Rapid fiber-detection technique by artificial intelligence in phase-contrast microscope images of simulated atmospheric samples.

Since the manufacture, import, and use of asbestos products have been completely abolished in Japan, the main cause of asbestos emissions into the atmosphere is the demolition and removal of buildings built with asbestos-containing materials. To detect and correct asbestos emissions from inappropriate demolition and removal operations at an early stage, a rapid method to measure atmospheric asbestos fibers is required. The current rapid measurement method is a combination of short-term atmospheric sampling and phase-contrast microscopy counting. However, visual counting takes a considerable amount of time and is not sufficiently fast. Using artificial intelligence (AI) to analyze microscope images to detect fibers may greatly reduce the time required for counting. Therefore, in this study, we investigated the use of AI image analysis for detecting fibers in phase-contrast microscope images. A series of simulated atmospheric samples prepared from standard samples of amosite and chrysotile were observed using a phase-contrast microscope. Images were captured, and training datasets were created from the counting results of expert analysts. We adopted 2 types of AI models-an instance segmentation model, namely the mask region-based convolutional neural network (Mask R-CNN), and a semantic segmentation model, namely the multi-level aggregation network (MA-Net)-that were trained to detect asbestos fibers. The accuracy of fiber detection achieved with the Mask R-CNN model was 57% for recall and 46% for precision, whereas the accuracy achieved with the MA-Net model was 95% for recall and 91% for precision. Therefore, satisfactory results were obtained with the MA-Net model. The time required for fiber detection was less than 1 s per image in both AI models, which was faster than the time required for counting by an expert analyst.

Manufactured doubt and the EPA 2020 chrysotile asbestos risk assessment.

While all forms of asbestos have been determined to be carcinogenic to humans by the International Agency for Research on Cancer (IARC) as well as other authoritative bodies, the relative carcinogenic potency of chrysotile continues to be argued, largely in the context of toxic tort litigation. Relatively few epidemiologic studies have investigated only a single form of asbestos; however, one study that included an asbestos textile plant located in Marshville, North Carolina that processed chrysotile asbestos was used by the United States Environmental Protection Agency (EPA) in 2020 to help inform the agency's chrysotile asbestos risk assessment. During the EPA proceedings toxic tort defense consultants submitted comments to the EPA docket and made public presentations asserting that the Marshville plant had processed amphibole asbestos types and should not be used for the chrysotile risk assessment. A detailed evaluation of defense consultant assertions and supporting information and a full assessment of the available information concerning asbestos types used at the Marshville plant was undertaken. The preponderance of evidence continues to support the conclusion that neither amosite nor crocidolite were likely to have been processed in the Marshville textile plant. Defense consultants' assertions about chrysotile use are not supported by the preponderance of evidence and constitute an example of manipulation of information to cast uncertainty and doubt rather than to seek truth and contribute to the body of scientific evidence.

Size characteristics of asbestiform fibers in lung tissue of animals that grazed in areas rich in ophiolitic outcrops in Central Calabria (Southern Italy).

In Calabria (Southern Italy) naturally occurring asbestos (NOA) mainly occurs in the ophiolitic sequences cropping in the Mount Reventino area. The most common type of asbestos detected was the amphibole tremolite; fibrous antigorite and minor chrysotile were also found. The development of asbestos-related diseases depends on, among other things, the morphological characteristics of fibers, length and width, affecting the durability of asbestos fibers in the lung. In this work fifteen lung samples of sheep, goats and wild boars, grazing around the Mount Reventino area were collected and asbestos fibers analysed. Observed fibers (357), of which 97 % were tremolite and 3 % antigorite fibers, were grouped according to species, grazing area and age of the animals. The aim of this work was to highlight any differences among the groupings and to compare our size results with data in literature related to exposed populations. Principal Component Analysis (PCA) highlighted a positive correlation between tremolite fiber length and width and revealed groupings in terms of animal age. The Kruskal-Wallis test showed statistically significant differences between fiber mean widths in young and old animals. 63 % observed asbestiform fibers were longer than 5 µm and 7 % of the fibers were longer than 20 µm (critical fiber length connected to the frustrated phagocytosis by the macrophage). Fibers conforming to the Stanton Hypothesis size (predictor of the carcinogenic potency of fibers) were 1 %. Our size parameters of fibers detected in the animal lungs were in fairly good agreement with literature data for human asbestos exposure to tremolite. These results confirmed that an animal-sentinel system could be used to monitor the natural background of the airborne breathable fibers exposure. In addition, the size correlation of animal-human breathed fibers could be useful to study their potential toxicity. Additional data are necessary for improving the agreement with human exposure data.

