Cumulative Retrospective Exposure Assessment (REA) as a predictor of amphibole asbestos lung burden: validation procedures and results for industrial hygiene and pathology estimates

Asbestos burden in lungs of mesothelioma patients with pleural plaques, lung fibrosis and/or ferruginous bodies at histology: a postmortem SEM-EDS study

The causal attribution of asbestos-related diseases to past asbestos exposures is of crucial importance in clinical and legal contexts. Often this evaluation is made based on the history of exposure, but this method presents important limitations. To assess past asbestos exposure, pleural plaques (PP), lung fibrosis and histological evidence of ferruginous bodies (FB) can be used in combination with anamnestic data. However, such markers have never been associated with a threshold value of inhaled asbestos. With this study we attempted to shed light on the dose-response relationship of PP, lung fibrosis and FBs, investigating if their prevalence in exposed individuals who died from malignant mesothelioma (MM) is related to the concentration of asbestos in lungs assessed using scanning electron microscopy equipped with energy dispersive spectroscopy. Moreover, we estimated the values of asbestos concentration in lungs associated with PP, lung fibrosis and FB. Lung fibrosis showed a significant positive relationship with asbestos lung content, whereas PP and FB did not. We identified, for the first time, critical lung concentrations of asbestos related to the presence of PP, lung fibrosis and FB at histology (respectively, 19 800, 26 400 and 27 400 fibers per gram of dry weight), that were all well-below the background levels of asbestos identified in our laboratory. Such data suggest that PP, lung fibrosis and FB at histology should be used with caution in the causal attribution of MM to past asbestos exposures, while evaluation of amphibole lung content using analytical electron microscopy should be preferred.

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.

Chronological trends in the causation of malignant mesothelioma: Fiber burden analysis of 619 cases over four decades

Malignant mesothelioma is a relatively rare malignancy with a strong association with prior asbestos exposure. A percentage of cases is not related to asbestos, and fiber analysis of lung tissue is a useful methodology for identifying idiopathic or spontaneous cases. We have performed fiber analyses in more than 600 cases of mesothelioma over the past four decades and were interested in looking for trends in terms of fiber types and concentrations as well as percentages of cases not related to asbestos. Demographic information was also considered including patient age, gender, and tumor location (pleural vs. peritoneal). The histologic pattern of the tumor and the presence or absence of pleural plaques or asbestosis were noted. Fiber analysis was performed in 619 cases, using the sodium hypochlorite technique for digestion of lung tissue samples. Asbestos bodies were counted by light microscopy (LM) and coated and uncoated fibers by scanning electron microscopy (EM). The results were stratified over four decades. Trends that were observed included increasing patient age, increasing percentage of women, increasing percentage of peritoneal cases, and increasing percentage of epithelial histological type. There was a decreasing trend in the percentage of patients with concomitant asbestosis (p < 0.001). The percentage of cases with an elevated lung asbestos content decreased from 90.5% in the 1980s to 54.1% in the 2010s (p < 0.001). This trend also held when the analysis was limited to 490 cases of pleural mesothelioma in men (91.8% in the 1980s vs. 65.1% in the 2010s). There was a decrease in the median asbestos body count by LM from 1390 asbestos bodies per gram of wet lung in the 1980s to 38 AB/gm in the 2010s. Similar trends were observed for each of the asbestos fiber types as detected by EM. We conclude that there has been a progressive decrease in lung fiber content of mesothelioma patients during the past four decades, with an increasing percentage of cases not related to asbestos and an increase in median patient age.

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.

Reconstructing historical exposure to asbestos: the validation of 'educated guesses'

BACKGROUND

In both the epidemiological and legal context, the causal attribution of asbestos-related lung diseases requires retrospective exposure assessment (REA).

AIMS

To assess the correlation between the retrospective assessment of occupational and anthropogenic environmental exposure to asbestos and its content in the lung tissue.

METHODS

Based on the available exposure information, a team of occupational physicians retrospectively assessed cumulative exposure to asbestos in 24 subjects who died of asbestos-related diseases. The asbestos lung content was analysed using analytical scanning electron microscope (SEM-EDS). The Log10 asbestos fibre count in the autoptic samples was predicted as a function of the Log10 estimated cumulative exposure using univariate regression analysis.

RESULTS

The median count of asbestos fibres by grams of dry weight (ff/gdw) in the lung tissue was 81 339 (range 0-2 135 849.06); it was 287 144 (range 0-2 135 849.06) among the occupationally exposed, and 29 671 (range 0-116 891) among the subjects who only had anthropogenic environmental and/or household exposure. Amphiboles, and particularly amosite (52%) and crocidolite (43%), were detected in all the study subjects. Chrysotile was not detected in any of the samples. Overall, the retrospective estimate of lifetime cumulative exposure to asbestos showed a moderate correlation with the total asbestos fibre count in the autoptic lung, with the regression model explaining 38-55% of the total variance.

