Quantitative relationships of exposure to chrysotile asbestos and mesothelioma mortality

Patient characteristics, treatment patterns, and survival outcomes for patients with malignant pleural mesothelioma in Denmark between 2011 and 2018: a nationwide population-based cohort study

BACKGROUND

Malignant pleural mesothelioma (MPM) is a rare thoracic malignancy with poor prognosis and limited treatment options. Immunotherapy shows potential for improved outcomes; however, real-world evidence on its use will take time to accumulate. This study examined patient characteristics, treatment patterns, overall survival (OS), and predictors of mortality among patients diagnosed with MPM in Denmark prior to the introduction of newer treatments.

METHODS

This historical cohort study based on routinely collected Danish National Registry data included adults newly diagnosed with MPM between 01 January 2011 and 31 May 2018. Summary statistics were used to describe patient characteristics and initial treatment. OS was estimated using Kaplan-Meier methods; Cox regression was used to compare patient mortality against the (age/sex-matched) general population and to investigate mortality predictors.

RESULTS

Overall, 880 patients were included; 44% had advanced MPM, 37% had non-advanced MPM, and 19% had unknown MPM stage. Median age at diagnosis was 71.9 years, and 82% of the patients were male. Within 180 days of diagnosis, no treatment was recorded for 215 patients (54%) with advanced MPM and 150 (46%) with non-advanced MPM. Median time-to-initial treatment (interquartile range) was 47 days (31-111) overall, 40 days (28-77) in patients with advanced MPM, and 53 days (35-121) with non-advanced MPM. Median OS was 13.7 months overall (non-advanced MPM: 18.0 months vs. advanced MPM: 10.0 months). Predictors of higher mortality were older age at diagnosis, histology, and advanced MPM stage.

INTERPRETATION

These findings provide a baseline upon which to evaluate MPM epidemiology as newer treatments are adopted in routine practice.

Asbestos ban policies and mesothelioma mortality in Greece

BACKGROUND

Malignant mesothelioma is a rare form of cancer that mostly affects the pleura and has a strong link to asbestos exposure. Greece banned the use of asbestos in 2005, however, the public was already aware of this substance in the 1980s. This research aims to present an overview of Greece's mesothelioma age-standardized mortality rates (ASMR) from 1983 to 2019 by age, gender, and geographic region and to determine whether the actions to ban asbestos impacted these rates.

METHODS

Data were retrieved by the Hellenic Statistical Authority (HSA) from death certificates that mentioned mesothelioma as the cause of death from 1983 to 2019 with details on the residence, gender, and age. Statistical analysis was performed using PRISM 6.0 software, a two-way ANOVA test, Trend analysis was conducted using Joinpoint Regression Program 5.0 software. The linear and non-linear model was used to calculate the age-standardized rates of annual percentage change (APC) and its 95% confidential interval (95% CI).

RESULTS

From 1983 to 2019, 850 total mesothelioma deaths were recorded, the majority of whom were males (634). A rate of 74.6% accounts for males and 25.4% for females, and the ratio of Males: Females was 3:1. Males' ASMR and the whole population's ASMR reached their highest levels in 2011 (0.93/100000person-years and 0.53/100000person-years, respectively). To look for potential changes between the first two decades of the 21st century, we compared the mean ASMR of each geographic region in Greece between two different 10-year subperiods (2000-2009 and 2010-2019). Except for Epirus, all regions of Greece had elevated regional ASMRs, particularly in those with the highest asbestos deposits. Notably, the ASMR in Epirus decreased from 0.54/100000person-years (2000-2009) to 0.31/100000person-years (2010-2019). After 2011, the ASMR for men and the general population stabilized. This stability is important since mesothelioma in men is associated with occupational asbestos exposure. The intriguing discovery of a lower ASMR in Epirus emphasizes the need to raise awareness of the condition and implement effective public health measures.

