONCLUSION

Nephrite mining increases the risk of lung cancer in nearby communities.

Banning asbestos in talcum powder: Time for action in India

Long-term use of asbestos-contaminated talcum power has been reported to be the main causative agent for carcinogenesis in many research studies. In recent developments Johnson & Johnson has lost multimillion-dollar lawsuits for being associated with the development of mesothelioma and ovarian cancer by its talc-based baby powder. In May 2020, the company announced, the end of the sale of its baby powder in the USA and Canada and in August 2022, announced the global discontinuation by 2023. However, in India vast proportions of people are using talc-based baby powder and the products are readily available in the market. The purpose of this communication is to create awareness and draw attention of authorities for effective regulation, including prohibition of sale and retraction of the contaminated talc-based products from the Indian market at the earliest.

An updated review of diffuse mesothelioma of the pleura - A sentinel health event of potential elongate mineral particle pathogenicity

There are approximately 400 inorganic minerals in the Earth's crust, some of which can be encountered as elongate mineral particles [EMPs] with dimensional characteristics similar to the six minerals known as asbestos and other asbestiform amphiboles with established human pathogenicity. In addition, the rapidly developing field of nanotechnology is producing an ever-increasing array of high aspect ratio engineered nanomaterials [HARNs] with physical dimensions and biodurability similar to the asbestos fiber types with recognized pathogenic potential. Many of these non-asbestos/non-asbestiform EMPs and HARNs with the potential for aerosolization into the breathing zones of workers and in individuals in non-occupational environments have not yet been thoroughly studied with respect to their potential human pathogenicity, a fact which obviously poses concerns for both occupational health and public health professionals. On the basis of dose-response considerations it seems reasonable to infer that if any of these non-regulated EMPs or HARNs actually are pathogenic, then those mineral fiber exposure-induced disorders associated with the lowest cumulative exposure doses of the commercial amphibole types of asbestos, that is, diffuse mesothelioma of the pleura, and its non-malignant correlate of benign parietal pleural plaques, are those which are most likely to occur following inhalational exposures to any of the non-regulated EMPs and HARNs. Because of that observation, this paper reviews certain aspects of diffuse mesothelioma, including a summary of recent changes in the nomenclature of diffuse mesothelioma of the pleura; of both the descriptive and the analytical epidemiology of the disease; of the etiologies of mesothelioma, both "exposure" related and endogenous in nature; and of the asbestos population attributable fraction for diffuse mesotheliomas in the USA, both historically and in the future.

Carbon nanotube pathogenicity conforms to a unified theory for mesothelioma causation by elongate materials and fibers

The purpose of this review is to elucidate how dimensional and durability characteristics of high aspect ratio nanomaterials (HARN), including carbon nanotubes (CNT) and metal nanowires (MeNW), contribute to understanding the fiber pathogenicity paradigm (FPP), including by explaining the structure-activity relationships (SAR) of a diverse range of natural and synthetic elongate materials that may or may not contribute to mesothelioma development in the lung. While the FPP was originally developed to explain the critical importance of asbestos and synthetic vitreous fiber length, width, aspect ratio and biopersistence in mesothelioma development, there are a vast number of additional inhalable materials that need to be considered in terms of pathogenic features that may contribute to mesothelioma or lack thereof. Not only does the ability to exert more exact control over the length and biopersistence of HARNs confirm the tenets of the FPP, but could be studied by implementating more appropriate toxicological tools for SAR analysis. This includes experimentation with carefully assembled libraries of CNTs and MeNWs, helping to establish more precise dimensional features for interfering in lymphatic drainage from the parietal pleura, triggering of lysosomal damage, frustrated phagocytosis and generation of chronic inflammation. The evidence includes data that long and rigid, but not short and flexible multi-wall CNTs are capable of generating mesotheliomas in rodents based on an adverse outcome pathway requiring access to pleural cavity, obstruction of pleural stomata, chronic inflammation and transformation of mesothelial cells. In addition to durability and dimensional characteristics, bending stiffness of CNTs is a critical factor in determining the shape and rigidity of pathogenic MWCNTs. While no evidence has been obtained in humans that CNT exposure leads to a mesothelioma outcome, it is important to monitor exposure levels and health effect impacts in workers to prevent adverse health outcomes in humans.

Cytotoxicity of fibrous antigorite from New Caledonia

Exposure to asbestos and asbestos-like minerals has been related to the development of severe lung diseases, including cancer and malignant mesothelioma (MM). A high incidence of non-occupational MM was observed in New Caledonia (France) in people living in proximity of serpentinite outcrops, containing chrysotile and fibrous antigorite. Antigorite is a magnesium silicate, which shares with chrysotile asbestos the chemical formula. To achieve information on antigorite toxicity, we investigated the physico-minero-chemical features relevant for toxicity and cellular effects elicited on murine macrophages (MH-S) and alveolar epithelial cells (A549) of three fibrous antigorites (f-Atg) collected in a Caledonian nickel lateritic ore and subjected to supergene alteration. Field Atg were milled to obtain samples suitable for toxicological studies with a similar particle size distribution. UICC chrysotile (Ctl) and a non-fibrous antigorite (nf-Atg) were used as reference minerals. A high variability in toxicity was observed depending on shape, chemical alteration, and surface reactivity. The antigorites shared with Ctl a similar surface area (16.3, 12.1, 20.3, 13.4, and 15.6 m²/g for f-Atg1, 2, 3, nf-Atg, and Ctl). f-Atg showed different level of pedogenetic weathering (Ni depletion f-Atg1 ≪ f-Atg2 and 3) and contained about 50% of elongated mineral particles, some of which exhibited high aspect ratios (AR > 10 μm, 20%, 26%, 31% for f-Atg1, 2, and 3, respectively). The minerals differed in bio-accessible iron at pH 4.5 (f-Atg1 ≪ f-Atg3, < f-Atg2, nf-Atg < Ctl), and surface reactivity (ROS release in solution, f-Atg1 ≪ f-Atg2, 3, nf-Atg, and Ctl). f-Atg2 and f-Atg3 induced oxidative stress and pro-inflammatory responses, while the less altered, poorly reactive sample (f-Atg1) induced negligible effects, as well nf-Atg. The slow dissolution kinetics observed in simulated body fluids may signal a high biopersistence. Overall, our work revealed a significative cellular toxicity of f-Atg that correlates with fibrous habit and surface reactivity.