CONCLUSIONS

Detailed information on occupational, environmental and household exposure circumstances would be indispensable for experienced industrial hygienists and/or occupational physicians to reliably assess past exposure to amphiboles or mixed types of asbestos.

Chemo-physical properties of asbestos bodies in human lung tissues studied at the nano-scale by non-invasive, label free x-ray imaging and spectroscopic techniques

In the lungs, asbestos develops an Fe-rich coating (Asbestos Body, AB) that becomes the actual interface between the foreign fibers and the host organism. Conventional approaches to study ABs require an invasive sample preparation that can alter them. In this work, a novel combination of x-ray tomography and spectroscopy allowed studying unaltered lung tissue samples with chrysotile and crocidolite asbestos. The thickness and mass density maps of the ABs obtained by x-ray tomography were used to derive a truly quantitative elemental analysis from scanning x-ray fluorescence spectroscopy data. The average mass density of the ABs is compatible with that of highly loaded ferritin, or hemosiderin. The composition of all ABs analyzed was similar, with only minor differences in the relative elemental fractions. Silicon concentration decreased in the core-to-rim direction, indicating a possible partial dissolution of the inner fiber. The Fe content in the ABs was higher than that possibly contained in chrysotile and crocidolite. This finding opens two opposite scenarios, the first with Fe coming from the fiber bulk and concentrating on the surface as long as the fiber dissolves, the second where the Fe that takes part to the formation of the AB originates from the host organism Fe-pool.

Retrospective Exposure Assessment Methods Used in Occupational Human Health Risk Assessment: A Systematic Review

As part of the assessment and management of chemical risk and occupational hygiene, retrospective exposure assessment (REA) to chemical agents can be defined as the estimate of exposure associated with a person's work history. The fundamental problem underlying the reconstruction of the exposure is that of transforming this type of information in quantitative terms to obtain an accurate estimate. REA can follow various approaches, some of which are technically complicated and both time and resource consuming. The aim of this systematic review is to present the techniques mainly used for occupational REA. In order to carry out this evaluation, a systematic review of the scientific literature was conducted. Forty-four studies were identified (published from 2010 to date) and analyzed. In exposure reconstruction studies, quantitative approaches should be preferable, especially when estimates will be used in the context of health impact assessment or epidemiology, although it is important to stress how, ideally, the experimental data available for the considered scenario should be used whenever possible as the main starting information base for further processing. To date, there is no single approach capable of providing an accurate estimate of exposure for each reasonably foreseeable condition and situation and the best approach generally depends on the level of information available for the specific case. The use of a combination of different reconstruction techniques can, therefore, represent a powerful tool for weighting and integrating data obtained through qualitative and quantitative approaches, in order to obtain the best possible estimate.

Occupational asbestos exposure after the ban: a job exposure matrix developed in Italy

Background

Asbestos is a well-known carcinogen for humans. The aim of this study is to develop a tool to estimate occupational asbestos exposure in Italy after the ban using information collected in a national dataset.

Methods

Data were collected from firm registries of workers exposed to asbestos in the period 1996–2016. Descriptive statistics (arithmetic mean, standard deviation, geometric mean and geometric standard deviation) were calculated for the main exposure-related variables (activity sector, occupational group and exposure period). An estimate of workers potentially exposed to asbestos was also performed.

Results

A total of 19 704 airborne measurements of asbestos exposure was selected from the national database of occupational exposures in the sectors of asbestos abatement. Overall, a geometric mean of 7.93 f l−1 was found, and chrysotile was the asbestos type that had more exposures (41%). A total of 46 422 workers was estimated to be potentially at asbestos exposure risk. Exposure data were summarized by calendar period, activity sector and occupational group.

Conclusions

The construction of a job exposure matrix for different occupation/industry combinations may allow the assessment of occupational exposure to asbestos in several removal and disposal activities, and the estimate of the risks associated with asbestos-related diseases in epidemiological studies.

Pulmonary Function and CT Scan Imaging at Low-Level Occupational Exposureto Asbestos

Background: In spite of the reduced exposure level, and its ban in numerous countries, compensation claims for asbestos-related diseases are far from decreasing. Methods: We used retrospective exposure assessment techniques to explore respiratory function and a computerized tomography (CT) scan in relation to past asbestos exposure in 115 male workers retired from an acrylic and polyester fiber plant. Based, on detailed information on exposure circumstances, we reconstructed a cumulative exposure estimate for each patient. Results: Time-weighted average exposure in our study population was 0.24 fibers/ml (95% confidence inteval (CI) 0.19-0.29), and the average cumulative exposure was 4.51 fibers/mL-years (95% CI 3.95-5.07). Exposure was elevated among maintenance workers, compared to other jobs (p = 0.00001). Respiratory function parameters did not vary in relation to the exposure estimates, nor to CT scan results. Risk of interstitial fibrosis showed a significant upward trend (Wald test for trend = 2.62, p = 0.009) with cumulative exposure to asbestos; risk associated with 5.26 fibers/mL-years or more, was 8-fold (95% CI 1.18-54.5). Conclusions: Our results suggest that a CT scan can detect pleuro-parenchymal lung alterations at asbestos exposure levels lower than previously thought, in absence of respiratory impairment. Further studies are required to validate our techniques of retrospective assessment of asbestos exposure.