CONCLUSIONS

In Greece, the annual ASMR for males and the whole population reached its highest level in 2011, which is positive and encouraging and may be a sign that the rate will stabilize during the following years. Moreover, this study showed that the actions made in the 1980s regarding public awareness and surveillance directly impacted the decrease in Epirus rates. Future research, continual awareness, information, and recording are needed to monitor the mesothelioma epidemic. The possible benefit of a mesothelioma registry and the epidemiological surveillance of asbestos-related diseases, particularly mesothelioma mortality, need to be addressed.

TRIAL REGISTRATION

Not applicable.

An updated evaluation of reported no-observed adverse effect levels for chrysotile, amosite, and crocidolite asbestos for lung cancer and mesothelioma

This analysis updates two previous analyses that evaluated the exposure-response relationships for lung cancer and mesothelioma in chrysotile-exposed cohorts. We reviewed recently published studies, as well as updated information from previous studies. Based on the 16 studies considered for chrysotile (<10% amphibole), we identified the "no-observed adverse effect level" (NOAEL) for lung cancer and/or mesothelioma; it should be noted that smoking or previous or concurrent occupational exposure to amphiboles (if it existed) was not controlled for. NOAEL values ranged from 2.3-<11.5 f/cc-years to 1600-3200 f/cc-years for lung cancer and from 100-<400 f/cc-years to 800-1599 f/cc-years for mesothelioma. The range of best-estimate NOAELs was estimated to be 97-175 f/cc-years for lung cancer and 250-379 f/cc-years for mesothelioma. None of the six cohorts of cement or friction product manufacturing workers exhibited an increased risk at any exposure level, while all but one of the six studies of textile workers reported an increased risk at one or more exposure levels. This is likely because friction and cement workers were exposed to much shorter chrysotile fibers. Only eight cases of peritoneal mesothelioma were reported in all studies on predominantly chrysotile-exposed cohorts combined. This analysis also proposed best-estimate amosite and crocidolite NOAELs for mesothelioma derived by the application of relative potency estimates to the best-estimate chrysotile NOAELs for mesothelioma and validated by epidemiology studies with exposure-response information. The best-estimate amosite and crocidolite NOAELs for mesothelioma were 2-5 f/cc-years and 0.6-1 f/cc-years, respectively. The rate of peritoneal mesothelioma in amosite- and crocidolite-exposed cohorts was between approximately 70- to 100-fold and several-hundred-fold higher than in chrysotile-exposed cohorts, respectively. These findings will help characterize potential worker and consumer health risks associated with historical and current chrysotile, amosite, and crocidolite exposures.

Iron links endogenous and exogenous nanoparticles

Current progress in biology and medical science is based on the observation at the level of nanometers via electron microscopy and computation. Of note, the size of most cells in higher species exists in a limited range from 5 to 50 μm. Recently, it was demonstrated that endogenous extracellular nanoparticles play a role in communication among various cellular types in a variety of contexts. Among them, exosomes in serum have been established as biomarkers for human diseases by analyzing the cargo molecules. No life on the earth can survive without iron. However, excess iron can be a risk for carcinogenesis in rodents and humans. Nano-sized molecules may cause unexpected bioeffects, including carcinogenesis, which is a process to establish cellular iron addiction with ferroptosis-resistance. Asbestos and carbon nanotubes are the typical examples, leading to carcinogenesis by the alteration of iron metabolism. Recently, we found that CD63, one of the representative markers of exosomes, is under the regulation of iron-responsive element/iron-regulatory protein system. This is a safe strategy to share excess iron in the form of holo-ferritin between iron-sufficient and -deficient cells. On the other hand, damaged cells may secrete holo-ferritin-loaded exosomes as in the case of macrophages in ferroptosis after asbestos exposure. These holo-ferritin-loaded exosomes can cause mutagenic DNA damage in the recipient mesothelial cells. Thus, there is an iron link between exogenous and endogenous nanoparticles, which requires further investigation for better understanding and the future applications.