Dimensions of elongate mineral particles and cancer: A review

CONTEXT

Based on a decade-long exploration, dimensions of elongate mineral particles are implicated as a pivotal component of their carcinogenic potency. This paper summarizes current understanding of the discovered relationships and their importance to the protection of public health.

OBJECTIVES

To demonstrate the relationships between cancer risk and dimensions (length, width, and other derivative characteristics) of mineral fibers by comparing the results and conclusions of previously published studies with newly published information.

METHODS

A database including 59 datasets comprising 341,949 records were utilized to characterize dimensions of elongate particles. The descriptive statistics, correlation and regression analysis, combined with Monte Carlo simulation, were used to select dimensional characteristics most relevant for mesothelioma and lung cancer risk prediction.

RESULTS

The highest correlation between mesothelioma potency factor and weight fraction of size categories is achieved for fibers with lengths >5.6 μm and widths ≤0.26 μm (R = 0.94, P < 0.02); no statistically significant potency was found for lengths <5 μm. These results are consistent with early published estimations, though are derived from a different approach. For combinations of amphiboles and chrysotile (with a consideration of a correction factor between mineral classes), the potency factors correlated most highly with a fraction of fibers longer than 5 μm and thinner than 0.2 μm for mesothelioma, and longer than 5 μm and thinner than 0.3 μm for lung cancer. Because the proportion of long, thin particles in asbestiform vs. non-asbestiform dusts is higher, the cancer potencies of the former are predicted at a significantly higher level. The analysis of particle dimensionality in human lung burden demonstrates positive selection for thinner fibers (especially for amosite and crocidolite) and prevailing fraction of asbestiform habit.

CONCLUSION

Dimensions of mineral fibers can be confirmed as one of the main drivers of their carcinogenicity. The width of fibers emerges as a primary potency predictor, and fibers of all widths with lengths shorter than 5 μm seem to be non-impactful for cancer risk. The mineral dust with a fibrous component is primarily carcinogenic if it contains amphibole fibers longer than 5 μm and thinner than 0.25 μm.

Mechanisms and shapes of causal exposure-response functions for asbestos in mesotheliomas and lung cancers

This paper summarizes recent insights into causal biological mechanisms underlying the carcinogenicity of asbestos. It addresses their implications for the shapes of exposure-response curves and considers recent epidemiologic trends in malignant mesotheliomas (MMs) and lung fiber burden studies. Since the commercial amphiboles crocidolite and amosite pose the highest risk of MMs and contain high levels of iron, endogenous and exogenous pathways of iron injury and repair are discussed. Some practical implications of recent developments are that: (1) Asbestos-cancer exposure-response relationships should be expected to have non-zero background rates; (2) Evidence from inflammation biology and other sources suggests that there are exposure concentration thresholds below which exposures do not increase inflammasome-mediated inflammation or resulting inflammation-mediated cancer risks above background risk rates; and (3) The size of the suggested exposure concentration threshold depends on both the detailed time patterns of exposure on a time scale of hours to days and also on the composition of asbestos fibers in terms of their physiochemical properties. These conclusions are supported by complementary strands of evidence including biomathematical modeling, cell biology and biochemistry of asbestos-cell interactions in vitro and in vivo, lung fiber burden analyses and epidemiology showing trends in human exposures and MM rates.

Pathogenic Potential of Respirable Spodumene Cleavage Fragments following Application of Regulatory Counting Criteria for Asbestiform Fibres

Health risks from exposure to lithium-bearing spodumene cleavage fragments are unknown. While asbestiform fibres can lead to fibrosis, mesothelioma and lung cancer, controversy remains whether non-asbestiform cleavage fragments, having equivalent dimensions, elicit similar pathologic responses. The mineralogy of respirable particles from two alpha (α)-spodumene concentrate grades (chemical and technical) were characterised using semi-quantitative X-ray diffraction (XRD). Particles were measured using scanning electron microscopy (SEM) and the dimensions (length [L], diameter [D], aspect ratio [AR]) applied to regulatory counting criteria for asbestiform fibres. Application of the current World Health Organization (WHO) and National Occupational Health and Safety Commission (NOHSC) counting criteria, L ˃ 5 µm, D ˂ 3 µm, AR ˃ 3:1, to 10 SEM images of each grade identified 47 countable particles in the chemical and 37 in the technical concentrate test samples. Of these particles, 17 and 16 in the chemical and technical test samples, respectively, satisfied the more rigorous, previously used Mines Safety and Inspection Regulations 1995 (Western Australia [WA]) criteria, L ˃ 5 µm and D ≤ 1 µm. The majority of the countable particles were consistent with α-spodumene cleavage fragments. These results suggest elongated α-spodumene particles may pose a health risk. It is recommended the precautionary principle be applied to respirable α-spodumene particles and the identification and control of dust hazards in spodumene extraction, handling and processing industries be implemented.