Distinguishing asbestos cement from fiber-reinforced cement through portable µ-Raman spectroscopy and portable X-ray fluorescence.

It is now widely acknowledged that asbestos can adversely affect human health; accordingly, in recent decades, fiber-reinforced cement (FRC) has been used as a substitute for asbestos cement (AC). This manuscript focuses on portable micro-Raman spectroscopy coupled with portable microscopy (p-µR) and portable X-ray fluorescence (p-XRF) as a means to identify chrysotile fibers in AC (Eternit) and fibers present in the asbestos-free FRC used as a substitute. Our results show that the simultaneous use of portable devices such as p-µR and p-XRF may be useful in quickly identifying fibrous chrysotile asbestos in Eternit, as well as polyvinyl fibers in new material FRC used as substitutes for Eternit. Chrysotile shows bands in the 800-200 cm-1 range, whereas polyvinyl alcohol fibers show bands in the 3000-800 cm-1 range. The p-XRF data on the two types of cement could possibly be used as a chemical fingerprint for the two different materials. Given that exposure to asbestos is a serious health hazard, its rapid and reliable detection in situ on residential buildings is important both for citizens and for administrative bodies charged with safeguarding public health. We believe that our study provides valuable insight into the potential use of portable devices for identifying asbestos and asbestos-free materials.

Evaluation of Airborne Asbestos Concentrations Associated with the Operation and Maintenance of Brakes and Clutches on Nonautomated Heavy Equipment.

This study evaluated the potential for chrysotile asbestos exposure during maintenance and operation of older, nonautomated heavy equipment with chrysotile-containing brake and clutch linings. Recent reports indicate that such equipment may be in current use in the U.S. and other locations, including developing countries, due to its lower cost and ease of maintenance compared to newer equipment. Personal and area airborne fiber concentrations were measured for cranes with draglines during brake and clutch repair, equipment operation, shop cleanup, and clothes handling of the mechanic's coveralls over a period of three days. The range of airborne chrysotile concentrations during the complete friction band replacement process, including band removal from the equipment, friction lining replacement, and reinstallation, ranged from 0.0053 to 0.0273 f/cc (phase contrast microscopy-equivalent or PCME) over 3.3 to 6.2 hours. Additional bench work tasks, including electric wire brushing, hand sanding, riveting, and compressed air use were also performed. Full shift airborne chrysotile concentrations (6.1-8.5 hours) for all combined maintenance activities were 0.0093, 0.0414, and 0.0445 f/cc (PCME), on days 1, 2, and 3, respectively. Personal short-term samples (14-36 minutes) for lining removal, installation, wire brushing, hand sanding, and compressed air use ranged from nondetect (ND) to 0.238 f/cc (PCME), below the U.S. Occupational Safety and Health Administration's (OSHA's) 30-minute excursion limit of 1 f/cc. Short-term samples during crane operation, shop cleanup, and simulated laundry activities with the mechanic's coveralls ranged from ND to 0.01 f/cc (PCME; 15-36 minutes). The results indicated that full-shift measured airborne chrysotile concentrations during the brake and clutch maintenance activities evaluated remained below the U.S. 8-hour time-weighted average (TWA) permissible exposure limit (PEL) for asbestos of 0.1 f/cc. The results are likely to be relevant to farmers, construction workers, and vehicle maintenance workers historically, as well as today for those who choose to continue using and maintaining such equipment.