The incidence of malignancies in asbestosis with chrysotile exposure: a large Chinese prospective cohort study

Background

Asbestos exposure is closely related to the occurrence and development of various malignancies. This prospective cohort study aimed to evaluate the incidence rate and potential risk factors in a cohort of asbestosis patients in China.

Methods

The incidence of malignancies was determined in patients who had been exposed to chrysotile asbestos and diagnosed with asbestosis sequentially at Beijing Chaoyang Hospital from 1 January 2007 to 31 December 2019. Cox regression analyses were used to analyze the correlations between clinical variables and asbestosis combined with malignancies.

Results

A total of 618 patients with asbestosis were identified, of whom 544 were eligible for analysis. Among them, 89 (16.36%) were diagnosed with various malignancies. The standardized incidence ratios (SIRs) of patients with asbestosis combined with malignancies were 16.61, 175, 5.23, and 8.77 for lung cancer, mesothelioma, breast cancer, and endometrial carcinoma, respectively. The risks of all malignancies and lung cancer increased with initial exposure before 17 years old, longer asbestos exposure, and smoking.

Conclusions

The SIRs of patients with asbestosis-related malignancies were significantly increased in lung cancer, mesothelioma, breast cancer, and endometrial carcinoma in a hospital-based Chinese cohort. Smoking and the duration of asbestos exposure increased the risk of lung cancer.

The health effects of short fiber chrysotile and amphibole asbestos

The potential toxic effects of short chrysotile and amphibole asbestos fibers with lengths <5 to ∼10 µm have been debated over the years. This stems from the large database of epidemiology, toxicology, and in-vitro studies, each of which often provides different information in understanding and differentiating the effects of short fibers. The epidemiology studies in which the cancer potency estimates were based upon relatively high exposure concentrations provide a conservative assessment that shorter fibers would have little if any effect, especially under controlled exposure or environmental conditions that may occur today. The QSAR models have shown that fiber aspect ratio and Mg content are excellent predictors of cancer potency and that short fibers/particles of amphibole would have no effect. The studies of motor vehicle mechanics and in particular workers who serviced chrysotile containing brakes with the majority of the fibers being short provides evidence that motor vehicle mechanics, including workers who were engaged in brake repair, are not at an increased risk of mesothelioma. Several inhalation toxicology studies clearly differentiated that short chrysotile and amphibole asbestos fibers did not produce a significant carcinogenic effect in the lung or pleural cavity. Because of dosing and lack of sensitivity to biosolubility, in vitro studies can be difficult to interpret; however, a number have differentiated short chrysotile and amphibole asbestos fibers from long fibers. Integral to understanding the importance of fiber length in determining possible health effects is an understanding of the biological and physiological function of the respiratory system. Short asbestos fibers, like innocuous dust, can be cleared through the tracheobronchial ciliated mucous transport, phagocytized by macrophages and cleared via the bronchial tree, and can also be removed through the lymphatic system. While the first two methods can remove them from the lung, with lymphatic transport through one-way valves, fibers are removed from the active area of the lung where the fiber-related disease has been shown to develop and can accumulate in lymphatic sumps and lymph nodes. While short asbestos fibers are present in most occupational or environmental exposures, the large body of studies strongly supports that they do not contribute to the health effects of asbestos exposure.

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.

A critical review of the 2020 EPA risk assessment for chrysotile and its many shortcomings