Authors' response to the letter to the editor on "characterization of asbestos exposures associated with the use of facial makeups"

We appreciate the opportunity to respond to the comments of the letter writer. The writer states in his Letter to the Editor that the findings in our publication are not interpretable and/or cannot be generalized due to the lack of understanding of the source mine and bulk content of the cosmetic talc used in the facial makeups. In brief, we performed an exposure simulation study using established industrial hygiene methods, planned and conducted by Certified Industrial Hygienists (CIHs), to assess asbestos exposures during the use of facial makeups that were found to contain very low levels of asbestos below the conventional detection limits of X-ray diffraction and polarized light microscopy. In total, 54 personal air samples and 72 area samples were collected from six different products. Out of the 126 samples collected and analyzed, asbestos was only found in eight samples (five personal samples and three area samples). A 95th percentile 24-h time-weighted average (TWA) result of 0.00008 fibers/cubic centimeter was calculated based on censored data and an assumed three applications per day. We believe these results may be of utility to understand the risk of low-level asbestos content in facial makeups regardless of source or bulk content, as described in our study, and do not find the writer's assertion of generalizability or interpretability to be compelling reasons not to apply our results, as is, for prospective purposes.

Updated Italian cohort data continues to confirm lack of mesothelioma risk in pooled cohort of international cosmetic talc miners and millers

OBJECTIVES

To assess potential mesothelioma risk following inhalation of cosmetic talc, we updated previous iterations of a pooled cohort analysis, post-study statistical power analysis, and confidence interval function analysis for a pooled cohort of international cosmetic talc miners/millers given new Italian cohort data.

METHODS

Five cohorts of cosmetic talc miners/millers were pooled. Expected numbers of mesotheliomas for each cohort were reported by the original authors. We based our post-study statistical power analysis on an a priori one-sided significance level of 0.05, and exact Poisson and approximate distribution probabilities. To evaluate the confidence interval function for the observed pooled mesothelioma standardized mortality ratios (SMRs), we calculated the probability for the upper 100(1-2α)% confidence limit that equals various SMRs of interest.

RESULTS

The pooled cohorts generated a total observation time of 135,524.38 person-years. Overall, 4.14 mesotheliomas were expected (mid-value estimate), though only one case of mesothelioma has been confirmed in the pooled cohort to date. We calculated 71% and 87% post-study power to detect a 2.5-fold or greater and a 3.0-fold or greater increase in mesothelioma, respectively. Our complimentary confidence interval function analysis demonstrated that the probability that the true mesothelioma SMR for the pooled cohort was at or above 2.0 or at or above 3.0 was 0.00235 and 0.00005, respectively.

CONCLUSIONS

Based on the updated results of our various analyses, the current epidemiological evidence from cosmetic talc miner/miller cohort studies continues to not support the hypothesis that the inhalation of cosmetic talc is associated with an increased risk of mesothelioma.

Dimensional characteristics of the major types of amphibole mineral particles and the implications for carcinogenic risk assessment

Context: Though some significant advances have been made in recent decades to evaluate the importance of size and morphology (habit) of elongate mineral particles (EMPs), further research is needed to better understand the role of each dimensional metric in determining the levels of cancer potency.Objective: To determine dimensional parameters most relevant for predicting cancer potency of durable elongate particles, specifically amphibole and durable silicate minerals generally.Methods: A database on dimensional and other relevant characteristics of elongate amphibole mineral particles was created, containing particle-by-particle information for 128 099 particles. Integral statistical characteristics on dimensionality of various amphibole types and morphological habits of EMPs were calculated, compared, and correlated with published mesothelioma and lung cancer potency factors.Results: The highest absolute Pearson correlation (r = 0.97, r² = 0.94, p < 0.05) was achieved between mesothelioma potency (R_M) and specific surface area. The highest correlation with adjusted lung cancer potency was found with particle aspect ratio (AR) (r = 0.80, r² = 0.64, p < 0.05). Cluster analysis demonstrates that fractions of thin fibers (width less than 0.15 and 0.25 µm) also closely relate both to lung cancer and R_M. Asbestiform and non-asbestiform populations of amphiboles significantly differ by dimensionality and carcinogenic potency.Conclusions: Dimensional parameters and morphological habits of EMPs are the main drivers for the observable difference in cancer potency among amphibole populations.

Letter to the Editor: Epidemiology holds a key to the validation of toxicological models for elongate mineral particles

•

Human epidemiological data remains the main source for information about health effects of elongate mineral particles.

•

There are limitations in using animal data (in vitro and in vivo) for quantification of risk.

•

Toxicological modeling is one of the most promising tools to estimate risks for workers and communities.

The authors reply to the comments of Drs. Gualtieri and di Giuseppe on the short communication by Wylie and Korchevskiy – Carcinogenicity of fibrous glaucophane: how to fill data gaps? (2021 Current Research in Toxicology Volume 2, pp. 202–203). The role of epidemiology in establishing the toxicity of elongate mineral particles is emphasized. The validation of quantitative structure–activity relationship (QSAR) models by disease outcome is mentioned as one of the most important tools in advancing the new approaches in mineral particle toxicology.

Dimensional determinants for the carcinogenic potency of elongate amphibole particles

CONTEXT

Carcinogenic properties of particulates depend, among other factors, on dimensional characteristics that affect their ability to reach sensitive tissue, to be removed or retained, and to interact with the cells.