US EPA's TSCA risk assessment approach: a case study of asbestos in automotive brakes.

The United States Environmental Protection Agency (US EPA) is currently refining its approach for risk assessments conducted under the amended Toxic Substances Control Act (TSCA), largely based on recommendations from the National Academies of Sciences, Engineering, and Medicine (NASEM). We identified several issues with the current TSCA risk assessment approach that were not addressed by NASEM in its recommendations. Here, we demonstrate these issues with a case study of the 'Risk Evaluation for Asbestos, Part 1: Chrysotile Asbestos,' which US EPA released in December 2020. In this evaluation, US EPA found that occupational and some consumer uses of automotive brakes and clutches that contain asbestos result in unreasonable risks. These risks were calculated from estimated exposures during brake work and an inhalation unit risk (IUR) developed for chrysotile asbestos. We found that US EPA overestimated risk as a result of unrealistic inputs to both the exposure and toxicity components of the risk equation, and because the Agency did not fully consider relevant epidemiology and toxicity evidence in its systematic review. Our evaluation demonstrates areas in which the TSCA risk assessment approach could be improved to result in risk evaluations that are supported by the available scientific evidence.

Asbestos Detection with Fluorescence Microscopy Images and Deep Learning.

Fluorescent probes can be used to detect various types of asbestos (serpentine and amphibole groups); however, the fiber counting using our previously developed software was not accurate for samples with low fiber concentration. Machine learning-based techniques (e.g., deep learning) for image analysis, particularly Convolutional Neural Networks (CNN), have been widely applied to many areas. The objectives of this study were to (1) create a database of a wide-range asbestos concentration (0-50 fibers/liter) fluorescence microscopy (FM) images in the laboratory; and (2) determine the applicability of the state-of-the-art object detection CNN model, YOLOv4, to accurately detect asbestos. We captured the fluorescence microscopy images containing asbestos and labeled the individual asbestos in the images. We trained the YOLOv4 model with the labeled images using one GTX 1660 Ti Graphics Processing Unit (GPU). Our results demonstrated the exceptional capacity of the YOLOv4 model to learn the fluorescent asbestos morphologies. The mean average precision at a threshold of 0.5 (mAP@0.5) was 96.1% ± 0.4%, using the National Institute for Occupational Safety and Health (NIOSH) fiber counting Method 7400 as a reference method. Compared to our previous counting software (Intec/HU), the YOLOv4 achieved higher accuracy (0.997 vs. 0.979), particularly much higher precision (0.898 vs. 0.418), recall (0.898 vs. 0.780) and F-1 score (0.898 vs. 0.544). In addition, the YOLOv4 performed much better for low fiber concentration samples (<15 fibers/liter) compared to Intec/HU. Therefore, the FM method coupled with YOLOv4 is remarkable in detecting asbestos fibers and differentiating them from other non-asbestos particles.

Airborne concentrations of chrysotile asbestos during operation of industrial crane controls and maintenance of associated arc chutes.

Some industrial crane control panels were historically equipped with chrysotile-containing arc chutes. Because of the paucity of data regarding potential exposure from such equipment, we used a simulation approach to quantify the release of chrysotile from arc chutes in two functional 1970s-era industrial crane control panels during operation and maintenance. Two experienced operators separately simulated operation of crane controls under load; one of these operators then simulated two arc chute maintenance protocols: sanding (protocol 1) and scraping, sanding, and blowing (protocol 2). The original arc chutes contained approximately 36% chrysotile. Personal breathing zone (PBZ) (n = 8) and area samples (n = 8) were collected and analyzed using phase contrast microscopy (PCM) and transmission electron microscopy. PCM-equivalent (PCME) concentrations were derived, from which 8-h time-weighted averages (TWA) were calculated. During operation, chrysotile was identified in one of the four PBZ samples, equivalent to a PCME concentration of 0.012 f/cm3 (8-h TWA: 0.011 f/cm3). During protocols 1 and 2, chrysotile was identified in all PBZ samples (n = 4); PCME concentrations (and corresponding 8-h TWA) were <0.013 and 0.021 f/cm3 (0.001 and 0.004 f/cm3) and 0.013 and 0.017 f/cm3 (0.003 f/cm3), respectively. Many of the airborne chrysotile fibers had matrix attached, supporting the low exposure potential during this work. These data indicate very low, if any, exposures to chrysotile asbestos during the simulated scenarios. In addition, these data could assist with refining assumptions in exposure reconstruction and inform the state-of-the science on low-level chrysotile exposure.