From 2018 to 2020, the United States Environmental Protection Agency (EPA) performed a risk evaluation of chrysotile asbestos to evaluate the hazards of asbestos-containing products (e.g. encapsulated products), including brakes and gaskets, allegedly currently sold in the United States. During the public review period, the EPA received more than 100 letters commenting on the proposed risk evaluation. The Science Advisory Committee on Chemicals (SACC), which peer reviewed the document, asked approximately 100 questions of the EPA that they expected to be addressed prior to publication of the final version of the risk assessment on 30 December 2020. After careful analysis, the authors of this manuscript found many significant scientific shortcomings in both the EPA's draft and final versions of the chrysotile risk evaluation. First, the EPA provided insufficient evidence regarding the current number of chrysotile-containing brakes and gaskets being sold in the United States, which influences the need for regulatory oversight. Second, the Agency did not give adequate consideration to the more than 200 air samples detailed in the published literature of auto mechanics who changed brakes in the 1970-1989 era. Third, the Agency did not consider more than 15 epidemiology studies indicating that exposures to encapsulated chrysotile asbestos in brakes and gaskets, which were generally in commerce from approximately 1950-1985, did not increase the incidence of any asbestos-related disease. Fourth, the concern about chrysotile asbestos being a mesothelioma hazard was based on populations in two facilities where mixed exposure to chrysotile and commercial amphibole asbestos (amosite and crocidolite) occurred. All 8 cases of pleural cancer and mesothelioma in the examined populations arose in facilities where amphiboles were present. It was therefore inappropriate to rely on these cohorts to predict the health risks of exposure to short fiber chrysotile, especially of those fibers filled with phenolic resins. Fifth, the suggested inhalation unit risk (IUR) for chrysotile asbestos was far too high since it was not markedly different than for amosite, despite the fact that the amphiboles are a far more potent carcinogen. Sixth, the approach to low dose modeling was not the most appropriate one in several respects, but, without question, it should have accounted for the background rate of mesothelioma in the general population. Just one month after this assessment was published, the National Academies of Science notified the EPA that the Agency's systematic review process was flawed. The result of the EPA's chrysotile asbestos risk evaluation is that society can expect dozens of years of scientifically unwarranted litigation. Due to an aging population and because some fraction of the population is naturally predisposed to mesothelioma given the presence of various genetic mutations in DNA repair mechanisms (e.g. BAP1 and others), the vast majority of mesotheliomas in the post-2035 era are expected to be spontaneous and unrelated in any way to exposure to asbestos. Due to the EPA's analysis, it is our belief that those who handled brakes and gaskets in the post-1985 era may now believe that those exposures were the cause of their mesothelioma, when a risk assessment based on the scientific weight of evidence would indicate otherwise.

Burden of Mortality from Asbestos-Related Diseases in Italy

Asbestos is one of the major worldwide occupational carcinogens. The global burden of asbestos-related diseases (ARDs) was estimated around 231,000 cases/year. Italy was one of the main European asbestos producers until the 1992 ban. The WHO recommended national programs, including epidemiological surveillance, to eliminate ARDs. The present paper shows the estimate of the burden of mortality from ARDs in Italy, established for the first time. National standardized rates of mortality from mesothelioma and asbestosis and their temporal trends, based on the National Institute of Statistics database, were computed. Deaths from lung cancer attributable to asbestos exposure were estimated using population-based case-control studies. Asbestos-related lung and ovarian cancer deaths attributable to occupational exposure were estimated, considering the Italian occupational cohort studies. In the 2010-2016 period, 4400 deaths/year attributable to asbestos were estimated: 1515 from mesothelioma, 58 from asbestosis, 2830 from lung and 16 from ovarian cancers. The estimates based on occupational cohorts showed that each year 271 deaths from mesothelioma, 302 from lung cancer and 16 from ovarian cancer were attributable to occupational asbestos exposure in industrial sectors with high asbestos levels. The important health impact of asbestos in Italy, 10-25 years after the ban, was highlighted. These results suggest the need for appropriate interventions in terms of prevention, health care and social security at the local level and could contribute to the global estimate of ARDs.