OBJECTIVE

To model mesothelioma and lung cancer potency of amphibole particles based on their dimensional characteristics and mineral habit (asbestiform vs. nonasbestiform) utilizing epidemiological data and detailed size information.

METHODS

The datasets from recently created depository of dimensional information of elongate mineral particles were used to correlate mesothelioma and lung cancer potency with the fraction of particles in a specific size range and the ratio of length and width in different powers. In addition, the cancer potency factors were estimated and compared for 30 asbestiform, 15 nonasbestiform, and 10 mixed datasets.

RESULTS

For particles longer than 5 µm, the highest correlation with mesothelioma potency was achieved for width <0.22 µm, and with lung cancer <0.28 µm. The statistical power of the correlation was observed to lose significance at a maximum width of 0.6-0.7 µm. Mesothelioma potency correlated with length in the power of 1.9 divided by width in the power of 2.97, lung cancer potency with length in the power of 0.4 divided by width in the power of 1.17. The predicted cancer potencies of asbestiform, nonasbestiform, and mixed categories were significantly different.

CONCLUSION

While additional studies in this direction are warranted, this paper should serve as an additional confirmation for the role of fiber dimensions in the carcinogenicity of amphibole elongate mineral particles (EMPs).

Integration of Evidence on Community Cancer Risks from Elongate Mineral Particles in Silver Bay, Minnesota

The potential for cancer-related risks to community members from ambient exposure to elongate mineral particles (EMPs) in taconite processing has not been formally evaluated. We evaluated 926 ambient air samples including 12,928 EMPs (particle structures with length-to-width ratio ≥3:1) collected over 26 years near a taconite processing facility in Silver Bay, Minnesota. Eighty-two percent of EMPs were ≤3 μm in length and 97% of EMPs had an average aspect ratio <20:1. A total of 935 (7.3%) EMPs had length >5 μm and AR ≥3:1. Average ambient concentration of NIOSH countable amphibole EMPs over all years was 0.000387 EMPs per cubic centimeter (EMP/cm³ ). Of 12,765 nonchrysotile EMPs, the number of amphiboles with length and width dimensions that correlate best with asbestos-related carcinogenicity ranged from four (0.03%) to 13 (0.1%) and the associated ambient amphibole air concentrations ranged from 0.000003 to 0.000007 EMP/cm³ . After 65 years of taconite processing in Silver Bay, evidence of an increased risk of mesothelioma and lung cancer in community members who did not work in the taconite industry is lacking. The absence of an increased risk of asbestos-related cancer in the Silver Bay community is coherent with supporting evidence from epidemiological and toxicological studies, as well as ambient exposure data and lake sediment data collected in Minnesota Iron Range communities. Collectively, the data provide consistent evidence that nonasbestiform amphibole minerals lack the carcinogenic potential exhibited by amphibole asbestos.

Potential airborne asbestos exposures in dentistry: a comprehensive review and risk assessment

Chrysotile was formerly used in the manufacture of casting ring liner (CRL) and periodontal dressing powder (PDP). The purpose of this study was to describe the potential for airborne asbestos exposure among dental professionals who may have used these products and to assess their risk of asbestos-related disease (ARD). Task-specific exposure data associated with CRL and PDP were identified and compared to regulatory standards for asbestos and health-based benchmarks. Personal airborne fiber concentrations ranged from 0.008-3.5 f/cc by PCM (duration: 3-420 minutes) for CRL (tearing, placement), and from <0.0044-<0.297 f/cc by PCM (duration: 5-28 minutes) for PDP (mixing). Eight-hour time-weighted average (TWA) exposures were calculated using the reported task-based airborne fiber concentrations and associated sampling durations. For CRL tasks, the upper-bound calculated 8-hour TWA of 0.022 f/cc (tearing, placement) did not exceed regulatory standards for asbestos (≥0.1 f/cc). All samples collected during the mixing of PDP resulted in non-measurable fiber concentrations. The greatest estimated cumulative asbestos exposure for dental professionals using CRL (tearing, placement) of 0.33 f/cc-years is well below "best estimate", published chrysotile no-observed-adverse-effect-levels (NOAEL) for ARD (lung cancer = 89-168 f/cc-years; pleural mesothelioma = 208-415 f/cc-years). As such, the use of asbestos-containing CRL and/or PDP is not expected to pose an increased risk of ARD among dental professionals. This conclusion is consistent with the lack of an increased risk of ARD reported in epidemiological studies of these occupations.

Asbestiform Amphiboles and Cleavage Fragments Analogues: Overview of Critical Dimensions, Aspect Ratios, Exposure and Health Effects

The term asbestos refers to a group of serpentine (chrysotile) and amphibole (amosite, crocidolite, anthophyllite, tremolite and actinolite) minerals with a fibrous habit. Their chemical-physical properties make them one of the most important inorganic materials for industrial purposes and technological applications. However, the extraction, use and marketing of these minerals have been prohibited due to proven harmful effects, mainly involving the respiratory system. In addition to the known six minerals classified as asbestos, the natural amphiboles and serpentine polymorphs antigorite and lizardite, despite having the same composition of asbestos, do not have the same morphology. These minerals develop chemical and geometric (length > 5 μm, width < 3 μm and length: diameter > 3:1), but not morphological, analogies with asbestos, which is regulated by the WHO. The debate about their potential hazardous properties is open and ongoing; therefore, their morphological characterization has a key role in establishing a reliable asbestos hazard scenario. This review focuses on evaluating the most relevant papers, evidencing the need for a reappraisal. Different in vitro, in vivo and epidemiological studies report information about cleavage fragments with critical dimensions similar to asbestos fibres, but very few works target fragments below 5 µm in length. Breathable smaller fibres could have deleterious effects on human health and cannot be disregarded from the risk assessment process. Furthermore, a few studies suggest that the carcinogenic nature of short fibres is not excluded. This review highlights that it is worth investigating the effects of this size range of elongated mineral particles and fibres.