[Asbestos exposure and related diseases among friction products workers (1971-2016)]. / Esposizione ad amianto e patologie correlate in addetti alla produzione di materiali di attrito (1971-2016).

SUMMARY: Worldwide studies have been published on the mortality of workers employed in asbestos-based materials for the production of clutches and brakes. However no one of these studies is related to Italian cases. Furthermore, not even surveys have been conducted in Italy to characterize the correlation between asbestos exposures and the possible occurring of asbestos-related disease. Our objectives are the following: i) to assess and quantify the asbestos exposure cases, ii) to describe the nature and the frequency of asbestos-related diseases among blue collar employees of an important factory producing brakes and clutches with chrysotile asbestos content from 1971 to 1993 and iii) to provide preliminary data on cumulative asbestos exposure estimated using lung fibre burden analysis. Critical appraisal of airborne asbestos fibre measurements and identification of cases of asbestos-related diseases between the blue collar employees, either notified to the local health authority or recovered from the Italian national Mesothelioma registry was investigated. Lung fibre burden analysis using the lung tissue samples from two deceased blue collar employees was also performed. Airborne asbestos fibre measurements (carried out in 1982) suggested asbestos fibres average concentrations of about 0.3 f/ml, while all 1992 measurements showed results below 0.1 f/ml. Furthermore, since 1988, we identified four cases of pleural plaques, three cases of asbestosis and seven cases of lung cancer. No case of malignant mesothelioma was found. In both lung cancer cases, analysed to measure the lung fibre burden, commercial amphiboles were absent or in limited concentration but chrysotile and, especially, tremolite asbestos were present in noticeable amount. In conclusion, since 1971 and up to early 1980s, exposure to chrysotile asbestos and talc, likely contaminated by tremolite, had been significant and comparable to levels causing asbestosis long-term risk. No case of malignant mesothelioma was found, that is consistent with the absence of amphiboles and with the lower risk of mesothelioma associated with the chrysotile asbestos. However a subset of the blue collar employees, the ones employed later on, could still have not reached the full risk condition, and so being still at risk of developing malignant mesothelioma. In the two lung cancer cases studied, the lung fibre burden was essentially made of chrysotile and tremolite. Lastly, lung cancer occurrence in the population of blue collar employees has been likely underestimated and the correct determination of lung cancer risk should be done through the mortality analysis of this population.

Chrysotile fibers in tissue adjacent to laryngeal squamous cell carcinoma in cases with a history of occupational asbestos exposure.