Role of PARP1 on DNA damage induced by mineral silicate chrysotile in bronchial epithelial and pleural mesothelial cells

To investigate whether poly (ADP ribose) polymerase-1 (PARP1) is involved in chrysotile-induced DNA damage in pleural mesothelial cells (MeT-5A) and bronchial epithelial cells (BEAS-2B), two PARP1-deficient cell lines were established. Efficiencies of RNA interference on PARP1 were detected by western blot and qPCR. Here, normal cells and PARP1-deficient cells were exposed to chrysotile, and DNA damage and DNA repair were detected by alkaline comet assay. All cells were treated with chrysotile at the indicated concentrations (5, 10, 20, and 40 μg/cm²) for 24 h and then the DNA repair capacity was observed for 12 and 24 h, respectively. The results showed that chrysotile caused DNA damage at an obvious dose-dependent manner in MeT-5A and BEAS-2B cells. In addition, MeT-5A cells had more persistent DNA damage than BEAS-2B. Compared to normal cells, the PARP1-deficient cells were more sensitive to DNA damage caused by chrysotile. In DNA repair experiments, all cell lines recovered from the damage over time. The results of relative repair percentage (RRP) of MeT-5A and BEAS-2B were higher than those of MeT-5A shPARP1 and BEAS-2B shPARP1 cells at all experimental concentrations (except 5 μg/cm²) at 12-h repair. However, RRP of BEAS-2B and BEAS-2B shPARP1 tended to be closer, and RRP of MeT-5A shPARP1 was still lower than that of MeT-5A at 24-h repair. All results suggest that PARP1 plays an important role in early repair of DNA damage in BEAS-2B and MeT-5A cells exposed to chrysotile.

21st Century Early Adult (55-74) Deaths from Brain-Disease-Deaths Compared to All Other Cause Mortality in the Major Western Countries - Exposing a Hidden Epidemic

OBJECTIVES

To examine early adult deaths (EAD) - people aged 55-74 due to brain disease deaths (BDD) compared to all other causes (AOC) in the 21st century in 21 major Western countries (MWC).

METHOD

EAD are below MWCc average life expectancy. All mortality drawn from the latest WHO data. The three global BDD categories consist of mental and behaviour disorder, nervous diseases and Alzheimer and other dementias. Mortality rates per million are analysed for people 55-74 years and total age-standardised death rates (ASDR). BDD rates between 2000-2015 compared against AOC of deaths for EAD and ASDR. Confidence Intervals determine any significant difference AOC and BDD over the period 2000-15, plus an examination of EAD in six separate global mortality categories.

RESULTS

EAD: The separate BDD categories for EAD significantly positively correlated, validating their combination as BDD. Every country's AOC 55-74 rates fell substantially, but fourteen country's BDD rose substantially (>20%) and all MWC countries BDD rose significantly more than AOC. ASDR: All nations total AOC fell substantially, whereas seventeen BDD rates rose substantially and every country's BDD significantly increased compared to AOC deaths. Six other EAD mortalities, circulatory, cancer, respiratory, compared to BDD produced Odds Ratios ranging from 1:1.54 to 1:2.36 such were the marked differences over the period.

DISCUSSION

Positive news is that AOC are down across all investigated countries in the 21st century. However, the extent of the EAD rises in just 16 years indicates that these BDD conditions are starting earlier suggesting multiple interactive environmental factors impacting upon brain related diseases.

Mesothelioma risk among those exposed to chrysotile asbestos only and mixtures that include amphibole: a case-control study in the USA, 1975-1980

OBJECTIVES

Occupational asbestos exposure is causally linked to mesothelioma. However, whether exposure to only chrysotile asbestos is associated with mesothelioma risk, and the heterogeneity in risk by different fibre types/lengths remains unclear. We investigated whether mesothelioma risk differs among workers exposed to only chrysotile asbestos compared with chrysotile and ≥1 amphibole (ie, amosite, tremolite, anthophyllite and crocidolite) over the working lifetime.