A quantitative weight of evidence assessment of Hill's guidelines for causal inference for cosmetic talc as a cause of mesothelioma

Cosmetic talc has been suggested to cause mesothelioma. To assess a potential causal relationship between cosmetic talc and mesothelioma, a quantitative weight of evidence analysis was performed in accordance with Hill's nine original guidelines for causal inference using a published empirical model to weight each respective guideline. Various epidemiological, toxicological, and exposure studies related to cosmetic talc and risk of mesothelioma were included in an evaluation of each of Hill's guidelines. Probabilities that the guidelines were true were assigned based on expert judgment. We applied a sensitivity analysis to evaluate the variability of our probability estimates. The overall probability of causality for cosmetic talc and mesothelioma was approximately 1.29% (range: 0.73%-3.96%). This low probability of causality supports the conclusion that cosmetic talc is not related to the development of mesothelioma.

Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes

Human exposures to asbestiform elongate mineral particles (EMP) may lead to diffuse fibrosis, lung cancer, malignant mesothelioma and autoimmune diseases. Cleavage fragments (CF) are chemically identical to asbestiform varieties (or habits) of the parent mineral, but no consensus exists on whether to treat them as asbestos from toxicological and regulatory standpoints. Alveolar macrophages (AM) are the first responders to inhaled particulates, participating in clearance and activating other resident and recruited immunocompetent cells, impacting the long-term outcomes. In this study we address how EMP of asbestiform versus non-asbestiform habit affect AM responses. Max Planck Institute (MPI) cells, a non-transformed mouse line that has an AM phenotype and genotype, were treated with mass-, surface area- (s.a.), and particle number- (p.n.) equivalent concentrations of respirable asbestiform and non-asbestiform riebeckite/tremolite EMP for 24 h. Cytotoxicity, cytokines secretion and transcriptional changes were evaluated. At the equal mass, asbestiform EMP were more cytotoxic, however EMP of both habits induced similar LDH leakage and decrease in viability at s.a. and p.n. equivalent doses. DNA damage assessment and cell cycle analysis revealed differences in the modes of cell death between asbestos and respective CF. There was an increase in chemokines, but not pro-inflammatory cytokines after all EMP treatments. Principal component analysis of the cytokine secretion showed close clustering for the s.a. and p.n. equivalent treatments. There were mineral- and habit-specific patterns of gene expression dysregulation at s.a. equivalent doses. Our study reveals the critical nature of EMP morphometric parameters for exposure assessment and dosing approaches used in toxicity studies.

Potential Airborne Asbestos Exposure and Risk Associated with the Historical Use of Cosmetic Talcum Powder Products

Over time, concerns have been raised regarding the potential for human exposure and risk from asbestos in cosmetic-talc-containing consumer products. In 1985, the U.S. Food and Drug Administration (FDA) conducted a risk assessment evaluating the potential inhalation asbestos exposure associated with the cosmetic talc consumer use scenario of powdering an infant during diapering, and found that risks were below levels associated with background asbestos exposures and risk. However, given the scope and age of the FDA's assessment, it was unknown whether the agency's conclusions remained relevant to current risk assessment practices, talc application scenarios, and exposure data. This analysis updates the previous FDA assessment by incorporating the current published exposure literature associated with consumer use of talcum powder and using the current U.S. Environmental Protection Agency's (EPA) nonoccupational asbestos risk assessment approach to estimate potential cumulative asbestos exposure and risk for four use scenarios: (1) infant exposure during diapering; (2) adult exposure from infant diapering; (3) adult exposure from face powdering; and (4) adult exposure from body powdering. The estimated range of cumulative asbestos exposure potential for all scenarios (assuming an asbestos content of 0.1%) ranged from 0.0000021 to 0.0096 f/cc-yr and resulted in risk estimates that were within or below EPA's acceptable target risk levels. Consistent with the original FDA findings, exposure and corresponding health risk in this range were orders of magnitude below upper-bound estimates of cumulative asbestos exposure and risk at ambient levels, which have not been associated with increased incidence of asbestos-related disease.

Occupational Lung Disease

Occupational exposures are a major cause of lung disease and disability worldwide. This article reviews the broad range of types of occupational lung diseases, including airways disease, pneumoconioses, and cancer. Common causes of occupational lung disease are reviewed with specific examples and clinical features. Emphasis on the importance of a detailed history to make an accurate diagnosis of an occupational lung disease is discussed.

Measurement of elongate mineral particles: What we should measure and how do we do it?