Asbestos describes a group of naturally occurring fibrous silicate mineral compounds that have been associated with a number of respiratory maladies, including mesothelioma and lung cancer. In addition, based primarily on epidemiologic studies, asbestos has been implicated as a risk factor for laryngeal and pharyngeal squamous cell carcinoma (SCC). The main objective of this work was to strengthen existing evidence via empirical demonstration of persistent asbestos fibers embedded in the tissue surrounding laryngeal and pharyngeal SCC, thus providing a more definitive biological link between exposure and disease. Six human papillomavirus (HPV)-negative laryngeal (n = 4) and pharyngeal (n = 2) SCC cases with a history working in an asbestos-exposed occupation were selected from a large population-based case-control study of head and neck cancer. A laryngeal SCC case with no history of occupational asbestos exposure was included as a control. Tissue cores were obtained from adjacent nonneoplastic tissue in tumor blocks from the initial primary tumor resection, and mineral fiber analysis was performed using a scanning electron microscope equipped with an energy dispersive X-ray analyzer (EDXA). Chrysotile asbestos fiber bundles were identified in 3/6 of evaluated cases with a history of occupational asbestos exposure. All three cases had tumors originating in the larynx. In addition, a wollastonite fiber of unclear significance was identified one of the HPV-negative pharyngeal SCC cases. No mineral fibers were identified in adjacent tissue of the case without occupational exposure. The presence of asbestos fibers in the epithelial tissue surrounding laryngeal SCC in cases with a history of occupational asbestos exposure adds a key line of physical evidence implicating asbestos as an etiologic factor.

Microbial diversity and mineral composition of weathered serpentine rock of the Khalilovsky massif.

Endolithic microbial communities survive nutrient and energy deficient conditions while contributing to the weathering of their mineral substrate. This study examined the mineral composition and microbial communities of fully serpentinized weathered rock from 0.1 to 6.5 m depth at a site within the Khalilovsky massif, Orenburg Region, Southern Ural Mountains, Russia. The mineral composition includes a major content of serpentinite family (mostly consisting of lizardite and chrysotile), magnesium hydrocarbonates (hydromagnesite with lesser amounts of hydrotalcite and pyroaurite) concentrated in the upper layers, and clay minerals. We found that the deep-seated weathered serpentinites are chrysotile-type minerals, while the middle and surface serpentinites mostly consist of lizardite and chrysotile types. Microbial community analysis, based on 16S rRNA gene sequencing, showed a similar diversity of phyla throughout the depth profile. The dominant bacterial phyla were the Actinobacteria (of which unclassified genera in the orders Acidimicrobiales and Actinomycetales were most numerous), Chloroflexi (dominated by an uncultured P2-11E order) and the Proteobacteria (predominantly class Betaproteobacteria). Densities of several groups of bacteria were negatively correlated with depth. Occurrence of the orders Actinomycetales, Gaiellales, Solirubrobacterales, Rhizobiales and Burkholderiales were positively correlated with depth. Our findings show that endolithic microbial communities of the Khalilovsky massif have similar diversity to those of serpentine soils and rocks, but are substantially different from those of the aqueous environments of actively serpentinizing systems.

Effects of calcareous and serpentinite parent material on the mineral characteristics of soils and plant material of Teucrium montanum L. (Lamiaceae).

The objective of this study was to determine eco-edaphic characteristics and influence of different substrates on mineral characteristics of facultative serpentinophyte. The total concentration of 20 elements Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, S, Se, and Zn in soil samples and aboveground parts of medicinal plant species Teucrium montanum from various calcareous and serpentinite habitats in the territory of Serbia was determined. The concentration of the elements was established by inductively coupled plasma optical emission spectrometry-ICP-OES. The obtained results showed that the quantities of certain elements Al, As, B, Ca, Cd, Cu, K, Li, P, Se, and Zn were detected more in the soil samples from calcareous habitats in comparison to the quantities of other metals Co, Cr, Fe, Mg, Mn, Na, Ni, which were more frequently found in the soil samples from the serpentinite habitats. Analyzed plant samples from calcareous habitats contained higher concentrations of Al, Ca, Li, and Zn as opposed to serpentinite containing higher concentrations of Co, Cr, Fe, Mg, Mn, Na, Ni, and Se. Examined species can accumulate macro- and microelements in different quantities, depending on the substrate type. Differences in the concentration of certain elements in the soil samples and aboveground parts of the T. montanum from calcareous and serpentinite habitats indicate significant phenotypic plasticity of the investigated species as well as the existence of specific serpentinite ecotypes developed by the activity of various edaphic factors.

Quantitative relationships of exposure to chrysotile asbestos and mesothelioma mortality.