METHODS

We analysed next-of-kin interview data including occupational histories for 580 white men (176 cases and 404 controls) from a case-control study of mesothelioma conducted in the USA in 1975-1980. Asbestos exposure was determined by an occupational hygienist using a job-exposure matrix and exposure categories included chrysotile only and nine chrysotile-amphibole mixtures. Logistic regression models were used to estimate the ORs and 95% CIs of mesothelioma, comparing each asbestos category to the unexposed group, adjusted for age at death and data source. Analysis of contrasts was used to assess overall heterogeneity and pair-wise differences in risk.

RESULTS

Exposure to long and short chrysotile only was associated with increased mesothelioma risk compared with the unexposed (OR=3.8 (95% CI 1.3 to 11.2)). The complex mixture of extra-long amosite, short and long chrysotile, tremolite and anthophyllite was associated with the highest risk (OR=12.8 (95% CI 4.1 to 40.2)). There was evidence for overall heterogeneity among the asbestos exposure categories (p heterogeneity=0.02). However, the lower risk observed for exposure to chrysotile only compared with the complex mixture was not significant (p difference=0.10).

CONCLUSIONS

Our findings suggest that policies aimed at regulating asbestos should target both pure chrysotile and mixtures that include amphibole.

The Molecular Basis of Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare, aggressive malignancy of the pleural lining associated with asbestos exposure in greater than 80% of cases. It is characterized by molecular heterogeneity both between patients and within individual tumors. Next-generation sequencing technology and novel computational techniques have resulted in a greater understanding of the epigenetic, genetic, and transcriptomic hallmarks of MPM. This article reviews these features and discusses the implications of advances in MPM molecular biology in clinical practice.

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.

Mortality and mesothelioma incidence among chrysotile asbestos miners in Balangero, Italy: A cohort study

BACKGROUND

We studied cancer mortality and mesothelioma incidence in 974 male workers employed at least 6 months at the Balangero mine (Italy), the largest chrysotile mine in Western Europe, active from 1917 to 1985.

METHODS

Vital status as of 31 May 2013, causes of deaths and mesothelioma incidence from 1990 were ascertained. Past exposure to asbestos by working area and calendar period was estimated, based on historical data of fibers concentrations. Individual cumulative exposure was assessed by applying estimates to the job history of cohort members. Standardized mortality ratios (SMRs) for selected causes and standardized incidence ratios for malignant mesothelioma (MM) were calculated based on regional reference rates. Poisson regression analysis was used to study MM and lung cancer risk by latency, duration, and cumulative exposure.

RESULTS

Mortality was increased for all causes (SMR = 1.28; 95% confidence interval [CI] = 1.17-1.40), pleural cancer (SMR = 4.30; 95% CI = 1.58-9.37), asbestosis (SMR = 375.06; 95% CI = 262.68-519.23). An increase was also found for lung cancer (SMR = 1.14; 95% CI =  0.81-1.55) and peritoneal cancer (SMR = 3.25; 95% CI = 0.39-11.75). The risk of both pleural and peritoneal cancer mortality and of mesothelioma incidence increased with increasing cumulative exposure, duration, and latency. Poisson regression analyses showed an increase in mesothelioma risk with cumulative asbestos exposure and suggest a similar trend for lung cancer. Asbestosis mortality also increased with cumulative exposure.

CONCLUSIONS

Among Balangero chrysotile miners and millers, the occurrence of malignant and nonmalignant asbestos-related diseases was increased by exposure, with dose-response relation. The study confirms the carcinogenicity of chrysotile asbestos, in particular for pleural mesothelioma.

Health impact of exposure to asbestos in polluted area of Southern Italy

The three main sources of asbestos pollution in the city of Bari, Puglia, the former Fibronit asbestos factory, the Torre Quetta beach, the former Rossani barracks and the history of their reclamation are described. The results of cohort studies on factory workers and case-control studies on asbestos exposure to the resident population and the onset of mesothelioma are also reported. Finally, the data of the regional register of mesothelioma related to residents in the city of Bari and four new cases with environmental exposure due to the former Rossani barracks are presented.

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.