The length distributions of single fibrils of Coalinga, UICC-B and wet dispersed chrysotile were measured by transmission electron microscopy (TEM). It was found that the distributions significantly diverged above approximately 10 μm (μm) in length, corresponding to differences in published results of animal experiments. This result is in contrast to published data in which counting of an insufficient number of fibers resulted in an erroneous conclusion that the length distribution of Coalinga chrysotile fibrils was indistinguishable from those of other sources of chrysotile. The size distributions of the respirable particle size fractions from acknowledged tremolite asbestos samples were found to be dominated by elongate particles longer than 5 μm that are within the dimensional range of non-asbestiform amphiboles. Prior studies have shown that these elongate particles obscure a correlation between a specific size range of particles and results of animal implantation studies that used tremolite of various morphologies. In the prior studies, a reference protocol was developed from four crushed non-asbestiform amphiboles to differentiate the size range of amphibole particles that correlates with the mesothelioma frequencies observed in the animal studies. In the work reported here, this correlation was tested with TEM analyses of amphiboles from Libby, MT, Sparta, NJ and Homestake mine, Lead, SD, which represent known environmental/occupational situations. Further TEM analyses of the tremolite samples used in the original animal implantation studies have also shown that the numbers of elongate tremolite particles with lengths ≤5 μm implanted into the animals are not correlated with the observed mesothelioma frequencies.

Pleural abnormalities and exposure to elongate mineral particles in Minnesota iron ore (taconite) workers

BACKGROUND

Iron ore (taconite) mining and processing are an important industry in northern Minnesota and western Michigan. Concerns around exposures have centered largely on exposure to non-asbestiform amphibole elongate mineral particles (EMPs) found in the eastern portion of the Minnesota iron range.

METHODS

A cross sectional survey was undertaken of current and former taconite workers and spouses along with a detailed exposure assessment. Participants provided an occupational history and had a chest radiograph performed.

RESULTS

A total of 1188 workers participated. Potential exposures to non-amphibole EMPs were evident across multiple jobs in all active mines. Pleural abnormalities were found in 16.8% of workers. There was an association of pleural abnormalities with cumulative EMP exposure that was not specific to the eastern portion of the range.

CONCLUSION

There was evidence of a mild to moderate increase in pleural abnormalities in this population of miners, associated with geographically non-specific cumulative EMP exposure.

A review of mortality associated with elongate mineral particle (EMP) exposure in occupational epidemiology studies of gold, talc, and taconite mining

BACKGROUND

Mining of gold, taconite, and talc may involve exposure to elongate mineral particles (EMP). The involved EMPs are typically non-asbestiform, include dimensions that regulatory definitions exclude, and have been less studied.

METHODS

A review of the literature was undertaken for this exposure and occupational epidemiological studies that occur in gold, talc, and taconite mining.

RESULTS

Quantitative EMP exposure information in these industries is incomplete. However, there are consistent findings of pneumoconiosis in each of these types of mining. A recent case-control study suggests a possible association between this exposure and mesothelioma. Lung cancer is inconsistently reported in these industries and is an unlikely outcome of non-asbestiform EMP exposure. There is evidence of cardiovascular mortality excess across all of these types of mining.

CONCLUSIONS

Non-malignant respiratory disease and cardiovascular mortality have been consistently increased in these industries. Further investigation, including additional insights for the role of non-asbestiform EMP, is warranted. Am. J. Ind. Med. 59:1047-1060, 2016. © 2016 Wiley Periodicals, Inc.

Anthophyllite asbestos: state of the science review

Anthophyllite is an amphibole form of asbestos historically used in only a limited number of products. No published resource currently exists that offers a complete overview of anthophyllite toxicity or of its effects on exposed human populations. We performed a review focusing on how anthophyllite toxicity was understood over time by conducting a comprehensive search of publicly available documents that discussed the use, mining, properties, toxicity, exposure and potential health effects of anthophyllite. Over 200 documents were identified; 114 contained relevant and useful information which we present chronologically in this assessment. Our analysis confirms that anthophyllite toxicity has not been well studied compared to other asbestos types. We found that toxicology studies in animals from the 1970s onward have indicated that, at sufficient doses, anthophyllite can cause asbestosis, lung cancer and mesothelioma. Studies of Finnish anthophyllite miners, conducted in the 1970s, found an increased incidence of asbestosis and lung cancer, but not mesothelioma. Not until the mid-1990s was an epidemiological link with mesothelioma in humans observed. Its presence in talc has been of recent significance in relation to potential asbestos exposure through the use of talc-containing products. Characterizing the health risks of anthophyllite is difficult, and distinguishing between its asbestiform and non-asbestiform mineral form is essential from both a toxicological and regulatory perspective. Anthophyllite toxicity has generally been assumed to be similar to other amphiboles from a regulatory standpoint, but some notable exceptions exist. In order to reach a more clear understanding of anthophyllite toxicity, significant additional study is needed. Copyright © 2016 John Wiley & Sons, Ltd.

Long-term toxicity of naturally occurring asbestos in male Fischer 344 rats

Naturally occurring asbestos (NOA) fibers are found in geologic deposits that may be disturbed by mining, earthworks, or natural processes, resulting in adverse health risks to exposed individuals. The toxicities of Libby amphibole and NOA samples including Sumas Mountain chrysotile (SM), El Dorado tremolite (ED), and Ontario ferroactinolite cleavage fragments (ON) were compared in male Fischer 344 (F344) rats 15 mo after exposure. Rat-respirable fractions of LA and SM displayed greater mean lengths and aspect ratios than ED and ON. After a single intratracheal (IT) instillation (0.5 or 1.5 mg/rat), persistent changes in ventilatory parameters and a significant increase in lung resistance at baseline and after methacholine aerosol dosing were found only in rats exposed to 1.5 mg SM. High-dose ED significantly elevated bronchoalveolar lavage lactate dehydrogenase (LDH) activity and protein levels, while high-dose SM increased γ-glutamyl transferase and LDH activities. A moderate degree of lung interstitial fibrosis after exposure to 1.5 mg SM persisted 15 mo after exposure, unchanged from previous findings at 3 mo. LA induced mild fibrosis, while ED and ON produced minimal and no apparent fibrosis, respectively. Bronchioloalveolar carcinoma was observed 15 mo after exposure to LA or ED. Data demonstrated that SM, given by bolus IT dosing on an equivalent mass basis, induced greater pulmonary function deficits, airway hyperresponsiveness, and interstitial fibrosis than other NOA, although unlike LA and ED, no apparent evidence for carcinogenicity was found. All NOA samples except ON cleavage fragments produced some degree of long-term toxicity.