Empirical model of mesothelioma potency factors for different mineral fibers based on their chemical composition and dimensionality

Context: The potency of various mineral fiber types to produce mesothelioma was previously evaluated for numerous cohorts, but the differences in potencies for distinct fiber types have yet to be explained. Objective: To develop an empirical model that would reconstruct mesothelioma potency factors for various types of fiber based on their chemical composition and dimensionality. Methods: Typical chemical composition and dimensionality metrics (aspect ratios) were obtained and combined with mesothelioma potency factors estimated by Hodgson and Darnton method for Quebec chrysotile, South Africa amosite, South Africa and Australian crocidolite, Russian anthophyllite, Libby amphiboles, and Turkey erionite. The forward stepwise log-log regression method was utilized to determine the best combination of input parameters. Results: Mesothelioma potency factors (R_M) for selected cohorts were effectively reconstructed utilizing the median aspect ratio of fibers and equivalent fractions of SiO₂, total Fe oxides or total equivalent Fe³⁺ as Fe₂O₃, and MgO. Modeled potency factors increase as the aspect ratio, SiO₂, and total Fe oxide (or Fe₂O₃) content grow, and as the MgO content diminishes. Correlation coefficients up to 0.999, p < 0.01, were achieved. The models also yield reasonable estimates of mesothelioma potencies for other fiber types, including Bolivian crocidolite, Russian chrysotile, fluoro-edenite, and others. Conclusion: In spite of the empirical approach, the proposed models provide a starting point for targeted studies of mesothelioma mechanisms by elucidating significant contributing physicochemical factors. The models have an exploratory and preliminary character but can potentially be useful to introduce quantitative structure-activity relationship approaches for the toxicology of fibrous minerals.

Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure

Asbestos exposure is the main etiology of malignant mesothelioma, but there are conflicting data on whether the intensity of exposure modulates the development of this disease. This study considered 594 patients with malignant mesothelioma for whom count data on asbestos bodies and fibers (per gram of wet lung tissue) were available. The relationships between age at diagnosis (a time-to-event outcome variable) and these two measures of internal asbestos exposure, along with other possible modulating factors (sex, tumor location, histological subtype and childhood exposure), were assessed on multivariable Cox proportional hazard models, stratifying by decade of birth year. For both measures of asbestos in lung tissue, younger age at diagnosis was associated with higher internal measures of exposure to asbestos. Stratified Cox analyses showed that for each doubling in asbestos body count patients were 1.07 times more likely to be diagnosed at a younger age [hazard ratio (HR) = 1.07; 95% confidence interval (CI), 1.04-1.09; P = 2.2 × 10-7] and for each doubling in asbestos fiber count patients were 1.13 times more likely to be diagnosed at a younger age (HR = 1.13; 95% CI, 1.09-1.17; P = 8.6 × 10-11). None of the other variables considered were associated with age at diagnosis. Our finding that tumors become clinically apparent at a younger age in heavily exposed subjects suggests that asbestos is involved not only in the malignant mesothelioma tumor initiation but, somehow, also in the progression of the disease.

A Bayesian Model and Stochastic Exposure (Dose) Estimation for Relative Exposure Risk Comparison Involving Asbestos-Containing Dropped Ceiling Panel Installation and Maintenance Tasks

Assessing exposures to hazards in order to characterize risk is at the core of occupational hygiene. Our study examined dropped ceiling systems commonly used in schools and commercial buildings and lay-in ceiling panels that may have contained asbestos prior to the mid to late 1970s. However, most ceiling panels and tiles do not contain asbestos. Since asbestos risk relates to dose, we estimated the distribution of eight-hour TWA concentrations and one-year exposures (a one-year dose equivalent) to asbestos fibers (asbestos f/cc-years) for five groups of workers who may encounter dropped ceilings: specialists, generalists, maintenance workers, nonprofessional do-it-yourself (DIY) persons, and other tradespersons who are bystanders to ceiling work. Concentration data (asbestos f/cc) were obtained through two exposure assessment studies in the field and one chamber study. Bayesian and stochastic models were applied to estimate distributions of eight-hour TWAs and annual exposures (dose). The eight-hour TWAs for all work categories were below current and historic occupational exposure limits (OELs). Exposures to asbestos fibers from dropped ceiling work would be categorized as "highly controlled" for maintenance workers and "well controlled" for remaining work categories, according to the American Industrial Hygiene Association exposure control rating system. Annual exposures (dose) were found to be greatest for specialists, followed by maintenance workers, generalists, bystanders, and DIY. On a comparative basis, modeled dose and thus risk from dropped ceilings for all work categories were orders of magnitude lower than published exposures for other sources of banned friable asbestos-containing building material commonly encountered in construction trades.