BACKGROUND: While asbestos has long been known to cause mesothelioma, quantitative exposure-response data on the relation of mesothelioma risk and exposure to chrysotile asbestos are sparse. METHODS: Quantitative relationships of mortality from mesothelioma and pleural cancer were investigated in an established cohort of 5397 asbestos textile manufacturing workers in North Carolina, USA. Eligible workers were those employed between 1950 and 1973 with mortality follow-up through 2003. Individual exposure to chrysotile fibres was estimated on the basis of 3420 air samples covering the entire study period linked to work history records. Exposure coefficients adjusted for age, race, and time-related covariates were estimated by Poisson regression. RESULTS: Positive, statistically significant associations were observed between mortality from all pleural cancer (including mesothelioma) and time since first exposure (TSFE) to asbestos (rate ratio [RR], 1.19; 95% confidence interval [CI], 1.06-1.34 per year), duration of exposure, and cumulative asbestos fibre exposure (RR, 1.15; 95% CI, 1.04-1.28 per 100 f-years/mL; 10-year lag). Analyses of the shape of exposure-response functions suggested a linear relationship with TSFE and a less-than-linear relationship with cumulative exposure. Restricting the analysis to years when mesothelioma was coded as a unique cause of death yielded stronger but less precise associations. CONCLUSIONS: These observations support with quantitative data the conclusion that chrysotile causes mesothelioma and encourage exposure-response analyses of mesothelioma in other cohorts exposed to chrysotile.

Adaptation and divergence in edaphic specialists and generalists: serpentine soil endemics in the California flora occur in barer serpentine habitats with lower soil calcium levels than serpentine tolerators.

PREMISE: Adaptation to harsh edaphic substrates has repeatedly led to the evolution of edaphic specialists and generalists. Yet, it is unclear what factors promote specialization versus generalization. Here, we search for habitat use patterns associated with serpentine endemics (specialists) and serpentine tolerators (generalists) to indirectly test the hypothesis that trade-offs associated with serpentine adaptation promote specialization. We predict that (1) endemics have adapted to chemically harsher and more bare serpentine habitats than tolerators, and (2) edaphic endemics show more habitat divergence from their sister species than tolerators do among on- and off-serpentine populations. METHODS: We selected 8 serpentine endemic and 9 serpentine tolerator species representing independent adaptation to serpentine. We characterized soil chemistry and microhabitat bareness from one serpentine taxon of each species and from a paired nonserpentine sister taxon, resulting in 8 endemic and 9 tolerator sister-taxa pairs. RESULTS: We find endemic serpentine taxa occur in serpentine habitats averaging twice as much bare ground as tolerator serpentine taxa and 25% less soil calcium, a limiting macronutrient in serpentine soils. We do not find strong evidence that habitat divergence between sister taxa of endemic pairs is greater than between sister taxa of tolerator pairs. CONCLUSIONS: These results suggest serpentine endemism is associated with adaptation to chemically harsher and more bare serpentine habitats. It may be that this adaptation trades off with competitive ability, which would support the longstanding, but rarely tested, competitive trade-off hypothesis.

Risk assessment of asbestos-cement roof sheets in Chekka, North Lebanon.

Asbestos-cement was manufactured and used in Lebanon since the early 1950s. Corrugated rooftops of asbestos-cement were mostly spread within residential areas throughout the country. These rooftops are subject to weathering factors which are known to increase friability and risk of hazardous fiber release. This study aimed at assessing the asbestos-cement rooftop friability and the possible emerging risks in the urban-industrial city of Chekka, North Lebanon. The evaluation of the asbestos-cement included two field assessment algorithms and a standardized pull-up test. Hazard of fiber emissions was assessed by a pull-up test method, whereas vulnerability was determined by a level of interaction between people and the rooftops. Geographic object-based image analysis was used to map hazard, vulnerability, and risk of asbestos rooftops in the study area. The field algorithms classified most rooftops in a bad state compared with the pull-up test which ranked most of them as good. The X-ray diffraction analysis showed the presence of serpentine and amphibole fibers, except for crocidolite, in some rooftop samples. Hazard, vulnerability, and risk maps of the sampled area showed how hazard potential was amplified by vulnerability of population to possible fiber emission.