A case-control study of mesothelioma in Minnesota iron ore (taconite) miners

OBJECTIVES

An excess of mesothelioma has been observed in iron ore miners in Northeastern Minnesota. Mining and processing of taconite iron ore generate exposures that include elongate mineral particles (EMPs) of amphibole and non-amphibole origin. We conducted a nested case-control study of mesothelioma in a cohort of 68,737 iron ore miners (haematite and taconite ore miners) to evaluate the association between mesothelioma, employment and EMP exposures from taconite mining.

METHODS

Mesothelioma cases (N=80) were identified through the Minnesota Cancer Surveillance System (MCSS) and death certificates. Four controls of similar age were selected for each case with 315 controls ultimately eligible for inclusion. Mesothelioma risk was evaluated by estimating rate ratios and 95% CIs with conditional logistic regression in relation to duration of taconite industry employment and cumulative EMP exposure [(EMP/cc)×years], defined by the National Institute for Occupational Safety and Health (NIOSH) 7400 method. Models were adjusted for employment in haematite mining and potential exposure to commercial asbestos products used in the industry.

RESULTS

All mesothelioma cases were male and 57 of the cases had work experience in the taconite industry. Mesothelioma was associated with the number of years employed in the taconite industry (RR=1.03, 95% CI 1.00 to 1.06) and cumulative EMP exposure (RR=1.10, 95% CI 0.97 to -1.24). No association was observed with employment in haematite mining.

CONCLUSIONS

These results support an association between mesothelioma and employment duration and possibly EMP exposure in taconite mining and processing. The type of EMP was not determined. The potential role of commercial asbestos cannot be entirely ruled out.

Cancer incidence among Minnesota taconite mining industry workers

PURPOSE

To evaluate cancer incidence among Minnesota taconite mining workers.

METHODS

We evaluated cancer incidence between 1988 and 2010 in a cohort of 40,720 Minnesota taconite mining workers used between 1937 and 1983. Standardized incidence ratios (SIRs) with 95% confidence intervals (CIs) were estimated by comparing numbers of incident cancers with frequencies in the Minnesota Cancer Surveillance System. SIRs for lung cancer by histologic subtypes were also estimated. We adjusted for out-of-state migration and conducted a probabilistic bias analysis for smoking-related cancers.

RESULTS

A total of 5700 cancers were identified, including 51 mesotheliomas and 973 lung cancers. The SIRs for lung cancer and mesothelioma were 1.3 (95% CI = 1.2-1.4) and 2.4 (95% CI = 1.8-3.2), respectively. Stomach, laryngeal, and bladder cancers were also elevated. However, adjusting for potential confounding by smoking attenuated the estimates for lung (SIR = 1.1, 95% CI = 1.0-1.3), laryngeal (SIR = 1.2, 95% CI = 0.8-1.6), oral (SIR = 0.9, 95% CI = 0.7-1.2), and bladder cancers (SIR = 1.0, 95% CI = 0.8-1.1).

CONCLUSIONS

Taconite workers may have an increased risk for certain cancers. Lifestyle and work-related factors may play a role in elevated morbidity. The extent to which mining-related exposures contribute to disease burden is being investigated.

Occupational exposures and lung cancer risk among Minnesota taconite mining workers

OBJECTIVE

To examine the association between employment duration, elongate mineral particle (EMP) exposure, silica exposure and the risk of lung cancer in the taconite mining industry.

METHODS

We conducted a nested case-control study of lung cancer within a cohort of Minnesota taconite iron mining workers employed by any of the mining companies in operation in 1983. Lung cancer cases were identified by vital records and cancer registry data through 2010. Two age-matched controls were selected from risk sets of cohort members alive and lung cancer free at the time of case diagnosis. Calendar time-specific exposure estimates were made for every job and were used to estimate workers' cumulative exposures. ORs and 95% CIs were estimated using conditional logistic regression. We evaluated total lung cancer risk and risk of histological subtype by total work duration and by cumulative EMP, and silica exposure by quartile of the exposure distribution.

RESULTS

A total of 1706 cases and 3381 controls were included in the analysis. After adjusting for work in haematite mining, asbestos exposure and sex, the OR for total duration of employment was 0.99 (95% CI 0.96 to 1.01). The ORs for quartile 4 versus 1 of EMP and silica exposure were 0.82 (95% CI 0.57 to 1.19) and 0.97 (95% CI 0.70 to 1.35), respectively. The risk of each histological subtype of lung cancer did not change with increasing exposure.

CONCLUSIONS

This study suggests that the estimated taconite mining exposures do not increase the risk of developing lung cancer.