The asbestos fibre burden in human lungs: new insights into the chrysotile debate

The traceability of asbestos fibres in human lungs is a matter of discussion especially for chrysotile. This issue is of high significance for differential diagnosis, risk assessment and occupational compensation. At present no intra-individual longitudinal information is available. This study addresses the question whether the asbestos fibre burden in human lungs decreases with time after exposure cessation.

The database of the German Mesothelioma Register was screened for patients with asbestos body counts of at least 500 fibres per gram of wet lung, which had been analysed twice from different tissue excisions at minimum intervals of 4 years.

Twelve datasets with individual longitudinal information were discovered with a median interval of about 8 years (range 4–21 years). Both examinations were performed after exposure cessation (median: surgery, 9.5 years; autopsy, 22 years). Pulmonary asbestos fibre burden was stable between both examinations (median 1623/4269 asbestos bodies per gram wet lung). Electron microscopy demonstrated a preponderance of chrysotile (median 80%).

This study is the first to present longitudinal intra-individual data about the asbestos fibre burden in living human lungs. The high biopersistence of amphiboles, but also of chrysotile, offers mechanistic explanations for fibre toxicity, especially the long latency period of asbestos-related diseases.

Intra-individual longitudinal data display: the asbestos fibre burden in living human lungs is stable over many yearshttp://ow.ly/VtPF30bRETz

Pleural malignant mesothelioma in dental laboratory technicians: A case series

Asbestos was used in dentistry as a binder in periodontal dressings and as lining material for casting rings and crucible. However, until now, only one case of malignant mesothelioma with occupational exposure to asbestos in dental practice has been reported. We present 4 pleural mesotheliomas out of 5344 cases identified in Lombardy, Italy, in 2000-2014. Three men had been working as dental laboratory technicians, with asbestos exposure for 10, 34, and 4 years, and one woman had been helping her husband for 30 years in manufacturing dental prostheses. The men described the use of asbestos as a lining material for casting rings, while the woman was not able to confirm this use. We confirm the association of malignant mesothelioma with dental technician work. Dental technicians suffering from mesothelioma should be questioned about past occupational asbestos exposure.

Carcinoma of the lung in the absence of asbestosis: The value of lung fiber burden analysis

Asbestos is universally recognized as a carcinogen for the lower respiratory tract. However, asbestos is a contributory factor in a small fraction of lung cancers, the vast majority of which are related to cigarette smoking. The challenge for the pathologist is to determine when a lung cancer may be attributed to past asbestos exposure. The finding of asbestosis either clinically or pathologically is a useful marker for such a determination. However, in the absence of asbestosis, it has been suggested that a fiber burden as determined by analytical electron microscopy within the range of asbestosis is sufficient for determination of a causal contribution. We report here an example of a case of lung cancer in which fiber burden studies showed an asbestos concentration within the range of asbestosis as determined by scanning electron microscopy (SEM).

Pleural mesothelioma and lung cancer risks in relation to occupational history and asbestos lung burden

BACKGROUND

We have conducted a population-based study of pleural mesothelioma patients with occupational histories and measured asbestos lung burdens in occupationally exposed workers and in the general population. The relationship between lung burden and risk, particularly at environmental exposure levels, will enable future mesothelioma rates in people born after 1965 who never installed asbestos to be predicted from their asbestos lung burdens.

METHODS

Following personal interview asbestos fibres longer than 5 µm were counted by transmission electron microscopy in lung samples obtained from 133 patients with mesothelioma and 262 patients with lung cancer. ORs for mesothelioma were converted to lifetime risks.

RESULTS

Lifetime mesothelioma risk is approximately 0.02% per 1000 amphibole fibres per gram of dry lung tissue over a more than 100-fold range, from 1 to 4 in the most heavily exposed building workers to less than 1 in 500 in most of the population. The asbestos fibres counted were amosite (75%), crocidolite (18%), other amphiboles (5%) and chrysotile (2%).

CONCLUSIONS

The approximate linearity of the dose-response together with lung burden measurements in younger people will provide reasonably reliable predictions of future mesothelioma rates in those born since 1965 whose risks cannot yet be seen in national rates. Burdens in those born more recently will indicate the continuing occupational and environmental hazards under current asbestos control regulations. Our results confirm the major contribution of amosite to UK mesothelioma incidence and the substantial contribution of non-occupational exposure, particularly in women.