[ANALYSIS OF MORBIDITY WITH TEMPORARY DISABILITY OF WORKERS IN THE ORE BENEFICIATION ON CHRYSOTILE PRODUCTION].

This study is aimed at studying the morbidity with temporary disability (MTD) of employee working in ore beneficiation at chrysotile production of JSC "Kostanay Minerals" . It was found that the incidence of MTD is higher among male male workers than in men in the control group, and the incidence of MTD in the compared professional groups decreases with an increase in work experience. This is possibly due to the fact that the organism of the trained workers is more stable due to the formation of protective adaptive mechanisms to the current production hazards. However, the revealed reliable differences between the main and control groups in the trainees group for 30 years or more rank them at risk. When analyzing the morbidity by class of disease in the compared groups, respiratory diseases take the first place. In the main group, the second place is occupied by diseases of the musculoskeletal system, in the control group - the class of illnesses "traumas and poisonings" with the share of domestic injuries accounting for 95,2%. The third place in the main group was occupied by the class of "trauma and poisoning", and in the control group - diseases of the musculoskeletal system. The obtained research results allow us to conclude that in the current conditions of industrial development of industry in the Republic of Kazakhstan, the continuous improvement of the most important preventive measures for labor protection and the prevention of occupational diseases on the basis of studying the morbidity with MTD remain relevant, they should be aimed at establishing the relationship between the kind of activity of workers with risks development of occupational diseases.

Characterization of asbestiform glaucophane-winchite in the Franciscan Complex blueschist, northern Diablo Range, California.

This paper presents a geologic and mineralogical investigation of asbestiform amphibole from blueschist in the Diablo Range, northern California. The analysis of fibers in air samples shows that the dominant blueschist amphibole composition ranges from glaucophane to subordinate winchite. In outcrop, blueschist amphibole exhibits a velvety luster, and its occurrence ranges from crosscutting veins to highly deformed foliated and lineated tectonites. TEM and SEM photographs reveal a highly fibrous habit typically associated with asbestiform amphiboles. Dimensional analysis reveals a mean fiber width of 0.27 µm, and lengths and aspect ratios are shorter than reported for commercially exploitable asbestos, with a mean length of 2.8 µm and mean aspect ratio of 11.5. The data are consistent with other research showing that the width population of fibers, and not length or aspect ratio, is the key indicator of the asbestiform habit. The blueschist data are compared to non-asbestiform hornblende amphibole in granitic rocks. The fiber concentration of the hornblende (458 MFG) is low compared to the blueschist amphibole (107,880 MFG) and chrysotile in serpentinite (196,066 MFG), indicating that under similar conditions, the exposure potential from cleaved particles could be several orders of magnitude lower than from asbestiform particles. The asbestiform habit of glaucophane is present at two other locations in the Franciscan Complex, suggesting that asbestiform blueschist amphibole may be characteristic within blueschist terranes, and rock formations containing asbestiform amphibole may be more common and widespread than previously assumed.

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.

Standardized methods for preparation and bi-variate length & diameter counting/sizing of aerosol and tissue digestion fiber samples.

Most fiber length distributions fit a log-normal distribution with their being many more shorter fibers present as compared to the longer fibers. As the longer fibers have been suggested to be more important for possible pathogenesis giving equal weight to all fiber lengths when sizing fibers will under sample the longer fibers. The methods described here, are based upon the optimization of fiber counting/sizing rules over a number years of experience and have been developed to provide a stable estimate of the mean number of particles and fibers present in the size ranges: particles, fibers < 5 µm; 5-20 µm; and >20 µm. These methods were first applied using TEM, however, with the development of high resolution SEM, it was found that higher reproducibility could be obtained with SEM.