Toxicological investigations on the respirable fraction of silicon carbide grain products by the in vitro vector model

Increased lung cancer incidence with workers at the production site of crude silicon carbide (SiC) using the Acheson process has been reported. Several agents derived from the process were discussed as causative factors. Recently concern had been expressed about the presence of cleavage fragments (CFs) in commercial products fulfilling the WHO criteria for fibers. This study has focused on the toxicological significance of such CFs. The test samples were respirable fractions of five different commercial samples of SiC grains. The CF content (scanning electron microscopy) was in the range 17-493 fibers/µg. Crystalline silica and whiskers could not be detected. Quartz DQ12, cristobalite, SiC whisker, UICC crocidolite and electrocorundum were used as control reference samples. Biological activity was assessed with the in vitro vector model (VM) on ex vivo rat and guinea pig alveolar macrophages (AMs). The dose range of the VM is derived from calculated AM loads from intratracheal instillation experiments and confirmed by measured AM loads from inhalation studies on alumina monohydrate particles with low biological activity: ≤120 pg/AM. The response of the references was clearly different from that of the SiC grains which yielded low toxicity overall. However, the parameter reactive oxygen species secreted by AMs was elevated at the higher SiC doses, but not related to the CF content of these samples. Our data showed that CFs seem to have no biological relevance. This is in agreement with results from recent studies in which no carcinogenic activity had been demonstrated for CFs.

The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry

Different dimensions of elongate mineral particles (EMP) have been proposed as being relevant to respiratory health end-points such as mesothelioma and lung cancer. In this article, a methodology for converting personal EMP exposures measured using the National Institute for Occupational Safety and Health (NIOSH) 7400/7402 methods to exposures based on other size-based definitions has been proposed and illustrated. Area monitoring for EMP in the taconite mines in Minnesota's Mesabi Iron Range was conducted using a Micro Orifice Uniform Deposit Impactor (MOUDI) size-fractionating sampler. EMP on stages of the MOUDI were counted and sized according to each EMP definition using an indirect-transfer transmission electron microscopy (ISO Method 13794). EMP were identified using energy-dispersive x-ray and electron diffraction analysis. Conversion factors between the EMP counts based on different definitions were estimated using (1) a linear regression model across all locations and (2) a location-specific ratio of the count based on each EMP definition to the NIOSH 7400/7402 count. The highest fractions of EMP concentrations were found for EMP that were 1-3 μm in length and 0.2-0.5 μm in width. Therefore, the current standard NIOSH Method 7400, which only counts EMP >5 μm in length and ≥ 3 in aspect ratio, may underestimate amphibole EMP exposures. At the same time, there was a high degree of correlation between the exposures estimated according to the different size-based metrics. Therefore, the various dimensional definitions probably do not result in different dose-response relationships in epidemiological analyses. Given the high degree of correlation between the various metrics, a result consistent with prior research, a more reasonable metric might be the measurement of all EMP irrespective of size. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: figures detailing EMP concentration.].

Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite

The physical properties of different types of asbestos may strongly affect health outcomes in exposed individuals. This study was designed to provide understanding of the comparative toxicity of naturally occurring asbestos (NOA) fibers including Libby amphibole (LA), Sumas Mountain chrysotile (SM), El Dorado tremolite (ED), and Ontario ferroactinolite (ON) cleavage fragments. Rat-respirable fractions (PM₂.₅) were prepared by water elutriation. Surface area was greater for SM (64.1 m²/g) than all other samples (range: 14.1-16.2 m²/g), whereas mean lengths and aspect ratios (ARs) for LA and SM were comparable and greater than ED and ON. Samples were delivered via a single intratracheal (IT) instillation at doses of 0.5 and 1.5mg/rat. One day post-IT instillation, low-dose NOA exposure resulted in a 3- to 4-fold increase in bronchoalveolar lavage fluid (BALF) cellularity compared with dispersion media (DM) controls, whereas high-dose exposure had a more severe effect on lung inflammation which varied by source. Although inducing less neutrophilic inflammation than ON and ED, exposure to either LA or SM resulted in a greater degree of acute lung injury. Three months post-IT instillation, most BALF parameters had returned to control levels, whereas the development of fibrosis persisted and was greatest in SM-exposed rats (SM > LA > ON > ED). These data demonstrate that fiber length and higher AR are directly correlated with the severity of fibrosis and that, in the rat, exposure to SM is more fibrogenic than LA which suggests that there may be cause for concern for people at risk of being exposed to NOA from the Sumas Mountain landslide.

Evaluation of tremolite asbestos exposures associated with the use of commercial products

Tremolite is a noncommercial form of amphibole mineral that is present in some chrysotile, talc, and vermiculite deposits. Inhalation of asbestiform tremolite is suspected to have caused or contributed to an increased incidence of mesothelioma in certain mining settings; however, very little is known about the magnitude of tremolite exposure that occurred at these locations, and even less is known regarding tremolite exposures that might have occurred during consumer use of chrysotile, talc, and vermiculite containing products. The purpose of this analysis is to evaluate the exposure-response relationship for tremolite asbestos and mesothelioma in high exposure settings (mining) and to develop estimates of tremolite asbestos exposure for various product use scenarios. Our interpretation of the tremolite asbestos exposure metrics reported for the Thetford chrysotile mines and the Libby vermiculite deposits suggests a lowest-observed-adverse-effect level (LOAEL) for mesothelioma of 35-73 f/cc-year. Using measured and estimated airborne tremolite asbestos concentrations for simulated and actual product use, we conservatively estimated the following cumulative tremolite asbestos exposures: career auto mechanic: 0.028 f/cc-year; non-occupational use of joint compound: 0.0006 f/cc-year; non-occupational use of vermiculite-containing gardening products: 0.034 f/cc-year; home-owner removal of Zonolite insulation: 0.0002 f/cc-year. While the estimated consumer tremolite exposures are far below the tremolite LOAELs derived herein, this analysis examines only a few of the hundreds of chrysotile- and talc-containing products.